Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

12 files changed, 6955 insertions, 0 deletions

diff --git a/third_party/rust/bindgen/codegen/bitfield_unit.rs b/third_party/rust/bindgen/codegen/bitfield_unit.rs
new file mode 100644
index 0000000000..73ec2bd629
--- /dev/null
+++ b/third_party/rust/bindgen/codegen/bitfield_unit.rs
@@ -0,0 +1,102 @@
+#[repr(C)]
+#[derive(Copy, Clone, Debug, Default, Eq, Hash, Ord, PartialEq, PartialOrd)]
+pub struct __BindgenBitfieldUnit<Storage> {
+    storage: Storage,
+}
+
+impl<Storage> __BindgenBitfieldUnit<Storage> {
+    #[inline]
+    pub const fn new(storage: Storage) -> Self {
+        Self { storage }
+    }
+}
+
+impl<Storage> __BindgenBitfieldUnit<Storage>
+where
+    Storage: AsRef<[u8]> + AsMut<[u8]>,
+{
+    #[inline]
+    pub fn get_bit(&self, index: usize) -> bool {
+        debug_assert!(index / 8 < self.storage.as_ref().len());
+
+        let byte_index = index / 8;
+        let byte = self.storage.as_ref()[byte_index];
+
+        let bit_index = if cfg!(target_endian = "big") {
+            7 - (index % 8)
+        } else {
+            index % 8
+        };
+
+        let mask = 1 << bit_index;
+
+        byte & mask == mask
+    }
+
+    #[inline]
+    pub fn set_bit(&mut self, index: usize, val: bool) {
+        debug_assert!(index / 8 < self.storage.as_ref().len());
+
+        let byte_index = index / 8;
+        let byte = &mut self.storage.as_mut()[byte_index];
+
+        let bit_index = if cfg!(target_endian = "big") {
+            7 - (index % 8)
+        } else {
+            index % 8
+        };
+
+        let mask = 1 << bit_index;
+        if val {
+            *byte |= mask;
+        } else {
+            *byte &= !mask;
+        }
+    }
+
+    #[inline]
+    pub fn get(&self, bit_offset: usize, bit_width: u8) -> u64 {
+        debug_assert!(bit_width <= 64);
+        debug_assert!(bit_offset / 8 < self.storage.as_ref().len());
+        debug_assert!(
+            (bit_offset + (bit_width as usize)) / 8 <=
+                self.storage.as_ref().len()
+        );
+
+        let mut val = 0;
+
+        for i in 0..(bit_width as usize) {
+            if self.get_bit(i + bit_offset) {
+                let index = if cfg!(target_endian = "big") {
+                    bit_width as usize - 1 - i
+                } else {
+                    i
+                };
+                val |= 1 << index;
+            }
+        }
+
+        val
+    }
+
+    #[inline]
+    pub fn set(&mut self, bit_offset: usize, bit_width: u8, val: u64) {
+        debug_assert!(bit_width <= 64);
+        debug_assert!(bit_offset / 8 < self.storage.as_ref().len());
+        debug_assert!(
+            (bit_offset + (bit_width as usize)) / 8 <=
+                self.storage.as_ref().len()
+        );
+
+        for i in 0..(bit_width as usize) {
+            let mask = 1 << i;
+            let val_bit_is_set = val & mask == mask;
+            let index = if cfg!(target_endian = "big") {
+                bit_width as usize - 1 - i
+            } else {
+                i
+            };
+            self.set_bit(index + bit_offset, val_bit_is_set);
+        }
+    }
+}
diff --git a/third_party/rust/bindgen/codegen/bitfield_unit_tests.rs b/third_party/rust/bindgen/codegen/bitfield_unit_tests.rs
new file mode 100644
index 0000000000..e143e4ea78
--- /dev/null
+++ b/third_party/rust/bindgen/codegen/bitfield_unit_tests.rs
@@ -0,0 +1,260 @@
+//! Tests for `__BindgenBitfieldUnit`.
+//!
+//! Note that bit-fields are allocated right to left (least to most significant
+//! bits).
+//!
+//! From the x86 PS ABI:
+//!
+//! ```c
+//! struct {
+//!     int j : 5;
+//!     int k : 6;
+//!     int m : 7;
+//! };
+//! ```
+//!
+//! ```ignore
+//! +------------------------------------------------------------+
+//! |                     |              |            |          |
+//! |       padding       |       m      |     k      |    j     |
+//! |31                 18|17          11|10         5|4        0|
+//! +------------------------------------------------------------+
+//! ```
+
+use super::bitfield_unit::__BindgenBitfieldUnit;
+
+#[test]
+fn bitfield_unit_get_bit() {
+    let unit = __BindgenBitfieldUnit::<[u8; 2]>::new([0b10011101, 0b00011101]);
+
+    let mut bits = vec![];
+    for i in 0..16 {
+        bits.push(unit.get_bit(i));
+    }
+
+    println!();
+    println!("bits = {:?}", bits);
+    assert_eq!(
+        bits,
+        &[
+            // 0b10011101
+            true, false, true, true, true, false, false, true,
+            // 0b00011101
+            true, false, true, true, true, false, false, false
+        ]
+    );
+}
+
+#[test]
+fn bitfield_unit_set_bit() {
+    let mut unit =
+        __BindgenBitfieldUnit::<[u8; 2]>::new([0b00000000, 0b00000000]);
+
+    for i in 0..16 {
+        if i % 3 == 0 {
+            unit.set_bit(i, true);
+        }
+    }
+
+    for i in 0..16 {
+        assert_eq!(unit.get_bit(i), i % 3 == 0);
+    }
+
+    let mut unit =
+        __BindgenBitfieldUnit::<[u8; 2]>::new([0b11111111, 0b11111111]);
+
+    for i in 0..16 {
+        if i % 3 == 0 {
+            unit.set_bit(i, false);
+        }
+    }
+
+    for i in 0..16 {
+        assert_eq!(unit.get_bit(i), i % 3 != 0);
+    }
+}
+
+macro_rules! bitfield_unit_get {
+    (
+        $(
+            With $storage:expr , then get($start:expr, $len:expr) is $expected:expr;
+        )*
+    ) => {
+        #[test]
+        fn bitfield_unit_get() {
+            $({
+                let expected = $expected;
+                let unit = __BindgenBitfieldUnit::<_>::new($storage);
+                let actual = unit.get($start, $len);
+
+                println!();
+                println!("expected = {:064b}", expected);
+                println!("actual   = {:064b}", actual);
+
+                assert_eq!(expected, actual);
+            })*
+        }
+   }
+}
+
+bitfield_unit_get! {
+    // Let's just exhaustively test getting the bits from a single byte, since
+    // there are few enough combinations...
+
+    With [0b11100010], then get(0, 1) is 0;
+    With [0b11100010], then get(1, 1) is 1;
+    With [0b11100010], then get(2, 1) is 0;
+    With [0b11100010], then get(3, 1) is 0;
+    With [0b11100010], then get(4, 1) is 0;
+    With [0b11100010], then get(5, 1) is 1;
+    With [0b11100010], then get(6, 1) is 1;
+    With [0b11100010], then get(7, 1) is 1;
+
+    With [0b11100010], then get(0, 2) is 0b10;
+    With [0b11100010], then get(1, 2) is 0b01;
+    With [0b11100010], then get(2, 2) is 0b00;
+    With [0b11100010], then get(3, 2) is 0b00;
+    With [0b11100010], then get(4, 2) is 0b10;
+    With [0b11100010], then get(5, 2) is 0b11;
+    With [0b11100010], then get(6, 2) is 0b11;
+
+    With [0b11100010], then get(0, 3) is 0b010;
+    With [0b11100010], then get(1, 3) is 0b001;
+    With [0b11100010], then get(2, 3) is 0b000;
+    With [0b11100010], then get(3, 3) is 0b100;
+    With [0b11100010], then get(4, 3) is 0b110;
+    With [0b11100010], then get(5, 3) is 0b111;
+
+    With [0b11100010], then get(0, 4) is 0b0010;
+    With [0b11100010], then get(1, 4) is 0b0001;
+    With [0b11100010], then get(2, 4) is 0b1000;
+    With [0b11100010], then get(3, 4) is 0b1100;
+    With [0b11100010], then get(4, 4) is 0b1110;
+
+    With [0b11100010], then get(0, 5) is 0b00010;
+    With [0b11100010], then get(1, 5) is 0b10001;
+    With [0b11100010], then get(2, 5) is 0b11000;
+    With [0b11100010], then get(3, 5) is 0b11100;
+
+    With [0b11100010], then get(0, 6) is 0b100010;
+    With [0b11100010], then get(1, 6) is 0b110001;
+    With [0b11100010], then get(2, 6) is 0b111000;
+
+    With [0b11100010], then get(0, 7) is 0b1100010;
+    With [0b11100010], then get(1, 7) is 0b1110001;
+
+    With [0b11100010], then get(0, 8) is 0b11100010;
+
+    // OK. Now let's test getting bits from across byte boundaries.
+
+    With [0b01010101, 0b11111111, 0b00000000, 0b11111111],
+    then get(0, 16) is 0b1111111101010101;
+
+    With [0b01010101, 0b11111111, 0b00000000, 0b11111111],
+    then get(1, 16) is 0b0111111110101010;
+
+    With [0b01010101, 0b11111111, 0b00000000, 0b11111111],
+    then get(2, 16) is 0b0011111111010101;
+
+    With [0b01010101, 0b11111111, 0b00000000, 0b11111111],
+    then get(3, 16) is 0b0001111111101010;
+
+    With [0b01010101, 0b11111111, 0b00000000, 0b11111111],
+    then get(4, 16) is 0b0000111111110101;
+
+    With [0b01010101, 0b11111111, 0b00000000, 0b11111111],
+    then get(5, 16) is 0b0000011111111010;
+
+    With [0b01010101, 0b11111111, 0b00000000, 0b11111111],
+    then get(6, 16) is 0b0000001111111101;
+
+    With [0b01010101, 0b11111111, 0b00000000, 0b11111111],
+    then get(7, 16) is 0b0000000111111110;
+
+    With [0b01010101, 0b11111111, 0b00000000, 0b11111111],
+    then get(8, 16) is 0b0000000011111111;
+}
+
+macro_rules! bitfield_unit_set {
+    (
+        $(
+            set($start:expr, $len:expr, $val:expr) is $expected:expr;
+        )*
+    ) => {
+        #[test]
+        fn bitfield_unit_set() {
+            $(
+                let mut unit = __BindgenBitfieldUnit::<[u8; 4]>::new([0, 0, 0, 0]);
+                unit.set($start, $len, $val);
+                let actual = unit.get(0, 32);
+
+                println!();
+                println!("set({}, {}, {:032b}", $start, $len, $val);
+                println!("expected = {:064b}", $expected);
+                println!("actual   = {:064b}", actual);
+
+                assert_eq!($expected, actual);
+            )*
+        }
+    }
+}
+
+bitfield_unit_set! {
+    // Once again, let's exhaustively test single byte combinations.
+
+    set(0, 1, 0b11111111) is 0b00000001;
+    set(1, 1, 0b11111111) is 0b00000010;
+    set(2, 1, 0b11111111) is 0b00000100;
+    set(3, 1, 0b11111111) is 0b00001000;
+    set(4, 1, 0b11111111) is 0b00010000;
+    set(5, 1, 0b11111111) is 0b00100000;
+    set(6, 1, 0b11111111) is 0b01000000;
+    set(7, 1, 0b11111111) is 0b10000000;
+
+    set(0, 2, 0b11111111) is 0b00000011;
+    set(1, 2, 0b11111111) is 0b00000110;
+    set(2, 2, 0b11111111) is 0b00001100;
+    set(3, 2, 0b11111111) is 0b00011000;
+    set(4, 2, 0b11111111) is 0b00110000;
+    set(5, 2, 0b11111111) is 0b01100000;
+    set(6, 2, 0b11111111) is 0b11000000;
+
+    set(0, 3, 0b11111111) is 0b00000111;
+    set(1, 3, 0b11111111) is 0b00001110;
+    set(2, 3, 0b11111111) is 0b00011100;
+    set(3, 3, 0b11111111) is 0b00111000;
+    set(4, 3, 0b11111111) is 0b01110000;
+    set(5, 3, 0b11111111) is 0b11100000;
+
+    set(0, 4, 0b11111111) is 0b00001111;
+    set(1, 4, 0b11111111) is 0b00011110;
+    set(2, 4, 0b11111111) is 0b00111100;
+    set(3, 4, 0b11111111) is 0b01111000;
+    set(4, 4, 0b11111111) is 0b11110000;
+
+    set(0, 5, 0b11111111) is 0b00011111;
+    set(1, 5, 0b11111111) is 0b00111110;
+    set(2, 5, 0b11111111) is 0b01111100;
+    set(3, 5, 0b11111111) is 0b11111000;
+
+    set(0, 6, 0b11111111) is 0b00111111;
+    set(1, 6, 0b11111111) is 0b01111110;
+    set(2, 6, 0b11111111) is 0b11111100;
+
+    set(0, 7, 0b11111111) is 0b01111111;
+    set(1, 7, 0b11111111) is 0b11111110;
+
+    set(0, 8, 0b11111111) is 0b11111111;
+
+    // And, now let's cross byte boundaries.
+
+    set(0, 16, 0b1111111111111111) is 0b00000000000000001111111111111111;
+    set(1, 16, 0b1111111111111111) is 0b00000000000000011111111111111110;
+    set(2, 16, 0b1111111111111111) is 0b00000000000000111111111111111100;
+    set(3, 16, 0b1111111111111111) is 0b00000000000001111111111111111000;
+    set(4, 16, 0b1111111111111111) is 0b00000000000011111111111111110000;
+    set(5, 16, 0b1111111111111111) is 0b00000000000111111111111111100000;
+    set(6, 16, 0b1111111111111111) is 0b00000000001111111111111111000000;
+    set(7, 16, 0b1111111111111111) is 0b00000000011111111111111110000000;
+    set(8, 16, 0b1111111111111111) is 0b00000000111111111111111100000000;
+}
diff --git a/third_party/rust/bindgen/codegen/dyngen.rs b/third_party/rust/bindgen/codegen/dyngen.rs
new file mode 100644
index 0000000000..5e734ccd15
--- /dev/null
+++ b/third_party/rust/bindgen/codegen/dyngen.rs
@@ -0,0 +1,201 @@
+use crate::codegen;
+use crate::ir::context::BindgenContext;
+use crate::ir::function::ClangAbi;
+use proc_macro2::Ident;
+
+/// Used to build the output tokens for dynamic bindings.
+#[derive(Default)]
+pub struct DynamicItems {
+    /// Tracks the tokens that will appears inside the library struct -- e.g.:
+    /// ```ignore
+    /// struct Lib {
+    ///    __library: ::libloading::Library,
+    ///    pub x: Result<unsafe extern ..., ::libloading::Error>, // <- tracks these
+    ///    ...
+    /// }
+    /// ```
+    struct_members: Vec<proc_macro2::TokenStream>,
+
+    /// Tracks the tokens that will appear inside the library struct's implementation, e.g.:
+    ///
+    /// ```ignore
+    /// impl Lib {
+    ///     ...
+    ///     pub unsafe fn foo(&self, ...) { // <- tracks these
+    ///         ...
+    ///     }
+    /// }
+    /// ```
+    struct_implementation: Vec<proc_macro2::TokenStream>,
+
+    /// Tracks the initialization of the fields inside the `::new` constructor of the library
+    /// struct, e.g.:
+    /// ```ignore
+    /// impl Lib {
+    ///
+    ///     pub unsafe fn new<P>(path: P) -> Result<Self, ::libloading::Error>
+    ///     where
+    ///         P: AsRef<::std::ffi::OsStr>,
+    ///     {
+    ///         ...
+    ///         let foo = __library.get(...) ...; // <- tracks these
+    ///         ...
+    ///     }
+    ///
+    ///     ...
+    /// }
+    /// ```
+    constructor_inits: Vec<proc_macro2::TokenStream>,
+
+    /// Tracks the information that is passed to the library struct at the end of the `::new`
+    /// constructor, e.g.:
+    /// ```ignore
+    /// impl LibFoo {
+    ///     pub unsafe fn new<P>(path: P) -> Result<Self, ::libloading::Error>
+    ///     where
+    ///         P: AsRef<::std::ffi::OsStr>,
+    ///     {
+    ///         ...
+    ///         Ok(LibFoo {
+    ///             __library: __library,
+    ///             foo,
+    ///             bar, // <- tracks these
+    ///             ...
+    ///         })
+    ///     }
+    /// }
+    /// ```
+    init_fields: Vec<proc_macro2::TokenStream>,
+}
+
+impl DynamicItems {
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    pub fn get_tokens(
+        &self,
+        lib_ident: Ident,
+        ctx: &BindgenContext,
+    ) -> proc_macro2::TokenStream {
+        let struct_members = &self.struct_members;
+        let constructor_inits = &self.constructor_inits;
+        let init_fields = &self.init_fields;
+        let struct_implementation = &self.struct_implementation;
+
+        let from_library = if ctx.options().wrap_unsafe_ops {
+            quote!(unsafe { Self::from_library(library) })
+        } else {
+            quote!(Self::from_library(library))
+        };
+
+        quote! {
+            extern crate libloading;
+
+            pub struct #lib_ident {
+                __library: ::libloading::Library,
+                #(#struct_members)*
+            }
+
+            impl #lib_ident {
+                pub unsafe fn new<P>(
+                    path: P
+                ) -> Result<Self, ::libloading::Error>
+                where P: AsRef<::std::ffi::OsStr> {
+                    let library = ::libloading::Library::new(path)?;
+                    #from_library
+                }
+
+                pub unsafe fn from_library<L>(
+                    library: L
+                ) -> Result<Self, ::libloading::Error>
+                where L: Into<::libloading::Library> {
+                    let __library = library.into();
+                    #( #constructor_inits )*
+                    Ok(#lib_ident {
+                        __library,
+                        #( #init_fields ),*
+                    })
+                }
+
+                #( #struct_implementation )*
+            }
+        }
+    }
+
+    #[allow(clippy::too_many_arguments)]
+    pub(crate) fn push(
+        &mut self,
+        ident: Ident,
+        abi: ClangAbi,
+        is_variadic: bool,
+        is_required: bool,
+        args: Vec<proc_macro2::TokenStream>,
+        args_identifiers: Vec<proc_macro2::TokenStream>,
+        ret: proc_macro2::TokenStream,
+        ret_ty: proc_macro2::TokenStream,
+        attributes: Vec<proc_macro2::TokenStream>,
+        ctx: &BindgenContext,
+    ) {
+        if !is_variadic {
+            assert_eq!(args.len(), args_identifiers.len());
+        }
+
+        let signature = quote! { unsafe extern #abi fn ( #( #args),* ) #ret };
+        let member = if is_required {
+            signature
+        } else {
+            quote! { Result<#signature, ::libloading::Error> }
+        };
+
+        self.struct_members.push(quote! {
+            pub #ident: #member,
+        });
+
+        // N.B: If the signature was required, it won't be wrapped in a Result<...>
+        //      and we can simply call it directly.
+        let fn_ = if is_required {
+            quote! { self.#ident }
+        } else {
+            quote! { self.#ident.as_ref().expect("Expected function, got error.") }
+        };
+        let call_body = if ctx.options().wrap_unsafe_ops {
+            quote!(unsafe { (#fn_)(#( #args_identifiers ),*) })
+        } else {
+            quote!((#fn_)(#( #args_identifiers ),*) )
+        };
+
+        // We can't implement variadic functions from C easily, so we allow to
+        // access the function pointer so that the user can call it just fine.
+        if !is_variadic {
+            self.struct_implementation.push(quote! {
+                #(#attributes)*
+                pub unsafe fn #ident ( &self, #( #args ),* ) -> #ret_ty {
+                    #call_body
+                }
+            });
+        }
+
+        // N.B: Unwrap the signature upon construction if it is required to be resolved.
+        let ident_str = codegen::helpers::ast_ty::cstr_expr(ident.to_string());
+        let library_get = if ctx.options().wrap_unsafe_ops {
+            quote!(unsafe { __library.get(#ident_str) })
+        } else {
+            quote!(__library.get(#ident_str))
+        };
+
+        self.constructor_inits.push(if is_required {
+            quote! {
+                let #ident = #library_get.map(|sym| *sym)?;
+            }
+        } else {
+            quote! {
+                let #ident = #library_get.map(|sym| *sym);
+            }
+        });
+
+        self.init_fields.push(quote! {
+            #ident
+        });
+    }
+}
diff --git a/third_party/rust/bindgen/codegen/error.rs b/third_party/rust/bindgen/codegen/error.rs
new file mode 100644
index 0000000000..c1bcf4e1cb
--- /dev/null
+++ b/third_party/rust/bindgen/codegen/error.rs
@@ -0,0 +1,33 @@
+use std::error;
+use std::fmt;
+
+/// Errors that can occur during code generation.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum Error {
+    /// Tried to generate an opaque blob for a type that did not have a layout.
+    NoLayoutForOpaqueBlob,
+
+    /// Tried to instantiate an opaque template definition, or a template
+    /// definition that is too difficult for us to understand (like a partial
+    /// template specialization).
+    InstantiationOfOpaqueType,
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.write_str(match *self {
+            Error::NoLayoutForOpaqueBlob => {
+                "Tried to generate an opaque blob, but had no layout"
+            }
+            Error::InstantiationOfOpaqueType => {
+                "Instantiation of opaque template type or partial template \
+                 specialization"
+            }
+        })
+    }
+}
+
+impl error::Error for Error {}
+
+/// A `Result` of `T` or an error of `bindgen::codegen::error::Error`.
+pub type Result<T> = ::std::result::Result<T, Error>;
diff --git a/third_party/rust/bindgen/codegen/helpers.rs b/third_party/rust/bindgen/codegen/helpers.rs
new file mode 100644
index 0000000000..088c7f9363
--- /dev/null
+++ b/third_party/rust/bindgen/codegen/helpers.rs
@@ -0,0 +1,311 @@
+//! Helpers for code generation that don't need macro expansion.
+
+use crate::ir::context::BindgenContext;
+use crate::ir::layout::Layout;
+use proc_macro2::{Ident, Span, TokenStream};
+use quote::TokenStreamExt;
+
+pub mod attributes {
+    use proc_macro2::{Ident, Span, TokenStream};
+    use std::str::FromStr;
+
+    pub fn repr(which: &str) -> TokenStream {
+        let which = Ident::new(which, Span::call_site());
+        quote! {
+            #[repr( #which )]
+        }
+    }
+
+    pub fn repr_list(which_ones: &[&str]) -> TokenStream {
+        let which_ones = which_ones
+            .iter()
+            .cloned()
+            .map(|one| TokenStream::from_str(one).expect("repr to be valid"));
+        quote! {
+            #[repr( #( #which_ones ),* )]
+        }
+    }
+
+    pub fn derives(which_ones: &[&str]) -> TokenStream {
+        let which_ones = which_ones
+            .iter()
+            .cloned()
+            .map(|one| TokenStream::from_str(one).expect("derive to be valid"));
+        quote! {
+            #[derive( #( #which_ones ),* )]
+        }
+    }
+
+    pub fn inline() -> TokenStream {
+        quote! {
+            #[inline]
+        }
+    }
+
+    pub fn must_use() -> TokenStream {
+        quote! {
+            #[must_use]
+        }
+    }
+
+    pub fn non_exhaustive() -> TokenStream {
+        quote! {
+            #[non_exhaustive]
+        }
+    }
+
+    pub fn doc(comment: String) -> TokenStream {
+        if comment.is_empty() {
+            quote!()
+        } else {
+            quote!(#[doc = #comment])
+        }
+    }
+
+    pub fn link_name(name: &str) -> TokenStream {
+        // LLVM mangles the name by default but it's already mangled.
+        // Prefixing the name with \u{1} should tell LLVM to not mangle it.
+        let name = format!("\u{1}{}", name);
+        quote! {
+            #[link_name = #name]
+        }
+    }
+}
+
+/// Generates a proper type for a field or type with a given `Layout`, that is,
+/// a type with the correct size and alignment restrictions.
+pub fn blob(ctx: &BindgenContext, layout: Layout) -> TokenStream {
+    let opaque = layout.opaque();
+
+    // FIXME(emilio, #412): We fall back to byte alignment, but there are
+    // some things that legitimately are more than 8-byte aligned.
+    //
+    // Eventually we should be able to `unwrap` here, but...
+    let ty_name = match opaque.known_rust_type_for_array(ctx) {
+        Some(ty) => ty,
+        None => {
+            warn!("Found unknown alignment on code generation!");
+            "u8"
+        }
+    };
+
+    let ty_name = Ident::new(ty_name, Span::call_site());
+
+    let data_len = opaque.array_size(ctx).unwrap_or(layout.size);
+
+    if data_len == 1 {
+        quote! {
+            #ty_name
+        }
+    } else {
+        quote! {
+            [ #ty_name ; #data_len ]
+        }
+    }
+}
+
+/// Integer type of the same size as the given `Layout`.
+pub fn integer_type(
+    ctx: &BindgenContext,
+    layout: Layout,
+) -> Option<TokenStream> {
+    let name = Layout::known_type_for_size(ctx, layout.size)?;
+    let name = Ident::new(name, Span::call_site());
+    Some(quote! { #name })
+}
+
+/// Generates a bitfield allocation unit type for a type with the given `Layout`.
+pub fn bitfield_unit(ctx: &BindgenContext, layout: Layout) -> TokenStream {
+    let mut tokens = quote! {};
+
+    if ctx.options().enable_cxx_namespaces {
+        tokens.append_all(quote! { root:: });
+    }
+
+    let size = layout.size;
+    tokens.append_all(quote! {
+        __BindgenBitfieldUnit<[u8; #size]>
+    });
+
+    tokens
+}
+
+pub mod ast_ty {
+    use crate::ir::context::BindgenContext;
+    use crate::ir::function::FunctionSig;
+    use crate::ir::layout::Layout;
+    use crate::ir::ty::FloatKind;
+    use proc_macro2::{self, TokenStream};
+    use std::str::FromStr;
+
+    pub fn c_void(ctx: &BindgenContext) -> TokenStream {
+        // ctypes_prefix takes precedence
+        match ctx.options().ctypes_prefix {
+            Some(ref prefix) => {
+                let prefix = TokenStream::from_str(prefix.as_str()).unwrap();
+                quote! {
+                    #prefix::c_void
+                }
+            }
+            None => {
+                if ctx.options().use_core &&
+                    ctx.options().rust_features.core_ffi_c_void
+                {
+                    quote! { ::core::ffi::c_void }
+                } else {
+                    quote! { ::std::os::raw::c_void }
+                }
+            }
+        }
+    }
+
+    pub fn raw_type(ctx: &BindgenContext, name: &str) -> TokenStream {
+        let ident = ctx.rust_ident_raw(name);
+        match ctx.options().ctypes_prefix {
+            Some(ref prefix) => {
+                let prefix = TokenStream::from_str(prefix.as_str()).unwrap();
+                quote! {
+                    #prefix::#ident
+                }
+            }
+            None => {
+                if ctx.options().use_core &&
+                    ctx.options().rust_features().core_ffi_c
+                {
+                    quote! {
+                        ::core::ffi::#ident
+                    }
+                } else {
+                    quote! {
+                        ::std::os::raw::#ident
+                    }
+                }
+            }
+        }
+    }
+
+    pub fn float_kind_rust_type(
+        ctx: &BindgenContext,
+        fk: FloatKind,
+        layout: Option<Layout>,
+    ) -> TokenStream {
+        // TODO: we probably should take the type layout into account more
+        // often?
+        //
+        // Also, maybe this one shouldn't be the default?
+        match (fk, ctx.options().convert_floats) {
+            (FloatKind::Float, true) => quote! { f32 },
+            (FloatKind::Double, true) => quote! { f64 },
+            (FloatKind::Float, false) => raw_type(ctx, "c_float"),
+            (FloatKind::Double, false) => raw_type(ctx, "c_double"),
+            (FloatKind::LongDouble, _) => {
+                match layout {
+                    Some(layout) => {
+                        match layout.size {
+                            4 => quote! { f32 },
+                            8 => quote! { f64 },
+                            // TODO(emilio): If rust ever gains f128 we should
+                            // use it here and below.
