APINotes: add initial stub of APINotesWriter

This adds the skeleton for serializing out the APINotes data from the
APINotes. The writer uses a private implementation pattern to reduce
the exposed surface to just the programmatic representation of the
APINotes and not expose the details of the bitcode encoding. The format
itself is not considered stable and should only be accessed through the
APINotes Reader and Writer types.

Differential Revision: https://reviews.llvm.org/D92797
Reviewed By: martong

Author: compnerd

clang/include/clang/APINotes/APINotesWriter.h

@@ -0,0 +1,37 @@
+//===-- APINotesWriter.h - API Notes Writer ---------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_APINOTES_WRITER_H
+#define LLVM_CLANG_APINOTES_WRITER_H
+
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/raw_ostream.h"
+
+#include <memory>
+
+namespace clang {
+class FileEntry;
+
+namespace api_notes {
+class APINotesWriter {
+  class Implementation;
+  std::unique_ptr<Implementation> Implementation;
+
+public:
+  APINotesWriter(llvm::StringRef ModuleName, const FileEntry *SF);
+  ~APINotesWriter();
+
+  APINotesWriter(const APINotesWriter &) = delete;
+  APINotesWriter &operator=(const APINotesWriter &) = delete;
+
+  void writeToStream(llvm::raw_ostream &OS);
+};
+} // namespace api_notes
+} // namespace clang
+
+#endif

clang/lib/APINotes/APINotesFormat.h

@@ -252,4 +252,36 @@ struct StoredObjCSelector {
 } // namespace api_notes
 } // namespace clang
 
+namespace llvm {
+template <> struct DenseMapInfo<clang::api_notes::StoredObjCSelector> {
+  typedef DenseMapInfo<unsigned> UnsignedInfo;
+
+  static inline clang::api_notes::StoredObjCSelector getEmptyKey() {
+    return clang::api_notes::StoredObjCSelector{UnsignedInfo::getEmptyKey(),
+                                                {}};
+  }
+
+  static inline clang::api_notes::StoredObjCSelector getTombstoneKey() {
+    return clang::api_notes::StoredObjCSelector{UnsignedInfo::getTombstoneKey(),
+                                                {}};
+  }
+
+  static unsigned
+  getHashValue(const clang::api_notes::StoredObjCSelector &Selector) {
+    auto hash = llvm::hash_value(Selector.NumPieces);
+    hash = hash_combine(hash, Selector.Identifiers.size());
+    for (auto piece : Selector.Identifiers)
+      hash = hash_combine(hash, static_cast<unsigned>(piece));
+    // FIXME: Mix upper/lower 32-bit values together to produce
+    // unsigned rather than truncating.
+    return hash;
+  }
+
+  static bool isEqual(const clang::api_notes::StoredObjCSelector &LHS,
+                      const clang::api_notes::StoredObjCSelector &RHS) {
+    return LHS.NumPieces == RHS.NumPieces && LHS.Identifiers == RHS.Identifiers;
+  }
+};
+} // namespace llvm
+
 #endif