Reinstate r281429, reverted in r281452, with a fix for its mishandling of

compiles without -fmodules-local-submodule-visibility. Original commit message:

[modules] When merging one definition into another, propagate the list of
re-exporting modules from the discarded definition to the retained definition.

llvm-svn: 284176

1 files changed, 13 insertions, 2 deletions

diff --git a/clang/include/clang/AST/ASTContext.h b/clang/include/clang/AST/ASTContext.h
index 3d777524b83..f5a9bd2da54 100644
--- a/clang/include/clang/AST/ASTContext.h
+++ b/clang/include/clang/AST/ASTContext.h
@@ -308,10 +308,18 @@ class ASTContext : public RefCountedBase<ASTContext> {
   /// merged into.
   llvm::DenseMap<Decl*, Decl*> MergedDecls;
 
+  /// The modules into which a definition has been merged, or a map from a
+  /// merged definition to its canonical definition. This is really a union of
+  /// a NamedDecl* and a vector of Module*.
+  struct MergedModulesOrCanonicalDef {
+    llvm::TinyPtrVector<Module*> MergedModules;
+    NamedDecl *CanonicalDef = nullptr;
+  };
+
   /// \brief A mapping from a defining declaration to a list of modules (other
   /// than the owning module of the declaration) that contain merged
   /// definitions of that entity.
-  llvm::DenseMap<NamedDecl*, llvm::TinyPtrVector<Module*>> MergedDefModules;
+  llvm::DenseMap<NamedDecl*, MergedModulesOrCanonicalDef> MergedDefModules;
 
   /// \brief Initializers for a module, in order. Each Decl will be either
   /// something that has a semantic effect on startup (such as a variable with
@@ -883,6 +891,7 @@ public:
   /// and should be visible whenever \p M is visible.
   void mergeDefinitionIntoModule(NamedDecl *ND, Module *M,
                                  bool NotifyListeners = true);
+  void mergeDefinitionIntoModulesOf(NamedDecl *ND, NamedDecl *Other);
   /// \brief Clean up the merged definition list. Call this if you might have
   /// added duplicates into the list.
   void deduplicateMergedDefinitonsFor(NamedDecl *ND);
@@ -893,7 +902,9 @@ public:
     auto MergedIt = MergedDefModules.find(Def);
     if (MergedIt == MergedDefModules.end())
       return None;
-    return MergedIt->second;
+    if (auto *CanonDef = MergedIt->second.CanonicalDef)
+      return getModulesWithMergedDefinition(CanonDef);
+    return MergedIt->second.MergedModules;
   }
 
   /// Add a declaration to the list of declarations that are initialized