Account for for<'a> types when checking for non-structural type in constant as pattern

When we encounter a constant in a pattern, we check if it is non-structural. If so, we check if the type implements `PartialEq`, but for types with escaping bound vars the check would be incorrect as is, so we break early. This is ok because these types would be filtered anyways.

Fix #134764.

Author: estebank

compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs

@@ -8,7 +8,9 @@ use rustc_infer::infer::TyCtxtInferExt;
 use rustc_infer::traits::Obligation;
 use rustc_middle::mir::interpret::ErrorHandled;
 use rustc_middle::thir::{FieldPat, Pat, PatKind};
-use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitableExt, TypeVisitor, ValTree};
+use rustc_middle::ty::{
+    self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitableExt, TypeVisitor, ValTree,
+};
 use rustc_middle::{mir, span_bug};
 use rustc_span::def_id::DefId;
 use rustc_span::{Span, sym};
@@ -387,7 +389,9 @@ fn extend_type_not_partial_eq<'tcx>(
 
     impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for UsedParamsNeedInstantiationVisitor<'tcx> {
         fn visit_ty(&mut self, ty: Ty<'tcx>) -> Self::Result {
-            if let ty::Adt(def, _args) = ty.kind() {
+            if let ty::Adt(def, _args) = ty.kind()
+                && !ty.has_escaping_bound_vars()
+            {
                 let ty_def_id = def.did();
                 let ty_def_span = self.tcx.def_span(ty_def_id);
                 let (impls_partial_eq, derived, structural, impl_def_id) =
@@ -412,7 +416,6 @@ fn extend_type_not_partial_eq<'tcx>(
                     _ => {}
                 };
             }
-            use rustc_middle::ty::TypeSuperVisitable;
             ty.super_visit_with(self)
         }
     }
@@ -468,6 +471,10 @@ fn type_has_partial_eq_impl<'tcx>(
     let partial_eq_trait_id = tcx.require_lang_item(hir::LangItem::PartialEq, None);
     let structural_partial_eq_trait_id = tcx.require_lang_item(hir::LangItem::StructuralPeq, None);
 
+    if ty.has_escaping_bound_vars() {
+        return (false, false, false, None);
+    }
+
     let partial_eq_obligation = Obligation::new(
         tcx,
         ObligationCause::dummy(),

tests/ui/consts/const_in_pattern/non_structural_with_escaping_bounds.rs

@@ -0,0 +1,15 @@
+#![feature(structural_match)]
+impl<T: ?Sized> std::marker::StructuralPartialEq for O<T> { }
+
+enum O<T: ?Sized> {
+    Some(*const T),
+    None,
+}
+
+const C: O<dyn for<'a> Fn(Box<dyn Fn(&'a u8)>)> = O::None;
+
+fn main() {
+    match O::None {
+        C => (), //~ ERROR constant of non-structural type
+    }
+}

tests/ui/consts/const_in_pattern/non_structural_with_escaping_bounds.stderr

@@ -0,0 +1,15 @@
+error: constant of non-structural type `O<dyn for<'a> Fn(Box<dyn Fn(&'a u8)>)>` in a pattern
+  --> $DIR/non_structural_with_escaping_bounds.rs:13:9
+   |
+LL | const C: O<dyn for<'a> Fn(Box<dyn Fn(&'a u8)>)> = O::None;
+   | ----------------------------------------------- constant defined here
+...
+LL |         C => (),
+   |         ^ constant of non-structural type
+   |
+   = note: see https://doc.rust-lang.org/stable/std/marker/trait.StructuralPartialEq.html for details
+   = note: `std::alloc::Global` must be annotated with `#[derive(PartialEq)]` to be usable in patterns
+   = note: `std::alloc::Global` must be annotated with `#[derive(PartialEq)]` to be usable in patterns
+
+error: aborting due to 1 previous error
+