Avoid verifying un-parented GenericTypeParamDecls

When deserializing, we delay parenting
GenericTypeParamDecls until we install the
GenericParamList on the parent declaration, using
a dummy parent of the ModuleDecl until this
happens.

However when deserializing GenericTypeParamTypes,
we don't necessarily get the opportunity to
deserialize the parent, leaving them with the
dummy parent.

We should probably consider not deserializing
GenericTypeParamDecls at all, we currently only do
it to preserve the sugar of the name, this could
be serialized on the type instead.

For now though, adjust the dummy parent to be the
SerializedASTFile, and tell the ASTVerifier to
skip verification for such generic params.

Author: hamishknight

lib/AST/ASTVerifier.cpp

@@ -2732,7 +2732,18 @@ class Verifier : public ASTWalker {
       PrettyStackTraceDecl debugStack("verifying GenericTypeParamDecl", GTPD);
 
       const DeclContext *DC = GTPD->getDeclContext();
-      if (!GTPD->getDeclContext()->isInnermostContextGeneric()) {
+
+      // Skip verification of deserialized generic param decls that have the
+      // the file set as their parent. This happens when they have not yet had
+      // their correct parent set.
+      // FIXME: This is a hack to workaround the fact that we don't necessarily
+      // parent a GenericTypeParamDecl if we just deserialize its type.
+      if (auto *fileDC = dyn_cast<FileUnit>(DC)) {
+        if (fileDC->getKind() == FileUnitKind::SerializedAST)
+          return;
+      }
+
+      if (!DC->isInnermostContextGeneric()) {
         Out << "DeclContext of GenericTypeParamDecl does not have "
                "generic params\n";
         abort();

lib/Serialization/Deserialization.cpp

@@ -2487,9 +2487,9 @@ class DeclDeserializer {
                                                         depth,
                                                         index);
 
-    // Always create GenericTypeParamDecls in the associated module;
-    // the real context will reparent them.
-    auto DC = MF.getAssociatedModule();
+    // Always create GenericTypeParamDecls in the associated file; the real
+    // context will reparent them.
+    auto *DC = MF.getFile();
     auto genericParam = MF.createDecl<GenericTypeParamDecl>(
         DC, MF.getIdentifier(nameID), SourceLoc(), depth, index);
     declOrOffset = genericParam;