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Add docs for get_remapped_def_id

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Santiago Pastorino 2022-08-09 16:39:02 -03:00
parent 457ff7c56c
commit 750a04ea7f
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1 changed files with 13 additions and 0 deletions
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13
compiler/rustc_ast_lowering/src/lib.rs
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@ -220,6 +220,19 @@ impl ResolverAstLoweringExt for ResolverAstLowering {
} }
fn get_remapped_def_id(&self, mut local_def_id: LocalDefId) -> LocalDefId { fn get_remapped_def_id(&self, mut local_def_id: LocalDefId) -> LocalDefId {
// `generics_def_id_map` is a stack of mappings. As we go deeper in impl traits nesting we
// push new mappings so we need to try first the latest mappings, hence `iter().rev()`.
//
// Consider:
//
// `fn test<'a, 'b>() -> impl Trait<&'a u8, Ty = impl Sized + 'b> {}`
//
// We would end with a generics_def_id_map like:
//
// `[[fn#'b -> impl_trait#'b], [fn#'b -> impl_sized#'b]]`
//
// for the opaque type generated on `impl Sized + 'b`, We want the result to be:
// impl_sized#'b, so iterating forward is the wrong thing to do.
for map in self.generics_def_id_map.iter().rev() { for map in self.generics_def_id_map.iter().rev() {
if let Some(r) = map.get(&local_def_id) { if let Some(r) = map.get(&local_def_id) {
debug!("def_id_remapper: remapping from `{local_def_id:?}` to `{r:?}`"); debug!("def_id_remapper: remapping from `{local_def_id:?}` to `{r:?}`");