+                            _ => super::integer_type(ctx, layout)
+                                .unwrap_or(quote! { f64 }),
+                        }
+                    }
+                    None => {
+                        debug_assert!(
+                            false,
+                            "How didn't we know the layout for a primitive type?"
+                        );
+                        quote! { f64 }
+                    }
+                }
+            }
+            (FloatKind::Float128, _) => {
+                if ctx.options().rust_features.i128_and_u128 {
+                    quote! { u128 }
+                } else {
+                    quote! { [u64; 2] }
+                }
+            }
+        }
+    }
+
+    pub fn int_expr(val: i64) -> TokenStream {
+        // Don't use quote! { #val } because that adds the type suffix.
+        let val = proc_macro2::Literal::i64_unsuffixed(val);
+        quote!(#val)
+    }
+
+    pub fn uint_expr(val: u64) -> TokenStream {
+        // Don't use quote! { #val } because that adds the type suffix.
+        let val = proc_macro2::Literal::u64_unsuffixed(val);
+        quote!(#val)
+    }
+
+    pub fn byte_array_expr(bytes: &[u8]) -> TokenStream {
+        let mut bytes: Vec<_> = bytes.to_vec();
+        bytes.push(0);
+        quote! { [ #(#bytes),* ] }
+    }
+
+    pub fn cstr_expr(mut string: String) -> TokenStream {
+        string.push('\0');
+        let b = proc_macro2::Literal::byte_string(string.as_bytes());
+        quote! {
+            #b
+        }
+    }
+
+    pub fn float_expr(ctx: &BindgenContext, f: f64) -> Result<TokenStream, ()> {
+        if f.is_finite() {
+            let val = proc_macro2::Literal::f64_unsuffixed(f);
+
+            return Ok(quote!(#val));
+        }
+
+        let prefix = ctx.trait_prefix();
+
+        if f.is_nan() {
+            return Ok(quote! {
+                ::#prefix::f64::NAN
+            });
+        }
+
+        if f.is_infinite() {
+            return Ok(if f.is_sign_positive() {
+                quote! {
+                    ::#prefix::f64::INFINITY
+                }
+            } else {
+                quote! {
+                    ::#prefix::f64::NEG_INFINITY
+                }
+            });
+        }
+
+        warn!("Unknown non-finite float number: {:?}", f);
+        Err(())
+    }
+
+    pub fn arguments_from_signature(
+        signature: &FunctionSig,
+        ctx: &BindgenContext,
+    ) -> Vec<TokenStream> {
+        let mut unnamed_arguments = 0;
+        signature
+            .argument_types()
+            .iter()
+            .map(|&(ref name, _ty)| match *name {
+                Some(ref name) => {
+                    let name = ctx.rust_ident(name);
+                    quote! { #name }
+                }
+                None => {
+                    unnamed_arguments += 1;
+                    let name =
+                        ctx.rust_ident(format!("arg{}", unnamed_arguments));
+                    quote! { #name }
+                }
+            })
+            .collect()
+    }
+}
diff --git a/third_party/rust/bindgen/codegen/impl_debug.rs b/third_party/rust/bindgen/codegen/impl_debug.rs
new file mode 100644
index 0000000000..0e2cd33ad5
--- /dev/null
+++ b/third_party/rust/bindgen/codegen/impl_debug.rs
@@ -0,0 +1,245 @@
+use crate::ir::comp::{BitfieldUnit, CompKind, Field, FieldData, FieldMethods};
+use crate::ir::context::BindgenContext;
+use crate::ir::item::{HasTypeParamInArray, IsOpaque, Item, ItemCanonicalName};
+use crate::ir::ty::{TypeKind, RUST_DERIVE_IN_ARRAY_LIMIT};
+
+pub fn gen_debug_impl(
+    ctx: &BindgenContext,
+    fields: &[Field],
+    item: &Item,
+    kind: CompKind,
+) -> proc_macro2::TokenStream {
+    let struct_name = item.canonical_name(ctx);
+    let mut format_string = format!("{} {{{{ ", struct_name);
+    let mut tokens = vec![];
+
+    if item.is_opaque(ctx, &()) {
+        format_string.push_str("opaque");
+    } else {
+        match kind {
+            CompKind::Union => {
+                format_string.push_str("union");
+            }
+            CompKind::Struct => {
+                let processed_fields = fields.iter().filter_map(|f| match f {
+                    Field::DataMember(ref fd) => fd.impl_debug(ctx, ()),
+                    Field::Bitfields(ref bu) => bu.impl_debug(ctx, ()),
+                });
+
+                for (i, (fstring, toks)) in processed_fields.enumerate() {
+                    if i > 0 {
+                        format_string.push_str(", ");
+                    }
+                    tokens.extend(toks);
+                    format_string.push_str(&fstring);
+                }
+            }
+        }
+    }
+
+    format_string.push_str(" }}");
+    tokens.insert(0, quote! { #format_string });
+
+    let prefix = ctx.trait_prefix();
+
+    quote! {
+        fn fmt(&self, f: &mut ::#prefix::fmt::Formatter<'_>) -> ::#prefix ::fmt::Result {
+            write!(f, #( #tokens ),*)
+        }
+    }
+}
+
+/// A trait for the things which we can codegen tokens that contribute towards a
+/// generated `impl Debug`.
+pub trait ImplDebug<'a> {
+    /// Any extra parameter required by this a particular `ImplDebug` implementation.
+    type Extra;
+
+    /// Generate a format string snippet to be included in the larger `impl Debug`
+    /// format string, and the code to get the format string's interpolation values.
+    fn impl_debug(
+        &self,
+        ctx: &BindgenContext,
+        extra: Self::Extra,
+    ) -> Option<(String, Vec<proc_macro2::TokenStream>)>;
+}
+
+impl<'a> ImplDebug<'a> for FieldData {
+    type Extra = ();
+
+    fn impl_debug(
+        &self,
+        ctx: &BindgenContext,
+        _: Self::Extra,
+    ) -> Option<(String, Vec<proc_macro2::TokenStream>)> {
+        if let Some(name) = self.name() {
+            ctx.resolve_item(self.ty()).impl_debug(ctx, name)
+        } else {
+            None
+        }
+    }
+}
+
+impl<'a> ImplDebug<'a> for BitfieldUnit {
+    type Extra = ();
+
+    fn impl_debug(
+        &self,
+        ctx: &BindgenContext,
+        _: Self::Extra,
+    ) -> Option<(String, Vec<proc_macro2::TokenStream>)> {
+        let mut format_string = String::new();
+        let mut tokens = vec![];
+        for (i, bitfield) in self.bitfields().iter().enumerate() {
+            if i > 0 {
+                format_string.push_str(", ");
+            }
+
+            if let Some(bitfield_name) = bitfield.name() {
+                format_string.push_str(&format!("{} : {{:?}}", bitfield_name));
+                let getter_name = bitfield.getter_name();
+                let name_ident = ctx.rust_ident_raw(getter_name);
+                tokens.push(quote! {
+                    self.#name_ident ()
+                });
+            }
+        }
+
+        Some((format_string, tokens))
+    }
+}
+
+impl<'a> ImplDebug<'a> for Item {
+    type Extra = &'a str;
+
+    fn impl_debug(
+        &self,
+        ctx: &BindgenContext,
+        name: &str,
+    ) -> Option<(String, Vec<proc_macro2::TokenStream>)> {
+        let name_ident = ctx.rust_ident(name);
+
+        // We don't know if blocklisted items `impl Debug` or not, so we can't
+        // add them to the format string we're building up.
+        if !ctx.allowlisted_items().contains(&self.id()) {
+            return None;
+        }
+
+        let ty = match self.as_type() {
+            Some(ty) => ty,
+            None => {
+                return None;
+            }
+        };
+
+        fn debug_print(
+            name: &str,
+            name_ident: proc_macro2::TokenStream,
+        ) -> Option<(String, Vec<proc_macro2::TokenStream>)> {
+            Some((
+                format!("{}: {{:?}}", name),
+                vec![quote! {
+                    self.#name_ident
+                }],
+            ))
+        }
+
+        match *ty.kind() {
+            // Handle the simple cases.
+            TypeKind::Void |
+            TypeKind::NullPtr |
+            TypeKind::Int(..) |
+            TypeKind::Float(..) |
+            TypeKind::Complex(..) |
+            TypeKind::Function(..) |
+            TypeKind::Enum(..) |
+            TypeKind::Reference(..) |
+            TypeKind::UnresolvedTypeRef(..) |
+            TypeKind::ObjCInterface(..) |
+            TypeKind::ObjCId |
+            TypeKind::Comp(..) |
+            TypeKind::ObjCSel => debug_print(name, quote! { #name_ident }),
+
+            TypeKind::TemplateInstantiation(ref inst) => {
+                if inst.is_opaque(ctx, self) {
+                    Some((format!("{}: opaque", name), vec![]))
+                } else {
+                    debug_print(name, quote! { #name_ident })
+                }
+            }
+
+            // The generic is not required to implement Debug, so we can not debug print that type
+            TypeKind::TypeParam => {
+                Some((format!("{}: Non-debuggable generic", name), vec![]))
+            }
+
+            TypeKind::Array(_, len) => {
+                // Generics are not required to implement Debug
+                if self.has_type_param_in_array(ctx) {
+                    Some((
+                        format!("{}: Array with length {}", name, len),
+                        vec![],
+                    ))
+                } else if len < RUST_DERIVE_IN_ARRAY_LIMIT ||
+                    ctx.options().rust_features().larger_arrays
+                {
+                    // The simple case
+                    debug_print(name, quote! { #name_ident })
+                } else if ctx.options().use_core {
+                    // There is no String in core; reducing field visibility to avoid breaking
+                    // no_std setups.
+                    Some((format!("{}: [...]", name), vec![]))
+                } else {
+                    // Let's implement our own print function
+                    Some((
+                        format!("{}: [{{}}]", name),
+                        vec![quote! {
+                            self.#name_ident
+                                .iter()
+                                .enumerate()
+                                .map(|(i, v)| format!("{}{:?}", if i > 0 { ", " } else { "" }, v))
+                                .collect::<String>()
+                        }],
+                    ))
+                }
+            }
+            TypeKind::Vector(_, len) => {
+                if ctx.options().use_core {
+                    // There is no format! in core; reducing field visibility to avoid breaking
+                    // no_std setups.
+                    Some((format!("{}(...)", name), vec![]))
+                } else {
+                    let self_ids = 0..len;
+                    Some((
+                        format!("{}({{}})", name),
+                        vec![quote! {
+                            #(format!("{:?}", self.#self_ids)),*
+                        }],
+                    ))
+                }
+            }
+
+            TypeKind::ResolvedTypeRef(t) |
+            TypeKind::TemplateAlias(t, _) |
+            TypeKind::Alias(t) |
+            TypeKind::BlockPointer(t) => {
+                // We follow the aliases
+                ctx.resolve_item(t).impl_debug(ctx, name)
+            }
+
+            TypeKind::Pointer(inner) => {
+                let inner_type = ctx.resolve_type(inner).canonical_type(ctx);
+                match *inner_type.kind() {
+                    TypeKind::Function(ref sig)
+                        if !sig.function_pointers_can_derive() =>
+                    {
+                        Some((format!("{}: FunctionPointer", name), vec![]))
+                    }
+                    _ => debug_print(name, quote! { #name_ident }),
+                }
+            }
+
+            TypeKind::Opaque => None,
+        }
+    }
+}
diff --git a/third_party/rust/bindgen/codegen/impl_partialeq.rs b/third_party/rust/bindgen/codegen/impl_partialeq.rs
new file mode 100644
index 0000000000..960306ffc6
--- /dev/null
+++ b/third_party/rust/bindgen/codegen/impl_partialeq.rs
@@ -0,0 +1,142 @@
+use crate::ir::comp::{CompInfo, CompKind, Field, FieldMethods};
+use crate::ir::context::BindgenContext;
+use crate::ir::item::{IsOpaque, Item};
+use crate::ir::ty::{TypeKind, RUST_DERIVE_IN_ARRAY_LIMIT};
+
+/// Generate a manual implementation of `PartialEq` trait for the
+/// specified compound type.
+pub fn gen_partialeq_impl(
+    ctx: &BindgenContext,
+    comp_info: &CompInfo,
+    item: &Item,
+    ty_for_impl: &proc_macro2::TokenStream,
+) -> Option<proc_macro2::TokenStream> {
+    let mut tokens = vec![];
+
+    if item.is_opaque(ctx, &()) {
+        tokens.push(quote! {
+            &self._bindgen_opaque_blob[..] == &other._bindgen_opaque_blob[..]
+        });
+    } else if comp_info.kind() == CompKind::Union {
+        assert!(!ctx.options().rust_features().untagged_union);
+        tokens.push(quote! {
+            &self.bindgen_union_field[..] == &other.bindgen_union_field[..]
+        });
+    } else {
+        for base in comp_info.base_members().iter() {
+            if !base.requires_storage(ctx) {
+                continue;
+            }
+
+            let ty_item = ctx.resolve_item(base.ty);
+            let field_name = &base.field_name;
+
+            if ty_item.is_opaque(ctx, &()) {
+                let field_name = ctx.rust_ident(field_name);
+                tokens.push(quote! {
+                    &self. #field_name [..] == &other. #field_name [..]
+                });
+            } else {
+                tokens.push(gen_field(ctx, ty_item, field_name));
+            }
+        }
+
+        for field in comp_info.fields() {
+            match *field {
+                Field::DataMember(ref fd) => {
+                    let ty_item = ctx.resolve_item(fd.ty());
+                    let name = fd.name().unwrap();
+                    tokens.push(gen_field(ctx, ty_item, name));
+                }
+                Field::Bitfields(ref bu) => {
+                    for bitfield in bu.bitfields() {
+                        if bitfield.name().is_some() {
+                            let getter_name = bitfield.getter_name();
+                            let name_ident = ctx.rust_ident_raw(getter_name);
+                            tokens.push(quote! {
+                                self.#name_ident () == other.#name_ident ()
+                            });
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    Some(quote! {
+        fn eq(&self, other: & #ty_for_impl) -> bool {
+            #( #tokens )&&*
+        }
+    })
+}
+
+fn gen_field(
+    ctx: &BindgenContext,
+    ty_item: &Item,
+    name: &str,
+) -> proc_macro2::TokenStream {
+    fn quote_equals(
+        name_ident: proc_macro2::Ident,
+    ) -> proc_macro2::TokenStream {
+        quote! { self.#name_ident == other.#name_ident }
+    }
+
+    let name_ident = ctx.rust_ident(name);
+    let ty = ty_item.expect_type();
+
+    match *ty.kind() {
+        TypeKind::Void |
+        TypeKind::NullPtr |
+        TypeKind::Int(..) |
+        TypeKind::Complex(..) |
+        TypeKind::Float(..) |
+        TypeKind::Enum(..) |
+        TypeKind::TypeParam |
+        TypeKind::UnresolvedTypeRef(..) |
+        TypeKind::Reference(..) |
+        TypeKind::ObjCInterface(..) |
+        TypeKind::ObjCId |
+        TypeKind::ObjCSel |
+        TypeKind::Comp(..) |
+        TypeKind::Pointer(_) |
+        TypeKind::Function(..) |
+        TypeKind::Opaque => quote_equals(name_ident),
+
+        TypeKind::TemplateInstantiation(ref inst) => {
+            if inst.is_opaque(ctx, ty_item) {
+                quote! {
+                    &self. #name_ident [..] == &other. #name_ident [..]
+                }
+            } else {
+                quote_equals(name_ident)
+            }
+        }
+
+        TypeKind::Array(_, len) => {
+            if len <= RUST_DERIVE_IN_ARRAY_LIMIT ||
+                ctx.options().rust_features().larger_arrays
+            {
+                quote_equals(name_ident)
+            } else {
+                quote! {
+                    &self. #name_ident [..] == &other. #name_ident [..]
+                }
+            }
+        }
+        TypeKind::Vector(_, len) => {
+            let self_ids = 0..len;
+            let other_ids = 0..len;
+            quote! {
+                #(self.#self_ids == other.#other_ids &&)* true
+            }
+        }
+
+        TypeKind::ResolvedTypeRef(t) |
+        TypeKind::TemplateAlias(t, _) |
+        TypeKind::Alias(t) |
+        TypeKind::BlockPointer(t) => {
+            let inner_item = ctx.resolve_item(t);
+            gen_field(ctx, inner_item, name)
+        }
+    }
+}
diff --git a/third_party/rust/bindgen/codegen/mod.rs b/third_party/rust/bindgen/codegen/mod.rs
new file mode 100644
index 0000000000..e537242710
--- /dev/null
+++ b/third_party/rust/bindgen/codegen/mod.rs
@@ -0,0 +1,5047 @@
+mod dyngen;
+mod error;
+mod helpers;
+mod impl_debug;
+mod impl_partialeq;
+mod postprocessing;
+pub mod struct_layout;
+
+#[cfg(test)]
+#[allow(warnings)]
+pub(crate) mod bitfield_unit;
+#[cfg(all(test, target_endian = "little"))]
+mod bitfield_unit_tests;
+
+use self::dyngen::DynamicItems;
+use self::helpers::attributes;
+use self::struct_layout::StructLayoutTracker;
+
+use super::BindgenOptions;
+
+use crate::ir::analysis::{HasVtable, Sizedness};
+use crate::ir::annotations::FieldAccessorKind;
+use crate::ir::comp::{
+    Bitfield, BitfieldUnit, CompInfo, CompKind, Field, FieldData, FieldMethods,
+    Method, MethodKind,
+};
+use crate::ir::context::{BindgenContext, ItemId};
+use crate::ir::derive::{
+    CanDerive, CanDeriveCopy, CanDeriveDebug, CanDeriveDefault, CanDeriveEq,
+    CanDeriveHash, CanDeriveOrd, CanDerivePartialEq, CanDerivePartialOrd,
+};
+use crate::ir::dot;
+use crate::ir::enum_ty::{Enum, EnumVariant, EnumVariantValue};
+use crate::ir::function::{
+    Abi, ClangAbi, Function, FunctionKind, FunctionSig, Linkage,
+};
+use crate::ir::int::IntKind;
+use crate::ir::item::{IsOpaque, Item, ItemCanonicalName, ItemCanonicalPath};
+use crate::ir::item_kind::ItemKind;
+use crate::ir::layout::Layout;
+use crate::ir::module::Module;
+use crate::ir::objc::{ObjCInterface, ObjCMethod};
+use crate::ir::template::{
+    AsTemplateParam, TemplateInstantiation, TemplateParameters,
+};
+use crate::ir::ty::{Type, TypeKind};
+use crate::ir::var::Var;
+
+use proc_macro2::{self, Ident, Span};
+use quote::TokenStreamExt;
+
+use crate::{Entry, HashMap, HashSet};
+use std::borrow::Cow;
+use std::cell::Cell;
+use std::collections::VecDeque;
+use std::fmt::Write;
+use std::iter;
+use std::ops;
+use std::str::FromStr;
+
+// Name of type defined in constified enum module
+pub static CONSTIFIED_ENUM_MODULE_REPR_NAME: &str = "Type";
+
+fn top_level_path(
+    ctx: &BindgenContext,
+    item: &Item,
+) -> Vec<proc_macro2::TokenStream> {
+    let mut path = vec![quote! { self }];
+
+    if ctx.options().enable_cxx_namespaces {
+        for _ in 0..item.codegen_depth(ctx) {
+            path.push(quote! { super });
+        }
+    }
+
+    path
+}
+
+fn root_import(
+    ctx: &BindgenContext,
+    module: &Item,
+) -> proc_macro2::TokenStream {
+    assert!(ctx.options().enable_cxx_namespaces, "Somebody messed it up");
+    assert!(module.is_module());
+
+    let mut path = top_level_path(ctx, module);
+
+    let root = ctx.root_module().canonical_name(ctx);
+    let root_ident = ctx.rust_ident(root);
+    path.push(quote! { #root_ident });
+
+    let mut tokens = quote! {};
+    tokens.append_separated(path, quote!(::));
+
+    quote! {
+        #[allow(unused_imports)]
+        use #tokens ;
+    }
+}
+
+bitflags! {
+    struct DerivableTraits: u16 {
+        const DEBUG       = 1 << 0;
+        const DEFAULT     = 1 << 1;
+        const COPY        = 1 << 2;
+        const CLONE       = 1 << 3;
+        const HASH        = 1 << 4;
+        const PARTIAL_ORD = 1 << 5;
+        const ORD         = 1 << 6;
+        const PARTIAL_EQ  = 1 << 7;
+        const EQ          = 1 << 8;
+    }
+}
+
+fn derives_of_item(
+    item: &Item,
+    ctx: &BindgenContext,
+    packed: bool,
+) -> DerivableTraits {
+    let mut derivable_traits = DerivableTraits::empty();
+
+    let all_template_params = item.all_template_params(ctx);
+
+    if item.can_derive_copy(ctx) && !item.annotations().disallow_copy() {
+        derivable_traits |= DerivableTraits::COPY;
+
+        if ctx.options().rust_features().builtin_clone_impls ||
+            !all_template_params.is_empty()
+        {
+            // FIXME: This requires extra logic if you have a big array in a
+            // templated struct. The reason for this is that the magic:
+            //     fn clone(&self) -> Self { *self }
+            // doesn't work for templates.
+            //
+            // It's not hard to fix though.
+            derivable_traits |= DerivableTraits::CLONE;
+        }
+    } else if packed {
+        // If the struct or union is packed, deriving from Copy is required for
+        // deriving from any other trait.
+        return derivable_traits;
+    }
+
+    if item.can_derive_debug(ctx) && !item.annotations().disallow_debug() {
+        derivable_traits |= DerivableTraits::DEBUG;
+    }
+
+    if item.can_derive_default(ctx) && !item.annotations().disallow_default() {
+        derivable_traits |= DerivableTraits::DEFAULT;
+    }
+
+    if item.can_derive_hash(ctx) {
+        derivable_traits |= DerivableTraits::HASH;
+    }
+
+    if item.can_derive_partialord(ctx) {
+        derivable_traits |= DerivableTraits::PARTIAL_ORD;
+    }
+
+    if item.can_derive_ord(ctx) {
+        derivable_traits |= DerivableTraits::ORD;
+    }
+
+    if item.can_derive_partialeq(ctx) {
+        derivable_traits |= DerivableTraits::PARTIAL_EQ;
+    }
+
+    if item.can_derive_eq(ctx) {
+        derivable_traits |= DerivableTraits::EQ;
+    }
+
+    derivable_traits
+}
+
+impl From<DerivableTraits> for Vec<&'static str> {
+    fn from(derivable_traits: DerivableTraits) -> Vec<&'static str> {
+        [
+            (DerivableTraits::DEBUG, "Debug"),
+            (DerivableTraits::DEFAULT, "Default"),
+            (DerivableTraits::COPY, "Copy"),
+            (DerivableTraits::CLONE, "Clone"),
+            (DerivableTraits::HASH, "Hash"),
+            (DerivableTraits::PARTIAL_ORD, "PartialOrd"),
+            (DerivableTraits::ORD, "Ord"),
+            (DerivableTraits::PARTIAL_EQ, "PartialEq"),
+            (DerivableTraits::EQ, "Eq"),
+        ]
+        .iter()
+        .filter_map(|&(flag, derive)| {
+            Some(derive).filter(|_| derivable_traits.contains(flag))
+        })
+        .collect()
+    }
+}
+
+struct CodegenResult<'a> {
+    items: Vec<proc_macro2::TokenStream>,
+    dynamic_items: DynamicItems,
+
+    /// A monotonic counter used to add stable unique id's to stuff that doesn't
+    /// need to be referenced by anything.
+    codegen_id: &'a Cell<usize>,
+
+    /// Whether a bindgen union has been generated at least once.
+    saw_bindgen_union: bool,
+
+    /// Whether an incomplete array has been generated at least once.
+    saw_incomplete_array: bool,
+
+    /// Whether Objective C types have been seen at least once.
+    saw_objc: bool,
+
+    /// Whether Apple block types have been seen at least once.
+    saw_block: bool,
+
+    /// Whether a bitfield allocation unit has been seen at least once.
+    saw_bitfield_unit: bool,
+
+    items_seen: HashSet<ItemId>,
+    /// The set of generated function/var names, needed because in C/C++ is
+    /// legal to do something like:
+    ///
+    /// ```c++
+    /// extern "C" {
+    ///   void foo();
+    ///   extern int bar;
+    /// }
+    ///
+    /// extern "C" {
+    ///   void foo();
+    ///   extern int bar;
+    /// }
+    /// ```
+    ///
+    /// Being these two different declarations.
+    functions_seen: HashSet<String>,
+    vars_seen: HashSet<String>,
+
+    /// Used for making bindings to overloaded functions. Maps from a canonical
+    /// function name to the number of overloads we have already codegen'd for
+    /// that name. This lets us give each overload a unique suffix.
+    overload_counters: HashMap<String, u32>,
+}
+
+impl<'a> CodegenResult<'a> {
+    fn new(codegen_id: &'a Cell<usize>) -> Self {
+        CodegenResult {
+            items: vec![],
+            dynamic_items: DynamicItems::new(),
+            saw_bindgen_union: false,
+            saw_incomplete_array: false,
+            saw_objc: false,
+            saw_block: false,
+            saw_bitfield_unit: false,
+            codegen_id,
+            items_seen: Default::default(),
+            functions_seen: Default::default(),
+            vars_seen: Default::default(),
+            overload_counters: Default::default(),
+        }
+    }
+
+    fn dynamic_items(&mut self) -> &mut DynamicItems {
+        &mut self.dynamic_items
+    }
+
+    fn saw_bindgen_union(&mut self) {
+        self.saw_bindgen_union = true;
+    }
+
+    fn saw_incomplete_array(&mut self) {
+        self.saw_incomplete_array = true;
+    }
+
+    fn saw_objc(&mut self) {
+        self.saw_objc = true;
+    }
+
+    fn saw_block(&mut self) {
+        self.saw_block = true;
+    }
+
+    fn saw_bitfield_unit(&mut self) {
+        self.saw_bitfield_unit = true;
+    }
+
+    fn seen<Id: Into<ItemId>>(&self, item: Id) -> bool {
+        self.items_seen.contains(&item.into())
+    }
+
+    fn set_seen<Id: Into<ItemId>>(&mut self, item: Id) {
+        self.items_seen.insert(item.into());
+    }
+
+    fn seen_function(&self, name: &str) -> bool {
+        self.functions_seen.contains(name)
+    }
+
+    fn saw_function(&mut self, name: &str) {
+        self.functions_seen.insert(name.into());
+    }
+
+    /// Get the overload number for the given function name. Increments the
+    /// counter internally so the next time we ask for the overload for this
+    /// name, we get the incremented value, and so on.
+    fn overload_number(&mut self, name: &str) -> u32 {
+        let counter = self.overload_counters.entry(name.into()).or_insert(0);
+        let number = *counter;
+        *counter += 1;
+        number
+    }
+
+    fn seen_var(&self, name: &str) -> bool {
+        self.vars_seen.contains(name)
+    }
+
+    fn saw_var(&mut self, name: &str) {
+        self.vars_seen.insert(name.into());
+    }
+
+    fn inner<F>(&mut self, cb: F) -> Vec<proc_macro2::TokenStream>
+    where
+        F: FnOnce(&mut Self),
+    {
+        let mut new = Self::new(self.codegen_id);
+
+        cb(&mut new);
+
+        self.saw_incomplete_array |= new.saw_incomplete_array;
+        self.saw_objc |= new.saw_objc;
+        self.saw_block |= new.saw_block;
+        self.saw_bitfield_unit |= new.saw_bitfield_unit;
+        self.saw_bindgen_union |= new.saw_bindgen_union;
+
+        new.items
+    }
+}
+
+impl<'a> ops::Deref for CodegenResult<'a> {
+    type Target = Vec<proc_macro2::TokenStream>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.items
+    }
+}
+
+impl<'a> ops::DerefMut for CodegenResult<'a> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.items
+    }
+}
+
+/// A trait to convert a rust type into a pointer, optionally const, to the same
+/// type.
