typeck: port "unconstrained opaque type" diag

Port the "unconstrained opaque type" diagnostic to using the diagnostic
derive.

Signed-off-by: David Wood <david.wood@huawei.com>

Author: davidtwco

compiler/rustc_error_messages/locales/en-US/typeck.ftl

@@ -90,3 +90,6 @@ typeck-add-return-type-missing-here = a return type might be missing here
 typeck-expected-default-return-type = expected `()` because of default return type
 
 typeck-expected-return-type = expected `{$expected}` because of return type
+
+typeck-unconstrained-opaque-type = unconstrained opaque type
+    .note = `{$name}` must be used in combination with a concrete type within the same module

compiler/rustc_typeck/src/collect/type_of.rs

@@ -14,6 +14,7 @@ use rustc_span::{Span, DUMMY_SP};
 
 use super::ItemCtxt;
 use super::{bad_placeholder, is_suggestable_infer_ty};
+use crate::errors::UnconstrainedOpaqueType;
 
 /// Computes the relevant generic parameter for a potential generic const argument.
 ///
@@ -682,13 +683,10 @@ fn find_opaque_ty_constraints(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Ty<'_> {
     match locator.found {
         Some(hidden) => hidden.ty,
         None => {
-            let span = tcx.def_span(def_id);
-            let name = tcx.item_name(tcx.local_parent(def_id).to_def_id());
-            let label = format!(
-                "`{}` must be used in combination with a concrete type within the same module",
-                name
-            );
-            tcx.sess.struct_span_err(span, "unconstrained opaque type").note(&label).emit();
+            tcx.sess.emit_err(UnconstrainedOpaqueType {
+                span: tcx.def_span(def_id),
+                name: tcx.item_name(tcx.local_parent(def_id).to_def_id()),
+            });
             tcx.ty_error()
         }
     }

compiler/rustc_typeck/src/errors.rs

@@ -228,3 +228,12 @@ pub enum ExpectedReturnTypeLabel<'tcx> {
         expected: Ty<'tcx>,
     },
 }
+
+#[derive(SessionDiagnostic)]
+#[error(slug = "typeck-unconstrained-opaque-type")]
+#[note]
+pub struct UnconstrainedOpaqueType {
+    #[primary_span]
+    pub span: Span,
+    pub name: Symbol,
+}