Auto merge of #119478 - bjorn3:no_serialize_specialization, r=wesleywiser

Avoid specialization in the metadata serialization code

With the exception of a perf-only specialization for byte slices and byte vectors.

This uses the same trick of introducing a new trait and having the Encodable and Decodable derives add a bound to it as used for TyEncoder/TyDecoder. The new code is clearer about which encoder/decoder uses which impl and it reduces the dependency of rustc on specialization, making it easier to remove support for specialization entirely or turn it into a construct that is only allowed for perf optimizations if we decide to do this.

Author: bors

Cargo.lock

@@ -4644,6 +4644,7 @@ dependencies = [
  "rustc_index",
  "rustc_macros",
  "rustc_serialize",
+ "rustc_span",
  "smallvec",
 ]
 

compiler/rustc_abi/src/lib.rs

@@ -16,7 +16,7 @@ use rustc_data_structures::stable_hasher::StableOrd;
 #[cfg(feature = "nightly")]
 use rustc_macros::HashStable_Generic;
 #[cfg(feature = "nightly")]
-use rustc_macros::{Decodable, Encodable};
+use rustc_macros::{Decodable_Generic, Encodable_Generic};
 #[cfg(feature = "nightly")]
 use std::iter::Step;
 
@@ -30,7 +30,7 @@ pub use layout::LayoutCalculator;
 pub trait HashStableContext {}
 
 #[derive(Clone, Copy, PartialEq, Eq, Default)]
-#[cfg_attr(feature = "nightly", derive(Encodable, Decodable, HashStable_Generic))]
+#[cfg_attr(feature = "nightly", derive(Encodable_Generic, Decodable_Generic, HashStable_Generic))]
 pub struct ReprFlags(u8);
 
 bitflags! {
@@ -52,7 +52,7 @@ bitflags! {
 rustc_data_structures::external_bitflags_debug! { ReprFlags }
 
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
-#[cfg_attr(feature = "nightly", derive(Encodable, Decodable, HashStable_Generic))]
+#[cfg_attr(feature = "nightly", derive(Encodable_Generic, Decodable_Generic, HashStable_Generic))]
 pub enum IntegerType {
     /// Pointer-sized integer type, i.e. `isize` and `usize`. The field shows signedness, e.g.
     /// `Pointer(true)` means `isize`.
@@ -73,7 +73,7 @@ impl IntegerType {
 
 /// Represents the repr options provided by the user.
 #[derive(Copy, Clone, Debug, Eq, PartialEq, Default)]
-#[cfg_attr(feature = "nightly", derive(Encodable, Decodable, HashStable_Generic))]
+#[cfg_attr(feature = "nightly", derive(Encodable_Generic, Decodable_Generic, HashStable_Generic))]
 pub struct ReprOptions {
     pub int: Option<IntegerType>,
     pub align: Option<Align>,
@@ -412,7 +412,7 @@ impl FromStr for Endian {
 
 /// Size of a type in bytes.
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
-#[cfg_attr(feature = "nightly", derive(Encodable, Decodable, HashStable_Generic))]
+#[cfg_attr(feature = "nightly", derive(Encodable_Generic, Decodable_Generic, HashStable_Generic))]
 pub struct Size {
     raw: u64,
 }
@@ -636,7 +636,7 @@ impl Step for Size {
 
 /// Alignment of a type in bytes (always a power of two).
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
-#[cfg_attr(feature = "nightly", derive(Encodable, Decodable, HashStable_Generic))]
+#[cfg_attr(feature = "nightly", derive(Encodable_Generic, Decodable_Generic, HashStable_Generic))]
 pub struct Align {
     pow2: u8,
 }
@@ -777,7 +777,7 @@ impl AbiAndPrefAlign {
 
 /// Integers, also used for enum discriminants.
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
-#[cfg_attr(feature = "nightly", derive(Encodable, Decodable, HashStable_Generic))]
+#[cfg_attr(feature = "nightly", derive(Encodable_Generic, Decodable_Generic, HashStable_Generic))]
 pub enum Integer {
     I8,
     I16,

compiler/rustc_ast/src/ast.rs

@@ -20,6 +20,7 @@
 
 pub use crate::format::*;
 pub use crate::util::parser::ExprPrecedence;
+pub use rustc_span::AttrId;
 pub use GenericArgs::*;
 pub use UnsafeSource::*;
 