+trait ToPtr {
+    fn to_ptr(self, is_const: bool) -> proc_macro2::TokenStream;
+}
+
+impl ToPtr for proc_macro2::TokenStream {
+    fn to_ptr(self, is_const: bool) -> proc_macro2::TokenStream {
+        if is_const {
+            quote! { *const #self }
+        } else {
+            quote! { *mut #self }
+        }
+    }
+}
+
+/// An extension trait for `proc_macro2::TokenStream` that lets us append any implicit
+/// template parameters that exist for some type, if necessary.
+trait AppendImplicitTemplateParams {
+    fn append_implicit_template_params(
+        &mut self,
+        ctx: &BindgenContext,
+        item: &Item,
+    );
+}
+
+impl AppendImplicitTemplateParams for proc_macro2::TokenStream {
+    fn append_implicit_template_params(
+        &mut self,
+        ctx: &BindgenContext,
+        item: &Item,
+    ) {
+        let item = item.id().into_resolver().through_type_refs().resolve(ctx);
+
+        match *item.expect_type().kind() {
+            TypeKind::UnresolvedTypeRef(..) => {
+                unreachable!("already resolved unresolved type refs")
+            }
+            TypeKind::ResolvedTypeRef(..) => {
+                unreachable!("we resolved item through type refs")
+            }
+
+            // None of these types ever have implicit template parameters.
+            TypeKind::Void |
+            TypeKind::NullPtr |
+            TypeKind::Pointer(..) |
+            TypeKind::Reference(..) |
+            TypeKind::Int(..) |
+            TypeKind::Float(..) |
+            TypeKind::Complex(..) |
+            TypeKind::Array(..) |
+            TypeKind::TypeParam |
+            TypeKind::Opaque |
+            TypeKind::Function(..) |
+            TypeKind::Enum(..) |
+            TypeKind::ObjCId |
+            TypeKind::ObjCSel |
+            TypeKind::TemplateInstantiation(..) => return,
+            _ => {}
+        }
+
+        let params: Vec<_> = item
+            .used_template_params(ctx)
+            .iter()
+            .map(|p| {
+                p.try_to_rust_ty(ctx, &())
+                    .expect("template params cannot fail to be a rust type")
+            })
+            .collect();
+        if !params.is_empty() {
+            self.append_all(quote! {
+                < #( #params ),* >
+            });
+        }
+    }
+}
+
+trait CodeGenerator {
+    /// Extra information from the caller.
+    type Extra;
+
+    /// Extra information returned to the caller.
+    type Return;
+
+    fn codegen<'a>(
+        &self,
+        ctx: &BindgenContext,
+        result: &mut CodegenResult<'a>,
+        extra: &Self::Extra,
+    ) -> Self::Return;
+}
+
+impl Item {
+    fn process_before_codegen(
+        &self,
+        ctx: &BindgenContext,
+        result: &mut CodegenResult,
+    ) -> bool {
+        if !self.is_enabled_for_codegen(ctx) {
+            return false;
+        }
+
+        if self.is_blocklisted(ctx) || result.seen(self.id()) {
+            debug!(
+                "<Item as CodeGenerator>::process_before_codegen: Ignoring hidden or seen: \
+                 self = {:?}",
+                self
+            );
+            return false;
+        }
+
+        if !ctx.codegen_items().contains(&self.id()) {
+            // TODO(emilio, #453): Figure out what to do when this happens
+            // legitimately, we could track the opaque stuff and disable the
+            // assertion there I guess.
+            warn!("Found non-allowlisted item in code generation: {:?}", self);
+        }
+
+        result.set_seen(self.id());
+        true
+    }
+}
+
+impl CodeGenerator for Item {
+    type Extra = ();
+    type Return = ();
+
+    fn codegen<'a>(
+        &self,
+        ctx: &BindgenContext,
+        result: &mut CodegenResult<'a>,
+        _extra: &(),
+    ) {
+        debug!("<Item as CodeGenerator>::codegen: self = {:?}", self);
+        if !self.process_before_codegen(ctx, result) {
+            return;
+        }
+
+        match *self.kind() {
+            ItemKind::Module(ref module) => {
+                module.codegen(ctx, result, self);
+            }
+            ItemKind::Function(ref fun) => {
+                fun.codegen(ctx, result, self);
+            }
+            ItemKind::Var(ref var) => {
+                var.codegen(ctx, result, self);
+            }
+            ItemKind::Type(ref ty) => {
+                ty.codegen(ctx, result, self);
+            }
+        }
+    }
+}
+
+impl CodeGenerator for Module {
+    type Extra = Item;
+    type Return = ();
+
+    fn codegen<'a>(
+        &self,
+        ctx: &BindgenContext,
+        result: &mut CodegenResult<'a>,
+        item: &Item,
+    ) {
+        debug!("<Module as CodeGenerator>::codegen: item = {:?}", item);
+
+        let codegen_self = |result: &mut CodegenResult,
+                            found_any: &mut bool| {
+            for child in self.children() {
+                if ctx.codegen_items().contains(child) {
+                    *found_any = true;
+                    ctx.resolve_item(*child).codegen(ctx, result, &());
+                }
+            }
+
+            if item.id() == ctx.root_module() {
+                if result.saw_block {
+                    utils::prepend_block_header(ctx, &mut *result);
+                }
+                if result.saw_bindgen_union {
+                    utils::prepend_union_types(ctx, &mut *result);
+                }
+                if result.saw_incomplete_array {
+                    utils::prepend_incomplete_array_types(ctx, &mut *result);
+                }
+                if ctx.need_bindgen_complex_type() {
+                    utils::prepend_complex_type(&mut *result);
+                }
+                if result.saw_objc {
+                    utils::prepend_objc_header(ctx, &mut *result);
+                }
+                if result.saw_bitfield_unit {
+                    utils::prepend_bitfield_unit_type(ctx, &mut *result);
+                }
+            }
+        };
+
+        if !ctx.options().enable_cxx_namespaces ||
+            (self.is_inline() &&
+                !ctx.options().conservative_inline_namespaces)
+        {
+            codegen_self(result, &mut false);
+            return;
+        }
+
+        let mut found_any = false;
+        let inner_items = result.inner(|result| {
+            result.push(root_import(ctx, item));
+
+            let path = item.namespace_aware_canonical_path(ctx).join("::");
+            if let Some(raw_lines) = ctx.options().module_lines.get(&path) {
+                for raw_line in raw_lines {
+                    found_any = true;
+                    result.push(
+                        proc_macro2::TokenStream::from_str(raw_line).unwrap(),
+                    );
+                }
+            }
+
+            codegen_self(result, &mut found_any);
+        });
+
+        // Don't bother creating an empty module.
+        if !found_any {
+            return;
+        }
+
+        let name = item.canonical_name(ctx);
+        let ident = ctx.rust_ident(name);
+        result.push(if item.id() == ctx.root_module() {
+            quote! {
+                #[allow(non_snake_case, non_camel_case_types, non_upper_case_globals)]
+                pub mod #ident {
+                    #( #inner_items )*
+                }
+            }
+        } else {
+            quote! {
+                pub mod #ident {
+                    #( #inner_items )*
+                }
+            }
+        });
+    }
+}
+
+impl CodeGenerator for Var {
+    type Extra = Item;
+    type Return = ();
+
+    fn codegen<'a>(
+        &self,
+        ctx: &BindgenContext,
+        result: &mut CodegenResult<'a>,
+        item: &Item,
+    ) {
+        use crate::ir::var::VarType;
+        debug!("<Var as CodeGenerator>::codegen: item = {:?}", item);
+        debug_assert!(item.is_enabled_for_codegen(ctx));
+
+        let canonical_name = item.canonical_name(ctx);
+
+        if result.seen_var(&canonical_name) {
+            return;
+        }
+        result.saw_var(&canonical_name);
+
+        let canonical_ident = ctx.rust_ident(&canonical_name);
+
+        // We can't generate bindings to static variables of templates. The
+        // number of actual variables for a single declaration are open ended
+        // and we don't know what instantiations do or don't exist.
+        if !item.all_template_params(ctx).is_empty() {
+            return;
+        }
+
+        let mut attrs = vec![];
+        if let Some(comment) = item.comment(ctx) {
+            attrs.push(attributes::doc(comment));
+        }
+
+        let ty = self.ty().to_rust_ty_or_opaque(ctx, &());
+
+        if let Some(val) = self.val() {
+            match *val {
+                VarType::Bool(val) => {
+                    result.push(quote! {
+                        #(#attrs)*
+                        pub const #canonical_ident : #ty = #val ;
+                    });
+                }
+                VarType::Int(val) => {
+                    let int_kind = self
+                        .ty()
+                        .into_resolver()
+                        .through_type_aliases()
+                        .through_type_refs()
+                        .resolve(ctx)
+                        .expect_type()
+                        .as_integer()
+                        .unwrap();
+                    let val = if int_kind.is_signed() {
+                        helpers::ast_ty::int_expr(val)
+                    } else {
+                        helpers::ast_ty::uint_expr(val as _)
+                    };
+                    result.push(quote! {
+                        #(#attrs)*
+                        pub const #canonical_ident : #ty = #val ;
+                    });
+                }
+                VarType::String(ref bytes) => {
+                    // Account the trailing zero.
+                    //
+                    // TODO: Here we ignore the type we just made up, probably
+                    // we should refactor how the variable type and ty id work.
+                    let len = bytes.len() + 1;
+                    let ty = quote! {
+                        [u8; #len]
+                    };
+
+                    match String::from_utf8(bytes.clone()) {
+                        Ok(string) => {
+                            let cstr = helpers::ast_ty::cstr_expr(string);
+                            if ctx
+                                .options()
+                                .rust_features
+                                .static_lifetime_elision
+                            {
+                                result.push(quote! {
+                                    #(#attrs)*
+                                    pub const #canonical_ident : &#ty = #cstr ;
+                                });
+                            } else {
+                                result.push(quote! {
+                                    #(#attrs)*
+                                    pub const #canonical_ident : &'static #ty = #cstr ;
+                                });
+                            }
+                        }
+                        Err(..) => {
+                            let bytes = helpers::ast_ty::byte_array_expr(bytes);
+                            result.push(quote! {
+                                #(#attrs)*
+                                pub const #canonical_ident : #ty = #bytes ;
+                            });
+                        }
+                    }
+                }
+                VarType::Float(f) => {
+                    if let Ok(expr) = helpers::ast_ty::float_expr(ctx, f) {
+                        result.push(quote! {
+                            #(#attrs)*
+                            pub const #canonical_ident : #ty = #expr ;
+                        });
+                    }
+                }
+                VarType::Char(c) => {
+                    result.push(quote! {
+                        #(#attrs)*
+                        pub const #canonical_ident : #ty = #c ;
+                    });
+                }
+            }
+        } else {
+            // If necessary, apply a `#[link_name]` attribute
+            let link_name = self.mangled_name().unwrap_or_else(|| self.name());
+            if !utils::names_will_be_identical_after_mangling(
+                &canonical_name,
+                link_name,
+                None,
+            ) {
+                attrs.push(attributes::link_name(link_name));
+            }
+
+            let maybe_mut = if self.is_const() {
+                quote! {}
+            } else {
+                quote! { mut }
+            };
+
+            let tokens = quote!(
+                extern "C" {
+                    #(#attrs)*
+                    pub static #maybe_mut #canonical_ident: #ty;
+                }
+            );
+
+            result.push(tokens);
+        }
+    }
+}
+
+impl CodeGenerator for Type {
+    type Extra = Item;
+    type Return = ();
+
+    fn codegen<'a>(
+        &self,
+        ctx: &BindgenContext,
+        result: &mut CodegenResult<'a>,
+        item: &Item,
+    ) {
+        debug!("<Type as CodeGenerator>::codegen: item = {:?}", item);
+        debug_assert!(item.is_enabled_for_codegen(ctx));
+
+        match *self.kind() {
+            TypeKind::Void |
+            TypeKind::NullPtr |
+            TypeKind::Int(..) |
+            TypeKind::Float(..) |
+            TypeKind::Complex(..) |
+            TypeKind::Array(..) |
+            TypeKind::Vector(..) |
+            TypeKind::Pointer(..) |
+            TypeKind::Reference(..) |
+            TypeKind::Function(..) |
+            TypeKind::ResolvedTypeRef(..) |
+            TypeKind::Opaque |
+            TypeKind::TypeParam => {
+                // These items don't need code generation, they only need to be
+                // converted to rust types in fields, arguments, and such.
+                // NOTE(emilio): If you add to this list, make sure to also add
+                // it to BindgenContext::compute_allowlisted_and_codegen_items.
+            }
+            TypeKind::TemplateInstantiation(ref inst) => {
+                inst.codegen(ctx, result, item)
+            }
+            TypeKind::BlockPointer(inner) => {
+                if !ctx.options().generate_block {
+                    return;
+                }
+
+                let inner_item =
+                    inner.into_resolver().through_type_refs().resolve(ctx);
+                let name = item.canonical_name(ctx);
+
+                let inner_rust_type = {
+                    if let TypeKind::Function(fnsig) =
+                        inner_item.kind().expect_type().kind()
+                    {
+                        utils::fnsig_block(ctx, fnsig)
+                    } else {
+                        panic!("invalid block typedef: {:?}", inner_item)
+                    }
+                };
+
+                let rust_name = ctx.rust_ident(name);
+
+                let mut tokens = if let Some(comment) = item.comment(ctx) {
+                    attributes::doc(comment)
+                } else {
+                    quote! {}
+                };
+
+                tokens.append_all(quote! {
+                    pub type #rust_name = #inner_rust_type ;
+                });
+
+                result.push(tokens);
+                result.saw_block();
+            }
+            TypeKind::Comp(ref ci) => ci.codegen(ctx, result, item),
+            TypeKind::TemplateAlias(inner, _) | TypeKind::Alias(inner) => {
+                let inner_item =
+                    inner.into_resolver().through_type_refs().resolve(ctx);
+                let name = item.canonical_name(ctx);
+                let path = item.canonical_path(ctx);
+
+                {
+                    let through_type_aliases = inner
+                        .into_resolver()
+                        .through_type_refs()
+                        .through_type_aliases()
+                        .resolve(ctx);
+
+                    // Try to catch the common pattern:
+                    //
+                    // typedef struct foo { ... } foo;
+                    //
+                    // here, and also other more complex cases like #946.
+                    if through_type_aliases.canonical_path(ctx) == path {
+                        return;
+                    }
+                }
+
+                // If this is a known named type, disallow generating anything
+                // for it too. If size_t -> usize conversions are enabled, we
+                // need to check that these conversions are permissible, but
+                // nothing needs to be generated, still.
+                let spelling = self.name().expect("Unnamed alias?");
+                if utils::type_from_named(ctx, spelling).is_some() {
+                    if let "size_t" | "ssize_t" = spelling {
+                        let layout = inner_item
+                            .kind()
+                            .expect_type()
+                            .layout(ctx)
+                            .expect("No layout?");
+                        assert_eq!(
+                            layout.size,
+                            ctx.target_pointer_size(),
+                            "Target platform requires `--no-size_t-is-usize`. The size of `{}` ({}) does not match the target pointer size ({})",
+                            spelling,
+                            layout.size,
+                            ctx.target_pointer_size(),
+                            );
+                        assert_eq!(
+                            layout.align,
+                            ctx.target_pointer_size(),
+                            "Target platform requires `--no-size_t-is-usize`. The alignment of `{}` ({}) does not match the target pointer size ({})",
+                            spelling,
+                            layout.align,
+                            ctx.target_pointer_size(),
+                        );
+                    }
+                    return;
+                }
+
+                let mut outer_params = item.used_template_params(ctx);
+
+                let is_opaque = item.is_opaque(ctx, &());
+                let inner_rust_type = if is_opaque {
+                    outer_params = vec![];
+                    self.to_opaque(ctx, item)
+                } else {
+                    // Its possible that we have better layout information than
+                    // the inner type does, so fall back to an opaque blob based
+                    // on our layout if converting the inner item fails.
+                    let mut inner_ty = inner_item
+                        .try_to_rust_ty_or_opaque(ctx, &())
+                        .unwrap_or_else(|_| self.to_opaque(ctx, item));
+                    inner_ty.append_implicit_template_params(ctx, inner_item);
+                    inner_ty
+                };
+
+                {
+                    // FIXME(emilio): This is a workaround to avoid generating
+                    // incorrect type aliases because of types that we haven't
+                    // been able to resolve (because, eg, they depend on a
+                    // template parameter).
+                    //
+                    // It's kind of a shame not generating them even when they
+                    // could be referenced, but we already do the same for items
+                    // with invalid template parameters, and at least this way
+                    // they can be replaced, instead of generating plain invalid
+                    // code.
+                    let inner_canon_type =
+                        inner_item.expect_type().canonical_type(ctx);
+                    if inner_canon_type.is_invalid_type_param() {
+                        warn!(
+                            "Item contained invalid named type, skipping: \
+                             {:?}, {:?}",
+                            item, inner_item
+                        );
+                        return;
+                    }
+                }
+
+                let rust_name = ctx.rust_ident(&name);
+
+                let mut tokens = if let Some(comment) = item.comment(ctx) {
+                    attributes::doc(comment)
+                } else {
+                    quote! {}
+                };
+
+                let alias_style = if ctx.options().type_alias.matches(&name) {
+                    AliasVariation::TypeAlias
+                } else if ctx.options().new_type_alias.matches(&name) {
+                    AliasVariation::NewType
+                } else if ctx.options().new_type_alias_deref.matches(&name) {
+                    AliasVariation::NewTypeDeref
+                } else {
+                    ctx.options().default_alias_style
+                };
+
+                // We prefer using `pub use` over `pub type` because of:
+                // https://github.com/rust-lang/rust/issues/26264
+                // These are the only characters allowed in simple
+                // paths, eg `good::dogs::Bront`.
+                if inner_rust_type.to_string().chars().all(|c| matches!(c, 'A'..='Z' | 'a'..='z' | '0'..='9' | ':' | '_' | ' ')) && outer_params.is_empty() &&
+                    !is_opaque &&
+                    alias_style == AliasVariation::TypeAlias &&
+                    inner_item.expect_type().canonical_type(ctx).is_enum()
+                {
+                    tokens.append_all(quote! {
+                        pub use
+                    });
+                    let path = top_level_path(ctx, item);
+                    tokens.append_separated(path, quote!(::));
+                    tokens.append_all(quote! {
+                        :: #inner_rust_type  as #rust_name ;
+                    });
+                    result.push(tokens);
+                    return;
+                }
+
+                tokens.append_all(match alias_style {
+                    AliasVariation::TypeAlias => quote! {
+                        pub type #rust_name
+                    },
+                    AliasVariation::NewType | AliasVariation::NewTypeDeref => {
+                        assert!(
+                            ctx.options().rust_features().repr_transparent,
+                            "repr_transparent feature is required to use {:?}",
+                            alias_style
+                        );
+
+                        let mut attributes =
+                            vec![attributes::repr("transparent")];
+                        let packed = false; // Types can't be packed in Rust.
+                        let derivable_traits =
+                            derives_of_item(item, ctx, packed);
+                        if !derivable_traits.is_empty() {
+                            let derives: Vec<_> = derivable_traits.into();
+                            attributes.push(attributes::derives(&derives))
+                        }
+
+                        quote! {
+                            #( #attributes )*
+                            pub struct #rust_name
+                        }
+                    }
+                });
+
+                let params: Vec<_> = outer_params
+                    .into_iter()
+                    .filter_map(|p| p.as_template_param(ctx, &()))
+                    .collect();
+                if params
+                    .iter()
+                    .any(|p| ctx.resolve_type(*p).is_invalid_type_param())
+                {
+                    warn!(
+                        "Item contained invalid template \
+                         parameter: {:?}",
+                        item
+                    );
+                    return;
+                }
+                let params: Vec<_> = params
+                    .iter()
+                    .map(|p| {
+                        p.try_to_rust_ty(ctx, &()).expect(
+                            "type parameters can always convert to rust ty OK",
+                        )
+                    })
+                    .collect();
+
+                if !params.is_empty() {
+                    tokens.append_all(quote! {
+                        < #( #params ),* >
+                    });
+                }
+
+                tokens.append_all(match alias_style {
+                    AliasVariation::TypeAlias => quote! {
+                        = #inner_rust_type ;
+                    },
+                    AliasVariation::NewType | AliasVariation::NewTypeDeref => {
+                        quote! {
+                            (pub #inner_rust_type) ;
+                        }
+                    }
+                });
+
+                if alias_style == AliasVariation::NewTypeDeref {
+                    let prefix = ctx.trait_prefix();
+                    tokens.append_all(quote! {
+                        impl ::#prefix::ops::Deref for #rust_name {
+                            type Target = #inner_rust_type;
+                            #[inline]
+                            fn deref(&self) -> &Self::Target {
+                                &self.0
+                            }
+                        }
+                        impl ::#prefix::ops::DerefMut for #rust_name {
+                            #[inline]
+                            fn deref_mut(&mut self) -> &mut Self::Target {
+                                &mut self.0
+                            }
+                        }
+                    });
+                }
+
+                result.push(tokens);
+            }
+            TypeKind::Enum(ref ei) => ei.codegen(ctx, result, item),
+            TypeKind::ObjCId | TypeKind::ObjCSel => {
+                result.saw_objc();
+            }
+            TypeKind::ObjCInterface(ref interface) => {
+                interface.codegen(ctx, result, item)
+            }
+            ref u @ TypeKind::UnresolvedTypeRef(..) => {
+                unreachable!("Should have been resolved after parsing {:?}!", u)
+            }
+        }
+    }
+}
+
+struct Vtable<'a> {
+    item_id: ItemId,
+    /// A reference to the originating compound object.
+    #[allow(dead_code)]
+    comp_info: &'a CompInfo,
+}
+
+impl<'a> Vtable<'a> {
+    fn new(item_id: ItemId, comp_info: &'a CompInfo) -> Self {
+        Vtable { item_id, comp_info }
+    }
+}
+
+impl<'a> CodeGenerator for Vtable<'a> {
+    type Extra = Item;
+    type Return = ();
+
+    fn codegen<'b>(
+        &self,
+        ctx: &BindgenContext,
+        result: &mut CodegenResult<'b>,
+        item: &Item,
+    ) {
+        assert_eq!(item.id(), self.item_id);
+        debug_assert!(item.is_enabled_for_codegen(ctx));
+        let name = ctx.rust_ident(self.canonical_name(ctx));
+
+        // For now, we will only generate vtables for classes that:
+        // - do not inherit from others (compilers merge VTable from primary parent class).
+        // - do not contain a virtual destructor (requires ordering; platforms generate different vtables).
+        if ctx.options().vtable_generation &&
+            self.comp_info.base_members().is_empty() &&
+            self.comp_info.destructor().is_none()
+        {
+            let class_ident = ctx.rust_ident(self.item_id.canonical_name(ctx));
+
+            let methods = self
+                .comp_info
+                .methods()
+                .iter()
+                .filter_map(|m| {
+                    if !m.is_virtual() {
+                        return None;
+                    }
+
+                    let function_item = ctx.resolve_item(m.signature());
+                    let function = function_item.expect_function();
+                    let signature_item = ctx.resolve_item(function.signature());
+                    let signature = match signature_item.expect_type().kind() {
+                        TypeKind::Function(ref sig) => sig,
+                        _ => panic!("Function signature type mismatch"),
+                    };
+
+                    // FIXME: Is there a canonical name without the class prepended?
+                    let function_name = function_item.canonical_name(ctx);
+
+                    // FIXME: Need to account for overloading with times_seen (separately from regular function path).
+                    let function_name = ctx.rust_ident(function_name);
+                    let mut args = utils::fnsig_arguments(ctx, signature);
+                    let ret = utils::fnsig_return_ty(ctx, signature);
+
+                    args[0] = if m.is_const() {
+                        quote! { this: *const #class_ident }
+                    } else {
+                        quote! { this: *mut #class_ident }
+                    };
+
+                    Some(quote! {
+                        pub #function_name : unsafe extern "C" fn( #( #args ),* ) #ret
+                    })
+                })
+                .collect::<Vec<_>>();
+
+            result.push(quote! {
+                #[repr(C)]
+                pub struct #name {
+                    #( #methods ),*
+                }
+            })
+        } else {
+            // For the cases we don't support, simply generate an empty struct.
+            let void = helpers::ast_ty::c_void(ctx);
+
+            result.push(quote! {
+                #[repr(C)]
+                pub struct #name ( #void );
+            });
+        }
+    }
+}
+
+impl<'a> ItemCanonicalName for Vtable<'a> {
+    fn canonical_name(&self, ctx: &BindgenContext) -> String {
+        format!("{}__bindgen_vtable", self.item_id.canonical_name(ctx))
+    }
+}
+
+impl<'a> TryToRustTy for Vtable<'a> {
+    type Extra = ();
+
+    fn try_to_rust_ty(
+        &self,
+        ctx: &BindgenContext,
+        _: &(),
+    ) -> error::Result<proc_macro2::TokenStream> {
+        let name = ctx.rust_ident(self.canonical_name(ctx));
+        Ok(quote! {
+            #name
+        })
+    }
+}
+
+impl CodeGenerator for TemplateInstantiation {
+    type Extra = Item;
+    type Return = ();
+
+    fn codegen<'a>(
+        &self,
+        ctx: &BindgenContext,
+        result: &mut CodegenResult<'a>,
+        item: &Item,
+    ) {
+        debug_assert!(item.is_enabled_for_codegen(ctx));
+
+        // Although uses of instantiations don't need code generation, and are
+        // just converted to rust types in fields, vars, etc, we take this
+        // opportunity to generate tests for their layout here. If the
+        // instantiation is opaque, then its presumably because we don't
+        // properly understand it (maybe because of specializations), and so we
+        // shouldn't emit layout tests either.
+        if !ctx.options().layout_tests || self.is_opaque(ctx, item) {
+            return;
+        }
+
+        // If there are any unbound type parameters, then we can't generate a
+        // layout test because we aren't dealing with a concrete type with a
+        // concrete size and alignment.
+        if ctx.uses_any_template_parameters(item.id()) {
+            return;
+        }
+
+        let layout = item.kind().expect_type().layout(ctx);
+
+        if let Some(layout) = layout {
+            let size = layout.size;
+            let align = layout.align;
+
+            let name = item.full_disambiguated_name(ctx);
+            let mut fn_name =
+                format!("__bindgen_test_layout_{}_instantiation", name);
+            let times_seen = result.overload_number(&fn_name);
+            if times_seen > 0 {
+                write!(&mut fn_name, "_{}", times_seen).unwrap();
+            }
+
+            let fn_name = ctx.rust_ident_raw(fn_name);
+
+            let prefix = ctx.trait_prefix();
+            let ident = item.to_rust_ty_or_opaque(ctx, &());
+            let size_of_expr = quote! {
+                ::#prefix::mem::size_of::<#ident>()
+            };
+            let align_of_expr = quote! {
+                ::#prefix::mem::align_of::<#ident>()
+            };
+
+            let item = quote! {
+                #[test]
+                fn #fn_name() {
+                    assert_eq!(#size_of_expr, #size,
+                               concat!("Size of template specialization: ",
+                                       stringify!(#ident)));
+                    assert_eq!(#align_of_expr, #align,
+                               concat!("Alignment of template specialization: ",
+                                       stringify!(#ident)));
+                }
+            };
+
+            result.push(item);
+        }
+    }
+}
+
+/// Trait for implementing the code generation of a struct or union field.
