Pass single quotes directly when reporting illegal vector component in CheckExtVector(), and offset the diagnostic arrow so it points to the offending component, rather than the '.' at the start of the component identifier.

Author: smallp-o-p

clang/lib/Sema/SemaExprMember.cpp

@@ -434,8 +434,10 @@ CheckExtVectorComponent(Sema &S, QualType baseType, ExprValueKind &VK,
   if (!HalvingSwizzle && *compStr) {
     // We didn't get to the end of the string. This means the component names
     // didn't come from the same set *or* we encountered an illegal name.
-    S.Diag(OpLoc, diag::err_ext_vector_component_name_illegal)
-      << StringRef(compStr, 1) << SourceRange(CompLoc);
+    size_t Offset = compStr - CompName->getNameStart() + 1;
+    S.Diag(OpLoc.getLocWithOffset(Offset),
+           diag::err_ext_vector_component_name_illegal)
+        << StringRef({'\'', *compStr, '\''}) << SourceRange(CompLoc);
     return QualType();
   }