//===--- UnusedUsingDeclsCheck.h - clang-tidy--------------------*- 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_TOOLS_EXTRA_CLANG_TIDY_MISC_UNUSED_USING_DECLS_H
#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MISC_UNUSED_USING_DECLS_H

#include "../ClangTidyCheck.h"
#include "../utils/FileExtensionsUtils.h"
#include "llvm/ADT/SmallPtrSet.h"
#include <vector>

namespace clang::tidy::misc {

/// Finds unused using declarations.
///
/// For the user-facing documentation see:
/// http://clang.llvm.org/extra/clang-tidy/checks/misc/unused-using-decls.html
class UnusedUsingDeclsCheck : public ClangTidyCheck {
public:
  UnusedUsingDeclsCheck(StringRef Name, ClangTidyContext *Context);
  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
  void onEndOfTranslationUnit() override;
  bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
    return LangOpts.CPlusPlus;
  }

private:
  void removeFromFoundDecls(const Decl *D);

  struct UsingDeclContext {
    explicit UsingDeclContext(const UsingDecl *FoundUsingDecl)
        : FoundUsingDecl(FoundUsingDecl) {}
    // A set saves all UsingShadowDecls introduced by a UsingDecl. A UsingDecl
    // can introduce multiple UsingShadowDecls in some cases (such as
    // overloaded functions).
    llvm::SmallPtrSet<const Decl *, 4> UsingTargetDecls;
    // The original UsingDecl.
    const UsingDecl *FoundUsingDecl;
    // The source range of the UsingDecl.
    CharSourceRange UsingDeclRange;
    // Whether the UsingDecl is used.
    bool IsUsed = false;
  };

  std::vector<UsingDeclContext> Contexts;
  llvm::SmallPtrSet<const Decl *, 32> UsingTargetDeclsCache;

  FileExtensionsSet HeaderFileExtensions;
};

} // namespace clang::tidy::misc

#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MISC_UNUSED_USING_DECLS_H