+trait FieldCodegen<'a> {
+    type Extra;
+
+    #[allow(clippy::too_many_arguments)]
+    fn codegen<F, M>(
+        &self,
+        ctx: &BindgenContext,
+        fields_should_be_private: bool,
+        accessor_kind: FieldAccessorKind,
+        parent: &CompInfo,
+        result: &mut CodegenResult,
+        struct_layout: &mut StructLayoutTracker,
+        fields: &mut F,
+        methods: &mut M,
+        extra: Self::Extra,
+    ) where
+        F: Extend<proc_macro2::TokenStream>,
+        M: Extend<proc_macro2::TokenStream>;
+}
+
+impl<'a> FieldCodegen<'a> for Field {
+    type Extra = ();
+
+    fn codegen<F, M>(
+        &self,
+        ctx: &BindgenContext,
+        fields_should_be_private: bool,
+        accessor_kind: FieldAccessorKind,
+        parent: &CompInfo,
+        result: &mut CodegenResult,
+        struct_layout: &mut StructLayoutTracker,
+        fields: &mut F,
+        methods: &mut M,
+        _: (),
+    ) where
+        F: Extend<proc_macro2::TokenStream>,
+        M: Extend<proc_macro2::TokenStream>,
+    {
+        match *self {
+            Field::DataMember(ref data) => {
+                data.codegen(
+                    ctx,
+                    fields_should_be_private,
+                    accessor_kind,
+                    parent,
+                    result,
+                    struct_layout,
+                    fields,
+                    methods,
+                    (),
+                );
+            }
+            Field::Bitfields(ref unit) => {
+                unit.codegen(
+                    ctx,
+                    fields_should_be_private,
+                    accessor_kind,
+                    parent,
+                    result,
+                    struct_layout,
+                    fields,
+                    methods,
+                    (),
+                );
+            }
+        }
+    }
+}
+
+fn wrap_union_field_if_needed(
+    ctx: &BindgenContext,
+    struct_layout: &StructLayoutTracker,
+    ty: proc_macro2::TokenStream,
+    result: &mut CodegenResult,
+) -> proc_macro2::TokenStream {
+    if struct_layout.is_rust_union() {
+        if struct_layout.can_copy_union_fields() {
+            ty
+        } else {
+            let prefix = ctx.trait_prefix();
+            quote! {
+                ::#prefix::mem::ManuallyDrop<#ty>
+            }
+        }
+    } else {
+        result.saw_bindgen_union();
+        if ctx.options().enable_cxx_namespaces {
+            quote! {
+                root::__BindgenUnionField<#ty>
+            }
+        } else {
+            quote! {
+                __BindgenUnionField<#ty>
+            }
+        }
+    }
+}
+
+impl<'a> FieldCodegen<'a> for FieldData {
+    type Extra = ();
+
+    fn codegen<F, M>(
+        &self,
+        ctx: &BindgenContext,
+        fields_should_be_private: bool,
+        accessor_kind: FieldAccessorKind,
+        parent: &CompInfo,
+        result: &mut CodegenResult,
+        struct_layout: &mut StructLayoutTracker,
+        fields: &mut F,
+        methods: &mut M,
+        _: (),
+    ) where
+        F: Extend<proc_macro2::TokenStream>,
+        M: Extend<proc_macro2::TokenStream>,
+    {
+        // Bitfields are handled by `FieldCodegen` implementations for
+        // `BitfieldUnit` and `Bitfield`.
+        assert!(self.bitfield_width().is_none());
+
+        let field_item =
+            self.ty().into_resolver().through_type_refs().resolve(ctx);
+        let field_ty = field_item.expect_type();
+        let mut ty = self.ty().to_rust_ty_or_opaque(ctx, &());
+        ty.append_implicit_template_params(ctx, field_item);
+
+        // NB: If supported, we use proper `union` types.
+        let ty = if parent.is_union() {
+            wrap_union_field_if_needed(ctx, struct_layout, ty, result)
+        } else if let Some(item) = field_ty.is_incomplete_array(ctx) {
+            result.saw_incomplete_array();
+
+            let inner = item.to_rust_ty_or_opaque(ctx, &());
+
+            if ctx.options().enable_cxx_namespaces {
+                quote! {
+                    root::__IncompleteArrayField<#inner>
+                }
+            } else {
+                quote! {
+                    __IncompleteArrayField<#inner>
+                }
+            }
+        } else {
+            ty
+        };
+
+        let mut field = quote! {};
+        if ctx.options().generate_comments {
+            if let Some(raw_comment) = self.comment() {
+                let comment = ctx.options().process_comment(raw_comment);
+                field = attributes::doc(comment);
+            }
+        }
+
+        let field_name = self
+            .name()
+            .map(|name| ctx.rust_mangle(name).into_owned())
+            .expect("Each field should have a name in codegen!");
+        let field_ident = ctx.rust_ident_raw(field_name.as_str());
+
+        if let Some(padding_field) =
+            struct_layout.saw_field(&field_name, field_ty, self.offset())
+        {
+            fields.extend(Some(padding_field));
+        }
+
+        let is_private = (!self.is_public() &&
+            ctx.options().respect_cxx_access_specs) ||
+            self.annotations()
+                .private_fields()
+                .unwrap_or(fields_should_be_private);
+
+        let accessor_kind =
+            self.annotations().accessor_kind().unwrap_or(accessor_kind);
+
+        if is_private {
+            field.append_all(quote! {
+                #field_ident : #ty ,
+            });
+        } else {
+            field.append_all(quote! {
+                pub #field_ident : #ty ,
+            });
+        }
+
+        fields.extend(Some(field));
+
+        // TODO: Factor the following code out, please!
+        if accessor_kind == FieldAccessorKind::None {
+            return;
+        }
+
+        let getter_name = ctx.rust_ident_raw(format!("get_{}", field_name));
+        let mutable_getter_name =
+            ctx.rust_ident_raw(format!("get_{}_mut", field_name));
+        let field_name = ctx.rust_ident_raw(field_name);
+
+        methods.extend(Some(match accessor_kind {
+            FieldAccessorKind::None => unreachable!(),
+            FieldAccessorKind::Regular => {
+                quote! {
+                    #[inline]
+                    pub fn #getter_name(&self) -> & #ty {
+                        &self.#field_name
+                    }
+
+                    #[inline]
+                    pub fn #mutable_getter_name(&mut self) -> &mut #ty {
+                        &mut self.#field_name
+                    }
+                }
+            }
+            FieldAccessorKind::Unsafe => {
+                quote! {
+                    #[inline]
+                    pub unsafe fn #getter_name(&self) -> & #ty {
+                        &self.#field_name
+                    }
+
+                    #[inline]
+                    pub unsafe fn #mutable_getter_name(&mut self) -> &mut #ty {
+                        &mut self.#field_name
+                    }
+                }
+            }
+            FieldAccessorKind::Immutable => {
+                quote! {
+                    #[inline]
+                    pub fn #getter_name(&self) -> & #ty {
+                        &self.#field_name
+                    }
+                }
+            }
+        }));
+    }
+}
+
+impl BitfieldUnit {
+    /// Get the constructor name for this bitfield unit.
+    fn ctor_name(&self) -> proc_macro2::TokenStream {
+        let ctor_name = Ident::new(
+            &format!("new_bitfield_{}", self.nth()),
+            Span::call_site(),
+        );
+        quote! {
+            #ctor_name
+        }
+    }
+}
+
+impl Bitfield {
+    /// Extend an under construction bitfield unit constructor with this
+    /// bitfield. This sets the relevant bits on the `__bindgen_bitfield_unit`
+    /// variable that's being constructed.
+    fn extend_ctor_impl(
+        &self,
+        ctx: &BindgenContext,
+        param_name: proc_macro2::TokenStream,
+        mut ctor_impl: proc_macro2::TokenStream,
+    ) -> proc_macro2::TokenStream {
+        let bitfield_ty = ctx.resolve_type(self.ty());
+        let bitfield_ty_layout = bitfield_ty
+            .layout(ctx)
+            .expect("Bitfield without layout? Gah!");
+        let bitfield_int_ty = helpers::integer_type(ctx, bitfield_ty_layout)
+            .expect(
+                "Should already have verified that the bitfield is \
+                 representable as an int",
+            );
+
+        let offset = self.offset_into_unit();
+        let width = self.width() as u8;
+        let prefix = ctx.trait_prefix();
+
+        ctor_impl.append_all(quote! {
+            __bindgen_bitfield_unit.set(
+                #offset,
+                #width,
+                {
+                    let #param_name: #bitfield_int_ty = unsafe {
+                        ::#prefix::mem::transmute(#param_name)
+                    };
+                    #param_name as u64
+                }
+            );
+        });
+
+        ctor_impl
+    }
+}
+
+fn access_specifier(
+    ctx: &BindgenContext,
+    is_pub: bool,
+) -> proc_macro2::TokenStream {
+    if is_pub || !ctx.options().respect_cxx_access_specs {
+        quote! { pub }
+    } else {
+        quote! {}
+    }
+}
+
+impl<'a> FieldCodegen<'a> for BitfieldUnit {
+    type Extra = ();
+
+    fn codegen<F, M>(
+        &self,
+        ctx: &BindgenContext,
+        fields_should_be_private: bool,
+        accessor_kind: FieldAccessorKind,
+        parent: &CompInfo,
+        result: &mut CodegenResult,
+        struct_layout: &mut StructLayoutTracker,
+        fields: &mut F,
+        methods: &mut M,
+        _: (),
+    ) where
+        F: Extend<proc_macro2::TokenStream>,
+        M: Extend<proc_macro2::TokenStream>,
+    {
+        use crate::ir::ty::RUST_DERIVE_IN_ARRAY_LIMIT;
+
+        result.saw_bitfield_unit();
+
+        let layout = self.layout();
+        let unit_field_ty = helpers::bitfield_unit(ctx, layout);
+        let field_ty = if parent.is_union() {
+            wrap_union_field_if_needed(
+                ctx,
+                struct_layout,
+                unit_field_ty.clone(),
+                result,
+            )
+        } else {
+            unit_field_ty.clone()
+        };
+
+        {
+            let align_field_name = format!("_bitfield_align_{}", self.nth());
+            let align_field_ident = ctx.rust_ident(align_field_name);
+            let align_ty = match self.layout().align {
+                n if n >= 8 => quote! { u64 },
+                4 => quote! { u32 },
+                2 => quote! { u16 },
+                _ => quote! { u8  },
+            };
+            let align_field = quote! {
+                pub #align_field_ident: [#align_ty; 0],
+            };
+            fields.extend(Some(align_field));
+        }
+
+        let unit_field_name = format!("_bitfield_{}", self.nth());
+        let unit_field_ident = ctx.rust_ident(&unit_field_name);
+
+        let ctor_name = self.ctor_name();
+        let mut ctor_params = vec![];
+        let mut ctor_impl = quote! {};
+
+        // We cannot generate any constructor if the underlying storage can't
+        // implement AsRef<[u8]> / AsMut<[u8]> / etc, or can't derive Default.
+        //
+        // We don't check `larger_arrays` here because Default does still have
+        // the 32 items limitation.
+        let mut generate_ctor = layout.size <= RUST_DERIVE_IN_ARRAY_LIMIT;
+
+        let mut access_spec = !fields_should_be_private;
+        for bf in self.bitfields() {
+            // Codegen not allowed for anonymous bitfields
+            if bf.name().is_none() {
+                continue;
+            }
+
+            if layout.size > RUST_DERIVE_IN_ARRAY_LIMIT &&
+                !ctx.options().rust_features().larger_arrays
+            {
+                continue;
+            }
+
+            access_spec &= bf.is_public();
+            let mut bitfield_representable_as_int = true;
+
+            bf.codegen(
+                ctx,
+                fields_should_be_private,
+                accessor_kind,
+                parent,
+                result,
+                struct_layout,
+                fields,
+                methods,
+                (&unit_field_name, &mut bitfield_representable_as_int),
+            );
+
+            // Generating a constructor requires the bitfield to be representable as an integer.
+            if !bitfield_representable_as_int {
+                generate_ctor = false;
+                continue;
+            }
+
+            let param_name = bitfield_getter_name(ctx, bf);
+            let bitfield_ty_item = ctx.resolve_item(bf.ty());
+            let bitfield_ty = bitfield_ty_item.expect_type();
+            let bitfield_ty =
+                bitfield_ty.to_rust_ty_or_opaque(ctx, bitfield_ty_item);
+
+            ctor_params.push(quote! {
+                #param_name : #bitfield_ty
+            });
+            ctor_impl = bf.extend_ctor_impl(ctx, param_name, ctor_impl);
+        }
+
+        let access_spec = access_specifier(ctx, access_spec);
+
+        let field = quote! {
+            #access_spec #unit_field_ident : #field_ty ,
+        };
+        fields.extend(Some(field));
+
+        if generate_ctor {
+            methods.extend(Some(quote! {
+                #[inline]
+                #access_spec fn #ctor_name ( #( #ctor_params ),* ) -> #unit_field_ty {
+                    let mut __bindgen_bitfield_unit: #unit_field_ty = Default::default();
+                    #ctor_impl
+                    __bindgen_bitfield_unit
+                }
+            }));
+        }
+
+        struct_layout.saw_bitfield_unit(layout);
+    }
+}
+
+fn bitfield_getter_name(
+    ctx: &BindgenContext,
+    bitfield: &Bitfield,
+) -> proc_macro2::TokenStream {
+    let name = bitfield.getter_name();
+    let name = ctx.rust_ident_raw(name);
+    quote! { #name }
+}
+
+fn bitfield_setter_name(
+    ctx: &BindgenContext,
+    bitfield: &Bitfield,
+) -> proc_macro2::TokenStream {
+    let setter = bitfield.setter_name();
+    let setter = ctx.rust_ident_raw(setter);
+    quote! { #setter }
+}
+
+impl<'a> FieldCodegen<'a> for Bitfield {
+    type Extra = (&'a str, &'a mut bool);
+
+    fn codegen<F, M>(
+        &self,
+        ctx: &BindgenContext,
+        fields_should_be_private: bool,
+        _accessor_kind: FieldAccessorKind,
+        parent: &CompInfo,
+        _result: &mut CodegenResult,
+        struct_layout: &mut StructLayoutTracker,
+        _fields: &mut F,
+        methods: &mut M,
+        (unit_field_name, bitfield_representable_as_int): (&'a str, &mut bool),
+    ) where
+        F: Extend<proc_macro2::TokenStream>,
+        M: Extend<proc_macro2::TokenStream>,
+    {
+        let prefix = ctx.trait_prefix();
+        let getter_name = bitfield_getter_name(ctx, self);
+        let setter_name = bitfield_setter_name(ctx, self);
+        let unit_field_ident = Ident::new(unit_field_name, Span::call_site());
+
+        let bitfield_ty_item = ctx.resolve_item(self.ty());
+        let bitfield_ty = bitfield_ty_item.expect_type();
+
+        let bitfield_ty_layout = bitfield_ty
+            .layout(ctx)
+            .expect("Bitfield without layout? Gah!");
+        let bitfield_int_ty =
+            match helpers::integer_type(ctx, bitfield_ty_layout) {
+                Some(int_ty) => {
+                    *bitfield_representable_as_int = true;
+                    int_ty
+                }
+                None => {
+                    *bitfield_representable_as_int = false;
+                    return;
+                }
+            };
+
+        let bitfield_ty =
+            bitfield_ty.to_rust_ty_or_opaque(ctx, bitfield_ty_item);
+
+        let offset = self.offset_into_unit();
+        let width = self.width() as u8;
+        let access_spec = access_specifier(
+            ctx,
+            self.is_public() && !fields_should_be_private,
+        );
+
+        if parent.is_union() && !struct_layout.is_rust_union() {
+            methods.extend(Some(quote! {
+                #[inline]
+                #access_spec fn #getter_name(&self) -> #bitfield_ty {
+                    unsafe {
+                        ::#prefix::mem::transmute(
+                            self.#unit_field_ident.as_ref().get(#offset, #width)
+                                as #bitfield_int_ty
+                        )
+                    }
+                }
+
+                #[inline]
+                #access_spec fn #setter_name(&mut self, val: #bitfield_ty) {
+                    unsafe {
+                        let val: #bitfield_int_ty = ::#prefix::mem::transmute(val);
+                        self.#unit_field_ident.as_mut().set(
+                            #offset,
+                            #width,
+                            val as u64
+                        )
+                    }
+                }
+            }));
+        } else {
+            methods.extend(Some(quote! {
+                #[inline]
+                #access_spec fn #getter_name(&self) -> #bitfield_ty {
+                    unsafe {
+                        ::#prefix::mem::transmute(
+                            self.#unit_field_ident.get(#offset, #width)
+                                as #bitfield_int_ty
+                        )
+                    }
+                }
+
+                #[inline]
+                #access_spec fn #setter_name(&mut self, val: #bitfield_ty) {
+                    unsafe {
+                        let val: #bitfield_int_ty = ::#prefix::mem::transmute(val);
+                        self.#unit_field_ident.set(
+                            #offset,
+                            #width,
+                            val as u64
+                        )
+                    }
+                }
+            }));
+        }
+    }
+}
+
+impl CodeGenerator for CompInfo {
+    type Extra = Item;
+    type Return = ();
+
+    fn codegen<'a>(
+        &self,
+        ctx: &BindgenContext,
+        result: &mut CodegenResult<'a>,
+        item: &Item,
+    ) {
+        debug!("<CompInfo as CodeGenerator>::codegen: item = {:?}", item);
+        debug_assert!(item.is_enabled_for_codegen(ctx));
+
+        // Don't output classes with template parameters that aren't types, and
+        // also don't output template specializations, neither total or partial.
+        if self.has_non_type_template_params() {
+            return;
+        }
+
+        let ty = item.expect_type();
+        let layout = ty.layout(ctx);
+        let mut packed = self.is_packed(ctx, layout.as_ref());
+
+        let canonical_name = item.canonical_name(ctx);
+        let canonical_ident = ctx.rust_ident(&canonical_name);
+
+        // Generate the vtable from the method list if appropriate.
+        //
+        // TODO: I don't know how this could play with virtual methods that are
+        // not in the list of methods found by us, we'll see. Also, could the
+        // order of the vtable pointers vary?
+        //
+        // FIXME: Once we generate proper vtables, we need to codegen the
+        // vtable, but *not* generate a field for it in the case that
+        // HasVtable::has_vtable_ptr is false but HasVtable::has_vtable is true.
+        //
+        // Also, we need to generate the vtable in such a way it "inherits" from
+        // the parent too.
+        let is_opaque = item.is_opaque(ctx, &());
+        let mut fields = vec![];
+        let mut struct_layout =
+            StructLayoutTracker::new(ctx, self, ty, &canonical_name);
+
+        if !is_opaque {
+            if item.has_vtable_ptr(ctx) {
+                let vtable = Vtable::new(item.id(), self);
+                vtable.codegen(ctx, result, item);
+
+                let vtable_type = vtable
+                    .try_to_rust_ty(ctx, &())
+                    .expect("vtable to Rust type conversion is infallible")
+                    .to_ptr(true);
+
+                fields.push(quote! {
+                    pub vtable_: #vtable_type ,
+                });
+
+                struct_layout.saw_vtable();
+            }
+
+            for base in self.base_members() {
+                if !base.requires_storage(ctx) {
+                    continue;
+                }
+
+                let inner_item = ctx.resolve_item(base.ty);
+                let mut inner = inner_item.to_rust_ty_or_opaque(ctx, &());
+                inner.append_implicit_template_params(ctx, inner_item);
+                let field_name = ctx.rust_ident(&base.field_name);
+
+                struct_layout.saw_base(inner_item.expect_type());
+
+                let access_spec = access_specifier(ctx, base.is_public());
+                fields.push(quote! {
+                    #access_spec #field_name: #inner,
+                });
+            }
+        }
+
+        let mut methods = vec![];
+        if !is_opaque {
+            let fields_should_be_private =
+                item.annotations().private_fields().unwrap_or(false);
+            let struct_accessor_kind = item
+                .annotations()
+                .accessor_kind()
+                .unwrap_or(FieldAccessorKind::None);
+            for field in self.fields() {
+                field.codegen(
+                    ctx,
+                    fields_should_be_private,
+                    struct_accessor_kind,
+                    self,
+                    result,
+                    &mut struct_layout,
+                    &mut fields,
+                    &mut methods,
+                    (),
+                );
+            }
+            // Check whether an explicit padding field is needed
+            // at the end.
+            if let Some(comp_layout) = layout {
+                fields.extend(
+                    struct_layout
+                        .add_tail_padding(&canonical_name, comp_layout),
+                );
+            }
+        }
+
+        if is_opaque {
+            // Opaque item should not have generated methods, fields.
+            debug_assert!(fields.is_empty());
+            debug_assert!(methods.is_empty());
+        }
+
+        let is_union = self.kind() == CompKind::Union;
+        let layout = item.kind().expect_type().layout(ctx);
+        let zero_sized = item.is_zero_sized(ctx);
+        let forward_decl = self.is_forward_declaration();
+
+        let mut explicit_align = None;
+
+        // C++ requires every struct to be addressable, so what C++ compilers do
+        // is making the struct 1-byte sized.
+        //
+        // This is apparently not the case for C, see:
+        // https://github.com/rust-lang/rust-bindgen/issues/551
+        //
+        // Just get the layout, and assume C++ if not.
+        //
+        // NOTE: This check is conveniently here to avoid the dummy fields we
+        // may add for unused template parameters.
+        if !forward_decl && zero_sized {
+            let has_address = if is_opaque {
+                // Generate the address field if it's an opaque type and
+                // couldn't determine the layout of the blob.
+                layout.is_none()
+            } else {
+                layout.map_or(true, |l| l.size != 0)
+            };
+
+            if has_address {
+                let layout = Layout::new(1, 1);
+                let ty = helpers::blob(ctx, Layout::new(1, 1));
+                struct_layout.saw_field_with_layout(
+                    "_address",
+                    layout,
+                    /* offset = */ Some(0),
+                );
+                fields.push(quote! {
+                    pub _address: #ty,
+                });
+            }
+        }
+
+        if is_opaque {
+            match layout {
+                Some(l) => {
+                    explicit_align = Some(l.align);
+
+                    let ty = helpers::blob(ctx, l);
+                    fields.push(quote! {
+                        pub _bindgen_opaque_blob: #ty ,
+                    });
+                }
+                None => {
+                    warn!("Opaque type without layout! Expect dragons!");
+                }
+            }
+        } else if !is_union && !zero_sized {
+            if let Some(padding_field) =
+                layout.and_then(|layout| struct_layout.pad_struct(layout))
+            {
+                fields.push(padding_field);
+            }
+
+            if let Some(layout) = layout {
+                if struct_layout.requires_explicit_align(layout) {
+                    if layout.align == 1 {
+                        packed = true;
+                    } else {
+                        explicit_align = Some(layout.align);
+                        if !ctx.options().rust_features.repr_align {
+                            let ty = helpers::blob(
+                                ctx,
+                                Layout::new(0, layout.align),
+                            );
+                            fields.push(quote! {
+                                pub __bindgen_align: #ty ,
+                            });
+                        }
+                    }
+                }
+            }
+        } else if is_union && !forward_decl {
+            // TODO(emilio): It'd be nice to unify this with the struct path
+            // above somehow.
+            let layout = layout.expect("Unable to get layout information?");
+            if struct_layout.requires_explicit_align(layout) {
+                explicit_align = Some(layout.align);
+            }
+
+            if !struct_layout.is_rust_union() {
+                let ty = helpers::blob(ctx, layout);
+                fields.push(quote! {
+                    pub bindgen_union_field: #ty ,
+                })
+            }
+        }
+
+        if forward_decl {
+            fields.push(quote! {
+                _unused: [u8; 0],
+            });
+        }
+
+        let mut generic_param_names = vec![];
+
+        for (idx, ty) in item.used_template_params(ctx).iter().enumerate() {
+            let param = ctx.resolve_type(*ty);
+            let name = param.name().unwrap();
+            let ident = ctx.rust_ident(name);
+            generic_param_names.push(ident.clone());
+
+            let prefix = ctx.trait_prefix();
+            let field_name = ctx.rust_ident(format!("_phantom_{}", idx));
+            fields.push(quote! {
+                pub #field_name : ::#prefix::marker::PhantomData<
+                    ::#prefix::cell::UnsafeCell<#ident>
+                > ,
+            });
+        }
+
+        let generics = if !generic_param_names.is_empty() {
+            let generic_param_names = generic_param_names.clone();
+            quote! {
+                < #( #generic_param_names ),* >
+            }
+        } else {
+            quote! {}
+        };
+
+        let mut attributes = vec![];
+        let mut needs_clone_impl = false;
+        let mut needs_default_impl = false;
+        let mut needs_debug_impl = false;
+        let mut needs_partialeq_impl = false;
+        if let Some(comment) = item.comment(ctx) {
+            attributes.push(attributes::doc(comment));
+        }
+        if packed && !is_opaque {
+            let n = layout.map_or(1, |l| l.align);
+            assert!(ctx.options().rust_features().repr_packed_n || n == 1);
+            let packed_repr = if n == 1 {
+                "packed".to_string()
+            } else {
+                format!("packed({})", n)
+            };
+            attributes.push(attributes::repr_list(&["C", &packed_repr]));
+        } else {
+            attributes.push(attributes::repr("C"));
+        }
+
+        if ctx.options().rust_features().repr_align {
+            if let Some(explicit) = explicit_align {
+                // Ensure that the struct has the correct alignment even in
+                // presence of alignas.
+                let explicit = helpers::ast_ty::int_expr(explicit as i64);
+                attributes.push(quote! {
+                    #[repr(align(#explicit))]
+                });
+            }
+        }
+
+        let derivable_traits = derives_of_item(item, ctx, packed);
+        if !derivable_traits.contains(DerivableTraits::DEBUG) {
+            needs_debug_impl = ctx.options().derive_debug &&
+                ctx.options().impl_debug &&
+                !ctx.no_debug_by_name(item) &&
+                !item.annotations().disallow_debug();
+        }
+
+        if !derivable_traits.contains(DerivableTraits::DEFAULT) {
+            needs_default_impl = ctx.options().derive_default &&
+                !self.is_forward_declaration() &&
+                !ctx.no_default_by_name(item) &&
+                !item.annotations().disallow_default();
+        }
+
+        let all_template_params = item.all_template_params(ctx);
+
+        if derivable_traits.contains(DerivableTraits::COPY) &&
+            !derivable_traits.contains(DerivableTraits::CLONE)
+        {
+            needs_clone_impl = true;
+        }
+
+        if !derivable_traits.contains(DerivableTraits::PARTIAL_EQ) {
+            needs_partialeq_impl = ctx.options().derive_partialeq &&
+                ctx.options().impl_partialeq &&
+                ctx.lookup_can_derive_partialeq_or_partialord(item.id()) ==
+                    CanDerive::Manually;
+        }
+
+        let mut derives: Vec<_> = derivable_traits.into();
+        derives.extend(item.annotations().derives().iter().map(String::as_str));
+
+        // The custom derives callback may return a list of derive attributes;
+        // add them to the end of the list.
+        let custom_derives = ctx.options().all_callbacks(|cb| {
+            cb.add_derives(&crate::callbacks::DeriveInfo {
+                name: &canonical_name,
+            })
+        });
+        // In most cases this will be a no-op, since custom_derives will be empty.
+        derives.extend(custom_derives.iter().map(|s| s.as_str()));
+
+        if !derives.is_empty() {
+            attributes.push(attributes::derives(&derives))
+        }
+
+        if item.must_use(ctx) {
+            attributes.push(attributes::must_use());
+        }
+
+        let mut tokens = if is_union && struct_layout.is_rust_union() {
+            quote! {
+                #( #attributes )*
+                pub union #canonical_ident
+            }
+        } else {
+            quote! {
+                #( #attributes )*
+                pub struct #canonical_ident
+            }
+        };
+
+        tokens.append_all(quote! {
+            #generics {
+                #( #fields )*
+            }
+        });
+        result.push(tokens);
+
+        // Generate the inner types and all that stuff.
+        //
+        // TODO: In the future we might want to be smart, and use nested
+        // modules, and whatnot.
