================ @@ -0,0 +1,129 @@ +//===----------------------------------------------------------------------===// +// +// 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 "SubstrSelfAssignmentCheck.h" +#include "../utils/Matchers.h" +#include "../utils/OptionsUtils.h" +#include "clang/AST/ASTContext.h" +#include "clang/AST/ExprCXX.h" +#include "clang/ASTMatchers/ASTMatchFinder.h" +#include "clang/Lex/Lexer.h" +#include <optional> +#include <string> + +using namespace clang::ast_matchers; + +namespace clang::tidy::performance { + +SubstrSelfAssignmentCheck::SubstrSelfAssignmentCheck(StringRef Name, + ClangTidyContext *Context) + : ClangTidyCheck(Name, Context), + StringLikeClasses(utils::options::parseStringList( + Options.get("StringLikeClasses", "::std::basic_string"))) {} + +void SubstrSelfAssignmentCheck::storeOptions( + ClangTidyOptions::OptionMap &Opts) { + Options.store(Opts, "StringLikeClasses", + utils::options::serializeStringList(StringLikeClasses)); +} + +void SubstrSelfAssignmentCheck::registerMatchers(MatchFinder *Finder) { + const auto VarRef = + ignoringParens(declRefExpr(to(varDecl().bind("var"))).bind("lhs")); + + const auto StringClass = + cxxRecordDecl(hasAnyName(StringLikeClasses)).bind("string-class"); + + // The static member 'npos' of the matched string class. A bare name + // comparison is not enough: a local variable or parameter that happens to + // be called 'npos' carries a real count, which has no single-'erase' + // rewrite. + const auto NposDecl = + varDecl(hasName("npos"), + hasDeclContext(cxxRecordDecl(equalsBoundNode("string-class")))); + + const auto Npos = + expr(ignoringParenImpCasts(anyOf(declRefExpr(hasDeclaration(NposDecl)), + memberExpr(hasDeclaration(NposDecl))))); + + const auto SubstrCall = + cxxMemberCallExpr( + callee(cxxMethodDecl(hasName("substr"), ofClass(StringClass))), + on(ignoringParens(declRefExpr(to(varDecl(equalsBoundNode("var")))))), + optionally(hasArgument(1, Npos.bind("npos-count")))) + .bind("substr"); + + // Match: s = s.substr(...), except in unevaluated contexts such as + // decltype or sizeof, where no temporary is ever materialized. + Finder->addMatcher( + cxxOperatorCallExpr( + hasOperatorName("="), hasArgument(0, VarRef), + hasArgument(1, SubstrCall), + unless(anyOf(hasAncestor(typeLoc()), + hasAncestor(expr(matchers::hasUnevaluatedContext()))))) + .bind("assign"), + this); +} + +void SubstrSelfAssignmentCheck::check(const MatchFinder::MatchResult &Result) { + const auto *AssignExpr = + Result.Nodes.getNodeAs<CXXOperatorCallExpr>("assign"); + const auto *LHS = Result.Nodes.getNodeAs<DeclRefExpr>("lhs"); + const auto *SubstrExpr = Result.Nodes.getNodeAs<CXXMemberCallExpr>("substr"); + const SourceManager &SM = *Result.SourceManager; + const LangOptions &LangOpts = Result.Context->getLangOpts(); + + // Count only explicitly-written arguments (exclude CXXDefaultArgExpr). + unsigned NumExplicitArgs = 0; + for (const Expr *Arg : SubstrExpr->arguments()) + if (!isa<CXXDefaultArgExpr>(Arg)) + ++NumExplicitArgs; + + // s = s.substr(pos) and s = s.substr(pos, npos) strip a prefix and can be + // rewritten as s.erase(0, pos). The truncation form s = s.substr(0, count) + // is diagnosed without a fix-it: s.erase(count) throws std::out_of_range + // for count > s.size() where substr merely clamps. The general + // two-argument form has no single-'erase' equivalent and is ignored. + // TODO: Also emit a fix-it for the truncation form when + // `count <= size()` can be proven. + const bool IsPrefixStrip = + NumExplicitArgs == 1 || + (NumExplicitArgs == 2 && + Result.Nodes.getNodeAs<Expr>("npos-count") != nullptr); + bool IsTruncation = false; + if (!IsPrefixStrip && NumExplicitArgs == 2) { + const auto *PosLiteral = + dyn_cast<IntegerLiteral>(SubstrExpr->getArg(0)->IgnoreParenImpCasts()); + IsTruncation = PosLiteral && PosLiteral->getValue() == 0; + } + if (!IsPrefixStrip && !IsTruncation) + return; + + // Rewriting a macro expansion is unsafe; emit the warning without a fix-it. + // TODO: Only emit this fix-it when `pos <= size()` can be proven. + std::optional<std::string> Replacement; + if (IsPrefixStrip && !AssignExpr->getBeginLoc().isMacroID() && + !AssignExpr->getEndLoc().isMacroID()) { + StringRef VarName = Lexer::getSourceText( + CharSourceRange::getTokenRange(LHS->getSourceRange()), SM, LangOpts); + StringRef PosText = Lexer::getSourceText( + CharSourceRange::getTokenRange(SubstrExpr->getArg(0)->getSourceRange()), + SM, LangOpts); + if (!VarName.empty() && !PosText.empty()) + Replacement = (VarName + ".erase(0, " + PosText + ")").str(); + } + + auto Diag = diag(AssignExpr->getOperatorLoc(), + "inefficient self-assignment via 'substr'; use 'erase' to " + "modify the string in-place"); + if (Replacement) + Diag << FixItHint::CreateReplacement(AssignExpr->getSourceRange(), + *Replacement); ---------------- zwuis wrote:
It's up to you, but we can use functions in `clang/Tooling/FixIt.h`. https://github.com/llvm/llvm-project/pull/209657 _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
