[Diagnostics] Even though missing conformance could be fixed by .rawValue still diagnose it as conformance issue

Conformance requirement failure is a more descriptive error,
augment it with a note about missing `.rawValue`.

Author: xedin

lib/Sema/CSDiagnostics.cpp

@@ -6841,8 +6841,6 @@ AbstractRawRepresentableFailure::getDiagnostic() const {
     return diag::cannot_convert_assign;
   } else if (locator->isLastElement<LocatorPathElt::ApplyArgToParam>()) {
     return diag::cannot_convert_argument_value;
-  } else if (locator->isLastElement<LocatorPathElt::AnyRequirement>()) {
-    return diag::type_does_not_conform;
   }
 
   return None;
@@ -6938,6 +6936,26 @@ void MissingRawRepresentableInitFailure::fixIt(
   }
 }
 
+bool MissingRawValueFailure::diagnoseAsError() {
+  auto *locator = getLocator();
+
+  if (locator->isLastElement<LocatorPathElt::AnyRequirement>()) {
+    MissingConformanceFailure failure(getSolution(), locator,
+                                      {RawReprType, ExpectedType});
+
+    auto diagnosed = failure.diagnoseAsError();
+    if (!diagnosed)
+      return false;
+
+    auto note = emitDiagnostic(diag::note_remapped_type, ".rawValue");
+    fixIt(note);
+
+    return true;
+  }
+
+  return AbstractRawRepresentableFailure::diagnoseAsError();
+}
+
 void MissingRawValueFailure::fixIt(InFlightDiagnostic &diagnostic) const {
   auto *E = getAsExpr(getAnchor());
   if (!E)

lib/Sema/CSDiagnostics.h

@@ -2273,6 +2273,8 @@ class MissingRawValueFailure final : public AbstractRawRepresentableFailure {
   Type getFromType() const override { return RawReprType; }
   Type getToType() const override { return ExpectedType; }
 
+  bool diagnoseAsError() override;
+
 private:
   void fixIt(InFlightDiagnostic &diagnostic) const override;
 };

test/ClangImporter/newtype_conformance.swift

@@ -16,11 +16,13 @@ func acceptHashable<T: Hashable>(_: T) {}
 // expected-note@-1 {{where 'T' = 'WrappedRef'}}
 // expected-note@-2 {{where 'T' = 'WrappedValue'}}
 func acceptComparable<T: Comparable>(_: T) {}
+// expected-note@-1 {{where 'T' = 'NSNotification.Name'}}
 
 func testNewTypeWrapper(x: NSNotification.Name, y: NSNotification.Name) {
   acceptEquatable(x)
   acceptHashable(x)
-  acceptComparable(x) // expected-error {{type 'NSNotification.Name' does not conform to protocol 'Comparable'}} {{19-19=.rawValue}}
+  acceptComparable(x) // expected-error {{global function 'acceptComparable' requires that 'NSNotification.Name' conform to 'Comparable'}}
+  // expected-note@-1 {{did you mean to use '.rawValue'?}} {{19-19=.rawValue}}
 
   _ = x == y
   _ = x != y