[modules] Add optional out-param to ASTReader::ReadAST for imported submodules.

Summary:
The Swift frontend is acquiring the ability to load non-module PCH files containing
bridging definitions from C/ObjC. As part of this work, it needs to know which submodules
were imported by a PCH in order to wrap them in local Swift modules. This information
is collected by ASTReader::ReadAST in a local vector, but is currently kept private.

The change here is just to make the type of the vector elements public, and provide
an optional out-parameter to the ReadAST method to provide the vector's contents to
a caller after a successful read.

Reviewers: manmanren, rsmith, doug.gregor

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D27580

llvm-svn: 289276

clang/include/clang/Serialization/ASTReader.h

@@ -821,6 +821,7 @@ private:
   // \brief A list of late parsed template function data.
   SmallVector<uint64_t, 1> LateParsedTemplates;
 
+public:
   struct ImportedSubmodule {
     serialization::SubmoduleID ID;
     SourceLocation ImportLoc;
@@ -829,6 +830,7 @@ private:
       : ID(ID), ImportLoc(ImportLoc) {}
   };
 
+private:
   /// \brief A list of modules that were imported by precompiled headers or
   /// any other non-module AST file.
   SmallVector<ImportedSubmodule, 2> ImportedModules;
@@ -1404,9 +1406,13 @@ public:
   /// \param ClientLoadCapabilities The set of client load-failure
   /// capabilities, represented as a bitset of the enumerators of
   /// LoadFailureCapabilities.
+  ///
+  /// \param Imported optional out-parameter to append the list of modules
+  /// that were imported by precompiled headers or any other non-module AST file
   ASTReadResult ReadAST(StringRef FileName, ModuleKind Type,
                         SourceLocation ImportLoc,
-                        unsigned ClientLoadCapabilities);
+                        unsigned ClientLoadCapabilities,
+                        SmallVectorImpl<ImportedSubmodule> *Imported = nullptr);
 
   /// \brief Make the entities in the given module and any of its (non-explicit)
   /// submodules visible to name lookup.

clang/lib/Serialization/ASTReader.cpp

@@ -3578,7 +3578,8 @@ static bool SkipCursorToBlock(BitstreamCursor &Cursor, unsigned BlockID) {
 ASTReader::ASTReadResult ASTReader::ReadAST(StringRef FileName,
                                             ModuleKind Type,
                                             SourceLocation ImportLoc,
-                                            unsigned ClientLoadCapabilities) {
+                                            unsigned ClientLoadCapabilities,
+                                            SmallVectorImpl<ImportedSubmodule> *Imported) {
   llvm::SaveAndRestore<SourceLocation>
     SetCurImportLocRAII(CurrentImportLoc, ImportLoc);
 
@@ -3744,6 +3745,10 @@ ASTReader::ASTReadResult ASTReader::ReadAST(StringRef FileName,
   }
   UnresolvedModuleRefs.clear();
 
+  if (Imported)
+    Imported->append(ImportedModules.begin(),
+                     ImportedModules.end());
+
   // FIXME: How do we load the 'use'd modules? They may not be submodules.
   // Might be unnecessary as use declarations are only used to build the
   // module itself.