Auto merge of #111869 - Dylan-DPC:rollup-9pydw08, r=Dylan-DPC

Rollup of 6 pull requests

Successful merges:

 - #111461 (Fix symbol conflict diagnostic mistakenly being shown instead of missing crate diagnostic)
 - #111579 (Also assume wrap-around discriminants in `as` MIR building)
 - #111704 (Remove return type sized check hack from hir typeck)
 - #111853 (Check opaques for mismatch during writeback)
 - #111854 (rustdoc: clean up `settings.css`)
 - #111860 (Don't ICE if method receiver fails to unify with `arbitrary_self_types`)

r? `@ghost`
`@rustbot` modify labels: rollup

2 files changed, 23 insertions, 7 deletions

diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index ecb191676c2..c9cd644fab0 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -37,7 +37,7 @@ use rustc_data_structures::intern::Interned;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::steal::Steal;
 use rustc_data_structures::tagged_ptr::CopyTaggedPtr;
-use rustc_errors::ErrorGuaranteed;
+use rustc_errors::{DiagnosticBuilder, ErrorGuaranteed, StashKey};
 use rustc_hir as hir;
 use rustc_hir::def::{CtorKind, CtorOf, DefKind, DocLinkResMap, LifetimeRes, Res};
 use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LocalDefId, LocalDefIdMap};
@@ -1439,14 +1439,26 @@ pub struct OpaqueHiddenType<'tcx> {
 }
 
 impl<'tcx> OpaqueHiddenType<'tcx> {
-    pub fn report_mismatch(&self, other: &Self, tcx: TyCtxt<'tcx>) -> ErrorGuaranteed {
+    pub fn report_mismatch(
+        &self,
+        other: &Self,
+        opaque_def_id: LocalDefId,
+        tcx: TyCtxt<'tcx>,
+    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
+        if let Some(diag) = tcx
+            .sess
+            .diagnostic()
+            .steal_diagnostic(tcx.def_span(opaque_def_id), StashKey::OpaqueHiddenTypeMismatch)
+        {
+            diag.cancel();
+        }
         // Found different concrete types for the opaque type.
         let sub_diag = if self.span == other.span {
             TypeMismatchReason::ConflictType { span: self.span }
         } else {
             TypeMismatchReason::PreviousUse { span: self.span }
         };
-        tcx.sess.emit_err(OpaqueHiddenTypeMismatch {
+        tcx.sess.create_err(OpaqueHiddenTypeMismatch {
             self_ty: self.ty,
             other_ty: other.ty,
             other_span: other.span,
diff --git a/compiler/rustc_middle/src/ty/typeck_results.rs b/compiler/rustc_middle/src/ty/typeck_results.rs
index 5a0571f4bb7..e04dbbff9a7 100644
--- a/compiler/rustc_middle/src/ty/typeck_results.rs
+++ b/compiler/rustc_middle/src/ty/typeck_results.rs
@@ -151,10 +151,14 @@ pub struct TypeckResults<'tcx> {
     /// this field will be set to `Some(ErrorGuaranteed)`.
     pub tainted_by_errors: Option<ErrorGuaranteed>,
 
-    /// All the opaque types that have hidden types set
-    /// by this function. We also store the
-    /// type here, so that mir-borrowck can use it as a hint for figuring out hidden types,
-    /// even if they are only set in dead code (which doesn't show up in MIR).
+    /// All the opaque types that have hidden types set by this function.
+    /// We also store the type here, so that the compiler can use it as a hint
+    /// for figuring out hidden types, even if they are only set in dead code
+    /// (which doesn't show up in MIR).
+    ///
+    /// These types are mapped back to the opaque's identity substitutions
+    /// (with erased regions), which is why we don't associated substs with any
+    /// of these usages.
     pub concrete_opaque_types: FxIndexMap<LocalDefId, ty::OpaqueHiddenType<'tcx>>,
 
     /// Tracks the minimum captures required for a closure;