+        for ty in self.inner_types() {
+            let child_item = ctx.resolve_item(*ty);
+            // assert_eq!(child_item.parent_id(), item.id());
+            child_item.codegen(ctx, result, &());
+        }
+
+        // NOTE: Some unexposed attributes (like alignment attributes) may
+        // affect layout, so we're bad and pray to the gods for avoid sending
+        // all the tests to shit when parsing things like max_align_t.
+        if self.found_unknown_attr() {
+            warn!(
+                "Type {} has an unknown attribute that may affect layout",
+                canonical_ident
+            );
+        }
+
+        if all_template_params.is_empty() {
+            if !is_opaque {
+                for var in self.inner_vars() {
+                    ctx.resolve_item(*var).codegen(ctx, result, &());
+                }
+            }
+
+            if ctx.options().layout_tests && !self.is_forward_declaration() {
+                if let Some(layout) = layout {
+                    let fn_name =
+                        format!("bindgen_test_layout_{}", canonical_ident);
+                    let fn_name = ctx.rust_ident_raw(fn_name);
+                    let prefix = ctx.trait_prefix();
+                    let size_of_expr = quote! {
+                        ::#prefix::mem::size_of::<#canonical_ident>()
+                    };
+                    let align_of_expr = quote! {
+                        ::#prefix::mem::align_of::<#canonical_ident>()
+                    };
+                    let size = layout.size;
+                    let align = layout.align;
+
+                    let check_struct_align = if align >
+                        ctx.target_pointer_size() &&
+                        !ctx.options().rust_features().repr_align
+                    {
+                        None
+                    } else {
+                        Some(quote! {
+                            assert_eq!(#align_of_expr,
+                                   #align,
+                                   concat!("Alignment of ", stringify!(#canonical_ident)));
+
+                        })
+                    };
+
+                    // FIXME when [issue #465](https://github.com/rust-lang/rust-bindgen/issues/465) ready
+                    let too_many_base_vtables = self
+                        .base_members()
+                        .iter()
+                        .filter(|base| base.ty.has_vtable(ctx))
+                        .count() >
+                        1;
+
+                    let should_skip_field_offset_checks =
+                        is_opaque || too_many_base_vtables;
+
+                    let check_field_offset = if should_skip_field_offset_checks
+                    {
+                        vec![]
+                    } else {
+                        self.fields()
+                            .iter()
+                            .filter_map(|field| match *field {
+                                Field::DataMember(ref f) if f.name().is_some() => Some(f),
+                                _ => None,
+                            })
+                            .flat_map(|field| {
+                                let name = field.name().unwrap();
+                                field.offset().map(|offset| {
+                                    let field_offset = offset / 8;
+                                    let field_name = ctx.rust_ident(name);
+                                    quote! {
+                                        assert_eq!(
+                                            unsafe {
+                                                ::#prefix::ptr::addr_of!((*ptr).#field_name) as usize - ptr as usize
+                                            },
+                                            #field_offset,
+                                            concat!("Offset of field: ", stringify!(#canonical_ident), "::", stringify!(#field_name))
+                                        );
+                                    }
+                                })
+                            })
+                            .collect()
+                    };
+
+                    let uninit_decl = if !check_field_offset.is_empty() {
+                        // FIXME: When MSRV >= 1.59.0, we can use
+                        // > const PTR: *const #canonical_ident = ::#prefix::mem::MaybeUninit::uninit().as_ptr();
+                        Some(quote! {
+                            // Use a shared MaybeUninit so that rustc with
+                            // opt-level=0 doesn't take too much stack space,
+                            // see #2218.
+                            const UNINIT: ::#prefix::mem::MaybeUninit<#canonical_ident> = ::#prefix::mem::MaybeUninit::uninit();
+                            let ptr = UNINIT.as_ptr();
+                        })
+                    } else {
+                        None
+                    };
+
+                    let item = quote! {
+                        #[test]
+                        fn #fn_name() {
+                            #uninit_decl
+                            assert_eq!(#size_of_expr,
+                                       #size,
+                                       concat!("Size of: ", stringify!(#canonical_ident)));
+                            #check_struct_align
+                            #( #check_field_offset )*
+                        }
+                    };
+                    result.push(item);
+                }
+            }
+
+            let mut method_names = Default::default();
+            if ctx.options().codegen_config.methods() {
+                for method in self.methods() {
+                    assert!(method.kind() != MethodKind::Constructor);
+                    method.codegen_method(
+                        ctx,
+                        &mut methods,
+                        &mut method_names,
+                        result,
+                        self,
+                    );
+                }
+            }
+
+            if ctx.options().codegen_config.constructors() {
+                for sig in self.constructors() {
+                    Method::new(
+                        MethodKind::Constructor,
+                        *sig,
+                        /* const */
+                        false,
+                    )
+                    .codegen_method(
+                        ctx,
+                        &mut methods,
+                        &mut method_names,
+                        result,
+                        self,
+                    );
+                }
+            }
+
+            if ctx.options().codegen_config.destructors() {
+                if let Some((kind, destructor)) = self.destructor() {
+                    debug_assert!(kind.is_destructor());
+                    Method::new(kind, destructor, false).codegen_method(
+                        ctx,
+                        &mut methods,
+                        &mut method_names,
+                        result,
+                        self,
+                    );
+                }
+            }
+        }
+
+        // NB: We can't use to_rust_ty here since for opaque types this tries to
+        // use the specialization knowledge to generate a blob field.
+        let ty_for_impl = quote! {
+            #canonical_ident #generics
+        };
+
+        if needs_clone_impl {
+            result.push(quote! {
+                impl #generics Clone for #ty_for_impl {
+                    fn clone(&self) -> Self { *self }
+                }
+            });
+        }
+
+        if needs_default_impl {
+            let prefix = ctx.trait_prefix();
+            let body = if ctx.options().rust_features().maybe_uninit {
+                quote! {
+                    let mut s = ::#prefix::mem::MaybeUninit::<Self>::uninit();
+                    unsafe {
+                        ::#prefix::ptr::write_bytes(s.as_mut_ptr(), 0, 1);
+                        s.assume_init()
+                    }
+                }
+            } else {
+                quote! {
+                    unsafe {
+                        let mut s: Self = ::#prefix::mem::uninitialized();
+                        ::#prefix::ptr::write_bytes(&mut s, 0, 1);
+                        s
+                    }
+                }
+            };
+            // Note we use `ptr::write_bytes()` instead of `mem::zeroed()` because the latter does
+            // not necessarily ensure padding bytes are zeroed. Some C libraries are sensitive to
+            // non-zero padding bytes, especially when forwards/backwards compatability is
+            // involved.
+            result.push(quote! {
+                impl #generics Default for #ty_for_impl {
+                    fn default() -> Self {
+                        #body
+                    }
+                }
+            });
+        }
+
+        if needs_debug_impl {
+            let impl_ = impl_debug::gen_debug_impl(
+                ctx,
+                self.fields(),
+                item,
+                self.kind(),
+            );
+
+            let prefix = ctx.trait_prefix();
+
+            result.push(quote! {
+                impl #generics ::#prefix::fmt::Debug for #ty_for_impl {
+                    #impl_
+                }
+            });
+        }
+
+        if needs_partialeq_impl {
+            if let Some(impl_) = impl_partialeq::gen_partialeq_impl(
+                ctx,
+                self,
+                item,
+                &ty_for_impl,
+            ) {
+                let partialeq_bounds = if !generic_param_names.is_empty() {
+                    let bounds = generic_param_names.iter().map(|t| {
+                        quote! { #t: PartialEq }
+                    });
+                    quote! { where #( #bounds ),* }
+                } else {
+                    quote! {}
+                };
+
+                let prefix = ctx.trait_prefix();
+                result.push(quote! {
+                    impl #generics ::#prefix::cmp::PartialEq for #ty_for_impl #partialeq_bounds {
+                        #impl_
+                    }
+                });
+            }
+        }
+
+        if !methods.is_empty() {
+            result.push(quote! {
+                impl #generics #ty_for_impl {
+                    #( #methods )*
+                }
+            });
+        }
+    }
+}
+
+trait MethodCodegen {
+    fn codegen_method<'a>(
+        &self,
+        ctx: &BindgenContext,
+        methods: &mut Vec<proc_macro2::TokenStream>,
+        method_names: &mut HashSet<String>,
+        result: &mut CodegenResult<'a>,
+        parent: &CompInfo,
+    );
+}
+
+impl MethodCodegen for Method {
+    fn codegen_method<'a>(
+        &self,
+        ctx: &BindgenContext,
+        methods: &mut Vec<proc_macro2::TokenStream>,
+        method_names: &mut HashSet<String>,
+        result: &mut CodegenResult<'a>,
+        _parent: &CompInfo,
+    ) {
+        assert!({
+            let cc = &ctx.options().codegen_config;
+            match self.kind() {
+                MethodKind::Constructor => cc.constructors(),
+                MethodKind::Destructor => cc.destructors(),
+                MethodKind::VirtualDestructor { .. } => cc.destructors(),
+                MethodKind::Static |
+                MethodKind::Normal |
+                MethodKind::Virtual { .. } => cc.methods(),
+            }
+        });
+
+        // TODO(emilio): We could generate final stuff at least.
+        if self.is_virtual() {
+            return; // FIXME
+        }
+
+        // First of all, output the actual function.
+        let function_item = ctx.resolve_item(self.signature());
+        if !function_item.process_before_codegen(ctx, result) {
+            return;
+        }
+        let function = function_item.expect_function();
+        let times_seen = function.codegen(ctx, result, function_item);
+        let times_seen = match times_seen {
+            Some(seen) => seen,
+            None => return,
+        };
+        let signature_item = ctx.resolve_item(function.signature());
+        let mut name = match self.kind() {
+            MethodKind::Constructor => "new".into(),
+            MethodKind::Destructor => "destruct".into(),
+            _ => function.name().to_owned(),
+        };
+
+        let signature = match *signature_item.expect_type().kind() {
+            TypeKind::Function(ref sig) => sig,
+            _ => panic!("How in the world?"),
+        };
+
+        let supported_abi = match signature.abi(ctx, Some(&*name)) {
+            ClangAbi::Known(Abi::ThisCall) => {
+                ctx.options().rust_features().thiscall_abi
+            }
+            ClangAbi::Known(Abi::Vectorcall) => {
+                ctx.options().rust_features().vectorcall_abi
+            }
+            ClangAbi::Known(Abi::CUnwind) => {
+                ctx.options().rust_features().c_unwind_abi
+            }
+            _ => true,
+        };
+
+        if !supported_abi {
+            return;
+        }
+
+        // Do not generate variadic methods, since rust does not allow
+        // implementing them, and we don't do a good job at it anyway.
+        if signature.is_variadic() {
+            return;
+        }
+
+        if method_names.contains(&name) {
+            let mut count = 1;
+            let mut new_name;
+
+            while {
+                new_name = format!("{}{}", name, count);
+                method_names.contains(&new_name)
+            } {
+                count += 1;
+            }
+
+            name = new_name;
+        }
+
+        method_names.insert(name.clone());
+
+        let mut function_name = function_item.canonical_name(ctx);
+        if times_seen > 0 {
+            write!(&mut function_name, "{}", times_seen).unwrap();
+        }
+        let function_name = ctx.rust_ident(function_name);
+        let mut args = utils::fnsig_arguments(ctx, signature);
+        let mut ret = utils::fnsig_return_ty(ctx, signature);
+
+        if !self.is_static() && !self.is_constructor() {
+            args[0] = if self.is_const() {
+                quote! { &self }
+            } else {
+                quote! { &mut self }
+            };
+        }
+
+        // If it's a constructor, we always return `Self`, and we inject the
+        // "this" parameter, so there's no need to ask the user for it.
+        //
+        // Note that constructors in Clang are represented as functions with
+        // return-type = void.
+        if self.is_constructor() {
+            args.remove(0);
+            ret = quote! { -> Self };
+        }
+
+        let mut exprs =
+            helpers::ast_ty::arguments_from_signature(signature, ctx);
+
+        let mut stmts = vec![];
+
+        // If it's a constructor, we need to insert an extra parameter with a
+        // variable called `__bindgen_tmp` we're going to create.
+        if self.is_constructor() {
+            let prefix = ctx.trait_prefix();
+            let tmp_variable_decl = if ctx
+                .options()
+                .rust_features()
+                .maybe_uninit
+            {
+                exprs[0] = quote! {
+                    __bindgen_tmp.as_mut_ptr()
+                };
+                quote! {
+                    let mut __bindgen_tmp = ::#prefix::mem::MaybeUninit::uninit()
+                }
+            } else {
+                exprs[0] = quote! {
+                    &mut __bindgen_tmp
+                };
+                quote! {
+                    let mut __bindgen_tmp = ::#prefix::mem::uninitialized()
+                }
+            };
+            stmts.push(tmp_variable_decl);
+        } else if !self.is_static() {
+            assert!(!exprs.is_empty());
+            exprs[0] = quote! {
+                self
+            };
+        };
+
+        let call = quote! {
+            #function_name (#( #exprs ),* )
+        };
+
+        stmts.push(call);
+
+        if self.is_constructor() {
+            stmts.push(if ctx.options().rust_features().maybe_uninit {
+                quote! {
+                    __bindgen_tmp.assume_init()
+                }
+            } else {
+                quote! {
+                    __bindgen_tmp
+                }
+            })
+        }
+
+        let block = ctx.wrap_unsafe_ops(quote! ( #( #stmts );*));
+
+        let mut attrs = vec![attributes::inline()];
+
+        if signature.must_use() &&
+            ctx.options().rust_features().must_use_function
+        {
+            attrs.push(attributes::must_use());
+        }
+
+        let name = ctx.rust_ident(&name);
+        methods.push(quote! {
+            #(#attrs)*
+            pub unsafe fn #name ( #( #args ),* ) #ret {
+                #block
+            }
+        });
+    }
+}
+
+/// A helper type that represents different enum variations.
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub enum EnumVariation {
+    /// The code for this enum will use a Rust enum. Note that creating this in unsafe code
+    /// (including FFI) with an invalid value will invoke undefined behaviour, whether or not
+    /// its marked as non_exhaustive.
+    Rust {
+        /// Indicates whether the generated struct should be `#[non_exhaustive]`
+        non_exhaustive: bool,
+    },
+    /// The code for this enum will use a newtype
+    NewType {
+        /// Indicates whether the newtype will have bitwise operators
+        is_bitfield: bool,
+        /// Indicates whether the variants will be represented as global constants
+        is_global: bool,
+    },
+    /// The code for this enum will use consts
+    Consts,
+    /// The code for this enum will use a module containing consts
+    ModuleConsts,
+}
+
+impl EnumVariation {
+    fn is_rust(&self) -> bool {
+        matches!(*self, EnumVariation::Rust { .. })
+    }
+
+    /// Both the `Const` and `ModuleConsts` variants will cause this to return
+    /// true.
+    fn is_const(&self) -> bool {
+        matches!(*self, EnumVariation::Consts | EnumVariation::ModuleConsts)
+    }
+}
+
+impl Default for EnumVariation {
+    fn default() -> EnumVariation {
+        EnumVariation::Consts
+    }
+}
+
+impl std::str::FromStr for EnumVariation {
+    type Err = std::io::Error;
+
+    /// Create a `EnumVariation` from a string.
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "rust" => Ok(EnumVariation::Rust {
+                non_exhaustive: false,
+            }),
+            "rust_non_exhaustive" => Ok(EnumVariation::Rust {
+                non_exhaustive: true,
+            }),
+            "bitfield" => Ok(EnumVariation::NewType {
+                is_bitfield: true,
+                is_global: false,
+            }),
+            "consts" => Ok(EnumVariation::Consts),
+            "moduleconsts" => Ok(EnumVariation::ModuleConsts),
+            "newtype" => Ok(EnumVariation::NewType {
+                is_bitfield: false,
+                is_global: false,
+            }),
+            "newtype_global" => Ok(EnumVariation::NewType {
+                is_bitfield: false,
+                is_global: true,
+            }),
+            _ => Err(std::io::Error::new(
+                std::io::ErrorKind::InvalidInput,
+                concat!(
+                    "Got an invalid EnumVariation. Accepted values ",
+                    "are 'rust', 'rust_non_exhaustive', 'bitfield', 'consts',",
+                    "'moduleconsts', 'newtype' and 'newtype_global'."
+                ),
+            )),
+        }
+    }
+}
+
+/// A helper type to construct different enum variations.
+enum EnumBuilder<'a> {
+    Rust {
+        attrs: Vec<proc_macro2::TokenStream>,
+        ident: Ident,
+        tokens: proc_macro2::TokenStream,
+        emitted_any_variants: bool,
+    },
+    NewType {
+        canonical_name: &'a str,
+        tokens: proc_macro2::TokenStream,
+        is_bitfield: bool,
+        is_global: bool,
+    },
+    Consts {
+        variants: Vec<proc_macro2::TokenStream>,
+    },
+    ModuleConsts {
+        module_name: &'a str,
+        module_items: Vec<proc_macro2::TokenStream>,
+    },
+}
+
+impl<'a> EnumBuilder<'a> {
+    /// Returns true if the builder is for a rustified enum.
+    fn is_rust_enum(&self) -> bool {
+        matches!(*self, EnumBuilder::Rust { .. })
+    }
+
+    /// Create a new enum given an item builder, a canonical name, a name for
+    /// the representation, and which variation it should be generated as.
+    fn new(
+        name: &'a str,
+        mut attrs: Vec<proc_macro2::TokenStream>,
+        repr: proc_macro2::TokenStream,
+        enum_variation: EnumVariation,
+    ) -> Self {
+        let ident = Ident::new(name, Span::call_site());
+
+        match enum_variation {
+            EnumVariation::NewType {
+                is_bitfield,
+                is_global,
+            } => EnumBuilder::NewType {
+                canonical_name: name,
+                tokens: quote! {
+                    #( #attrs )*
+                    pub struct #ident (pub #repr);
+                },
+                is_bitfield,
+                is_global,
+            },
+
+            EnumVariation::Rust { .. } => {
+                // `repr` is guaranteed to be Rustified in Enum::codegen
+                attrs.insert(0, quote! { #[repr( #repr )] });
+                let tokens = quote!();
+                EnumBuilder::Rust {
+                    attrs,
+                    ident,
+                    tokens,
+                    emitted_any_variants: false,
+                }
+            }
+
+            EnumVariation::Consts => {
+                let mut variants = Vec::new();
+
+                variants.push(quote! {
+                    #( #attrs )*
+                    pub type #ident = #repr;
+                });
+
+                EnumBuilder::Consts { variants }
+            }
+
+            EnumVariation::ModuleConsts => {
+                let ident = Ident::new(
+                    CONSTIFIED_ENUM_MODULE_REPR_NAME,
+                    Span::call_site(),
+                );
+                let type_definition = quote! {
+                    #( #attrs )*
+                    pub type #ident = #repr;
+                };
+
+                EnumBuilder::ModuleConsts {
+                    module_name: name,
+                    module_items: vec![type_definition],
+                }
+            }
+        }
+    }
+
+    /// Add a variant to this enum.
+    fn with_variant<'b>(
+        self,
+        ctx: &BindgenContext,
+        variant: &EnumVariant,
+        mangling_prefix: Option<&str>,
+        rust_ty: proc_macro2::TokenStream,
+        result: &mut CodegenResult<'b>,
+        is_ty_named: bool,
+    ) -> Self {
+        let variant_name = ctx.rust_mangle(variant.name());
+        let is_rust_enum = self.is_rust_enum();
+        let expr = match variant.val() {
+            EnumVariantValue::Boolean(v) if is_rust_enum => {
+                helpers::ast_ty::uint_expr(v as u64)
+            }
+            EnumVariantValue::Boolean(v) => quote!(#v),
+            EnumVariantValue::Signed(v) => helpers::ast_ty::int_expr(v),
+            EnumVariantValue::Unsigned(v) => helpers::ast_ty::uint_expr(v),
+        };
+
+        let mut doc = quote! {};
+        if ctx.options().generate_comments {
+            if let Some(raw_comment) = variant.comment() {
+                let comment = ctx.options().process_comment(raw_comment);
+                doc = attributes::doc(comment);
+            }
+        }
+
+        match self {
+            EnumBuilder::Rust {
+                attrs,
+                ident,
+                tokens,
+                emitted_any_variants: _,
+            } => {
+                let name = ctx.rust_ident(variant_name);
+                EnumBuilder::Rust {
+                    attrs,
+                    ident,
+                    tokens: quote! {
+                        #tokens
+                        #doc
+                        #name = #expr,
+                    },
+                    emitted_any_variants: true,
+                }
+            }
+
+            EnumBuilder::NewType {
+                canonical_name,
+                is_global,
+                ..
+            } => {
+                if ctx.options().rust_features().associated_const &&
+                    is_ty_named &&
+                    !is_global
+                {
+                    let enum_ident = ctx.rust_ident(canonical_name);
+                    let variant_ident = ctx.rust_ident(variant_name);
+
+                    result.push(quote! {
+                        impl #enum_ident {
+                            #doc
+                            pub const #variant_ident : #rust_ty = #rust_ty ( #expr );
+                        }
+                    });
+                } else {
+                    let ident = ctx.rust_ident(match mangling_prefix {
+                        Some(prefix) => {
+                            Cow::Owned(format!("{}_{}", prefix, variant_name))
+                        }
+                        None => variant_name,
+                    });
+                    result.push(quote! {
+                        #doc
+                        pub const #ident : #rust_ty = #rust_ty ( #expr );
+                    });
+                }
+
+                self
+            }
+
+            EnumBuilder::Consts { .. } => {
+                let constant_name = match mangling_prefix {
+                    Some(prefix) => {
+                        Cow::Owned(format!("{}_{}", prefix, variant_name))
+                    }
+                    None => variant_name,
+                };
+
+                let ident = ctx.rust_ident(constant_name);
+                result.push(quote! {
+                    #doc
+                    pub const #ident : #rust_ty = #expr ;
+                });
+
+                self
+            }
+            EnumBuilder::ModuleConsts {
+                module_name,
+                mut module_items,
+            } => {
+                let name = ctx.rust_ident(variant_name);
+                let ty = ctx.rust_ident(CONSTIFIED_ENUM_MODULE_REPR_NAME);
+                module_items.push(quote! {
+                    #doc
+                    pub const #name : #ty = #expr ;
+                });
+
+                EnumBuilder::ModuleConsts {
+                    module_name,
+                    module_items,
+                }
+            }
+        }
+    }
+
+    fn build<'b>(
+        self,
+        ctx: &BindgenContext,
+        rust_ty: proc_macro2::TokenStream,
+        result: &mut CodegenResult<'b>,
+    ) -> proc_macro2::TokenStream {
+        match self {
+            EnumBuilder::Rust {
+                attrs,
+                ident,
+                tokens,
+                emitted_any_variants,
+                ..
+            } => {
+                let variants = if !emitted_any_variants {
+                    quote!(__bindgen_cannot_repr_c_on_empty_enum = 0)
+                } else {
+                    tokens
+                };
+
+                quote! {
+                    #( #attrs )*
+                    pub enum #ident {
+                        #variants
+                    }
+                }
+            }
+            EnumBuilder::NewType {
+                canonical_name,
+                tokens,
+                is_bitfield,
+                ..
+            } => {
+                if !is_bitfield {
+                    return tokens;
+                }
+
+                let rust_ty_name = ctx.rust_ident_raw(canonical_name);
+                let prefix = ctx.trait_prefix();
+
+                result.push(quote! {
+                    impl ::#prefix::ops::BitOr<#rust_ty> for #rust_ty {
+                        type Output = Self;
+
+                        #[inline]
+                        fn bitor(self, other: Self) -> Self {
+                            #rust_ty_name(self.0 | other.0)
+                        }
+                    }
+                });
+
+                result.push(quote! {
+                    impl ::#prefix::ops::BitOrAssign for #rust_ty {
+                        #[inline]
+                        fn bitor_assign(&mut self, rhs: #rust_ty) {
+                            self.0 |= rhs.0;
+                        }
+                    }
+                });
+
+                result.push(quote! {
+                    impl ::#prefix::ops::BitAnd<#rust_ty> for #rust_ty {
+                        type Output = Self;
+
+                        #[inline]
+                        fn bitand(self, other: Self) -> Self {
+                            #rust_ty_name(self.0 & other.0)
+                        }
+                    }
+                });
+
+                result.push(quote! {
+                    impl ::#prefix::ops::BitAndAssign for #rust_ty {
+                        #[inline]
+                        fn bitand_assign(&mut self, rhs: #rust_ty) {
+                            self.0 &= rhs.0;
+                        }
+                    }
+                });
+
+                tokens
+            }
+            EnumBuilder::Consts { variants, .. } => quote! { #( #variants )* },
+            EnumBuilder::ModuleConsts {
+                module_items,
+                module_name,
+                ..
+            } => {
+                let ident = ctx.rust_ident(module_name);
+                quote! {
+                    pub mod #ident {
+                        #( #module_items )*
+                    }
+                }
+            }
+        }
+    }
+}
+
+impl CodeGenerator for Enum {
+    type Extra = Item;
+    type Return = ();
+
+    fn codegen<'a>(
+        &self,
+        ctx: &BindgenContext,
+        result: &mut CodegenResult<'a>,
+        item: &Item,
+    ) {
+        debug!("<Enum as CodeGenerator>::codegen: item = {:?}", item);
+        debug_assert!(item.is_enabled_for_codegen(ctx));
+
+        let name = item.canonical_name(ctx);
+        let ident = ctx.rust_ident(&name);
+        let enum_ty = item.expect_type();
+        let layout = enum_ty.layout(ctx);
+        let variation = self.computed_enum_variation(ctx, item);
+
+        let repr_translated;
+        let repr = match self.repr().map(|repr| ctx.resolve_type(repr)) {
+            Some(repr)
+                if !ctx.options().translate_enum_integer_types &&
+                    !variation.is_rust() =>
+            {
+                repr
+            }
+            repr => {
+                // An enum's integer type is translated to a native Rust
+                // integer type in 3 cases:
+                // * the enum is Rustified and we need a translated type for
+                //   the repr attribute
+                // * the representation couldn't be determined from the C source
+                // * it was explicitly requested as a bindgen option
+
+                let kind = match repr {
+                    Some(repr) => match *repr.canonical_type(ctx).kind() {
+                        TypeKind::Int(int_kind) => int_kind,
+                        _ => panic!("Unexpected type as enum repr"),
+                    },
+                    None => {
+                        warn!(
+                            "Guessing type of enum! Forward declarations of enums \
+                             shouldn't be legal!"
+                        );
+                        IntKind::Int
+                    }
+                };
+
+                let signed = kind.is_signed();
+                let size = layout
+                    .map(|l| l.size)
+                    .or_else(|| kind.known_size())
+                    .unwrap_or(0);
+
+                let translated = match (signed, size) {
+                    (true, 1) => IntKind::I8,
+                    (false, 1) => IntKind::U8,
+                    (true, 2) => IntKind::I16,
+                    (false, 2) => IntKind::U16,
+                    (true, 4) => IntKind::I32,
+                    (false, 4) => IntKind::U32,
+                    (true, 8) => IntKind::I64,
+                    (false, 8) => IntKind::U64,
+                    _ => {
+                        warn!(
+                            "invalid enum decl: signed: {}, size: {}",
+                            signed, size
+                        );
+                        IntKind::I32
+                    }
+                };
+
+                repr_translated =
+                    Type::new(None, None, TypeKind::Int(translated), false);
+                &repr_translated
+            }
+        };
+
+        let mut attrs = vec![];
+
+        // TODO(emilio): Delegate this to the builders?
