[clang] [APINotes] Upstream APINotesReader (PR #66769)

[Saleem Abdulrasool via cfe-commits]

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+//===--- APINotesReader.h - API Notes Reader --------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the \c APINotesReader class that reads source API notes
+// data providing additional information about source code as a separate input,
+// such as the non-nil/nilable annotations for method parameters.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_APINOTES_READER_H
+#define LLVM_CLANG_APINOTES_READER_H
+
+#include "clang/APINotes/Types.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/VersionTuple.h"
+#include <memory>
+
+namespace clang {
+namespace api_notes {
+
+/// A class that reads API notes data from a binary file that was written by
+/// the \c APINotesWriter.
+class APINotesReader {
+  class Implementation;
+  std::unique_ptr<Implementation> Implementation;
+
+  APINotesReader(llvm::MemoryBuffer *InputBuffer,
+                 llvm::VersionTuple SwiftVersion, bool &Failed);
+
+public:
+  /// Create a new API notes reader from the given member buffer, which
+  /// contains the contents of a binary API notes file.
+  ///
+  /// \returns the new API notes reader, or null if an error occurred.
+  static std::unique_ptr<APINotesReader>
+  get(std::unique_ptr<llvm::MemoryBuffer> InputBuffer,
+      llvm::VersionTuple SwiftVersion);
+
+  ~APINotesReader();
+
+  APINotesReader(const APINotesReader &) = delete;
+  APINotesReader &operator=(const APINotesReader &) = delete;
+
+  /// Captures the completed versioned information for a particular part of
+  /// API notes, including both unversioned API notes and each versioned API
+  /// note for that particular entity.
+  template <typename T> class VersionedInfo {
+    /// The complete set of results.
+    llvm::SmallVector<std::pair<llvm::VersionTuple, T>, 1> Results;
+
+    /// The index of the result that is the "selected" set based on the desired
+    /// Swift version, or \c Results.size() if nothing matched.
+    unsigned Selected;
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compnerd wrote:

does it make sense to use `std::optional<unsigned>` instead?

https://github.com/llvm/llvm-project/pull/66769