Rollup merge of rust-lang#87524 - FabianWolff:issue-87495, r=Aaron1011

Fix ICE in `diagnostic_hir_wf_check`

Fixes rust-lang#87495. The [documentation for `ObligationCauseCode::WellFormed`](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_infer/traits/enum.ObligationCauseCode.html#variant.WellFormed) says that

> it is always correct [...] to specify `WellFormed(None)`

instead of `WellFormed(Some(...))`, which seems to have caused the issue here, as `diagnostic_hir_wf_check` does not expect to be called with an associated constant and will ICE:

https://github.com/rust-lang/rust/blob/fd853c00e255559255885aadff9e93a1760c8728/compiler/rustc_typeck/src/hir_wf_check.rs#L131-L134

Therefore, I have changed `check_associated_item()` to pass a `WellFormed(None)` for associated constants.

r? ``@Aaron1011``

Author: JohnTitor

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -240,8 +240,8 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
 
         let mut err = match *error {
             SelectionError::Unimplemented => {
-                // If this obligation was generated as a result of well-formed checking, see if we
-                // can get a better error message by performing HIR-based well formed checking.
+                // If this obligation was generated as a result of well-formedness checking, see if we
+                // can get a better error message by performing HIR-based well-formedness checking.
                 if let ObligationCauseCode::WellFormed(Some(wf_loc)) =
                     root_obligation.cause.code.peel_derives()
                 {

compiler/rustc_typeck/src/hir_wf_check.rs

@@ -38,20 +38,20 @@ fn diagnostic_hir_wf_check<'tcx>(
     // given the type `Option<MyStruct<u8>>`, we will check
     // `Option<MyStruct<u8>>`, `MyStruct<u8>`, and `u8`.
     // For each type, we perform a well-formed check, and see if we get
-    // an erorr that matches our expected predicate. We keep save
+    // an error that matches our expected predicate. We save
     // the `ObligationCause` corresponding to the *innermost* type,
     // which is the most specific type that we can point to.
     // In general, the different components of an `hir::Ty` may have
-    // completely differentr spans due to macro invocations. Pointing
+    // completely different spans due to macro invocations. Pointing
     // to the most accurate part of the type can be the difference
     // between a useless span (e.g. the macro invocation site)
-    // and a useful span (e.g. a user-provided type passed in to the macro).
+    // and a useful span (e.g. a user-provided type passed into the macro).
     //
     // This approach is quite inefficient - we redo a lot of work done
     // by the normal WF checker. However, this code is run at most once
     // per reported error - it will have no impact when compilation succeeds,
-    // and should only have an impact if a very large number of errors are
-    // displaydd to the user.
+    // and should only have an impact if a very large number of errors is
+    // displayed to the user.
     struct HirWfCheck<'tcx> {
         tcx: TyCtxt<'tcx>,
         predicate: ty::Predicate<'tcx>,
@@ -126,10 +126,12 @@ fn diagnostic_hir_wf_check<'tcx>(
         WellFormedLoc::Ty(_) => match hir.get(hir_id) {
             hir::Node::ImplItem(item) => match item.kind {
                 hir::ImplItemKind::TyAlias(ty) => Some(ty),
+                hir::ImplItemKind::Const(ty, _) => Some(ty),
                 ref item => bug!("Unexpected ImplItem {:?}", item),
             },
             hir::Node::TraitItem(item) => match item.kind {
                 hir::TraitItemKind::Type(_, ty) => ty,
+                hir::TraitItemKind::Const(ty, _) => Some(ty),
                 ref item => bug!("Unexpected TraitItem {:?}", item),
             },
             hir::Node::Item(item) => match item.kind {

src/test/ui/wf/issue-87495.rs

@@ -0,0 +1,8 @@
+// Regression test for the ICE described in #87495.
+
+trait T {
+    const CONST: (bool, dyn T);
+    //~^ ERROR: the trait `T` cannot be made into an object [E0038]
+}
+
+fn main() {}

src/test/ui/wf/issue-87495.stderr

@@ -0,0 +1,18 @@
+error[E0038]: the trait `T` cannot be made into an object
+  --> $DIR/issue-87495.rs:4:25
+   |
+LL |     const CONST: (bool, dyn T);
+   |                         ^^^^^ `T` cannot be made into an object
+   |
+   = help: consider moving `CONST` to another trait
+note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
+  --> $DIR/issue-87495.rs:4:11
+   |
+LL | trait T {
+   |       - this trait cannot be made into an object...
+LL |     const CONST: (bool, dyn T);
+   |           ^^^^^ ...because it contains this associated `const`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0038`.