+        match variation {
+            EnumVariation::Rust { non_exhaustive } => {
+                if non_exhaustive &&
+                    ctx.options().rust_features().non_exhaustive
+                {
+                    attrs.push(attributes::non_exhaustive());
+                } else if non_exhaustive &&
+                    !ctx.options().rust_features().non_exhaustive
+                {
+                    panic!("The rust target you're using doesn't seem to support non_exhaustive enums");
+                }
+            }
+            EnumVariation::NewType { .. } => {
+                if ctx.options().rust_features.repr_transparent {
+                    attrs.push(attributes::repr("transparent"));
+                } else {
+                    attrs.push(attributes::repr("C"));
+                }
+            }
+            _ => {}
+        };
+
+        if let Some(comment) = item.comment(ctx) {
+            attrs.push(attributes::doc(comment));
+        }
+
+        if item.must_use(ctx) {
+            attrs.push(attributes::must_use());
+        }
+
+        if !variation.is_const() {
+            let packed = false; // Enums can't be packed in Rust.
+            let mut derives = derives_of_item(item, ctx, packed);
+            // For backwards compat, enums always derive
+            // Clone/Eq/PartialEq/Hash, even if we don't generate those by
+            // default.
+            derives.insert(
+                DerivableTraits::CLONE |
+                    DerivableTraits::HASH |
+                    DerivableTraits::PARTIAL_EQ |
+                    DerivableTraits::EQ,
+            );
+            let mut derives: Vec<_> = derives.into();
+            for derive in item.annotations().derives().iter() {
+                if !derives.contains(&derive.as_str()) {
+                    derives.push(derive);
+                }
+            }
+
+            // The custom derives callback may return a list of derive attributes;
+            // add them to the end of the list.
+            let custom_derives = ctx.options().all_callbacks(|cb| {
+                cb.add_derives(&crate::callbacks::DeriveInfo { name: &name })
+            });
+            // In most cases this will be a no-op, since custom_derives will be empty.
+            derives.extend(custom_derives.iter().map(|s| s.as_str()));
+
+            attrs.push(attributes::derives(&derives));
+        }
+
+        fn add_constant<'a>(
+            ctx: &BindgenContext,
+            enum_: &Type,
+            // Only to avoid recomputing every time.
+            enum_canonical_name: &Ident,
+            // May be the same as "variant" if it's because the
+            // enum is unnamed and we still haven't seen the
+            // value.
+            variant_name: &Ident,
+            referenced_name: &Ident,
+            enum_rust_ty: proc_macro2::TokenStream,
+            result: &mut CodegenResult<'a>,
+        ) {
+            let constant_name = if enum_.name().is_some() {
+                if ctx.options().prepend_enum_name {
+                    format!("{}_{}", enum_canonical_name, variant_name)
+                } else {
+                    format!("{}", variant_name)
+                }
+            } else {
+                format!("{}", variant_name)
+            };
+            let constant_name = ctx.rust_ident(constant_name);
+
+            result.push(quote! {
+                pub const #constant_name : #enum_rust_ty =
+                    #enum_canonical_name :: #referenced_name ;
+            });
+        }
+
+        let repr = repr.to_rust_ty_or_opaque(ctx, item);
+
+        let mut builder = EnumBuilder::new(&name, attrs, repr, variation);
+
+        // A map where we keep a value -> variant relation.
+        let mut seen_values = HashMap::<_, Ident>::default();
+        let enum_rust_ty = item.to_rust_ty_or_opaque(ctx, &());
+        let is_toplevel = item.is_toplevel(ctx);
+
+        // Used to mangle the constants we generate in the unnamed-enum case.
+        let parent_canonical_name = if is_toplevel {
+            None
+        } else {
+            Some(item.parent_id().canonical_name(ctx))
+        };
+
+        let constant_mangling_prefix = if ctx.options().prepend_enum_name {
+            if enum_ty.name().is_none() {
+                parent_canonical_name.as_deref()
+            } else {
+                Some(&*name)
+            }
+        } else {
+            None
+        };
+
+        // NB: We defer the creation of constified variants, in case we find
+        // another variant with the same value (which is the common thing to
+        // do).
+        let mut constified_variants = VecDeque::new();
+
+        let mut iter = self.variants().iter().peekable();
+        while let Some(variant) =
+            iter.next().or_else(|| constified_variants.pop_front())
+        {
+            if variant.hidden() {
+                continue;
+            }
+
+            if variant.force_constification() && iter.peek().is_some() {
+                constified_variants.push_back(variant);
+                continue;
+            }
+
+            match seen_values.entry(variant.val()) {
+                Entry::Occupied(ref entry) => {
+                    if variation.is_rust() {
+                        let variant_name = ctx.rust_mangle(variant.name());
+                        let mangled_name =
+                            if is_toplevel || enum_ty.name().is_some() {
+                                variant_name
+                            } else {
+                                let parent_name =
+                                    parent_canonical_name.as_ref().unwrap();
+
+                                Cow::Owned(format!(
+                                    "{}_{}",
+                                    parent_name, variant_name
+                                ))
+                            };
+
+                        let existing_variant_name = entry.get();
+                        // Use associated constants for named enums.
+                        if enum_ty.name().is_some() &&
+                            ctx.options().rust_features().associated_const
+                        {
+                            let enum_canonical_name = &ident;
+                            let variant_name =
+                                ctx.rust_ident_raw(&*mangled_name);
+                            result.push(quote! {
+                                impl #enum_rust_ty {
+                                    pub const #variant_name : #enum_rust_ty =
+                                        #enum_canonical_name :: #existing_variant_name ;
+                                }
+                            });
+                        } else {
+                            add_constant(
+                                ctx,
+                                enum_ty,
+                                &ident,
+                                &Ident::new(&mangled_name, Span::call_site()),
+                                existing_variant_name,
+                                enum_rust_ty.clone(),
+                                result,
+                            );
+                        }
+                    } else {
+                        builder = builder.with_variant(
+                            ctx,
+                            variant,
+                            constant_mangling_prefix,
+                            enum_rust_ty.clone(),
+                            result,
+                            enum_ty.name().is_some(),
+                        );
+                    }
+                }
+                Entry::Vacant(entry) => {
+                    builder = builder.with_variant(
+                        ctx,
+                        variant,
+                        constant_mangling_prefix,
+                        enum_rust_ty.clone(),
+                        result,
+                        enum_ty.name().is_some(),
+                    );
+
+                    let variant_name = ctx.rust_ident(variant.name());
+
+                    // If it's an unnamed enum, or constification is enforced,
+                    // we also generate a constant so it can be properly
+                    // accessed.
+                    if (variation.is_rust() && enum_ty.name().is_none()) ||
+                        variant.force_constification()
+                    {
+                        let mangled_name = if is_toplevel {
+                            variant_name.clone()
+                        } else {
+                            let parent_name =
+                                parent_canonical_name.as_ref().unwrap();
+
+                            Ident::new(
+                                &format!("{}_{}", parent_name, variant_name),
+                                Span::call_site(),
+                            )
+                        };
+
+                        add_constant(
+                            ctx,
+                            enum_ty,
+                            &ident,
+                            &mangled_name,
+                            &variant_name,
+                            enum_rust_ty.clone(),
+                            result,
+                        );
+                    }
+
+                    entry.insert(variant_name);
+                }
+            }
+        }
+
+        let item = builder.build(ctx, enum_rust_ty, result);
+        result.push(item);
+    }
+}
+
+/// Enum for the default type of macro constants.
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub enum MacroTypeVariation {
+    /// Use i32 or i64
+    Signed,
+    /// Use u32 or u64
+    Unsigned,
+}
+
+impl MacroTypeVariation {
+    /// Convert a `MacroTypeVariation` to its str representation.
+    pub fn as_str(&self) -> &str {
+        match self {
+            MacroTypeVariation::Signed => "signed",
+            MacroTypeVariation::Unsigned => "unsigned",
+        }
+    }
+}
+
+impl Default for MacroTypeVariation {
+    fn default() -> MacroTypeVariation {
+        MacroTypeVariation::Unsigned
+    }
+}
+
+impl std::str::FromStr for MacroTypeVariation {
+    type Err = std::io::Error;
+
+    /// Create a `MacroTypeVariation` from a string.
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "signed" => Ok(MacroTypeVariation::Signed),
+            "unsigned" => Ok(MacroTypeVariation::Unsigned),
+            _ => Err(std::io::Error::new(
+                std::io::ErrorKind::InvalidInput,
+                concat!(
+                    "Got an invalid MacroTypeVariation. Accepted values ",
+                    "are 'signed' and 'unsigned'"
+                ),
+            )),
+        }
+    }
+}
+
+/// Enum for how aliases should be translated.
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub enum AliasVariation {
+    /// Convert to regular Rust alias
+    TypeAlias,
+    /// Create a new type by wrapping the old type in a struct and using #[repr(transparent)]
+    NewType,
+    /// Same as NewStruct but also impl Deref to be able to use the methods of the wrapped type
+    NewTypeDeref,
+}
+
+impl AliasVariation {
+    /// Convert an `AliasVariation` to its str representation.
+    pub fn as_str(&self) -> &str {
+        match self {
+            AliasVariation::TypeAlias => "type_alias",
+            AliasVariation::NewType => "new_type",
+            AliasVariation::NewTypeDeref => "new_type_deref",
+        }
+    }
+}
+
+impl Default for AliasVariation {
+    fn default() -> AliasVariation {
+        AliasVariation::TypeAlias
+    }
+}
+
+impl std::str::FromStr for AliasVariation {
+    type Err = std::io::Error;
+
+    /// Create an `AliasVariation` from a string.
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "type_alias" => Ok(AliasVariation::TypeAlias),
+            "new_type" => Ok(AliasVariation::NewType),
+            "new_type_deref" => Ok(AliasVariation::NewTypeDeref),
+            _ => Err(std::io::Error::new(
+                std::io::ErrorKind::InvalidInput,
+                concat!(
+                    "Got an invalid AliasVariation. Accepted values ",
+                    "are 'type_alias', 'new_type', and 'new_type_deref'"
+                ),
+            )),
+        }
+    }
+}
+
+/// Enum for how non-Copy unions should be translated.
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub enum NonCopyUnionStyle {
+    /// Wrap members in a type generated by bindgen.
+    BindgenWrapper,
+    /// Wrap members in [`::core::mem::ManuallyDrop`].
+    ///
+    /// Note: `ManuallyDrop` was stabilized in Rust 1.20.0, do not use it if your
+    /// MSRV is lower.
+    ManuallyDrop,
+}
+
+impl NonCopyUnionStyle {
+    /// Convert an `NonCopyUnionStyle` to its str representation.
+    pub fn as_str(&self) -> &'static str {
+        match self {
+            Self::BindgenWrapper => "bindgen_wrapper",
+            Self::ManuallyDrop => "manually_drop",
+        }
+    }
+}
+
+impl Default for NonCopyUnionStyle {
+    fn default() -> Self {
+        Self::BindgenWrapper
+    }
+}
+
+impl std::str::FromStr for NonCopyUnionStyle {
+    type Err = std::io::Error;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "bindgen_wrapper" => Ok(Self::BindgenWrapper),
+            "manually_drop" => Ok(Self::ManuallyDrop),
+            _ => Err(std::io::Error::new(
+                std::io::ErrorKind::InvalidInput,
+                concat!(
+                    "Got an invalid NonCopyUnionStyle. Accepted values ",
+                    "are 'bindgen_wrapper' and 'manually_drop'"
+                ),
+            )),
+        }
+    }
+}
+
+/// Fallible conversion to an opaque blob.
+///
+/// Implementors of this trait should provide the `try_get_layout` method to
+/// fallibly get this thing's layout, which the provided `try_to_opaque` trait
+/// method will use to convert the `Layout` into an opaque blob Rust type.
+trait TryToOpaque {
+    type Extra;
+
+    /// Get the layout for this thing, if one is available.
+    fn try_get_layout(
+        &self,
+        ctx: &BindgenContext,
+        extra: &Self::Extra,
+    ) -> error::Result<Layout>;
+
+    /// Do not override this provided trait method.
+    fn try_to_opaque(
+        &self,
+        ctx: &BindgenContext,
+        extra: &Self::Extra,
+    ) -> error::Result<proc_macro2::TokenStream> {
+        self.try_get_layout(ctx, extra)
+            .map(|layout| helpers::blob(ctx, layout))
+    }
+}
+
+/// Infallible conversion of an IR thing to an opaque blob.
+///
+/// The resulting layout is best effort, and is unfortunately not guaranteed to
+/// be correct. When all else fails, we fall back to a single byte layout as a
+/// last resort, because C++ does not permit zero-sized types. See the note in
+/// the `ToRustTyOrOpaque` doc comment about fallible versus infallible traits
+/// and when each is appropriate.
+///
+/// Don't implement this directly. Instead implement `TryToOpaque`, and then
+/// leverage the blanket impl for this trait.
+trait ToOpaque: TryToOpaque {
+    fn get_layout(&self, ctx: &BindgenContext, extra: &Self::Extra) -> Layout {
+        self.try_get_layout(ctx, extra)
+            .unwrap_or_else(|_| Layout::for_size(ctx, 1))
+    }
+
+    fn to_opaque(
+        &self,
+        ctx: &BindgenContext,
+        extra: &Self::Extra,
+    ) -> proc_macro2::TokenStream {
+        let layout = self.get_layout(ctx, extra);
+        helpers::blob(ctx, layout)
+    }
+}
+
+impl<T> ToOpaque for T where T: TryToOpaque {}
+
+/// Fallible conversion from an IR thing to an *equivalent* Rust type.
+///
+/// If the C/C++ construct represented by the IR thing cannot (currently) be
+/// represented in Rust (for example, instantiations of templates with
+/// const-value generic parameters) then the impl should return an `Err`. It
+/// should *not* attempt to return an opaque blob with the correct size and
+/// alignment. That is the responsibility of the `TryToOpaque` trait.
+trait TryToRustTy {
+    type Extra;
+
+    fn try_to_rust_ty(
+        &self,
+        ctx: &BindgenContext,
+        extra: &Self::Extra,
+    ) -> error::Result<proc_macro2::TokenStream>;
+}
+
+/// Fallible conversion to a Rust type or an opaque blob with the correct size
+/// and alignment.
+///
+/// Don't implement this directly. Instead implement `TryToRustTy` and
+/// `TryToOpaque`, and then leverage the blanket impl for this trait below.
+trait TryToRustTyOrOpaque: TryToRustTy + TryToOpaque {
+    type Extra;
+
+    fn try_to_rust_ty_or_opaque(
+        &self,
+        ctx: &BindgenContext,
+        extra: &<Self as TryToRustTyOrOpaque>::Extra,
+    ) -> error::Result<proc_macro2::TokenStream>;
+}
+
+impl<E, T> TryToRustTyOrOpaque for T
+where
+    T: TryToRustTy<Extra = E> + TryToOpaque<Extra = E>,
+{
+    type Extra = E;
+
+    fn try_to_rust_ty_or_opaque(
+        &self,
+        ctx: &BindgenContext,
+        extra: &E,
+    ) -> error::Result<proc_macro2::TokenStream> {
+        self.try_to_rust_ty(ctx, extra).or_else(|_| {
+            if let Ok(layout) = self.try_get_layout(ctx, extra) {
+                Ok(helpers::blob(ctx, layout))
+            } else {
+                Err(error::Error::NoLayoutForOpaqueBlob)
+            }
+        })
+    }
+}
+
+/// Infallible conversion to a Rust type, or an opaque blob with a best effort
+/// of correct size and alignment.
+///
+/// Don't implement this directly. Instead implement `TryToRustTy` and
+/// `TryToOpaque`, and then leverage the blanket impl for this trait below.
+///
+/// ### Fallible vs. Infallible Conversions to Rust Types
+///
+/// When should one use this infallible `ToRustTyOrOpaque` trait versus the
+/// fallible `TryTo{RustTy, Opaque, RustTyOrOpaque}` triats? All fallible trait
+/// implementations that need to convert another thing into a Rust type or
+/// opaque blob in a nested manner should also use fallible trait methods and
+/// propagate failure up the stack. Only infallible functions and methods like
+/// CodeGenerator implementations should use the infallible
+/// `ToRustTyOrOpaque`. The further out we push error recovery, the more likely
+/// we are to get a usable `Layout` even if we can't generate an equivalent Rust
+/// type for a C++ construct.
+trait ToRustTyOrOpaque: TryToRustTy + ToOpaque {
+    type Extra;
+
+    fn to_rust_ty_or_opaque(
+        &self,
+        ctx: &BindgenContext,
+        extra: &<Self as ToRustTyOrOpaque>::Extra,
+    ) -> proc_macro2::TokenStream;
+}
+
+impl<E, T> ToRustTyOrOpaque for T
+where
+    T: TryToRustTy<Extra = E> + ToOpaque<Extra = E>,
+{
+    type Extra = E;
+
+    fn to_rust_ty_or_opaque(
+        &self,
+        ctx: &BindgenContext,
+        extra: &E,
+    ) -> proc_macro2::TokenStream {
+        self.try_to_rust_ty(ctx, extra)
+            .unwrap_or_else(|_| self.to_opaque(ctx, extra))
+    }
+}
+
+impl<T> TryToOpaque for T
+where
+    T: Copy + Into<ItemId>,
+{
+    type Extra = ();
+
+    fn try_get_layout(
+        &self,
+        ctx: &BindgenContext,
+        _: &(),
+    ) -> error::Result<Layout> {
+        ctx.resolve_item((*self).into()).try_get_layout(ctx, &())
+    }
+}
+
+impl<T> TryToRustTy for T
+where
+    T: Copy + Into<ItemId>,
+{
+    type Extra = ();
+
+    fn try_to_rust_ty(
+        &self,
+        ctx: &BindgenContext,
+        _: &(),
+    ) -> error::Result<proc_macro2::TokenStream> {
+        ctx.resolve_item((*self).into()).try_to_rust_ty(ctx, &())
+    }
+}
+
+impl TryToOpaque for Item {
+    type Extra = ();
+
+    fn try_get_layout(
+        &self,
+        ctx: &BindgenContext,
+        _: &(),
+    ) -> error::Result<Layout> {
+        self.kind().expect_type().try_get_layout(ctx, self)
+    }
+}
+
+impl TryToRustTy for Item {
+    type Extra = ();
+
+    fn try_to_rust_ty(
+        &self,
+        ctx: &BindgenContext,
+        _: &(),
+    ) -> error::Result<proc_macro2::TokenStream> {
+        self.kind().expect_type().try_to_rust_ty(ctx, self)
+    }
+}
+
+impl TryToOpaque for Type {
+    type Extra = Item;
+
+    fn try_get_layout(
+        &self,
+        ctx: &BindgenContext,
+        _: &Item,
+    ) -> error::Result<Layout> {
+        self.layout(ctx).ok_or(error::Error::NoLayoutForOpaqueBlob)
+    }
+}
+
+impl TryToRustTy for Type {
+    type Extra = Item;
+
+    fn try_to_rust_ty(
+        &self,
+        ctx: &BindgenContext,
+        item: &Item,
+    ) -> error::Result<proc_macro2::TokenStream> {
+        use self::helpers::ast_ty::*;
+
+        match *self.kind() {
+            TypeKind::Void => Ok(c_void(ctx)),
+            // TODO: we should do something smart with nullptr, or maybe *const
+            // c_void is enough?
+            TypeKind::NullPtr => Ok(c_void(ctx).to_ptr(true)),
+            TypeKind::Int(ik) => {
+                match ik {
+                    IntKind::Bool => Ok(quote! { bool }),
+                    IntKind::Char { .. } => Ok(raw_type(ctx, "c_char")),
+                    IntKind::SChar => Ok(raw_type(ctx, "c_schar")),
+                    IntKind::UChar => Ok(raw_type(ctx, "c_uchar")),
+                    IntKind::Short => Ok(raw_type(ctx, "c_short")),
+                    IntKind::UShort => Ok(raw_type(ctx, "c_ushort")),
+                    IntKind::Int => Ok(raw_type(ctx, "c_int")),
+                    IntKind::UInt => Ok(raw_type(ctx, "c_uint")),
+                    IntKind::Long => Ok(raw_type(ctx, "c_long")),
+                    IntKind::ULong => Ok(raw_type(ctx, "c_ulong")),
+                    IntKind::LongLong => Ok(raw_type(ctx, "c_longlong")),
+                    IntKind::ULongLong => Ok(raw_type(ctx, "c_ulonglong")),
+                    IntKind::WChar => {
+                        let layout = self
+                            .layout(ctx)
+                            .expect("Couldn't compute wchar_t's layout?");
+                        let ty = Layout::known_type_for_size(ctx, layout.size)
+                            .expect("Non-representable wchar_t?");
+                        let ident = ctx.rust_ident_raw(ty);
+                        Ok(quote! { #ident })
+                    }
+
+                    IntKind::I8 => Ok(quote! { i8 }),
+                    IntKind::U8 => Ok(quote! { u8 }),
+                    IntKind::I16 => Ok(quote! { i16 }),
+                    IntKind::U16 => Ok(quote! { u16 }),
+                    IntKind::I32 => Ok(quote! { i32 }),
+                    IntKind::U32 => Ok(quote! { u32 }),
+                    IntKind::I64 => Ok(quote! { i64 }),
+                    IntKind::U64 => Ok(quote! { u64 }),
+                    IntKind::Custom { name, .. } => {
+                        Ok(proc_macro2::TokenStream::from_str(name).unwrap())
+                    }
+                    IntKind::U128 => {
+                        Ok(if ctx.options().rust_features.i128_and_u128 {
+                            quote! { u128 }
+                        } else {
+                            // Best effort thing, but wrong alignment
+                            // unfortunately.
+                            quote! { [u64; 2] }
+                        })
+                    }
+                    IntKind::I128 => {
+                        Ok(if ctx.options().rust_features.i128_and_u128 {
+                            quote! { i128 }
+                        } else {
+                            quote! { [u64; 2] }
+                        })
+                    }
+                }
+            }
+            TypeKind::Float(fk) => {
+                Ok(float_kind_rust_type(ctx, fk, self.layout(ctx)))
+            }
+            TypeKind::Complex(fk) => {
+                let float_path =
+                    float_kind_rust_type(ctx, fk, self.layout(ctx));
+
+                ctx.generated_bindgen_complex();
+                Ok(if ctx.options().enable_cxx_namespaces {
+                    quote! {
+                        root::__BindgenComplex<#float_path>
+                    }
+                } else {
+                    quote! {
+                        __BindgenComplex<#float_path>
+                    }
+                })
+            }
+            TypeKind::Function(ref fs) => {
+                // We can't rely on the sizeof(Option<NonZero<_>>) ==
+                // sizeof(NonZero<_>) optimization with opaque blobs (because
+                // they aren't NonZero), so don't *ever* use an or_opaque
+                // variant here.
+                let ty = fs.try_to_rust_ty(ctx, &())?;
+
+                let prefix = ctx.trait_prefix();
+                Ok(quote! {
+                    ::#prefix::option::Option<#ty>
+                })
+            }
+            TypeKind::Array(item, len) | TypeKind::Vector(item, len) => {
+                let ty = item.try_to_rust_ty(ctx, &())?;
+                Ok(quote! {
+                    [ #ty ; #len ]
+                })
+            }
+            TypeKind::Enum(..) => {
+                let path = item.namespace_aware_canonical_path(ctx);
+                let path = proc_macro2::TokenStream::from_str(&path.join("::"))
+                    .unwrap();
+                Ok(quote!(#path))
+            }
+            TypeKind::TemplateInstantiation(ref inst) => {
+                inst.try_to_rust_ty(ctx, item)
+            }
+            TypeKind::ResolvedTypeRef(inner) => inner.try_to_rust_ty(ctx, &()),
+            TypeKind::TemplateAlias(..) |
+            TypeKind::Alias(..) |
+            TypeKind::BlockPointer(..) => {
+                if self.is_block_pointer() && !ctx.options().generate_block {
+                    let void = c_void(ctx);
+                    return Ok(void.to_ptr(/* is_const = */ false));
+                }
+
+                if item.is_opaque(ctx, &()) &&
+                    item.used_template_params(ctx)
+                        .into_iter()
+                        .any(|param| param.is_template_param(ctx, &()))
+                {
+                    self.try_to_opaque(ctx, item)
+                } else if let Some(ty) = self
+                    .name()
+                    .and_then(|name| utils::type_from_named(ctx, name))
+                {
+                    Ok(ty)
+                } else {
+                    utils::build_path(item, ctx)
+                }
+            }
+            TypeKind::Comp(ref info) => {
+                let template_params = item.all_template_params(ctx);
+                if info.has_non_type_template_params() ||
+                    (item.is_opaque(ctx, &()) && !template_params.is_empty())
+                {
+                    return self.try_to_opaque(ctx, item);
+                }
+
+                utils::build_path(item, ctx)
+            }
+            TypeKind::Opaque => self.try_to_opaque(ctx, item),
+            TypeKind::Pointer(inner) | TypeKind::Reference(inner) => {
+                let is_const = ctx.resolve_type(inner).is_const();
+
+                let inner =
+                    inner.into_resolver().through_type_refs().resolve(ctx);
+                let inner_ty = inner.expect_type();
+
+                let is_objc_pointer =
+                    matches!(inner_ty.kind(), TypeKind::ObjCInterface(..));
+
+                // Regardless if we can properly represent the inner type, we
+                // should always generate a proper pointer here, so use
+                // infallible conversion of the inner type.
+                let mut ty = inner.to_rust_ty_or_opaque(ctx, &());
+                ty.append_implicit_template_params(ctx, inner);
+
+                // Avoid the first function pointer level, since it's already
+                // represented in Rust.
+                if inner_ty.canonical_type(ctx).is_function() || is_objc_pointer
+                {
+                    Ok(ty)
+                } else {
+                    Ok(ty.to_ptr(is_const))
+                }
+            }
+            TypeKind::TypeParam => {
+                let name = item.canonical_name(ctx);
+                let ident = ctx.rust_ident(name);
+                Ok(quote! {
+                    #ident
+                })
+            }
+            TypeKind::ObjCSel => Ok(quote! {
+                objc::runtime::Sel
+            }),
+            TypeKind::ObjCId => Ok(quote! {
+                id
+            }),
+            TypeKind::ObjCInterface(ref interface) => {
+                let name = ctx.rust_ident(interface.name());
+                Ok(quote! {
+                    #name
+                })
+            }
+            ref u @ TypeKind::UnresolvedTypeRef(..) => {
+                unreachable!("Should have been resolved after parsing {:?}!", u)
+            }
+        }
+    }
+}
+
+impl TryToOpaque for TemplateInstantiation {
+    type Extra = Item;
+
+    fn try_get_layout(
+        &self,
+        ctx: &BindgenContext,
+        item: &Item,
+    ) -> error::Result<Layout> {
+        item.expect_type()
+            .layout(ctx)
+            .ok_or(error::Error::NoLayoutForOpaqueBlob)
+    }
+}
+
+impl TryToRustTy for TemplateInstantiation {
+    type Extra = Item;
+
+    fn try_to_rust_ty(
+        &self,
+        ctx: &BindgenContext,
+        item: &Item,
+    ) -> error::Result<proc_macro2::TokenStream> {
+        if self.is_opaque(ctx, item) {
+            return Err(error::Error::InstantiationOfOpaqueType);
+        }
+
+        let def = self
+            .template_definition()
+            .into_resolver()
+            .through_type_refs()
+            .resolve(ctx);
+
+        let mut ty = quote! {};
+        let def_path = def.namespace_aware_canonical_path(ctx);
+        ty.append_separated(
+            def_path.into_iter().map(|p| ctx.rust_ident(p)),
+            quote!(::),
+        );
+
+        let def_params = def.self_template_params(ctx);
+        if def_params.is_empty() {
+            // This can happen if we generated an opaque type for a partial
+            // template specialization, and we've hit an instantiation of
+            // that partial specialization.
+            extra_assert!(def.is_opaque(ctx, &()));
+            return Err(error::Error::InstantiationOfOpaqueType);
+        }
+
+        // TODO: If the definition type is a template class/struct
+        // definition's member template definition, it could rely on
+        // generic template parameters from its outer template
+        // class/struct. When we emit bindings for it, it could require
+        // *more* type arguments than we have here, and we will need to
+        // reconstruct them somehow. We don't have any means of doing
+        // that reconstruction at this time.
+
+        let template_args = self
+            .template_arguments()
+            .iter()
+            .zip(def_params.iter())
+            // Only pass type arguments for the type parameters that
+            // the def uses.
