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//===- RedundantStringCStrCheck.cpp - Check for redundant c_str calls -----===//
//
// 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 implements a check for redundant calls of c_str() on strings.
//
//===----------------------------------------------------------------------===//
#include "RedundantStringCStrCheck.h"
#include "clang/Lex/Lexer.h"
#include "clang/Tooling/FixIt.h"
using namespace clang::ast_matchers;
namespace clang {
namespace tidy {
namespace readability {
namespace {
// Return true if expr needs to be put in parens when it is an argument of a
// prefix unary operator, e.g. when it is a binary or ternary operator
// syntactically.
bool needParensAfterUnaryOperator(const Expr &ExprNode) {
if (isa<clang::BinaryOperator>(&ExprNode) ||
isa<clang::ConditionalOperator>(&ExprNode)) {
return true;
}
if (const auto *Op = dyn_cast<CXXOperatorCallExpr>(&ExprNode)) {
return Op->getNumArgs() == 2 && Op->getOperator() != OO_PlusPlus &&
Op->getOperator() != OO_MinusMinus && Op->getOperator() != OO_Call &&
Op->getOperator() != OO_Subscript;
}
return false;
}
// Format a pointer to an expression: prefix with '*' but simplify
// when it already begins with '&'. Return empty string on failure.
std::string
formatDereference(const ast_matchers::MatchFinder::MatchResult &Result,
const Expr &ExprNode) {
if (const auto *Op = dyn_cast<clang::UnaryOperator>(&ExprNode)) {
if (Op->getOpcode() == UO_AddrOf) {
// Strip leading '&'.
return std::string(tooling::fixit::getText(
*Op->getSubExpr()->IgnoreParens(), *Result.Context));
}
}
StringRef Text = tooling::fixit::getText(ExprNode, *Result.Context);
if (Text.empty())
return std::string();
// Add leading '*'.
if (needParensAfterUnaryOperator(ExprNode)) {
return (llvm::Twine("*(") + Text + ")").str();
}
return (llvm::Twine("*") + Text).str();
}
AST_MATCHER(MaterializeTemporaryExpr, isBoundToLValue) {
return Node.isBoundToLvalueReference();
}
} // end namespace
void RedundantStringCStrCheck::registerMatchers(
ast_matchers::MatchFinder *Finder) {
// Match expressions of type 'string' or 'string*'.
const auto StringDecl = type(hasUnqualifiedDesugaredType(recordType(
hasDeclaration(cxxRecordDecl(hasName("::std::basic_string"))))));
const auto StringExpr =
expr(anyOf(hasType(StringDecl), hasType(qualType(pointsTo(StringDecl)))));
// Match string constructor.
const auto StringConstructorExpr = expr(anyOf(
cxxConstructExpr(argumentCountIs(1),
hasDeclaration(cxxMethodDecl(hasName("basic_string")))),
cxxConstructExpr(
argumentCountIs(2),
hasDeclaration(cxxMethodDecl(hasName("basic_string"))),
// If present, the second argument is the alloc object which must not
// be present explicitly.
hasArgument(1, cxxDefaultArgExpr()))));
// Match a call to the string 'c_str()' method.
const auto StringCStrCallExpr =
cxxMemberCallExpr(on(StringExpr.bind("arg")),
callee(memberExpr().bind("member")),
callee(cxxMethodDecl(hasAnyName("c_str", "data"))))
.bind("call");
const auto HasRValueTempParent =
hasParent(materializeTemporaryExpr(unless(isBoundToLValue())));
// Detect redundant 'c_str()' calls through a string constructor.
// If CxxConstructExpr is the part of some CallExpr we need to
// check that matched ParamDecl of the ancestor CallExpr is not rvalue.
