better spans for WF errors

Author: RalfJung

compiler/rustc_passes/src/abi_test.rs

@@ -118,7 +118,7 @@ fn dump_abi_of_fn_type(tcx: TyCtxt<'_>, item_def_id: LocalDefId, attr: &Attribut
     let param_env = tcx.param_env(item_def_id);
     let ty = tcx.type_of(item_def_id).instantiate_identity();
     let span = tcx.def_span(item_def_id);
-    if !ensure_wf(tcx, param_env, ty, span) {
+    if !ensure_wf(tcx, param_env, ty, item_def_id, span) {
         return;
     }
     let meta_items = attr.meta_item_list().unwrap_or_default();

compiler/rustc_passes/src/layout_test.rs

@@ -38,12 +38,17 @@ pub fn ensure_wf<'tcx>(
     tcx: TyCtxt<'tcx>,
     param_env: ParamEnv<'tcx>,
     ty: Ty<'tcx>,
+    def_id: LocalDefId,
     span: Span,
 ) -> bool {
     let pred = ty::ClauseKind::WellFormed(ty.into());
     let obligation = traits::Obligation::new(
         tcx,
-        traits::ObligationCause::dummy_with_span(span),
+        traits::ObligationCause::new(
+            span,
+            def_id,
+            traits::ObligationCauseCode::WellFormed(Some(traits::WellFormedLoc::Ty(def_id))),
+        ),
         param_env,
         pred,
     );
@@ -64,7 +69,7 @@ fn dump_layout_of(tcx: TyCtxt<'_>, item_def_id: LocalDefId, attr: &Attribute) {
     let param_env = tcx.param_env(item_def_id);
     let ty = tcx.type_of(item_def_id).instantiate_identity();
     let span = tcx.def_span(item_def_id.to_def_id());
-    if !ensure_wf(tcx, param_env, ty, span) {
+    if !ensure_wf(tcx, param_env, ty, item_def_id, span) {
         return;
     }
     match tcx.layout_of(param_env.and(ty)) {

tests/ui/abi/debug.stderr

@@ -852,10 +852,10 @@ LL | type TestAbiNeSign = (fn(i32), fn(u32));
    | ^^^^^^^^^^^^^^^^^^
 
 error[E0277]: the size for values of type `str` cannot be known at compilation time
-  --> $DIR/debug.rs:53:1
+  --> $DIR/debug.rs:53:46
    |
 LL | type TestAbiEqNonsense = (fn((str, str)), fn((str, str)));
-   | ^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |                                              ^^^^^^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `str`
    = note: only the last element of a tuple may have a dynamically sized type

tests/ui/associated-types/issue-85103.rs renamed to tests/ui/associated-types/issue-85103-layout-debug.rs

@@ -0,0 +1,16 @@
+error[E0277]: the trait bound `[E]: ToOwned` is not satisfied
+  --> $DIR/issue-85103.rs:6:21
+   |
+LL | type Edges<'a, E> = Cow<'a, [E]>;
+   |                     ^^^^^^^^^^^^ the trait `ToOwned` is not implemented for `[E]`
+   |
+note: required by a bound in `Cow`
+  --> $SRC_DIR/alloc/src/borrow.rs:LL:COL
+help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
+   |
+LL | type Edges<'a, E> where [E]: ToOwned = Cow<'a, [E]>;
+   |                   ++++++++++++++++++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/associated-types/issue-85103-layout-debug.stderr

@@ -558,10 +558,10 @@ LL | const C: () = ();
    | ^^^^^^^^^^^
 
 error[E0277]: the size for values of type `str` cannot be known at compilation time
-  --> $DIR/debug.rs:78:1
+  --> $DIR/debug.rs:78:19
    |
 LL | type Impossible = (str, str);
-   | ^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |                   ^^^^^^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `str`
    = note: only the last element of a tuple may have a dynamically sized type