ASTMatcher.cpp

class Checker : public clang::ast_matchers::MatchFinder::MatchCallback {
public:
  using MatchResult = clang::ast_matchers::MatchFinder::MatchResult;

  Checker(bool RewriteOption, clang::Rewriter &Rewriter)
      : RewriteOption(RewriteOption), Rewriter(Rewriter) {}

  void run(const MatchResult &Result) {
    const auto *Target = Result.Nodes.getNodeAs<clang::CXXMethodDecl>("target");

    if (!needsOverride(*Target))
      return;

    auto &Diagnostics = Result.Context->getDiagnostics();
    const auto ID =
        Diagnostics.getCustomDiagID(clang::DiagnosticsEngine::Warning,
                                    "method '%0' should be declared override");

    clang::SourceLocation InsertionPoint =
        findInsertionPoint(*Target, *Result.Context);

    clang::DiagnosticBuilder Diagnostic =
        Diagnostics.Report(InsertionPoint, ID);
    Diagnostic.AddString(Target->getName());

    if (RewriteOption) {
      Rewriter.InsertText(InsertionPoint, " override ");
    } else {
      const auto FixIt =
          clang::FixItHint::CreateInsertion(InsertionPoint, "override");
      Diagnostic.AddFixItHint(FixIt);
    }
  }

private:
  bool RewriteOption;

  clang::Rewriter &Rewriter;

  bool needsOverride(const clang::CXXMethodDecl &MethodDecl) {
    if (!MethodDecl.size_overridden_methods())
      return false;
    const auto &Attrs = MethodDecl.getAttrs();
    return std::none_of(Attrs.begin(), Attrs.end(), [](const auto *Attr) {
      return Attr->getSpelling() == "override";
    });
  }

  clang::SourceLocation
  findInsertionPoint(const clang::CXXMethodDecl &MethodDecl,
                     const clang::ASTContext &Context) {
    clang::SourceLocation Location;

    /// Find the end of the parameter list.
    if (MethodDecl.param_empty()) {
      const unsigned Offset = MethodDecl.getName().size();
      Location = MethodDecl.getLocation().getLocWithOffset(Offset);
    } else {
      const clang::ParmVarDecl *Last = *std::prev(MethodDecl.param_end());
      Location = Last->getEndLoc();
    }

    Location = clang::Lexer::findLocationAfterToken(
        Location, clang::tok::r_paren, Context.getSourceManager(),
        Context.getLangOpts(),
        /*skipWhiteSpace=*/true);

    return Location.getLocWithOffset(-1);
  }
};