1 files changed, 263 insertions, 0 deletions
diff --git a/gfx/wr/peek-poke/peek-poke-derive/src/lib.rs b/gfx/wr/peek-poke/peek-poke-derive/src/lib.rs
new file mode 100644
index 0000000000..ac20b2b922
--- /dev/null
+++ b/gfx/wr/peek-poke/peek-poke-derive/src/lib.rs
@@ -0,0 +1,263 @@
+// Copyright 2019 The Servo Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use proc_macro2::{Span, TokenStream};
+use quote::quote;
+use syn::{Ident, Index, TraitBound};
+use synstructure::{decl_derive, Structure, BindStyle, AddBounds};
+use unicode_xid::UnicodeXID;
+
+// Internal method for sanitizing an identifier for hygiene purposes.
+fn sanitize_ident(s: &str) -> Ident {
+    let mut res = String::with_capacity(s.len());
+    for mut c in s.chars() {
+        if !UnicodeXID::is_xid_continue(c) {
+            c = '_'
+        }
+        // Deduplicate consecutive _ characters.
+        if res.ends_with('_') && c == '_' {
+            continue;
+        }
+        res.push(c);
+    }
+    Ident::new(&res, Span::call_site())
+}
+
+/// Calculates size type for number of variants (used for enums)
+fn get_discriminant_size_type(len: usize) -> TokenStream {
+    if len <= <u8>::max_value() as usize {
+        quote! { u8 }
+    } else if len <= <u16>::max_value() as usize {
+        quote! { u16 }
+    } else {
+        quote! { u32 }
+    }
+}
+
+fn is_struct(s: &Structure) -> bool {
+    // a single variant with no prefix is 'struct'
+    matches!(&s.variants()[..], [v] if v.prefix.is_none())
+}
+
+fn derive_max_size(s: &Structure) -> TokenStream {
+    let max_size = s.variants().iter().fold(quote!(0), |acc, vi| {
+        let variant_size = vi.bindings().iter().fold(quote!(0), |acc, bi| {
+            // compute size of each variant by summing the sizes of its bindings
+            let ty = &bi.ast().ty;
+            quote!(#acc + <#ty>::max_size())
+        });
+
+        // find the maximum of each variant
+        quote! {
+            max(#acc, #variant_size)
+        }
+    });
+
+    let body = if is_struct(s) {
+        max_size
+    } else {
+        let discriminant_size_type = get_discriminant_size_type(s.variants().len());
+        quote! {
+            #discriminant_size_type ::max_size() + #max_size
+        }
+    };
+
+    quote! {
+        #[inline(always)]
+        fn max_size() -> usize {
+            use std::cmp::max;
+            #body
+        }
+    }
+}
+
+fn derive_peek_from_for_enum(s: &mut Structure) -> TokenStream {
+    assert!(!is_struct(s));
+    s.bind_with(|_| BindStyle::Move);
+
+    let num_variants = s.variants().len();
+    let discriminant_size_type = get_discriminant_size_type(num_variants);
+    let body = s
+        .variants()
+        .iter()
+        .enumerate()
+        .fold(quote!(), |acc, (i, vi)| {
+            let bindings = vi
+                .bindings()
+                .iter()
+                .map(|bi| quote!(#bi))
+                .collect::<Vec<_>>();
+
+            let variant_pat = Index::from(i);
+            let poke_exprs = bindings.iter().fold(quote!(), |acc, bi| {
+                quote! {
+                    #acc
+                    let (#bi, bytes) = peek_poke::peek_from_default(bytes);
+                }
+            });
+            let construct = vi.construct(|_, i| {
+                let bi = &bindings[i];
+                quote!(#bi)
+            });
+
+            quote! {
+                #acc
+                #variant_pat => {
+                    #poke_exprs
+                    *output = #construct;
+                    bytes
+                }
+            }
+        });
+
+    let type_name = s.ast().ident.to_string();
+    let max_tag_value = num_variants - 1;
+
+    quote! {
+        #[inline(always)]
+        unsafe fn peek_from(bytes: *const u8, output: *mut Self) -> *const u8 {
+            let (variant, bytes) = peek_poke::peek_from_default::<#discriminant_size_type>(bytes);
+            match variant {
+                #body
+                out_of_range_tag => {
