llvm/clang/include/clang/AST/ExternalASTMerger.h

//===--- ExternalASTMerger.h - Merging External AST Interface ---*- 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 declares the ExternalASTMerger, which vends a combination of ASTs
//  from several different ASTContext/FileManager pairs
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_CLANG_AST_EXTERNALASTMERGER_H
#define LLVM_CLANG_AST_EXTERNALASTMERGER_H

#include "clang/AST/ASTImporter.h"
#include "clang/AST/ASTImporterSharedState.h"
#include "clang/AST/ExternalASTSource.h"
#include "llvm/Support/raw_ostream.h"

namespace clang {

/// ExternalASTSource implementation that merges information from several
/// ASTContexts.
///
/// ExternalASTMerger maintains a vector of ASTImporters that it uses to import
/// (potentially incomplete) Decls and DeclContexts from the source ASTContexts
/// in response to ExternalASTSource API calls.
///
/// When lookup occurs in the resulting imported DeclContexts, the original
/// DeclContexts need to be queried.  Roughly, there are three cases here:
///
/// - The DeclContext of origin can be found by simple name lookup.  In this
///   case, no additional state is required.
///
/// - The DeclContext of origin is different from what would be found by name
///   lookup.  In this case, Origins contains an entry overriding lookup and
///   specifying the correct pair of DeclContext/ASTContext.
///
/// - The DeclContext of origin was determined by another ExternalASTMerger.
///   (This is possible when the source ASTContext for one of the Importers has
///   its own ExternalASTMerger).  The origin must be properly forwarded in this
///   case.
///
/// ExternalASTMerger's job is to maintain the data structures necessary to
/// allow this.  The data structures themselves can be extracted (read-only) and
/// copied for re-use.
class ExternalASTMerger : public ExternalASTSource { … };

} // end namespace clang

#endif