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//===- RedundantStringCStrCheck.cpp - Check for redundant c_str calls -----===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements a check for redundant calls of c_str() on strings.
//
//===----------------------------------------------------------------------===//
#include "RedundantStringCStrCheck.h"
#include "clang/Lex/Lexer.h"
namespace clang {
using namespace ast_matchers;
namespace {
template <typename T>
StringRef getText(const ast_matchers::MatchFinder::MatchResult &Result,
T const &Node) {
return Lexer::getSourceText(
CharSourceRange::getTokenRange(Node.getSourceRange()),
*Result.SourceManager, Result.Context->getLangOpts());
}
// 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 getText(Result, *Op->getSubExpr()->IgnoreParens());
}
}
StringRef Text = getText(Result, ExprNode);
if (Text.empty())
return std::string();
// Add leading '*'.
if (needParensAfterUnaryOperator(ExprNode)) {
return (llvm::Twine("*(") + Text + ")").str();
}
return (llvm::Twine("*") + Text).str();
}
const char StringConstructor[] =
"::std::basic_string<char, std::char_traits<char>, std::allocator<char> >"
"::basic_string";
const char StringCStrMethod[] =
"::std::basic_string<char, std::char_traits<char>, std::allocator<char> >"
"::c_str";
} // end namespace
namespace tidy {
namespace readability {
void RedundantStringCStrCheck::registerMatchers(
ast_matchers::MatchFinder *Finder) {
// Only register the matchers for C++; the functionality currently does not
// provide any benefit to other languages, despite being benign.
if (!getLangOpts().CPlusPlus)
return;
Finder->addMatcher(
constructExpr(
hasDeclaration(methodDecl(hasName(StringConstructor))),
argumentCountIs(2),
// The first argument must have the form x.c_str() or p->c_str()
// where the method is string::c_str(). We can use the copy
// constructor of string instead (or the compiler might share
// the string object).
hasArgument(
0, memberCallExpr(callee(memberExpr().bind("member")),
callee(methodDecl(hasName(StringCStrMethod))),
on(expr().bind("arg"))).bind("call")),
// The second argument is the alloc object which must not be
// present explicitly.
hasArgument(1, defaultArgExpr())),
this);
Finder->addMatcher(
constructExpr(
// 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(
methodDecl(anyOf(hasName("::llvm::StringRef::StringRef"),
hasName("::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, memberCallExpr(callee(memberExpr().bind("member")),
callee(methodDecl(hasName(StringCStrMethod))),
on(expr().bind("arg"))).bind("call"))),
this);
}
void RedundantStringCStrCheck::check(const MatchFinder::MatchResult &Result) {
const auto *Call = Result.Nodes.getStmtAs<CallExpr>("call");
const auto *Arg = Result.Nodes.getStmtAs<Expr>("arg");
bool Arrow = Result.Nodes.getStmtAs<MemberExpr>("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) : getText(Result, *Arg).str();
if (ArgText.empty())
return;
diag(Call->getLocStart(), "redundant call to `c_str()`")
<< FixItHint::CreateReplacement(Call->getSourceRange(), ArgText);
}
} // namespace readability
} // namespace tidy
} // namespace clang
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