[PATCH] D122691: [clang][Sema] Add flag to LookupName to force C/ObjC codepath

[Alex Langford via Phabricator via cfe-commits]

bulbazord created this revision.
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Motivation: The intent here is for use in Swift.
When building a clang module for swift consumption, swift adds an
extension block to the module for name lookup purposes. Swift calls
this a SwiftLookupTable. One purpose that this serves is to handle
conflicting names between ObjC classes and ObjC protocols. They exist in
different namespaces in ObjC programs, but in Swift they would exist in
the same namespace. Swift handles this by appending a suffix to a
protocol name if it shares a name with a class. For example, if you have
an ObjC class named "Foo" and a protocol with the same name, the
protocol would be renamed to "FooProtocol" when imported into swift.

When constructing the previously mentioned SwiftLookupTable, we use
`Sema::LookupName` to look up name conflicts for the previous problem.
By this time, the Parser has long finished its job so the call to
`LookupName` gets `nullptr` for its Scope (`TUScope` will be `nullptr`
by this point). The C/ObjC path does not have this problem because it
only uses the Scope in specific scenarios. The C++ codepath uses the
Scope quite extensively and will fail early on if the Scope it gets is
null. In our very specific case of looking up ObjC classes with a
specific name, we want to force `sema::LookupName` to take the C/ObjC
codepath even if C++ or ObjC++ is enabled.

I'm not sure how to test this, unfortunately. That being said, I have an
accompanying downstream patch to swift that exercises this codepath.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D122691

Files:
  clang/include/clang/Sema/Sema.h
  clang/lib/Sema/SemaLookup.cpp


Index: clang/lib/Sema/SemaLookup.cpp
===================================================================
--- clang/lib/Sema/SemaLookup.cpp
+++ clang/lib/Sema/SemaLookup.cpp
@@ -1931,13 +1931,14 @@
 /// used to diagnose ambiguities.
 ///
 /// @returns \c true if lookup succeeded and false otherwise.
-bool Sema::LookupName(LookupResult &R, Scope *S, bool AllowBuiltinCreation) {
+bool Sema::LookupName(LookupResult &R, Scope *S, bool AllowBuiltinCreation,
+                      bool ForceNoCPlusPlus) {
   DeclarationName Name = R.getLookupName();
   if (!Name) return false;
 
   LookupNameKind NameKind = R.getLookupKind();
 
-  if (!getLangOpts().CPlusPlus) {
+  if (!getLangOpts().CPlusPlus || ForceNoCPlusPlus) {
     // Unqualified name lookup in C/Objective-C is purely lexical, so
     // search in the declarations attached to the name.
     if (NameKind == Sema::LookupRedeclarationWithLinkage) {
Index: clang/include/clang/Sema/Sema.h
===================================================================
--- clang/include/clang/Sema/Sema.h
+++ clang/include/clang/Sema/Sema.h
@@ -4217,8 +4217,8 @@
                                 = NotForRedeclaration);
   bool LookupBuiltin(LookupResult &R);
   void LookupNecessaryTypesForBuiltin(Scope *S, unsigned ID);
-  bool LookupName(LookupResult &R, Scope *S,
-                  bool AllowBuiltinCreation = false);
+  bool LookupName(LookupResult &R, Scope *S, bool AllowBuiltinCreation = false,
+                  bool ForceNoCPlusPlus = false);
   bool LookupQualifiedName(LookupResult &R, DeclContext *LookupCtx,
                            bool InUnqualifiedLookup = false);
   bool LookupQualifiedName(LookupResult &R, DeclContext *LookupCtx,


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