--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/clang-tools-extra/clang-tidy/utils/NamespaceAliaser.cpp	Thu Feb 13 15:10:13 2020 +0900
@@ -0,0 +1,96 @@
+//===---------- NamespaceAliaser.cpp - clang-tidy -------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "NamespaceAliaser.h"
+
+#include "ASTUtils.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/Lex/Lexer.h"
+namespace clang {
+namespace tidy {
+namespace utils {
+
+using namespace ast_matchers;
+
+NamespaceAliaser::NamespaceAliaser(const SourceManager &SourceMgr)
+    : SourceMgr(SourceMgr) {}
+
+AST_MATCHER_P(NamespaceAliasDecl, hasTargetNamespace,
+              ast_matchers::internal::Matcher<NamespaceDecl>, innerMatcher) {
+  return innerMatcher.matches(*Node.getNamespace(), Finder, Builder);
+}
+
+Optional<FixItHint>
+NamespaceAliaser::createAlias(ASTContext &Context, const Stmt &Statement,
+                              StringRef Namespace,
+                              const std::vector<std::string> &Abbreviations) {
+  const FunctionDecl *Function = getSurroundingFunction(Context, Statement);
+  if (!Function || !Function->hasBody())
+    return None;
+
+  if (AddedAliases[Function].count(Namespace.str()) != 0)
+    return None;
+
+  // FIXME: Doesn't consider the order of declarations.
+  // If we accidentally pick an alias defined later in the function,
+  // the output won't compile.
+  // FIXME: Also doesn't consider file or class-scope aliases.
+
+  const auto *ExistingAlias = selectFirst<NamedDecl>(
+      "alias", match(functionDecl(hasBody(compoundStmt(has(declStmt(
+                         has(namespaceAliasDecl(hasTargetNamespace(hasName(
+                                                    std::string(Namespace))))
+                                 .bind("alias"))))))),
+                     *Function, Context));
+
+  if (ExistingAlias != nullptr) {
+    AddedAliases[Function][Namespace.str()] = ExistingAlias->getName().str();
+    return None;
+  }
+
+  for (const auto &Abbreviation : Abbreviations) {
+    DeclarationMatcher ConflictMatcher = namedDecl(hasName(Abbreviation));
+    const auto HasConflictingChildren =
+        !match(findAll(ConflictMatcher), *Function, Context).empty();
+    const auto HasConflictingAncestors =
+        !match(functionDecl(hasAncestor(decl(has(ConflictMatcher)))), *Function,
+               Context)
+             .empty();
+    if (HasConflictingAncestors || HasConflictingChildren)
+      continue;
+
+    std::string Declaration =
+        (llvm::Twine("\nnamespace ") + Abbreviation + " = " + Namespace + ";")
+            .str();
+    SourceLocation Loc =
+        Lexer::getLocForEndOfToken(Function->getBody()->getBeginLoc(), 0,
+                                   SourceMgr, Context.getLangOpts());
+    AddedAliases[Function][Namespace.str()] = Abbreviation;
+    return FixItHint::CreateInsertion(Loc, Declaration);
+  }
+
+  return None;
+}
+
+std::string NamespaceAliaser::getNamespaceName(ASTContext &Context,
+                                               const Stmt &Statement,
+                                               StringRef Namespace) const {
+  const auto *Function = getSurroundingFunction(Context, Statement);
+  auto FunctionAliases = AddedAliases.find(Function);
+  if (FunctionAliases != AddedAliases.end()) {
+    if (FunctionAliases->second.count(Namespace) != 0) {
+      return FunctionAliases->second.find(Namespace)->getValue();
+    }
+  }
+  return Namespace.str();
+}
+
+} // namespace utils
+} // namespace tidy
+} // namespace clang