@@ -30,7 +31,6 @@ use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_data_structures::sync::Lrc;
 use rustc_macros::HashStable_Generic;
-use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
 use rustc_span::source_map::{respan, Spanned};
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{ErrorGuaranteed, Span, DUMMY_SP};
@@ -2682,22 +2682,6 @@ pub enum AttrStyle {
     Inner,
 }
 
-rustc_index::newtype_index! {
-    #[orderable]
-    #[debug_format = "AttrId({})"]
-    pub struct AttrId {}
-}
-
-impl<S: Encoder> Encodable<S> for AttrId {
-    fn encode(&self, _s: &mut S) {}
-}
-
-impl<D: Decoder> Decodable<D> for AttrId {
-    default fn decode(_: &mut D) -> AttrId {
-        panic!("cannot decode `AttrId` with `{}`", std::any::type_name::<D>());
-    }
-}
-
 /// A list of attributes.
 pub type AttrVec = ThinVec<Attribute>;
 

compiler/rustc_ast/src/tokenstream.rs

@@ -21,8 +21,8 @@ use crate::AttrVec;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::sync::{self, Lrc};
 use rustc_macros::HashStable_Generic;
-use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
-use rustc_span::{sym, Span, Symbol, DUMMY_SP};
+use rustc_serialize::{Decodable, Encodable};
+use rustc_span::{sym, Span, SpanDecoder, SpanEncoder, Symbol, DUMMY_SP};
 use smallvec::{smallvec, SmallVec};
 
 use std::borrow::Cow;
@@ -150,14 +150,14 @@ impl fmt::Debug for LazyAttrTokenStream {
     }
 }
 
-impl<S: Encoder> Encodable<S> for LazyAttrTokenStream {
+impl<S: SpanEncoder> Encodable<S> for LazyAttrTokenStream {
     fn encode(&self, s: &mut S) {
         // Used by AST json printing.
         Encodable::encode(&self.to_attr_token_stream(), s);
     }
 }
 
-impl<D: Decoder> Decodable<D> for LazyAttrTokenStream {
+impl<D: SpanDecoder> Decodable<D> for LazyAttrTokenStream {
     fn decode(_d: &mut D) -> Self {
         panic!("Attempted to decode LazyAttrTokenStream");
     }

compiler/rustc_data_structures/src/sorted_map.rs

@@ -16,7 +16,7 @@ pub use index_map::SortedIndexMultiMap;
 /// stores data in a more compact way. It also supports accessing contiguous
 /// ranges of elements as a slice, and slices of already sorted elements can be
 /// inserted efficiently.
-#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Encodable, Decodable)]
+#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Encodable_Generic, Decodable_Generic)]
 pub struct SortedMap<K, V> {
     data: Vec<(K, V)>,
 }

compiler/rustc_data_structures/src/svh.rs

@@ -10,7 +10,7 @@ use std::fmt;
 
 use crate::stable_hasher;
 
-#[derive(Copy, Clone, PartialEq, Eq, Debug, Encodable, Decodable, Hash)]
+#[derive(Copy, Clone, PartialEq, Eq, Debug, Encodable_Generic, Decodable_Generic, Hash)]
 pub struct Svh {
     hash: Fingerprint,
 }

compiler/rustc_data_structures/src/unord.rs

@@ -226,7 +226,7 @@ trait UnordCollection {}
 ///
 /// See [MCP 533](https://github.com/rust-lang/compiler-team/issues/533)
 /// for more information.
-#[derive(Debug, Eq, PartialEq, Clone, Encodable, Decodable)]
+#[derive(Debug, Eq, PartialEq, Clone, Encodable_Generic, Decodable_Generic)]
 pub struct UnordSet<V: Eq + Hash> {
     inner: FxHashSet<V>,
 }
@@ -417,7 +417,7 @@ impl<HCX, V: Hash + Eq + HashStable<HCX>> HashStable<HCX> for UnordSet<V> {
 ///
 /// See [MCP 533](https://github.com/rust-lang/compiler-team/issues/533)
 /// for more information.
-#[derive(Debug, Eq, PartialEq, Clone, Encodable, Decodable)]
+#[derive(Debug, Eq, PartialEq, Clone, Encodable_Generic, Decodable_Generic)]
 pub struct UnordMap<K: Eq + Hash, V> {
     inner: FxHashMap<K, V>,
 }
@@ -626,7 +626,7 @@ impl<HCX, K: Hash + Eq + HashStable<HCX>, V: HashStable<HCX>> HashStable<HCX> fo
 ///
 /// See [MCP 533](https://github.com/rust-lang/compiler-team/issues/533)
 /// for more information.
-#[derive(Default, Debug, Eq, PartialEq, Clone, Encodable, Decodable)]
+#[derive(Default, Debug, Eq, PartialEq, Clone, Encodable_Generic, Decodable_Generic)]
 pub struct UnordBag<V> {
     inner: Vec<V>,
 }

compiler/rustc_index/src/bit_set.rs

@@ -10,7 +10,7 @@ use arrayvec::ArrayVec;
 use smallvec::{smallvec, SmallVec};
 
