1//===- RedundantStringCStrCheck.cpp - Check for redundant c_str calls -----===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file implements a check for redundant calls of c_str() on strings.
10//
11//===----------------------------------------------------------------------===//
12
13#include "RedundantStringCStrCheck.h"
14#include "../utils/FixItHintUtils.h"
15#include "../utils/Matchers.h"
16#include "../utils/OptionsUtils.h"
17#include "clang/Lex/Lexer.h"
18#include "clang/Tooling/FixIt.h"
19
20using namespace clang::ast_matchers;
21
22namespace clang::tidy::readability {
23
24namespace {
25
26AST_MATCHER(MaterializeTemporaryExpr, isBoundToLValue) {
27 return Node.isBoundToLvalueReference();
28}
29
30} // end namespace
31
32RedundantStringCStrCheck::RedundantStringCStrCheck(StringRef Name,
33 ClangTidyContext *Context)
34 : ClangTidyCheck(Name, Context),
35 StringParameterFunctions(utils::options::parseStringList(
36 Option: Options.get(LocalName: "StringParameterFunctions", Default: ""))) {
37 if (getLangOpts().CPlusPlus20)
38 StringParameterFunctions.emplace_back(args: "::std::format");
39 if (getLangOpts().CPlusPlus23)
40 StringParameterFunctions.emplace_back(args: "::std::print");
41}
42
43void RedundantStringCStrCheck::registerMatchers(
44 ast_matchers::MatchFinder *Finder) {
45 // Match expressions of type 'string' or 'string*'.
46 const auto StringDecl = type(hasUnqualifiedDesugaredType(InnerMatcher: recordType(
47 hasDeclaration(InnerMatcher: cxxRecordDecl(hasName(Name: "::std::basic_string"))))));
48 const auto StringExpr =
49 expr(anyOf(hasType(InnerMatcher: StringDecl), hasType(InnerMatcher: qualType(pointsTo(InnerMatcher: StringDecl)))));
50
51 // Match string constructor.
52 const auto StringConstructorExpr = expr(anyOf(
53 cxxConstructExpr(argumentCountIs(N: 1),
54 hasDeclaration(InnerMatcher: cxxMethodDecl(hasName(Name: "basic_string")))),
55 cxxConstructExpr(argumentCountIs(N: 2),
56 hasDeclaration(InnerMatcher: cxxMethodDecl(hasName(Name: "basic_string"))),
57 // If present, the second argument is the alloc object
58 // which must not be present explicitly.
59 hasArgument(N: 1, InnerMatcher: cxxDefaultArgExpr()))));
60
61 // Match string constructor.
62 const auto StringViewConstructorExpr = cxxConstructExpr(
63 argumentCountIs(N: 1),
64 hasDeclaration(InnerMatcher: cxxMethodDecl(hasName(Name: "basic_string_view"))));
65
66 // Match a call to the string 'c_str()' method.
67 const auto StringCStrCallExpr =
68 cxxMemberCallExpr(on(InnerMatcher: StringExpr.bind(ID: "arg")),
69 callee(InnerMatcher: memberExpr().bind(ID: "member")),
70 callee(InnerMatcher: cxxMethodDecl(hasAnyName("c_str", "data"))))
71 .bind(ID: "call");
72 const auto HasRValueTempParent =
73 hasParent(materializeTemporaryExpr(unless(isBoundToLValue())));
74 // Detect redundant 'c_str()' calls through a string constructor.
75 // If CxxConstructExpr is the part of some CallExpr we need to
76 // check that matched ParamDecl of the ancestor CallExpr is not rvalue.