Finder->addMatcher(
traverse(
TK_AsIs,
cxxConstructExpr(
StringConstructorExpr, hasArgument(0, StringCStrCallExpr),
unless(anyOf(HasRValueTempParent, hasParent(cxxBindTemporaryExpr(
HasRValueTempParent)))))),
this);
// Detect: 's == str.c_str()' -> 's == str'
Finder->addMatcher(
cxxOperatorCallExpr(
hasAnyOverloadedOperatorName("<", ">", ">=", "<=", "!=", "==", "+"),
anyOf(allOf(hasArgument(0, StringExpr),
hasArgument(1, StringCStrCallExpr)),
allOf(hasArgument(0, StringCStrCallExpr),
hasArgument(1, StringExpr)))),
this);
// Detect: 'dst += str.c_str()' -> 'dst += str'
// Detect: 's = str.c_str()' -> 's = str'
Finder->addMatcher(
cxxOperatorCallExpr(hasAnyOverloadedOperatorName("=", "+="),
hasArgument(0, StringExpr),
hasArgument(1, StringCStrCallExpr)),
this);
// Detect: 'dst.append(str.c_str())' -> 'dst.append(str)'
Finder->addMatcher(
cxxMemberCallExpr(on(StringExpr), callee(decl(cxxMethodDecl(hasAnyName(
"append", "assign", "compare")))),
argumentCountIs(1), hasArgument(0, StringCStrCallExpr)),
this);
// Detect: 'dst.compare(p, n, str.c_str())' -> 'dst.compare(p, n, str)'
Finder->addMatcher(
cxxMemberCallExpr(on(StringExpr),
callee(decl(cxxMethodDecl(hasName("compare")))),
argumentCountIs(3), hasArgument(2, StringCStrCallExpr)),
this);
// Detect: 'dst.find(str.c_str())' -> 'dst.find(str)'
Finder->addMatcher(
cxxMemberCallExpr(on(StringExpr),
callee(decl(cxxMethodDecl(hasAnyName(
"find", "find_first_not_of", "find_first_of",
"find_last_not_of", "find_last_of", "rfind")))),
anyOf(argumentCountIs(1), argumentCountIs(2)),
hasArgument(0, StringCStrCallExpr)),
this);
// Detect: 'dst.insert(pos, str.c_str())' -> 'dst.insert(pos, str)'
Finder->addMatcher(
cxxMemberCallExpr(on(StringExpr),
callee(decl(cxxMethodDecl(hasName("insert")))),
argumentCountIs(2), hasArgument(1, StringCStrCallExpr)),
this);
// Detect redundant 'c_str()' calls through a StringRef constructor.
Finder->addMatcher(
traverse(
TK_AsIs,
cxxConstructExpr(
// Implicit constructors of these classes are overloaded
// wrt. string types and they internally make a StringRef
// referring to the argument. Passing a string directly to
// them is preferred to passing a char pointer.
hasDeclaration(cxxMethodDecl(hasAnyName(
"::llvm::StringRef::StringRef", "::llvm::Twine::Twine"))),
argumentCountIs(1),
// The only argument must have the form x.c_str() or p->c_str()
// where the method is string::c_str(). StringRef also has
// a constructor from string which is more efficient (avoids
// strlen), so we can construct StringRef from the string
// directly.
hasArgument(0, StringCStrCallExpr))),
this);
}
void RedundantStringCStrCheck::check(const MatchFinder::MatchResult &Result) {
const auto *Call = Result.Nodes.getNodeAs<CallExpr>("call");
const auto *Arg = Result.Nodes.getNodeAs<Expr>("arg");
const auto *Member = Result.Nodes.getNodeAs<MemberExpr>("member");
bool Arrow = Member->isArrow();
// Replace the "call" node with the "arg" node, prefixed with '*'
// if the call was using '->' rather than '.'.
std::string ArgText =
Arrow ? formatDereference(Result, *Arg)
: tooling::fixit::getText(*Arg, *Result.Context).str();
if (ArgText.empty())
return;
diag(Call->getBeginLoc(), "redundant call to %0")
<< Member->getMemberDecl()
<< FixItHint::CreateReplacement(Call->getSourceRange(), ArgText);
}
} // namespace readability
} // namespace tidy
} // namespace clang
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