+            .filter(|&(_, param)| ctx.uses_template_parameter(def.id(), *param))
+            .map(|(arg, _)| {
+                let arg = arg.into_resolver().through_type_refs().resolve(ctx);
+                let mut ty = arg.try_to_rust_ty(ctx, &())?;
+                ty.append_implicit_template_params(ctx, arg);
+                Ok(ty)
+            })
+            .collect::<error::Result<Vec<_>>>()?;
+
+        if template_args.is_empty() {
+            return Ok(ty);
+        }
+
+        Ok(quote! {
+            #ty < #( #template_args ),* >
+        })
+    }
+}
+
+impl TryToRustTy for FunctionSig {
+    type Extra = ();
+
+    fn try_to_rust_ty(
+        &self,
+        ctx: &BindgenContext,
+        _: &(),
+    ) -> error::Result<proc_macro2::TokenStream> {
+        // TODO: we might want to consider ignoring the reference return value.
+        let ret = utils::fnsig_return_ty(ctx, self);
+        let arguments = utils::fnsig_arguments(ctx, self);
+        let abi = self.abi(ctx, None);
+
+        match abi {
+            ClangAbi::Known(Abi::ThisCall)
+                if !ctx.options().rust_features().thiscall_abi =>
+            {
+                warn!("Skipping function with thiscall ABI that isn't supported by the configured Rust target");
+                Ok(proc_macro2::TokenStream::new())
+            }
+            ClangAbi::Known(Abi::Vectorcall)
+                if !ctx.options().rust_features().vectorcall_abi =>
+            {
+                warn!("Skipping function with vectorcall ABI that isn't supported by the configured Rust target");
+                Ok(proc_macro2::TokenStream::new())
+            }
+            ClangAbi::Known(Abi::CUnwind)
+                if !ctx.options().rust_features().c_unwind_abi =>
+            {
+                warn!("Skipping function with C-unwind ABI that isn't supported by the configured Rust target");
+                Ok(proc_macro2::TokenStream::new())
+            }
+            _ => Ok(quote! {
+                unsafe extern #abi fn ( #( #arguments ),* ) #ret
+            }),
+        }
+    }
+}
+
+impl CodeGenerator for Function {
+    type Extra = Item;
+
+    /// If we've actually generated the symbol, the number of times we've seen
+    /// it.
+    type Return = Option<u32>;
+
+    fn codegen<'a>(
+        &self,
+        ctx: &BindgenContext,
+        result: &mut CodegenResult<'a>,
+        item: &Item,
+    ) -> Self::Return {
+        debug!("<Function as CodeGenerator>::codegen: item = {:?}", item);
+        debug_assert!(item.is_enabled_for_codegen(ctx));
+
+        // We can't currently do anything with Internal functions so just
+        // avoid generating anything for them.
+        match self.linkage() {
+            Linkage::Internal => return None,
+            Linkage::External => {}
+        }
+
+        // Pure virtual methods have no actual symbol, so we can't generate
+        // something meaningful for them.
+        let is_dynamic_function = match self.kind() {
+            FunctionKind::Method(ref method_kind)
+                if method_kind.is_pure_virtual() =>
+            {
+                return None;
+            }
+            FunctionKind::Function => {
+                ctx.options().dynamic_library_name.is_some()
+            }
+            _ => false,
+        };
+
+        // Similar to static member variables in a class template, we can't
+        // generate bindings to template functions, because the set of
+        // instantiations is open ended and we have no way of knowing which
+        // monomorphizations actually exist.
+        if !item.all_template_params(ctx).is_empty() {
+            return None;
+        }
+
+        let name = self.name();
+        let mut canonical_name = item.canonical_name(ctx);
+        let mangled_name = self.mangled_name();
+
+        {
+            let seen_symbol_name = mangled_name.unwrap_or(&canonical_name);
+
+            // TODO: Maybe warn here if there's a type/argument mismatch, or
+            // something?
+            if result.seen_function(seen_symbol_name) {
+                return None;
+            }
+            result.saw_function(seen_symbol_name);
+        }
+
+        let signature_item = ctx.resolve_item(self.signature());
+        let signature = signature_item.kind().expect_type().canonical_type(ctx);
+        let signature = match *signature.kind() {
+            TypeKind::Function(ref sig) => sig,
+            _ => panic!("Signature kind is not a Function: {:?}", signature),
+        };
+
+        let args = utils::fnsig_arguments(ctx, signature);
+        let ret = utils::fnsig_return_ty(ctx, signature);
+
+        let mut attributes = vec![];
+
+        if ctx.options().rust_features().must_use_function {
+            let must_use = signature.must_use() || {
+                let ret_ty = signature
+                    .return_type()
+                    .into_resolver()
+                    .through_type_refs()
+                    .resolve(ctx);
+                ret_ty.must_use(ctx)
+            };
+
+            if must_use {
+                attributes.push(attributes::must_use());
+            }
+        }
+
+        if let Some(comment) = item.comment(ctx) {
+            attributes.push(attributes::doc(comment));
+        }
+
+        let abi = match signature.abi(ctx, Some(name)) {
+            ClangAbi::Known(Abi::ThisCall)
+                if !ctx.options().rust_features().thiscall_abi =>
+            {
+                warn!("Skipping function with thiscall ABI that isn't supported by the configured Rust target");
+                return None;
+            }
+            ClangAbi::Known(Abi::Vectorcall)
+                if !ctx.options().rust_features().vectorcall_abi =>
+            {
+                warn!("Skipping function with vectorcall ABI that isn't supported by the configured Rust target");
+                return None;
+            }
+            ClangAbi::Known(Abi::CUnwind)
+                if !ctx.options().rust_features().c_unwind_abi =>
+            {
+                warn!("Skipping function with C-unwind ABI that isn't supported by the configured Rust target");
+                return None;
+            }
+            ClangAbi::Known(Abi::Win64) if signature.is_variadic() => {
+                warn!("Skipping variadic function with Win64 ABI that isn't supported");
+                return None;
+            }
+            ClangAbi::Unknown(unknown_abi) => {
+                panic!(
+                    "Invalid or unknown abi {:?} for function {:?} ({:?})",
+                    unknown_abi, canonical_name, self
+                );
+            }
+            abi => abi,
+        };
+
+        // Handle overloaded functions by giving each overload its own unique
+        // suffix.
+        let times_seen = result.overload_number(&canonical_name);
+        if times_seen > 0 {
+            write!(&mut canonical_name, "{}", times_seen).unwrap();
+        }
+
+        let link_name = mangled_name.unwrap_or(name);
+        if !is_dynamic_function &&
+            !utils::names_will_be_identical_after_mangling(
+                &canonical_name,
+                link_name,
+                Some(abi),
+            )
+        {
+            attributes.push(attributes::link_name(link_name));
+        }
+
+        // Unfortunately this can't piggyback on the `attributes` list because
+        // the #[link(wasm_import_module)] needs to happen before the `extern
+        // "C"` block. It doesn't get picked up properly otherwise
+        let wasm_link_attribute =
+            ctx.options().wasm_import_module_name.as_ref().map(|name| {
+                quote! { #[link(wasm_import_module = #name)] }
+            });
+
+        let ident = ctx.rust_ident(canonical_name);
+        let tokens = quote! {
+            #wasm_link_attribute
+            extern #abi {
+                #(#attributes)*
+                pub fn #ident ( #( #args ),* ) #ret;
+            }
+        };
+
+        // If we're doing dynamic binding generation, add to the dynamic items.
+        if is_dynamic_function {
+            let args_identifiers =
+                utils::fnsig_argument_identifiers(ctx, signature);
+            let return_item = ctx.resolve_item(signature.return_type());
+            let ret_ty = match *return_item.kind().expect_type().kind() {
+                TypeKind::Void => quote! {()},
+                _ => return_item.to_rust_ty_or_opaque(ctx, &()),
+            };
+            result.dynamic_items().push(
+                ident,
+                abi,
+                signature.is_variadic(),
+                ctx.options().dynamic_link_require_all,
+                args,
+                args_identifiers,
+                ret,
+                ret_ty,
+                attributes,
+                ctx,
+            );
+        } else {
+            result.push(tokens);
+        }
+        Some(times_seen)
+    }
+}
+
+fn objc_method_codegen(
+    ctx: &BindgenContext,
+    method: &ObjCMethod,
+    methods: &mut Vec<proc_macro2::TokenStream>,
+    class_name: Option<&str>,
+    rust_class_name: &str,
+    prefix: &str,
+) {
+    // This would ideally resolve the method into an Item, and use
+    // Item::process_before_codegen; however, ObjC methods are not currently
+    // made into function items.
+    let name = format!("{}::{}{}", rust_class_name, prefix, method.rust_name());
+    if ctx.options().blocklisted_items.matches(name) {
+        return;
+    }
+
+    let signature = method.signature();
+    let fn_args = utils::fnsig_arguments(ctx, signature);
+    let fn_ret = utils::fnsig_return_ty(ctx, signature);
+
+    let sig = if method.is_class_method() {
+        let fn_args = fn_args.clone();
+        quote! {
+            ( #( #fn_args ),* ) #fn_ret
+        }
+    } else {
+        let fn_args = fn_args.clone();
+        let args = iter::once(quote! { &self }).chain(fn_args.into_iter());
+        quote! {
+            ( #( #args ),* ) #fn_ret
+        }
+    };
+
+    let methods_and_args = method.format_method_call(&fn_args);
+
+    let body = {
+        let body = if method.is_class_method() {
+            let class_name = ctx.rust_ident(
+                class_name
+                    .expect("Generating a class method without class name?"),
+            );
+            quote!(msg_send!(class!(#class_name), #methods_and_args))
+        } else {
+            quote!(msg_send!(*self, #methods_and_args))
+        };
+
+        ctx.wrap_unsafe_ops(body)
+    };
+
+    let method_name =
+        ctx.rust_ident(format!("{}{}", prefix, method.rust_name()));
+
+    methods.push(quote! {
+        unsafe fn #method_name #sig where <Self as std::ops::Deref>::Target: objc::Message + Sized {
+            #body
+        }
+    });
+}
+
+impl CodeGenerator for ObjCInterface {
+    type Extra = Item;
+    type Return = ();
+
+    fn codegen<'a>(
+        &self,
+        ctx: &BindgenContext,
+        result: &mut CodegenResult<'a>,
+        item: &Item,
+    ) {
+        debug_assert!(item.is_enabled_for_codegen(ctx));
+
+        let mut impl_items = vec![];
+        let rust_class_name = item.path_for_allowlisting(ctx)[1..].join("::");
+
+        for method in self.methods() {
+            objc_method_codegen(
+                ctx,
+                method,
+                &mut impl_items,
+                None,
+                &rust_class_name,
+                "",
+            );
+        }
+
+        for class_method in self.class_methods() {
+            let ambiquity = self
+                .methods()
+                .iter()
+                .map(|m| m.rust_name())
+                .any(|x| x == class_method.rust_name());
+            let prefix = if ambiquity { "class_" } else { "" };
+            objc_method_codegen(
+                ctx,
+                class_method,
+                &mut impl_items,
+                Some(self.name()),
+                &rust_class_name,
+                prefix,
+            );
+        }
+
+        let trait_name = ctx.rust_ident(self.rust_name());
+        let trait_constraints = quote! {
+            Sized + std::ops::Deref
+        };
+        let trait_block = if self.is_template() {
+            let template_names: Vec<Ident> = self
+                .template_names
+                .iter()
+                .map(|g| ctx.rust_ident(g))
+                .collect();
+
+            quote! {
+                pub trait #trait_name <#(#template_names:'static),*> : #trait_constraints {
+                    #( #impl_items )*
+                }
+            }
+        } else {
+            quote! {
+                pub trait #trait_name : #trait_constraints {
+                    #( #impl_items )*
+                }
+            }
+        };
+
+        let class_name = ctx.rust_ident(self.name());
+        if !self.is_category() && !self.is_protocol() {
+            let struct_block = quote! {
+                #[repr(transparent)]
+                #[derive(Debug, Copy, Clone)]
+                pub struct #class_name(pub id);
+                impl std::ops::Deref for #class_name {
+                    type Target = objc::runtime::Object;
+                    fn deref(&self) -> &Self::Target {
+                        unsafe {
+                            &*self.0
+                        }
+                    }
+                }
+                unsafe impl objc::Message for #class_name { }
+                impl #class_name {
+                    pub fn alloc() -> Self {
+                        Self(unsafe {
+                            msg_send!(class!(#class_name), alloc)
+                        })
+                    }
+                }
+            };
+            result.push(struct_block);
+            let mut protocol_set: HashSet<ItemId> = Default::default();
+            for protocol_id in self.conforms_to.iter() {
+                protocol_set.insert(*protocol_id);
+                let protocol_name = ctx.rust_ident(
+                    ctx.resolve_type(protocol_id.expect_type_id(ctx))
+                        .name()
+                        .unwrap(),
+                );
+                let impl_trait = quote! {
+                    impl #protocol_name for #class_name { }
+                };
+                result.push(impl_trait);
+            }
+            let mut parent_class = self.parent_class;
+            while let Some(parent_id) = parent_class {
+                let parent = parent_id
+                    .expect_type_id(ctx)
+                    .into_resolver()
+                    .through_type_refs()
+                    .resolve(ctx)
+                    .expect_type()
+                    .kind();
+
+                let parent = match parent {
+                    TypeKind::ObjCInterface(ref parent) => parent,
+                    _ => break,
+                };
+                parent_class = parent.parent_class;
+
+                let parent_name = ctx.rust_ident(parent.rust_name());
+                let impl_trait = if parent.is_template() {
+                    let template_names: Vec<Ident> = parent
+                        .template_names
+                        .iter()
+                        .map(|g| ctx.rust_ident(g))
+                        .collect();
+                    quote! {
+                        impl <#(#template_names :'static),*> #parent_name <#(#template_names),*> for #class_name {
+                        }
+                    }
+                } else {
+                    quote! {
+                        impl #parent_name for #class_name { }
+                    }
+                };
+                result.push(impl_trait);
+                for protocol_id in parent.conforms_to.iter() {
+                    if protocol_set.insert(*protocol_id) {
+                        let protocol_name = ctx.rust_ident(
+                            ctx.resolve_type(protocol_id.expect_type_id(ctx))
+                                .name()
+                                .unwrap(),
+                        );
+                        let impl_trait = quote! {
+                            impl #protocol_name for #class_name { }
+                        };
+                        result.push(impl_trait);
+                    }
+                }
+                if !parent.is_template() {
+                    let parent_struct_name = parent.name();
+                    let child_struct_name = self.name();
+                    let parent_struct = ctx.rust_ident(parent_struct_name);
+                    let from_block = quote! {
+                        impl From<#class_name> for #parent_struct {
+                            fn from(child: #class_name) -> #parent_struct {
+                                #parent_struct(child.0)
+                            }
+                        }
+                    };
+                    result.push(from_block);
+
+                    let error_msg = format!(
+                        "This {} cannot be downcasted to {}",
+                        parent_struct_name, child_struct_name
+                    );
+                    let try_into_block = quote! {
+                        impl std::convert::TryFrom<#parent_struct> for #class_name {
+                            type Error = &'static str;
+                            fn try_from(parent: #parent_struct) -> Result<#class_name, Self::Error> {
+                                let is_kind_of : bool = unsafe { msg_send!(parent, isKindOfClass:class!(#class_name))};
+                                if is_kind_of {
+                                    Ok(#class_name(parent.0))
+                                } else {
+                                    Err(#error_msg)
+                                }
+                            }
+                        }
+                    };
+                    result.push(try_into_block);
+                }
+            }
+        }
+
+        if !self.is_protocol() {
+            let impl_block = if self.is_template() {
+                let template_names: Vec<Ident> = self
+                    .template_names
+                    .iter()
+                    .map(|g| ctx.rust_ident(g))
+                    .collect();
+                quote! {
+                    impl <#(#template_names :'static),*> #trait_name <#(#template_names),*> for #class_name {
+                    }
+                }
+            } else {
+                quote! {
+                    impl #trait_name for #class_name {
+                    }
+                }
+            };
+            result.push(impl_block);
+        }
+
+        result.push(trait_block);
+        result.saw_objc();
+    }
+}
+
+pub(crate) fn codegen(
+    context: BindgenContext,
+) -> (proc_macro2::TokenStream, BindgenOptions, Vec<String>) {
+    context.gen(|context| {
+        let _t = context.timer("codegen");
+        let counter = Cell::new(0);
+        let mut result = CodegenResult::new(&counter);
+
+        debug!("codegen: {:?}", context.options());
+
+        if context.options().emit_ir {
+            let codegen_items = context.codegen_items();
+            for (id, item) in context.items() {
+                if codegen_items.contains(&id) {
+                    println!("ir: {:?} = {:#?}", id, item);
+                }
+            }
+        }
+
+        if let Some(path) = context.options().emit_ir_graphviz.as_ref() {
+            match dot::write_dot_file(context, path) {
+                Ok(()) => info!(
+                    "Your dot file was generated successfully into: {}",
+                    path
+                ),
+                Err(e) => warn!("{}", e),
+            }
+        }
+
+        if let Some(spec) = context.options().depfile.as_ref() {
+            match spec.write(context.deps()) {
+                Ok(()) => info!(
+                    "Your depfile was generated successfully into: {}",
+                    spec.depfile_path.display()
+                ),
+                Err(e) => warn!("{}", e),
+            }
+        }
+
+        context.resolve_item(context.root_module()).codegen(
+            context,
+            &mut result,
+            &(),
+        );
+
+        if let Some(ref lib_name) = context.options().dynamic_library_name {
+            let lib_ident = context.rust_ident(lib_name);
+            let dynamic_items_tokens =
+                result.dynamic_items().get_tokens(lib_ident, context);
+            result.push(dynamic_items_tokens);
+        }
+
+        postprocessing::postprocessing(result.items, context.options())
+    })
+}
+
+pub mod utils {
+    use super::{error, ToRustTyOrOpaque};
+    use crate::ir::context::BindgenContext;
+    use crate::ir::function::{Abi, ClangAbi, FunctionSig};
+    use crate::ir::item::{Item, ItemCanonicalPath};
+    use crate::ir::ty::TypeKind;
+    use proc_macro2;
+    use std::borrow::Cow;
+    use std::mem;
+    use std::str::FromStr;
+
+    pub fn prepend_bitfield_unit_type(
+        ctx: &BindgenContext,
+        result: &mut Vec<proc_macro2::TokenStream>,
+    ) {
+        let bitfield_unit_src = include_str!("./bitfield_unit.rs");
+        let bitfield_unit_src = if ctx.options().rust_features().min_const_fn {
+            Cow::Borrowed(bitfield_unit_src)
+        } else {
+            Cow::Owned(bitfield_unit_src.replace("const fn ", "fn "))
+        };
+        let bitfield_unit_type =
+            proc_macro2::TokenStream::from_str(&bitfield_unit_src).unwrap();
+        let bitfield_unit_type = quote!(#bitfield_unit_type);
+
+        let items = vec![bitfield_unit_type];
+        let old_items = mem::replace(result, items);
+        result.extend(old_items);
+    }
+
+    pub fn prepend_objc_header(
+        ctx: &BindgenContext,
+        result: &mut Vec<proc_macro2::TokenStream>,
+    ) {
+        let use_objc = if ctx.options().objc_extern_crate {
+            quote! {
+                #[macro_use]
+                extern crate objc;
+            }
+        } else {
+            quote! {
+                use objc::{self, msg_send, sel, sel_impl, class};
+            }
+        };
+
+        let id_type = quote! {
+            #[allow(non_camel_case_types)]
+            pub type id = *mut objc::runtime::Object;
+        };
+
+        let items = vec![use_objc, id_type];
+        let old_items = mem::replace(result, items);
+        result.extend(old_items.into_iter());
+    }
+
+    pub fn prepend_block_header(
+        ctx: &BindgenContext,
+        result: &mut Vec<proc_macro2::TokenStream>,
+    ) {
+        let use_block = if ctx.options().block_extern_crate {
+            quote! {
+                extern crate block;
+            }
+        } else {
+            quote! {
+                use block;
+            }
+        };
+
+        let items = vec![use_block];
+        let old_items = mem::replace(result, items);
+        result.extend(old_items.into_iter());
+    }
+
+    pub fn prepend_union_types(
+        ctx: &BindgenContext,
+        result: &mut Vec<proc_macro2::TokenStream>,
+    ) {
+        let prefix = ctx.trait_prefix();
+
+        // If the target supports `const fn`, declare eligible functions
+        // as `const fn` else just `fn`.
+        let const_fn = if ctx.options().rust_features().min_const_fn {
+            quote! { const fn }
+        } else {
+            quote! { fn }
+        };
+
+        // TODO(emilio): The fmt::Debug impl could be way nicer with
+        // std::intrinsics::type_name, but...
+        let union_field_decl = quote! {
+            #[repr(C)]
+            pub struct __BindgenUnionField<T>(::#prefix::marker::PhantomData<T>);
+        };
+
+        let transmute =
+            ctx.wrap_unsafe_ops(quote!(::#prefix::mem::transmute(self)));
+
+        let union_field_impl = quote! {
+            impl<T> __BindgenUnionField<T> {
+                #[inline]
+                pub #const_fn new() -> Self {
+                    __BindgenUnionField(::#prefix::marker::PhantomData)
+                }
+
+                #[inline]
+                pub unsafe fn as_ref(&self) -> &T {
+                    #transmute
+                }
+
+                #[inline]
+                pub unsafe fn as_mut(&mut self) -> &mut T {
+                    #transmute
+                }
+            }
+        };
+
+        let union_field_default_impl = quote! {
+            impl<T> ::#prefix::default::Default for __BindgenUnionField<T> {
+                #[inline]
+                fn default() -> Self {
+                    Self::new()
+                }
+            }
+        };
+
+        let union_field_clone_impl = quote! {
+            impl<T> ::#prefix::clone::Clone for __BindgenUnionField<T> {
+                #[inline]
+                fn clone(&self) -> Self {
+                    Self::new()
+                }
+            }
+        };
+
+        let union_field_copy_impl = quote! {
+            impl<T> ::#prefix::marker::Copy for __BindgenUnionField<T> {}
+        };
+
+        let union_field_debug_impl = quote! {
+            impl<T> ::#prefix::fmt::Debug for __BindgenUnionField<T> {
+                fn fmt(&self, fmt: &mut ::#prefix::fmt::Formatter<'_>)
+                       -> ::#prefix::fmt::Result {
+                    fmt.write_str("__BindgenUnionField")
+                }
+            }
+        };
+
+        // The actual memory of the filed will be hashed, so that's why these
+        // field doesn't do anything with the hash.
+        let union_field_hash_impl = quote! {
+            impl<T> ::#prefix::hash::Hash for __BindgenUnionField<T> {
+                fn hash<H: ::#prefix::hash::Hasher>(&self, _state: &mut H) {
+                }
+            }
+        };
+
+        let union_field_partialeq_impl = quote! {
+            impl<T> ::#prefix::cmp::PartialEq for __BindgenUnionField<T> {
+               fn eq(&self, _other: &__BindgenUnionField<T>) -> bool {
+                   true
+               }
+           }
+        };
+
+        let union_field_eq_impl = quote! {
+           impl<T> ::#prefix::cmp::Eq for __BindgenUnionField<T> {
+           }
+        };
+
+        let items = vec![
+            union_field_decl,
+            union_field_impl,
+            union_field_default_impl,
+            union_field_clone_impl,
+            union_field_copy_impl,
+            union_field_debug_impl,
+            union_field_hash_impl,
+            union_field_partialeq_impl,
+            union_field_eq_impl,
+        ];
+
+        let old_items = mem::replace(result, items);
+        result.extend(old_items.into_iter());
+    }
+
+    pub fn prepend_incomplete_array_types(
+        ctx: &BindgenContext,
+        result: &mut Vec<proc_macro2::TokenStream>,
+    ) {
+        let prefix = ctx.trait_prefix();
+
+        // If the target supports `const fn`, declare eligible functions
+        // as `const fn` else just `fn`.
+        let const_fn = if ctx.options().rust_features().min_const_fn {
+            quote! { const fn }
+        } else {
+            quote! { fn }
+        };
+
+        let incomplete_array_decl = quote! {
+            #[repr(C)]
+            #[derive(Default)]
+            pub struct __IncompleteArrayField<T>(
+                ::#prefix::marker::PhantomData<T>, [T; 0]);
+        };
+
+        let from_raw_parts = ctx.wrap_unsafe_ops(quote! (
+            ::#prefix::slice::from_raw_parts(self.as_ptr(), len)
+        ));
+        let from_raw_parts_mut = ctx.wrap_unsafe_ops(quote! (
+            ::#prefix::slice::from_raw_parts_mut(self.as_mut_ptr(), len)
+        ));
+
+        let incomplete_array_impl = quote! {
+            impl<T> __IncompleteArrayField<T> {
+                #[inline]
+                pub #const_fn new() -> Self {
+                    __IncompleteArrayField(::#prefix::marker::PhantomData, [])
+                }
+
+                #[inline]
+                pub fn as_ptr(&self) -> *const T {
+                    self as *const _ as *const T
+                }
+
+                #[inline]
+                pub fn as_mut_ptr(&mut self) -> *mut T {
+                    self as *mut _ as *mut T
+                }
+
+                #[inline]
+                pub unsafe fn as_slice(&self, len: usize) -> &[T] {
+                    #from_raw_parts
+                }
+
+                #[inline]
+                pub unsafe fn as_mut_slice(&mut self, len: usize) -> &mut [T] {
+                    #from_raw_parts_mut
+                }
+            }
+        };
+
+        let incomplete_array_debug_impl = quote! {
+            impl<T> ::#prefix::fmt::Debug for __IncompleteArrayField<T> {
+                fn fmt(&self, fmt: &mut ::#prefix::fmt::Formatter<'_>)
+                       -> ::#prefix::fmt::Result {
+                    fmt.write_str("__IncompleteArrayField")
+                }
+            }
+        };
+
+        let items = vec![
+            incomplete_array_decl,
+            incomplete_array_impl,
+            incomplete_array_debug_impl,
+        ];
+
+        let old_items = mem::replace(result, items);
+        result.extend(old_items.into_iter());
+    }
+
+    pub fn prepend_complex_type(result: &mut Vec<proc_macro2::TokenStream>) {
+        let complex_type = quote! {
+            #[derive(PartialEq, Copy, Clone, Hash, Debug, Default)]
+            #[repr(C)]
+            pub struct __BindgenComplex<T> {
+                pub re: T,
+                pub im: T
+            }
+        };
+
+        let items = vec![complex_type];
+        let old_items = mem::replace(result, items);
+        result.extend(old_items.into_iter());
+    }
+
+    pub fn build_path(
+        item: &Item,
+        ctx: &BindgenContext,
+    ) -> error::Result<proc_macro2::TokenStream> {
+        let path = item.namespace_aware_canonical_path(ctx);
+        let tokens =
+            proc_macro2::TokenStream::from_str(&path.join("::")).unwrap();
+
+        Ok(tokens)
+    }
+
+    fn primitive_ty(
+        ctx: &BindgenContext,
+        name: &str,
+    ) -> proc_macro2::TokenStream {
+        let ident = ctx.rust_ident_raw(name);
+        quote! {
+            #ident
+        }
+    }
+
+    pub fn type_from_named(
+        ctx: &BindgenContext,
+        name: &str,
+    ) -> Option<proc_macro2::TokenStream> {
+        // FIXME: We could use the inner item to check this is really a
+        // primitive type but, who the heck overrides these anyway?
