[Clang] Improve designated inits diagnostic location

[void]

Summary

A "null" designator won't have a valid location. Try to approximate this
location as best we can in that situation.

Closes 61118
Closes 46132

[void]

Remove extraneous space.

[shafik]

Thank you for taking care of this, LGTM

clang/lib/Sema/SemaInit.cpp

2646

nitpick, I think the comment should be above the if statement

[rsmith]

clang/test/SemaCXX/cxx2b-designated-initializers.cpp

14

Why are we rejecting this?

[aaron.ballman]

clang/test/SemaCXX/cxx2b-designated-initializers.cpp

14

That's existing behavior: https://godbolt.org/z/48ThKbTor but we don't get the behavior when it's not a template (https://godbolt.org/z/f3zWaqdWr) or in C (https://godbolt.org/z/P1TqG43nG), so I agree that this should be accepted.

[void]

clang/test/SemaCXX/cxx2b-designated-initializers.cpp

14

Also, if the "auto" above is changed to "int" this compiles just fine.

clang/lib/Sema/SemaInit.cpp

if (!KnownField) {
           SemaRef.diagnoseTypo(
               Corrected,
               SemaRef.PDiag(diag::err_field_designator_unknown_suggest)
                 << FieldName << CurrentObjectType);
           KnownField = Corrected.getCorrectionDeclAs<FieldDecl>();
           hadError = true;
         } else {
           // Typo correction didn't find anything.
-          SemaRef.Diag(D->getFieldLoc(), diag::err_field_designator_unknown)
-            << FieldName << CurrentObjectType;
+          SourceLocation Loc = D->getFieldLoc();
+
+          // The loc can be invalid with a "null" designator (i.e. an anonymous
+          // union/struct). Do our best to approximate the location.
+          if (Loc.isInvalid())
+            Loc = IList->getBeginLoc();
+
+          SemaRef.Diag(Loc, diag::err_field_designator_unknown)
+            << FieldName << CurrentObjectType << DIE->getSourceRange();
           ++Index;
           return true;
         }
       }
     }
 
     unsigned NumBases = 0;
     if (auto *CXXRD = dyn_cast<CXXRecordDecl>(RT->getDecl()))

clang/test/SemaCXX/cxx2b-designated-initializers.cpp

+// RUN: %clang_cc1 -std=c++2b -fsyntax-only -verify %s
+
+namespace PR61118 {
+
+union S {
+  struct {
+    int a;
+  };
+};
+
+void f(int x, auto) {
+  const S result { // expected-error {{field designator (null) does not refer to any field in type 'const S'}}
+    .a = x
+  };
+}
+
+void g(void) {
+  f(0, 0); // expected-note {{in instantiation of function template specialization 'PR61118::f<int>' requested here}}
+}
+
+} // end namespace PR61118