Auto merge of #99217 - lcnr:implied-bounds-pre-norm, r=lcnr

consider unnormalized types for implied bounds

extracted, and slightly modified, from #98900

The idea here is that generally, rustc is split into things which can assume its inputs are well formed[^1], and things which have verify that themselves.

Generally most predicates should only deal with well formed inputs, e.g. a `&'a &'b (): Trait` predicate should be able to assume that `'b: 'a` holds. Normalization can loosen wf requirements (see #91068) and must therefore not be used in places which still have to check well formedness. The only such place should hopefully be `WellFormed` predicates

fixes #87748 and #98543

r? `@jackh726` cc `@rust-lang/types`

[^1]: These places may still encounter non-wf inputs and have to deal with them without causing an ICE as we may check for well formedness out of order.

compiler/rustc_trait_selection/src/traits/project.rs

@@ -619,6 +619,15 @@ impl<'a, 'b, 'tcx> TypeFolder<'tcx> for AssocTypeNormalizer<'a, 'b, 'tcx> {
             constant.eval(self.selcx.tcx(), self.param_env)
         }
     }
+
+    #[inline]
+    fn fold_predicate(&mut self, p: ty::Predicate<'tcx>) -> ty::Predicate<'tcx> {
+        if p.allow_normalization() && needs_normalization(&p, self.param_env.reveal()) {
+            p.super_fold_with(self)
+        } else {
+            p
+        }
+    }
 }
 
 pub struct BoundVarReplacer<'me, 'tcx> {

compiler/rustc_trait_selection/src/traits/query/normalize.rs

@@ -351,4 +351,16 @@ impl<'cx, 'tcx> FallibleTypeFolder<'tcx> for QueryNormalizer<'cx, 'tcx> {
             mir::ConstantKind::Val(_, _) => constant.try_super_fold_with(self)?,
         })
     }
+
+    #[inline]
+    fn try_fold_predicate(
+        &mut self,
+        p: ty::Predicate<'tcx>,
+    ) -> Result<ty::Predicate<'tcx>, Self::Error> {
+        if p.allow_normalization() && needs_normalization(&p, self.param_env.reveal()) {
+            p.try_super_fold_with(self)
+        } else {
+            Ok(p)
+        }
+    }
 }