Merge pull request #37887 from xedin/rdar-78097387

[Diagnostics] Make sure extension type repr is available before using it

Author: xedin

include/swift/AST/Decl.h

@@ -1315,6 +1315,9 @@ class ExtensionDecl final : public GenericContext, public Decl,
   bool alreadyBoundToNominal() const { return NextExtension.getInt(); }
 
   /// Retrieve the extended type definition as written in the source, if it exists.
+  ///
+  /// Repr would not be available if the extension was been loaded
+  /// from a serialized module.
   TypeRepr *getExtendedTypeRepr() const { return ExtendedTypeRepr; }
 
   /// Retrieve the set of protocols that this type inherits (i.e,

lib/Sema/CSDiagnostics.cpp

@@ -7432,9 +7432,15 @@ bool InvalidMemberRefOnProtocolMetatype::diagnoseAsError() {
   if (auto *whereClause = extension->getTrailingWhereClause()) {
     auto sourceRange = whereClause->getSourceRange();
     note.fixItInsertAfter(sourceRange.End, ", Self == <#Type#> ");
-  } else {
-    auto nameRepr = extension->getExtendedTypeRepr();
-    note.fixItInsertAfter(nameRepr->getEndLoc(), " where Self == <#Type#>");
+  } else if (auto nameRepr = extension->getExtendedTypeRepr()) {
+    // Type repr is not always available so we need to be defensive
+    // about its presence and validity.
+    if (nameRepr->isInvalid())
+      return true;
+
+    if (auto noteLoc = nameRepr->getEndLoc()) {
+      note.fixItInsertAfter(noteLoc, " where Self == <#Type#>");
+    }
   }
 
   return true;