1 files changed, 130 insertions, 0 deletions
diff --git a/vendor/zerovec-derive/src/varule.rs b/vendor/zerovec-derive/src/varule.rs
new file mode 100644
index 000000000..4a586f954
--- /dev/null
+++ b/vendor/zerovec-derive/src/varule.rs
@@ -0,0 +1,130 @@
+// This file is part of ICU4X. For terms of use, please see the file
+// called LICENSE at the top level of the ICU4X source tree
+// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
+
+use crate::utils::{self, FieldInfo};
+use proc_macro2::Span;
+use proc_macro2::TokenStream as TokenStream2;
+use quote::quote;
+use syn::spanned::Spanned;
+use syn::{Data, DeriveInput, Error, Ident};
+
+/// Implementation for derive(VarULE). `custom_varule_validator` validates the last field bytes `last_field_bytes`
+/// if specified, if not, the VarULE implementation will be used.
+pub fn derive_impl(
+    input: &DeriveInput,
+    custom_varule_validator: Option<TokenStream2>,
+) -> TokenStream2 {
+    if !utils::has_valid_repr(&input.attrs, |r| r == "packed" || r == "transparent") {
+        return Error::new(
+            input.span(),
+            "derive(VarULE) must be applied to a #[repr(packed)] or #[repr(transparent)] type",
+        )
+        .to_compile_error();
+    }
+    if input.generics.type_params().next().is_some()
+        || input.generics.lifetimes().next().is_some()
+        || input.generics.const_params().next().is_some()
+    {
+        return Error::new(
+            input.generics.span(),
+            "derive(VarULE) must be applied to a struct without any generics",
+        )
+        .to_compile_error();
+    }
+    let struc = if let Data::Struct(ref s) = input.data {
+        if s.fields.iter().next().is_none() {
+            return Error::new(
+                input.span(),
+                "derive(VarULE) must be applied to a non-empty struct",
+            )
+            .to_compile_error();
+        }
+        s
+    } else {
+        return Error::new(input.span(), "derive(VarULE) must be applied to a struct")
+            .to_compile_error();
+    };
+
+    let n_fields = struc.fields.len();
+
+    let ule_fields = FieldInfo::make_list(struc.fields.iter().take(n_fields - 1));
+
+    let sizes = ule_fields.iter().map(|f| {
+        let ty = &f.field.ty;
+        quote!(::core::mem::size_of::<#ty>())
+    });
+    let (validators, remaining_offset) = if n_fields > 1 {
+        // generate ULE validators
+        crate::ule::generate_ule_validators(&ule_fields)
+    } else {
+        // no ULE subfields
+        (
+            quote!(
+                const ZERO: usize = 0;
+            ),
+            Ident::new("ZERO", Span::call_site()),
+        )
+    };
+
+    let unsized_field = &struc
+        .fields
+        .iter()
+        .next_back()
+        .expect("Already verified that struct is not empty")
+        .ty;
+
+    let name = &input.ident;
+    let ule_size = Ident::new(
+        &format!("__IMPL_VarULE_FOR_{name}_ULE_SIZE"),
+        Span::call_site(),
+    );
+
+    let last_field_validator = if let Some(custom_varule_validator) = custom_varule_validator {
+        custom_varule_validator
+    } else {
+        quote!(<#unsized_field as zerovec::ule::VarULE>::validate_byte_slice(last_field_bytes)?;)
+    };
+
+    // Safety (based on the safety checklist on the ULE trait):
+    //  1. #name does not include any uninitialized or padding bytes
+    //     (achieved by enforcing #[repr(transparent)] or #[repr(packed)] on a struct of only ULE types)
+    //  2. #name is aligned to 1 byte.
+    //     (achieved by enforcing #[repr(transparent)] or #[repr(packed)] on a struct of only ULE types)
+    //  3. The impl of `validate_byte_slice()` returns an error if any byte is not valid.
+    //  4. The impl of `validate_byte_slice()` returns an error if the slice cannot be used in its entirety
+    //  5. The impl of `from_byte_slice_unchecked()` returns a reference to the same data.
+    //  6. The other VarULE methods use the default impl
+    //  7. [This impl does not enforce the non-safety equality constraint, it is up to the user to do so, ideally via a custom derive]
+    quote! {
+        // The size of the ULE section of this type
+        const #ule_size: usize = 0 #(+ #sizes)*;
+        unsafe impl zerovec::ule::VarULE for #name {
+            #[inline]
+            fn validate_byte_slice(bytes: &[u8]) -> Result<(), zerovec::ZeroVecError> {
+
+                if bytes.len() < #ule_size {
+                    return Err(zerovec::ZeroVecError::parse::<Self>());
+                }
+                #validators
+                debug_assert_eq!(#remaining_offset, #ule_size);
+                #[allow(clippy::indexing_slicing)] // TODO explain
+                let last_field_bytes = &bytes[#remaining_offset..];
+                #last_field_validator
+                Ok(())
+            }
+            #[inline]
+            unsafe fn from_byte_slice_unchecked(bytes: &[u8]) -> &Self {
+                // just the unsized part
+                #[allow(clippy::indexing_slicing)] // TODO explain
+                let unsized_bytes = &bytes[#ule_size..];
+                let unsized_ref = <#unsized_field as zerovec::ule::VarULE>::from_byte_slice_unchecked(unsized_bytes);
+                // We should use the pointer metadata APIs here when they are stable: https://github.com/rust-lang/rust/issues/81513
+                // For now we rely on all DST metadata being a usize to extract it via a fake slice pointer
+                let (_ptr, metadata): (usize, usize) = ::core::mem::transmute(unsized_ref);
+                let entire_struct_as_slice: *const [u8] = ::core::slice::from_raw_parts(bytes.as_ptr(), metadata);
+                &*(entire_struct_as_slice as *const Self)
+            }
+        }
+    }
+}