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Rollup merge of #135149 - compiler-errors:mangle, r=oli-obk

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Use a post-monomorphization typing env when mangling components that come from impls

When mangling associated methods of impls, we were previously using the wrong param-env. Instead of using a fully monomorphized param-env like we usually do in codegen, we were taking the post-analysis param-env, and treating it as an early binder to *re-substitute* the impl args. I've pointed out the problematic old code in an inline comment.

This would give us param-envs with possibly trivial predicates that would prevent normalization via param-env shadowing.

In the example test linked below, `tests/ui/symbol-names/normalize-in-param-env.rs`, this happens when we mangle the impl `impl<P: Point2> MyFrom<P::S> for P` with the substitution `P = Vec2`. Because the where clause of the impl is `P: Point2`, which elaborates to `[P: Point2, P: Point, <P as Point>::S projects-to <P as Point2>::S2]` and the fact that `impl Point2 for Vec2` normalizes `Vec2::S2` to `Vec2::S`, this causes a cycle.

The proper fix here is to use a fully monomorphized param-env for the case where the impl is properly substituted.

Fixes #135143

While #134081 uncovered this bug for legacy symbol mangling, it was preexisting for v0 symbol mangling. This PR fixes both. The test requires a "hack" because we strip the args of the instance we're printing for legacy symbol mangling except for drop glue, so we box a closure to ensure we generate drop glue.

r? oli-obk
This commit is contained in:
Matthias Krüger 2025-01-07 21:39:41 +01:00 • committed by GitHub
commit 3e12d4d152
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4 changed files with 99 additions and 38 deletions
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40
compiler/rustc_middle/src/ty/print/mod.rs
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@ -45,10 +45,25 @@ pub trait Printer<'tcx>: Sized {
&mut self,
impl_def_id: DefId,
args: &'tcx [GenericArg<'tcx>],
self_ty: Ty<'tcx>,
trait_ref: Option<ty::TraitRef<'tcx>>,
) -> Result<(), PrintError> {
self.default_print_impl_path(impl_def_id, args, self_ty, trait_ref)
let tcx = self.tcx();
let self_ty = tcx.type_of(impl_def_id);
let impl_trait_ref = tcx.impl_trait_ref(impl_def_id);
let (self_ty, impl_trait_ref) = if tcx.generics_of(impl_def_id).count() <= args.len() {
(
self_ty.instantiate(tcx, args),
impl_trait_ref.map(|impl_trait_ref| impl_trait_ref.instantiate(tcx, args)),
)
} else {
// We are probably printing a nested item inside of an impl.
// Use the identity substitutions for the impl.
(
self_ty.instantiate_identity(),
impl_trait_ref.map(|impl_trait_ref| impl_trait_ref.instantiate_identity()),
)
};
self.default_print_impl_path(impl_def_id, self_ty, impl_trait_ref)
}
fn print_region(&mut self, region: ty::Region<'tcx>) -> Result<(), PrintError>;
@ -107,23 +122,7 @@ pub trait Printer<'tcx>: Sized {
self.path_crate(def_id.krate)
}
DefPathData::Impl => {
let generics = self.tcx().generics_of(def_id);
let self_ty = self.tcx().type_of(def_id);
let impl_trait_ref = self.tcx().impl_trait_ref(def_id);
let (self_ty, impl_trait_ref) = if args.len() >= generics.count() {
(
self_ty.instantiate(self.tcx(), args),
impl_trait_ref.map(|i| i.instantiate(self.tcx(), args)),
)
} else {
(
self_ty.instantiate_identity(),
impl_trait_ref.map(|i| i.instantiate_identity()),
)
};
self.print_impl_path(def_id, args, self_ty, impl_trait_ref)
}
DefPathData::Impl => self.print_impl_path(def_id, args),
_ => {
let parent_def_id = DefId { index: key.parent.unwrap(), ..def_id };
@ -201,7 +200,6 @@ pub trait Printer<'tcx>: Sized {
fn default_print_impl_path(
&mut self,
impl_def_id: DefId,
_args: &'tcx [GenericArg<'tcx>],
self_ty: Ty<'tcx>,
impl_trait_ref: Option<ty::TraitRef<'tcx>>,
) -> Result<(), PrintError> {