77 Finder->addMatcher(
78 NodeMatch: traverse(
79 TK: TK_AsIs,
80 InnerMatcher: cxxConstructExpr(
81 anyOf(StringConstructorExpr, StringViewConstructorExpr),
82 hasArgument(N: 0, InnerMatcher: StringCStrCallExpr),
83 unless(anyOf(HasRValueTempParent, hasParent(cxxBindTemporaryExpr(
84 HasRValueTempParent)))))),
85 Action: this);
86
87 // Detect: 's == str.c_str()' -> 's == str'
88 Finder->addMatcher(
89 NodeMatch: cxxOperatorCallExpr(
90 hasAnyOverloadedOperatorName("<", ">", ">=", "<=", "!=", "==", "+"),
91 anyOf(allOf(hasArgument(N: 0, InnerMatcher: StringExpr),
92 hasArgument(N: 1, InnerMatcher: StringCStrCallExpr)),
93 allOf(hasArgument(N: 0, InnerMatcher: StringCStrCallExpr),
94 hasArgument(N: 1, InnerMatcher: StringExpr)))),
95 Action: this);
96
97 // Detect: 'dst += str.c_str()' -> 'dst += str'
98 // Detect: 's = str.c_str()' -> 's = str'
99 Finder->addMatcher(
100 NodeMatch: cxxOperatorCallExpr(hasAnyOverloadedOperatorName("=", "+="),
101 hasArgument(N: 0, InnerMatcher: StringExpr),
102 hasArgument(N: 1, InnerMatcher: StringCStrCallExpr)),
103 Action: this);
104
105 // Detect: 'dst.append(str.c_str())' -> 'dst.append(str)'
106 Finder->addMatcher(
107 NodeMatch: cxxMemberCallExpr(on(InnerMatcher: StringExpr),
108 callee(InnerMatcher: decl(cxxMethodDecl(
109 hasAnyName("append", "assign", "compare")))),
110 argumentCountIs(N: 1), hasArgument(N: 0, InnerMatcher: StringCStrCallExpr)),
111 Action: this);
112
113 // Detect: 'dst.compare(p, n, str.c_str())' -> 'dst.compare(p, n, str)'
114 Finder->addMatcher(
115 NodeMatch: cxxMemberCallExpr(on(InnerMatcher: StringExpr),
116 callee(InnerMatcher: decl(cxxMethodDecl(hasName(Name: "compare")))),
117 argumentCountIs(N: 3), hasArgument(N: 2, InnerMatcher: StringCStrCallExpr)),
118 Action: this);
119
120 // Detect: 'dst.find(str.c_str())' -> 'dst.find(str)'
121 Finder->addMatcher(
122 NodeMatch: cxxMemberCallExpr(on(InnerMatcher: StringExpr),
123 callee(InnerMatcher: decl(cxxMethodDecl(hasAnyName(
124 "find", "find_first_not_of", "find_first_of",
125 "find_last_not_of", "find_last_of", "rfind")))),
126 anyOf(argumentCountIs(N: 1), argumentCountIs(N: 2)),
127 hasArgument(N: 0, InnerMatcher: StringCStrCallExpr)),
128 Action: this);
129
130 // Detect: 'dst.insert(pos, str.c_str())' -> 'dst.insert(pos, str)'
131 Finder->addMatcher(
132 NodeMatch: cxxMemberCallExpr(on(InnerMatcher: StringExpr),
133 callee(InnerMatcher: decl(cxxMethodDecl(hasName(Name: "insert")))),
134 argumentCountIs(N: 2), hasArgument(N: 1, InnerMatcher: StringCStrCallExpr)),
135 Action: this);
136
137 // Detect redundant 'c_str()' calls through a StringRef constructor.
138 Finder->addMatcher(
139 NodeMatch: traverse(
140 TK: TK_AsIs,
141 InnerMatcher: cxxConstructExpr(
142 // Implicit constructors of these classes are overloaded
143 // wrt. string types and they internally make a StringRef
144 // referring to the argument. Passing a string directly to
145 // them is preferred to passing a char pointer.
146 hasDeclaration(InnerMatcher: cxxMethodDecl(hasAnyName(
147 "::llvm::StringRef::StringRef", "::llvm::Twine::Twine"))),
148 argumentCountIs(N: 1),
149 // The only argument must have the form x.c_str() or p->c_str()
150 // where the method is string::c_str(). StringRef also has
151 // a constructor from string which is more efficient (avoids
152 // strlen), so we can construct StringRef from the string
153 // directly.
154 hasArgument(N: 0, InnerMatcher: StringCStrCallExpr))),
155 Action: this);
156
157 if (!StringParameterFunctions.empty()) {
158 // Detect redundant 'c_str()' calls in parameters passed to std::format in
159 // C++20 onwards and std::print in C++23 onwards.
160 Finder->addMatcher(
161 NodeMatch: traverse(TK: TK_AsIs,
162 InnerMatcher: callExpr(callee(InnerMatcher: functionDecl(matchers::matchesAnyListedName(
163 NameList: StringParameterFunctions))),
164 forEachArgumentWithParam(ArgMatcher: StringCStrCallExpr,
165 ParamMatcher: parmVarDecl()))),
166 Action: this);
167 }
168}
169
170void RedundantStringCStrCheck::check(const MatchFinder::MatchResult &Result) {
171 const auto *Call = Result.Nodes.getNodeAs<CallExpr>(ID: "call");
172 const auto *Arg = Result.Nodes.getNodeAs<Expr>(ID: "arg");
173 const auto *Member = Result.Nodes.getNodeAs<MemberExpr>(ID: "member");
174 bool Arrow = Member->isArrow();
175 // Replace the "call" node with the "arg" node, prefixed with '*'
176 // if the call was using '->' rather than '.'.
177 std::string ArgText =
178 Arrow ? utils::fixit::formatDereference(ExprNode: *Arg, Context: *Result.Context)
179 : tooling::fixit::getText(Node: *Arg, Context: *Result.Context).str();
180 if (ArgText.empty())
181 return;
182
183 diag(Loc: Call->getBeginLoc(), Description: "redundant call to %0")
184 << Member->getMemberDecl()
185 << FixItHint::CreateReplacement(Call->getSourceRange(), ArgText);
186}
187
188} // namespace clang::tidy::readability
189

source code of clang-tools-extra/clang-tidy/readability/RedundantStringCStrCheck.cpp