+                    panic!("WRDL: memory corruption detected while parsing {} - enum tag should be <= {}, but was {}",
+                        #type_name, #max_tag_value, out_of_range_tag);
+                }
+            }
+        }
+    }
+}
+
+fn derive_peek_from_for_struct(s: &mut Structure) -> TokenStream {
+    assert!(is_struct(&s));
+
+    s.variants_mut()[0].bind_with(|_| BindStyle::RefMut);
+    let pat = s.variants()[0].pat();
+    let peek_exprs = s.variants()[0].bindings().iter().fold(quote!(), |acc, bi| {
+        let ty = &bi.ast().ty;
+        quote! {
+            #acc
+            let bytes = <#ty>::peek_from(bytes, #bi);
+        }
+    });
+
+    let body = quote! {
+        #pat => {
+            #peek_exprs
+            bytes
+        }
+    };
+
+    quote! {
+        #[inline(always)]
+        unsafe fn peek_from(bytes: *const u8, output: *mut Self) -> *const u8 {
+            match &mut (*output) {
+                #body
+            }
+        }
+    }
+}
+
+fn derive_poke_into(s: &Structure) -> TokenStream {
+    let is_struct = is_struct(&s);
+    let discriminant_size_type = get_discriminant_size_type(s.variants().len());
+    let body = s
+        .variants()
+        .iter()
+        .enumerate()
+        .fold(quote!(), |acc, (i, vi)| {
+            let init = if !is_struct {
+                let index = Index::from(i);
+                quote! {
+                    let bytes = #discriminant_size_type::poke_into(&#index, bytes);
+                }
+            } else {
+                quote!()
+            };
+            let variant_pat = vi.pat();
+            let poke_exprs = vi.bindings().iter().fold(init, |acc, bi| {
+                quote! {
+                    #acc
+                    let bytes = #bi.poke_into(bytes);
+                }
+            });
+
+            quote! {
+                #acc
+                #variant_pat => {
+                    #poke_exprs
+                    bytes
+                }
+            }
+        });
+
+    quote! {
+        #[inline(always)]
+        unsafe fn poke_into(&self, bytes: *mut u8) -> *mut u8 {
+            match &*self {
+                #body
+            }
+        }
+    }
+}
+
+fn peek_poke_derive(mut s: Structure) -> TokenStream {
+    s.binding_name(|_, i| Ident::new(&format!("__self_{}", i), Span::call_site()));
+
+    let max_size_fn = derive_max_size(&s);
+    let poke_into_fn = derive_poke_into(&s);
+    let peek_from_fn = if is_struct(&s) {
+        derive_peek_from_for_struct(&mut s)
+    } else {
+        derive_peek_from_for_enum(&mut s)
+    };
+
+    let poke_impl = s.gen_impl(quote! {
+        extern crate peek_poke;
+
+        gen unsafe impl peek_poke::Poke for @Self {
+            #max_size_fn
+            #poke_into_fn
+        }
+    });
+
+    // To implement `fn peek_from` we require that types implement `Default`
+    // trait to create temporary values. This code does the addition all
+    // manually until https://github.com/mystor/synstructure/issues/24 is fixed.
+    let default_trait = syn::parse_str::<TraitBound>("::std::default::Default").unwrap();
+    let peek_trait = syn::parse_str::<TraitBound>("peek_poke::Peek").unwrap();
+
+    let ast = s.ast();
+    let name = &ast.ident;
+    let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl();
+    let mut where_clause = where_clause.cloned();
+    s.add_trait_bounds(&default_trait, &mut where_clause, AddBounds::Generics);
+    s.add_trait_bounds(&peek_trait, &mut where_clause, AddBounds::Generics);
+
+    let dummy_const: Ident = sanitize_ident(&format!("_DERIVE_peek_poke_Peek_FOR_{}", name));
+
+    let peek_impl = quote! {
+        #[allow(non_upper_case_globals)]
+        const #dummy_const: () = {
+            extern crate peek_poke;
+
+            impl #impl_generics peek_poke::Peek for #name #ty_generics #where_clause {
+                #peek_from_fn
+            }
+        };
+    };
+
+    quote! {
+        #poke_impl
+        #peek_impl
+    }
+}
+
+decl_derive!([PeekPoke] => peek_poke_derive);