+        Some(match name {
+            "int8_t" => primitive_ty(ctx, "i8"),
+            "uint8_t" => primitive_ty(ctx, "u8"),
+            "int16_t" => primitive_ty(ctx, "i16"),
+            "uint16_t" => primitive_ty(ctx, "u16"),
+            "int32_t" => primitive_ty(ctx, "i32"),
+            "uint32_t" => primitive_ty(ctx, "u32"),
+            "int64_t" => primitive_ty(ctx, "i64"),
+            "uint64_t" => primitive_ty(ctx, "u64"),
+
+            "size_t" if ctx.options().size_t_is_usize => {
+                primitive_ty(ctx, "usize")
+            }
+            "uintptr_t" => primitive_ty(ctx, "usize"),
+
+            "ssize_t" if ctx.options().size_t_is_usize => {
+                primitive_ty(ctx, "isize")
+            }
+            "intptr_t" | "ptrdiff_t" => primitive_ty(ctx, "isize"),
+            _ => return None,
+        })
+    }
+
+    pub fn fnsig_return_ty(
+        ctx: &BindgenContext,
+        sig: &FunctionSig,
+    ) -> proc_macro2::TokenStream {
+        if sig.is_divergent() {
+            return quote! { -> ! };
+        }
+
+        let return_item = ctx.resolve_item(sig.return_type());
+        if let TypeKind::Void = *return_item.kind().expect_type().kind() {
+            quote! {}
+        } else {
+            let ret_ty = return_item.to_rust_ty_or_opaque(ctx, &());
+            quote! {
+                -> #ret_ty
+            }
+        }
+    }
+
+    pub fn fnsig_arguments(
+        ctx: &BindgenContext,
+        sig: &FunctionSig,
+    ) -> Vec<proc_macro2::TokenStream> {
+        use super::ToPtr;
+
+        let mut unnamed_arguments = 0;
+        let mut args = sig
+            .argument_types()
+            .iter()
+            .map(|&(ref name, ty)| {
+                let arg_item = ctx.resolve_item(ty);
+                let arg_ty = arg_item.kind().expect_type();
+
+                // From the C90 standard[1]:
+                //
+                //     A declaration of a parameter as "array of type" shall be
+                //     adjusted to "qualified pointer to type", where the type
+                //     qualifiers (if any) are those specified within the [ and ] of
+                //     the array type derivation.
+                //
+                // [1]: http://c0x.coding-guidelines.com/6.7.5.3.html
+                let arg_ty = match *arg_ty.canonical_type(ctx).kind() {
+                    TypeKind::Array(t, _) => {
+                        let stream =
+                            if ctx.options().array_pointers_in_arguments {
+                                arg_ty.to_rust_ty_or_opaque(ctx, arg_item)
+                            } else {
+                                t.to_rust_ty_or_opaque(ctx, &())
+                            };
+                        stream.to_ptr(ctx.resolve_type(t).is_const())
+                    }
+                    TypeKind::Pointer(inner) => {
+                        let inner = ctx.resolve_item(inner);
+                        let inner_ty = inner.expect_type();
+                        if let TypeKind::ObjCInterface(ref interface) =
+                            *inner_ty.canonical_type(ctx).kind()
+                        {
+                            let name = ctx.rust_ident(interface.name());
+                            quote! {
+                                #name
+                            }
+                        } else {
+                            arg_item.to_rust_ty_or_opaque(ctx, &())
+                        }
+                    }
+                    _ => arg_item.to_rust_ty_or_opaque(ctx, &()),
+                };
+
+                let arg_name = match *name {
+                    Some(ref name) => ctx.rust_mangle(name).into_owned(),
+                    None => {
+                        unnamed_arguments += 1;
+                        format!("arg{}", unnamed_arguments)
+                    }
+                };
+
+                assert!(!arg_name.is_empty());
+                let arg_name = ctx.rust_ident(arg_name);
+
+                quote! {
+                    #arg_name : #arg_ty
+                }
+            })
+            .collect::<Vec<_>>();
+
+        if sig.is_variadic() {
+            args.push(quote! { ... })
+        }
+
+        args
+    }
+
+    pub fn fnsig_argument_identifiers(
+        ctx: &BindgenContext,
+        sig: &FunctionSig,
+    ) -> Vec<proc_macro2::TokenStream> {
+        let mut unnamed_arguments = 0;
+        let args = sig
+            .argument_types()
+            .iter()
+            .map(|&(ref name, _ty)| {
+                let arg_name = match *name {
+                    Some(ref name) => ctx.rust_mangle(name).into_owned(),
+                    None => {
+                        unnamed_arguments += 1;
+                        format!("arg{}", unnamed_arguments)
+                    }
+                };
+
+                assert!(!arg_name.is_empty());
+                let arg_name = ctx.rust_ident(arg_name);
+
+                quote! {
+                    #arg_name
+                }
+            })
+            .collect::<Vec<_>>();
+
+        args
+    }
+
+    pub fn fnsig_block(
+        ctx: &BindgenContext,
+        sig: &FunctionSig,
+    ) -> proc_macro2::TokenStream {
+        let args = sig.argument_types().iter().map(|&(_, ty)| {
+            let arg_item = ctx.resolve_item(ty);
+
+            arg_item.to_rust_ty_or_opaque(ctx, &())
+        });
+
+        let return_item = ctx.resolve_item(sig.return_type());
+        let ret_ty =
+            if let TypeKind::Void = *return_item.kind().expect_type().kind() {
+                quote! { () }
+            } else {
+                return_item.to_rust_ty_or_opaque(ctx, &())
+            };
+
+        quote! {
+            *const ::block::Block<(#(#args,)*), #ret_ty>
+        }
+    }
+
+    // Returns true if `canonical_name` will end up as `mangled_name` at the
+    // machine code level, i.e. after LLVM has applied any target specific
+    // mangling.
+    pub(crate) fn names_will_be_identical_after_mangling(
+        canonical_name: &str,
+        mangled_name: &str,
+        call_conv: Option<ClangAbi>,
+    ) -> bool {
+        // If the mangled name and the canonical name are the same then no
+        // mangling can have happened between the two versions.
+        if canonical_name == mangled_name {
+            return true;
+        }
+
+        // Working with &[u8] makes indexing simpler than with &str
+        let canonical_name = canonical_name.as_bytes();
+        let mangled_name = mangled_name.as_bytes();
+
+        let (mangling_prefix, expect_suffix) = match call_conv {
+            Some(ClangAbi::Known(Abi::C)) |
+            // None is the case for global variables
+            None => {
+                (b'_', false)
+            }
+            Some(ClangAbi::Known(Abi::Stdcall)) => (b'_', true),
+            Some(ClangAbi::Known(Abi::Fastcall)) => (b'@', true),
+
+            // This is something we don't recognize, stay on the safe side
+            // by emitting the `#[link_name]` attribute
+            Some(_) => return false,
+        };
+
+        // Check that the mangled name is long enough to at least contain the
+        // canonical name plus the expected prefix.
+        if mangled_name.len() < canonical_name.len() + 1 {
+            return false;
+        }
+
+        // Return if the mangled name does not start with the prefix expected
+        // for the given calling convention.
+        if mangled_name[0] != mangling_prefix {
+            return false;
+        }
+
+        // Check that the mangled name contains the canonical name after the
+        // prefix
+        if &mangled_name[1..canonical_name.len() + 1] != canonical_name {
+            return false;
+        }
+
+        // If the given calling convention also prescribes a suffix, check that
+        // it exists too
+        if expect_suffix {
+            let suffix = &mangled_name[canonical_name.len() + 1..];
+
+            // The shortest suffix is "@0"
+            if suffix.len() < 2 {
+                return false;
+            }
+
+            // Check that the suffix starts with '@' and is all ASCII decimals
+            // after that.
+            if suffix[0] != b'@' || !suffix[1..].iter().all(u8::is_ascii_digit)
+            {
+                return false;
+            }
+        } else if mangled_name.len() != canonical_name.len() + 1 {
+            // If we don't expect a prefix but there is one, we need the
+            // #[link_name] attribute
+            return false;
+        }
+
+        true
+    }
+}
diff --git a/third_party/rust/bindgen/codegen/postprocessing/merge_extern_blocks.rs b/third_party/rust/bindgen/codegen/postprocessing/merge_extern_blocks.rs
new file mode 100644
index 0000000000..05e7e9ef39
--- /dev/null
+++ b/third_party/rust/bindgen/codegen/postprocessing/merge_extern_blocks.rs
@@ -0,0 +1,66 @@
+use syn::{
+    visit_mut::{visit_item_mod_mut, VisitMut},
+    Item, ItemForeignMod, ItemMod,
+};
+
+pub(super) fn merge_extern_blocks(item_mod: &mut ItemMod) {
+    Visitor.visit_item_mod_mut(item_mod)
+}
+
+struct Visitor;
+
+impl VisitMut for Visitor {
+    fn visit_item_mod_mut(&mut self, item_mod: &mut ItemMod) {
+        if let Some((_, ref mut items)) = item_mod.content {
+            // Keep all the extern blocks in a different `Vec` for faster search.
+            let mut extern_blocks = Vec::<ItemForeignMod>::new();
+
+            for item in std::mem::take(items) {
+                if let Item::ForeignMod(ItemForeignMod {
+                    attrs,
+                    abi,
+                    brace_token,
+                    items: extern_block_items,
+                }) = item
+                {
+                    let mut exists = false;
+                    for extern_block in &mut extern_blocks {
+                        // Check if there is a extern block with the same ABI and
+                        // attributes.
+                        if extern_block.attrs == attrs &&
+                            extern_block.abi == abi
+                        {
+                            // Merge the items of the two blocks.
+                            extern_block
+                                .items
+                                .extend_from_slice(&extern_block_items);
+                            exists = true;
+                            break;
+                        }
+                    }
+                    // If no existing extern block had the same ABI and attributes, store
+                    // it.
+                    if !exists {
+                        extern_blocks.push(ItemForeignMod {
+                            attrs,
+                            abi,
+                            brace_token,
+                            items: extern_block_items,
+                        });
+                    }
+                } else {
+                    // If the item is not an extern block, we don't have to do anything and just
+                    // push it back.
+                    items.push(item);
+                }
+            }
+
+            // Move all the extern blocks alongside the rest of the items.
+            for extern_block in extern_blocks {
+                items.push(Item::ForeignMod(extern_block));
+            }
+        }
+
+        visit_item_mod_mut(self, item_mod)
+    }
+}
diff --git a/third_party/rust/bindgen/codegen/postprocessing/mod.rs b/third_party/rust/bindgen/codegen/postprocessing/mod.rs
new file mode 100644
index 0000000000..1d5a4983bd
--- /dev/null
+++ b/third_party/rust/bindgen/codegen/postprocessing/mod.rs
@@ -0,0 +1,66 @@
+use proc_macro2::TokenStream;
+use quote::ToTokens;
+use syn::{parse2, ItemMod};
+
+use crate::BindgenOptions;
+
+mod merge_extern_blocks;
+mod sort_semantically;
+
+use merge_extern_blocks::merge_extern_blocks;
+use sort_semantically::sort_semantically;
+
+struct PostProcessingPass {
+    should_run: fn(&BindgenOptions) -> bool,
+    run: fn(&mut ItemMod),
+}
+
+// TODO: This can be a const fn when mutable references are allowed in const
+// context.
+macro_rules! pass {
+    ($pass:ident) => {
+        PostProcessingPass {
+            should_run: |options| options.$pass,
+            run: |item_mod| $pass(item_mod),
+        }
+    };
+}
+
+const PASSES: &[PostProcessingPass] =
+    &[pass!(merge_extern_blocks), pass!(sort_semantically)];
+
+pub(crate) fn postprocessing(
+    items: Vec<TokenStream>,
+    options: &BindgenOptions,
+) -> TokenStream {
+    let require_syn = PASSES.iter().any(|pass| (pass.should_run)(options));
+    if !require_syn {
+        return items.into_iter().collect();
+    }
+    let module_wrapped_tokens =
+        quote!(mod wrapper_for_postprocessing_hack { #( #items )* });
+
+    // This syn business is a hack, for now. This means that we are re-parsing already
+    // generated code using `syn` (as opposed to `quote`) because `syn` provides us more
+    // control over the elements.
+    // One caveat is that some of the items coming from `quote`d output might have
+    // multiple items within them. Hence, we have to wrap the incoming in a `mod`.
+    // The `unwrap` here is deliberate because bindgen should generate valid rust items at all
+    // times.
+    let mut item_mod = parse2::<ItemMod>(module_wrapped_tokens).unwrap();
+
+    for pass in PASSES {
+        if (pass.should_run)(options) {
+            (pass.run)(&mut item_mod);
+        }
+    }
+
+    let synful_items = item_mod
+        .content
+        .map(|(_, items)| items)
+        .unwrap_or_default()
+        .into_iter()
+        .map(|item| item.into_token_stream());
+
+    quote! { #( #synful_items )* }
+}
diff --git a/third_party/rust/bindgen/codegen/postprocessing/sort_semantically.rs b/third_party/rust/bindgen/codegen/postprocessing/sort_semantically.rs
new file mode 100644
index 0000000000..4f23ab73a3
--- /dev/null
+++ b/third_party/rust/bindgen/codegen/postprocessing/sort_semantically.rs
@@ -0,0 +1,38 @@
+use syn::{
+    visit_mut::{visit_item_mod_mut, VisitMut},
+    Item, ItemMod,
+};
+
+pub(super) fn sort_semantically(item_mod: &mut ItemMod) {
+    Visitor.visit_item_mod_mut(item_mod)
+}
+
+struct Visitor;
+
+impl VisitMut for Visitor {
+    fn visit_item_mod_mut(&mut self, item_mod: &mut ItemMod) {
+        if let Some((_, ref mut items)) = item_mod.content {
+            items.sort_by_key(|item| match item {
+                Item::Type(_) => 0,
+                Item::Struct(_) => 1,
+                Item::Const(_) => 2,
+                Item::Fn(_) => 3,
+                Item::Enum(_) => 4,
+                Item::Union(_) => 5,
+                Item::Static(_) => 6,
+                Item::Trait(_) => 7,
+                Item::TraitAlias(_) => 8,
+                Item::Impl(_) => 9,
+                Item::Mod(_) => 10,
+                Item::Use(_) => 11,
+                Item::Verbatim(_) => 12,
+                Item::ExternCrate(_) => 13,
+                Item::ForeignMod(_) => 14,
+                Item::Macro(_) => 15,
+                Item::Macro2(_) => 16,
+                _ => 18,
+            });
+        }
+        visit_item_mod_mut(self, item_mod)
+    }
+}
diff --git a/third_party/rust/bindgen/codegen/struct_layout.rs b/third_party/rust/bindgen/codegen/struct_layout.rs
new file mode 100644
index 0000000000..ddac1b0abb
--- /dev/null
+++ b/third_party/rust/bindgen/codegen/struct_layout.rs
@@ -0,0 +1,444 @@
+//! Helpers for code generation that need struct layout
+
+use super::helpers;
+
+use crate::ir::comp::CompInfo;
+use crate::ir::context::BindgenContext;
+use crate::ir::layout::Layout;
+use crate::ir::ty::{Type, TypeKind};
+use proc_macro2::{self, Ident, Span};
+use std::cmp;
+
+const MAX_GUARANTEED_ALIGN: usize = 8;
+
+/// Trace the layout of struct.
+#[derive(Debug)]
+pub struct StructLayoutTracker<'a> {
+    name: &'a str,
+    ctx: &'a BindgenContext,
+    comp: &'a CompInfo,
+    is_packed: bool,
+    known_type_layout: Option<Layout>,
+    is_rust_union: bool,
+    can_copy_union_fields: bool,
+    latest_offset: usize,
+    padding_count: usize,
+    latest_field_layout: Option<Layout>,
+    max_field_align: usize,
+    last_field_was_bitfield: bool,
+}
+
+/// Returns a size aligned to a given value.
+pub fn align_to(size: usize, align: usize) -> usize {
+    if align == 0 {
+        return size;
+    }
+
+    let rem = size % align;
+    if rem == 0 {
+        return size;
+    }
+
+    size + align - rem
+}
+
+/// Returns the lower power of two byte count that can hold at most n bits.
+pub fn bytes_from_bits_pow2(mut n: usize) -> usize {
+    if n == 0 {
+        return 0;
+    }
+
+    if n <= 8 {
+        return 1;
+    }
+
+    if !n.is_power_of_two() {
+        n = n.next_power_of_two();
+    }
+
+    n / 8
+}
+
+#[test]
+fn test_align_to() {
+    assert_eq!(align_to(1, 1), 1);
+    assert_eq!(align_to(1, 2), 2);
+    assert_eq!(align_to(1, 4), 4);
+    assert_eq!(align_to(5, 1), 5);
+    assert_eq!(align_to(17, 4), 20);
+}
+
+#[test]
+fn test_bytes_from_bits_pow2() {
+    assert_eq!(bytes_from_bits_pow2(0), 0);
+    for i in 1..9 {
+        assert_eq!(bytes_from_bits_pow2(i), 1);
+    }
+    for i in 9..17 {
+        assert_eq!(bytes_from_bits_pow2(i), 2);
+    }
+    for i in 17..33 {
+        assert_eq!(bytes_from_bits_pow2(i), 4);
+    }
+}
+
+impl<'a> StructLayoutTracker<'a> {
+    pub fn new(
+        ctx: &'a BindgenContext,
+        comp: &'a CompInfo,
+        ty: &'a Type,
+        name: &'a str,
+    ) -> Self {
+        let known_type_layout = ty.layout(ctx);
+        let is_packed = comp.is_packed(ctx, known_type_layout.as_ref());
+        let (is_rust_union, can_copy_union_fields) =
+            comp.is_rust_union(ctx, known_type_layout.as_ref(), name);
+        StructLayoutTracker {
+            name,
+            ctx,
+            comp,
+            is_packed,
+            known_type_layout,
+            is_rust_union,
+            can_copy_union_fields,
+            latest_offset: 0,
+            padding_count: 0,
+            latest_field_layout: None,
+            max_field_align: 0,
+            last_field_was_bitfield: false,
+        }
+    }
+
+    pub fn can_copy_union_fields(&self) -> bool {
+        self.can_copy_union_fields
+    }
+
+    pub fn is_rust_union(&self) -> bool {
+        self.is_rust_union
+    }
+
+    pub fn saw_vtable(&mut self) {
+        debug!("saw vtable for {}", self.name);
+
+        let ptr_size = self.ctx.target_pointer_size();
+        self.latest_offset += ptr_size;
+        self.latest_field_layout = Some(Layout::new(ptr_size, ptr_size));
+        self.max_field_align = ptr_size;
+    }
+
+    pub fn saw_base(&mut self, base_ty: &Type) {
+        debug!("saw base for {}", self.name);
+        if let Some(layout) = base_ty.layout(self.ctx) {
+            self.align_to_latest_field(layout);
+
+            self.latest_offset += self.padding_bytes(layout) + layout.size;
+            self.latest_field_layout = Some(layout);
+            self.max_field_align = cmp::max(self.max_field_align, layout.align);
+        }
+    }
+
+    pub fn saw_bitfield_unit(&mut self, layout: Layout) {
+        debug!("saw bitfield unit for {}: {:?}", self.name, layout);
+
+        self.align_to_latest_field(layout);
+
+        self.latest_offset += layout.size;
+
+        debug!(
+            "Offset: <bitfield>: {} -> {}",
+            self.latest_offset - layout.size,
+            self.latest_offset
+        );
+
+        self.latest_field_layout = Some(layout);
+        self.last_field_was_bitfield = true;
+        // NB: We intentionally don't update the max_field_align here, since our
+        // bitfields code doesn't necessarily guarantee it, so we need to
+        // actually generate the dummy alignment.
+    }
+
+    /// Returns a padding field if necessary for a given new field _before_
+    /// adding that field.
+    pub fn saw_field(
+        &mut self,
+        field_name: &str,
+        field_ty: &Type,
+        field_offset: Option<usize>,
+    ) -> Option<proc_macro2::TokenStream> {
+        let mut field_layout = field_ty.layout(self.ctx)?;
+
+        if let TypeKind::Array(inner, len) =
+            *field_ty.canonical_type(self.ctx).kind()
+        {
+            // FIXME(emilio): As an _ultra_ hack, we correct the layout returned
+            // by arrays of structs that have a bigger alignment than what we
+            // can support.
+            //
+            // This means that the structs in the array are super-unsafe to
+            // access, since they won't be properly aligned, but there's not too
+            // much we can do about it.
+            if let Some(layout) = self.ctx.resolve_type(inner).layout(self.ctx)
+            {
+                if layout.align > MAX_GUARANTEED_ALIGN {
+                    field_layout.size =
+                        align_to(layout.size, layout.align) * len;
+                    field_layout.align = MAX_GUARANTEED_ALIGN;
+                }
+            }
+        }
+        self.saw_field_with_layout(field_name, field_layout, field_offset)
+    }
+
+    pub fn saw_field_with_layout(
+        &mut self,
+        field_name: &str,
+        field_layout: Layout,
+        field_offset: Option<usize>,
+    ) -> Option<proc_macro2::TokenStream> {
+        let will_merge_with_bitfield = self.align_to_latest_field(field_layout);
+
+        let is_union = self.comp.is_union();
+        let padding_bytes = match field_offset {
+            Some(offset) if offset / 8 > self.latest_offset => {
+                offset / 8 - self.latest_offset
+            }
+            _ => {
+                if will_merge_with_bitfield ||
+                    field_layout.align == 0 ||
+                    is_union
+                {
+                    0
+                } else if !self.is_packed {
+                    self.padding_bytes(field_layout)
+                } else if let Some(l) = self.known_type_layout {
+                    self.padding_bytes(l)
+                } else {
+                    0
+                }
+            }
+        };
+
+        self.latest_offset += padding_bytes;
+
+        let padding_layout = if self.is_packed || is_union {
+            None
+        } else {
+            let force_padding = self.ctx.options().force_explicit_padding;
+
+            // Otherwise the padding is useless.
+            let need_padding = force_padding ||
+                padding_bytes >= field_layout.align ||
+                field_layout.align > MAX_GUARANTEED_ALIGN;
+
+            debug!(
+                "Offset: <padding>: {} -> {}",
+                self.latest_offset - padding_bytes,
+                self.latest_offset
+            );
+
+            debug!(
+                "align field {} to {}/{} with {} padding bytes {:?}",
+                field_name,
+                self.latest_offset,
+                field_offset.unwrap_or(0) / 8,
+                padding_bytes,
+                field_layout
+            );
+
+            let padding_align = if force_padding {
+                1
+            } else {
+                cmp::min(field_layout.align, MAX_GUARANTEED_ALIGN)
+            };
+
+            if need_padding && padding_bytes != 0 {
+                Some(Layout::new(padding_bytes, padding_align))
+            } else {
+                None
+            }
+        };
+
+        self.latest_offset += field_layout.size;
+        self.latest_field_layout = Some(field_layout);
+        self.max_field_align =
+            cmp::max(self.max_field_align, field_layout.align);
+        self.last_field_was_bitfield = false;
+
+        debug!(
+            "Offset: {}: {} -> {}",
+            field_name,
+            self.latest_offset - field_layout.size,
+            self.latest_offset
+        );
+
+        padding_layout.map(|layout| self.padding_field(layout))
+    }
+
+    pub fn add_tail_padding(
+        &mut self,
+        comp_name: &str,
+        comp_layout: Layout,
+    ) -> Option<proc_macro2::TokenStream> {
+        // Only emit an padding field at the end of a struct if the
+        // user configures explicit padding.
+        if !self.ctx.options().force_explicit_padding {
+            return None;
+        }
+
+        // Padding doesn't make sense for rust unions.
+        if self.is_rust_union {
+            return None;
+        }
+
+        if self.latest_offset == comp_layout.size {
+            // This struct does not contain tail padding.
+            return None;
+        }
+
+        trace!(
+            "need a tail padding field for {}: offset {} -> size {}",
+            comp_name,
+            self.latest_offset,
+            comp_layout.size
+        );
+        let size = comp_layout.size - self.latest_offset;
+        Some(self.padding_field(Layout::new(size, 0)))
+    }
+
+    pub fn pad_struct(
+        &mut self,
+        layout: Layout,
+    ) -> Option<proc_macro2::TokenStream> {
+        debug!(
+            "pad_struct:\n\tself = {:#?}\n\tlayout = {:#?}",
+            self, layout
+        );
+
+        if layout.size < self.latest_offset {
+            warn!(
+                "Calculated wrong layout for {}, too more {} bytes",
+                self.name,
+                self.latest_offset - layout.size
+            );
+            return None;
+        }
+
+        let padding_bytes = layout.size - self.latest_offset;
+        if padding_bytes == 0 {
+            return None;
+        }
+
+        let repr_align = self.ctx.options().rust_features().repr_align;
+
+        // We always pad to get to the correct size if the struct is one of
+        // those we can't align properly.
+        //
+        // Note that if the last field we saw was a bitfield, we may need to pad
+        // regardless, because bitfields don't respect alignment as strictly as
+        // other fields.
+        if padding_bytes >= layout.align ||
+            (self.last_field_was_bitfield &&
+                padding_bytes >= self.latest_field_layout.unwrap().align) ||
+            (!repr_align && layout.align > MAX_GUARANTEED_ALIGN)
+        {
+            let layout = if self.is_packed {
+                Layout::new(padding_bytes, 1)
+            } else if self.last_field_was_bitfield ||
+                layout.align > MAX_GUARANTEED_ALIGN
+            {
+                // We've already given up on alignment here.
+                Layout::for_size(self.ctx, padding_bytes)
+            } else {
+                Layout::new(padding_bytes, layout.align)
+            };
+
+            debug!("pad bytes to struct {}, {:?}", self.name, layout);
+
+            Some(self.padding_field(layout))
+        } else {
+            None
+        }
+    }
+
+    pub fn requires_explicit_align(&self, layout: Layout) -> bool {
+        let repr_align = self.ctx.options().rust_features().repr_align;
+
+        // Always force explicit repr(align) for stuff more than 16-byte aligned
+        // to work-around https://github.com/rust-lang/rust/issues/54341.
+        //
+        // Worst-case this just generates redundant alignment attributes.
+        if repr_align && self.max_field_align >= 16 {
+            return true;
+        }
+
+        if self.max_field_align >= layout.align {
+            return false;
+        }
+
+        // We can only generate up-to a 8-bytes of alignment unless we support
+        // repr(align).
+        repr_align || layout.align <= MAX_GUARANTEED_ALIGN
+    }
+
+    fn padding_bytes(&self, layout: Layout) -> usize {
+        align_to(self.latest_offset, layout.align) - self.latest_offset
+    }
+
+    fn padding_field(&mut self, layout: Layout) -> proc_macro2::TokenStream {
+        let ty = helpers::blob(self.ctx, layout);
+        let padding_count = self.padding_count;
+
+        self.padding_count += 1;
+
+        let padding_field_name = Ident::new(
+            &format!("__bindgen_padding_{}", padding_count),
+            Span::call_site(),
+        );
+
+        self.max_field_align = cmp::max(self.max_field_align, layout.align);
+
+        quote! {
+            pub #padding_field_name : #ty ,
+        }
+    }
+
+    /// Returns whether the new field is known to merge with a bitfield.
+    ///
+    /// This is just to avoid doing the same check also in pad_field.
+    fn align_to_latest_field(&mut self, new_field_layout: Layout) -> bool {
+        if self.is_packed {
+            // Skip to align fields when packed.
+            return false;
+        }
+
+        let layout = match self.latest_field_layout {
+            Some(l) => l,
+            None => return false,
+        };
+
+        // If it was, we may or may not need to align, depending on what the
+        // current field alignment and the bitfield size and alignment are.
+        debug!(
+            "align_to_bitfield? {}: {:?} {:?}",
+            self.last_field_was_bitfield, layout, new_field_layout
+        );
+
+        // Avoid divide-by-zero errors if align is 0.
+        let align = cmp::max(1, layout.align);
+
+        if self.last_field_was_bitfield &&
+            new_field_layout.align <= layout.size % align &&
+            new_field_layout.size <= layout.size % align
+        {
+            // The new field will be coalesced into some of the remaining bits.
+            //
+            // FIXME(emilio): I think this may not catch everything?
+            debug!("Will merge with bitfield");
+            return true;
+        }
+
+        // Else, just align the obvious way.
+        self.latest_offset += self.padding_bytes(layout);
+        false
+    }
+}