Avoid specialization for AttrId deserialization

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_metadata/src/rmeta/decoder.rs

@@ -416,15 +416,12 @@ impl<'a, 'tcx> Decodable<DecodeContext<'a, 'tcx>> for ExpnIndex {
     }
 }
 
-impl<'a, 'tcx> Decodable<DecodeContext<'a, 'tcx>> for ast::AttrId {
-    #[inline]
-    fn decode(d: &mut DecodeContext<'a, 'tcx>) -> ast::AttrId {
-        let sess = d.sess.expect("can't decode AttrId without Session");
+impl<'a, 'tcx> SpanDecoder for DecodeContext<'a, 'tcx> {
+    fn decode_attr_id(&mut self) -> rustc_span::AttrId {
+        let sess = self.sess.expect("can't decode AttrId without Session");
         sess.parse_sess.attr_id_generator.mk_attr_id()
     }
-}
 
-impl<'a, 'tcx> SpanDecoder for DecodeContext<'a, 'tcx> {
     fn decode_crate_num(&mut self) -> CrateNum {
         let cnum = CrateNum::from_u32(self.read_u32());
         self.map_encoded_cnum_to_current(cnum)

compiler/rustc_middle/src/query/on_disk_cache.rs

@@ -741,6 +741,10 @@ impl<'a, 'tcx> SpanDecoder for CacheDecoder<'a, 'tcx> {
             panic!("Failed to convert DefPathHash {def_path_hash:?}")
         })
     }
+
+    fn decode_attr_id(&mut self) -> rustc_span::AttrId {
+        panic!("cannot decode `AttrId` with `CacheDecoder`");
+    }
 }
 
 impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for &'tcx UnordSet<LocalDefId> {

compiler/rustc_span/src/lib.rs

@@ -1019,6 +1019,12 @@ impl Default for Span {
     }
 }
 
+rustc_index::newtype_index! {
+    #[orderable]
+    #[debug_format = "AttrId({})"]
+    pub struct AttrId {}
+}
+
 pub trait SpanEncoder: Encoder {
     fn encode_span(&mut self, span: Span);
     fn encode_symbol(&mut self, symbol: Symbol);
@@ -1106,6 +1112,11 @@ impl<E: SpanEncoder> Encodable<E> for DefId {
     }
 }
 
+impl<E: SpanEncoder> Encodable<E> for AttrId {
+    fn encode(&self, _s: &mut E) {
+        // A fresh id will be generated when decoding
+    }
+}
 pub trait SpanDecoder: Decoder {
     fn decode_span(&mut self) -> Span;
     fn decode_symbol(&mut self) -> Symbol;
@@ -1114,6 +1125,7 @@ pub trait SpanDecoder: Decoder {
     fn decode_crate_num(&mut self) -> CrateNum;
     fn decode_def_index(&mut self) -> DefIndex;
     fn decode_def_id(&mut self) -> DefId;
+    fn decode_attr_id(&mut self) -> AttrId;
 }
 
 impl SpanDecoder for MemDecoder<'_> {
@@ -1147,6 +1159,10 @@ impl SpanDecoder for MemDecoder<'_> {
     fn decode_def_id(&mut self) -> DefId {
         DefId { krate: Decodable::decode(self), index: Decodable::decode(self) }
     }
+
+    fn decode_attr_id(&mut self) -> AttrId {
+        panic!("cannot decode `AttrId` with `MemDecoder`");
+    }
 }
 
 impl<D: SpanDecoder> Decodable<D> for Span {
@@ -1191,6 +1207,12 @@ impl<D: SpanDecoder> Decodable<D> for DefId {
     }
 }
 
+impl<D: SpanDecoder> Decodable<D> for AttrId {
+    fn decode(s: &mut D) -> AttrId {
+        s.decode_attr_id()
+    }
+}
+
 /// Insert `source_map` into the session globals for the duration of the
 /// closure's execution.
 pub fn set_source_map<T, F: FnOnce() -> T>(source_map: Lrc<SourceMap>, f: F) -> T {