Auto merge of #94732 - nnethercote:infallible-encoder, r=bjorn3

Make `Encodable` and `Encoder` infallible.

A follow-up to #93066.

r? `@ghost`

Author: bors

compiler/rustc_ast/src/ast.rs

@@ -31,7 +31,7 @@ use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_data_structures::sync::Lrc;
 use rustc_data_structures::thin_vec::ThinVec;
 use rustc_macros::HashStable_Generic;
-use rustc_serialize::{self, Decoder, Encoder};
+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::{Span, DUMMY_SP};
@@ -2472,13 +2472,11 @@ rustc_index::newtype_index! {
     }
 }
 
-impl<S: Encoder> rustc_serialize::Encodable<S> for AttrId {
-    fn encode(&self, _s: &mut S) -> Result<(), S::Error> {
-        Ok(())
-    }
+impl<S: Encoder> Encodable<S> for AttrId {
+    fn encode(&self, _s: &mut S) {}
 }
 
-impl<D: Decoder> rustc_serialize::Decodable<D> for AttrId {
+impl<D: Decoder> Decodable<D> for AttrId {
     fn decode(_: &mut D) -> AttrId {
         crate::attr::mk_attr_id()
     }

compiler/rustc_ast/src/ptr.rs

@@ -121,8 +121,8 @@ impl<D: Decoder, T: 'static + Decodable<D>> Decodable<D> for P<T> {
 }
 
 impl<S: Encoder, T: Encodable<S>> Encodable<S> for P<T> {
-    fn encode(&self, s: &mut S) -> Result<(), S::Error> {
-        (**self).encode(s)
+    fn encode(&self, s: &mut S) {
+        (**self).encode(s);
     }
 }
 
@@ -191,8 +191,8 @@ impl<'a, T> IntoIterator for &'a P<[T]> {
 }
 
 impl<S: Encoder, T: Encodable<S>> Encodable<S> for P<[T]> {
-    fn encode(&self, s: &mut S) -> Result<(), S::Error> {
-        Encodable::encode(&**self, s)
+    fn encode(&self, s: &mut S) {
+        Encodable::encode(&**self, s);
     }
 }