 #[cfg(feature = "nightly")]
-use rustc_macros::{Decodable, Encodable};
+use rustc_macros::{Decodable_Generic, Encodable_Generic};
 
 use crate::{Idx, IndexVec};
 
@@ -112,7 +112,7 @@ macro_rules! bit_relations_inherent_impls {
 /// to or greater than the domain size. All operations that involve two bitsets
 /// will panic if the bitsets have differing domain sizes.
 ///
-#[cfg_attr(feature = "nightly", derive(Decodable, Encodable))]
+#[cfg_attr(feature = "nightly", derive(Decodable_Generic, Encodable_Generic))]
 #[derive(Eq, PartialEq, Hash)]
 pub struct BitSet<T> {
     domain_size: usize,
@@ -1590,7 +1590,7 @@ impl<T: Idx> From<BitSet<T>> for GrowableBitSet<T> {
 ///
 /// All operations that involve a row and/or column index will panic if the
 /// index exceeds the relevant bound.
-#[cfg_attr(feature = "nightly", derive(Decodable, Encodable))]
+#[cfg_attr(feature = "nightly", derive(Decodable_Generic, Encodable_Generic))]
 #[derive(Clone, Eq, PartialEq, Hash)]
 pub struct BitMatrix<R: Idx, C: Idx> {
     num_rows: usize,
@@ -2020,7 +2020,7 @@ impl std::fmt::Debug for FiniteBitSet<u32> {
 
 /// A fixed-sized bitset type represented by an integer type. Indices outwith than the range
 /// representable by `T` are considered set.
-#[cfg_attr(feature = "nightly", derive(Decodable, Encodable))]
+#[cfg_attr(feature = "nightly", derive(Decodable_Generic, Encodable_Generic))]
 #[derive(Copy, Clone, Eq, PartialEq)]
 pub struct FiniteBitSet<T: FiniteBitSetTy>(pub T);
 

compiler/rustc_macros/src/lib.rs

@@ -56,6 +56,8 @@ decl_derive!(
     hash_stable::hash_stable_no_context_derive
 );
 
+decl_derive!([Decodable_Generic] => serialize::decodable_generic_derive);
+decl_derive!([Encodable_Generic] => serialize::encodable_generic_derive);
 decl_derive!([Decodable] => serialize::decodable_derive);
 decl_derive!([Encodable] => serialize::encodable_derive);
 decl_derive!([TyDecodable] => serialize::type_decodable_derive);

compiler/rustc_macros/src/serialize.rs

@@ -31,6 +31,14 @@ pub fn meta_decodable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2:
 }
 
 pub fn decodable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
+    let decoder_ty = quote! { __D };
+    s.add_impl_generic(parse_quote! {#decoder_ty: ::rustc_span::SpanDecoder});
+    s.add_bounds(synstructure::AddBounds::Generics);
+
+    decodable_body(s, decoder_ty)
+}
+
+pub fn decodable_generic_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
     let decoder_ty = quote! { __D };
     s.add_impl_generic(parse_quote! {#decoder_ty: ::rustc_serialize::Decoder});
     s.add_bounds(synstructure::AddBounds::Generics);
@@ -129,6 +137,14 @@ pub fn meta_encodable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2:
 }
 
 pub fn encodable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
+    let encoder_ty = quote! { __E };
+    s.add_impl_generic(parse_quote! { #encoder_ty: ::rustc_span::SpanEncoder});
+    s.add_bounds(synstructure::AddBounds::Generics);
+
+    encodable_body(s, encoder_ty, false)
+}
+
+pub fn encodable_generic_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
     let encoder_ty = quote! { __E };
     s.add_impl_generic(parse_quote! { #encoder_ty: ::rustc_serialize::Encoder});
     s.add_bounds(synstructure::AddBounds::Generics);