GCI: Check where-clauses for well-formedness at the def site

Author: fmease

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -306,9 +306,7 @@ fn check_item<'tcx>(tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>) -> Result<()
         hir::ItemKind::Static(ty, ..) => {
             check_item_type(tcx, def_id, ty.span, UnsizedHandling::Forbid)
         }
-        hir::ItemKind::Const(ty, ..) => {
-            check_item_type(tcx, def_id, ty.span, UnsizedHandling::Forbid)
-        }
+        hir::ItemKind::Const(ty, ..) => check_const_item(tcx, def_id, ty.span, item.span),
         hir::ItemKind::Struct(_, hir_generics) => {
             let res = check_type_defn(tcx, item, false);
             check_variances_for_type_defn(tcx, item, hir_generics);
@@ -1280,6 +1278,7 @@ enum UnsizedHandling {
     AllowIfForeignTail,
 }
 
+// FIXME(fmease): Rename to check_static_item once LTAs don't use it anymore (#136432)
 fn check_item_type(
     tcx: TyCtxt<'_>,
     item_id: LocalDefId,
@@ -1338,6 +1337,34 @@ fn check_item_type(
     })
 }
 
+fn check_const_item(
+    tcx: TyCtxt<'_>,
+    def_id: LocalDefId,
+    ty_span: Span,
+    item_span: Span,
+) -> Result<(), ErrorGuaranteed> {
+    enter_wf_checking_ctxt(tcx, ty_span, def_id, |wfcx| {
+        let ty = tcx.type_of(def_id).instantiate_identity();
+        let ty = wfcx.normalize(ty_span, Some(WellFormedLoc::Ty(def_id)), ty);
+
+        wfcx.register_wf_obligation(ty_span, Some(WellFormedLoc::Ty(def_id)), ty.into());
+        wfcx.register_bound(
+            traits::ObligationCause::new(
+                ty_span,
+                wfcx.body_def_id,
+                ObligationCauseCode::WellFormed(None),
+            ),
+            wfcx.param_env,
+            ty,
+            tcx.require_lang_item(LangItem::Sized, None),
+        );
+
+        check_where_clauses(wfcx, item_span, def_id);
+
+        Ok(())
+    })
+}
+
 #[instrument(level = "debug", skip(tcx, hir_self_ty, hir_trait_ref))]
 fn check_impl<'tcx>(
     tcx: TyCtxt<'tcx>,

tests/ui/generic-const-items/def-site-predicates-wf.rs

@@ -0,0 +1,9 @@
+//! Ensure that we check the predicates for well-formedness at the definition site.
+#![feature(generic_const_items)]
+#![allow(incomplete_features)]
+
+const _: () = ()
+where
+    Vec<str>: Sized; //~ ERROR the size for values of type `str` cannot be known at compilation time
+
+fn main() {}

tests/ui/generic-const-items/def-site-predicates-wf.stderr

@@ -0,0 +1,13 @@
+error[E0277]: the size for values of type `str` cannot be known at compilation time
+  --> $DIR/def-site-predicates-wf.rs:7:15
+   |
+LL |     Vec<str>: Sized;
+   |               ^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `str`
+note: required by an implicit `Sized` bound in `Vec`
+  --> $SRC_DIR/alloc/src/vec/mod.rs:LL:COL
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.