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 "clang/Lex/Lexer.h"
15 #include "clang/Tooling/FixIt.h"
16 
17 using namespace clang::ast_matchers;
18 
19 namespace clang {
20 namespace tidy {
21 namespace readability {
22 
23 namespace {
24 
25 // Return true if expr needs to be put in parens when it is an argument of a
26 // prefix unary operator, e.g. when it is a binary or ternary operator
27 // syntactically.
28 bool needParensAfterUnaryOperator(const Expr &ExprNode) {
29   if (isa<clang::BinaryOperator>(&ExprNode) ||
30       isa<clang::ConditionalOperator>(&ExprNode)) {
31     return true;
32   }
33   if (const auto *Op = dyn_cast<CXXOperatorCallExpr>(&ExprNode)) {
34     return Op->getNumArgs() == 2 && Op->getOperator() != OO_PlusPlus &&
35            Op->getOperator() != OO_MinusMinus && Op->getOperator() != OO_Call &&
36            Op->getOperator() != OO_Subscript;
37   }
38   return false;
39 }
40 
41 // Format a pointer to an expression: prefix with '*' but simplify
42 // when it already begins with '&'.  Return empty string on failure.
43 std::string
44 formatDereference(const ast_matchers::MatchFinder::MatchResult &Result,
45                   const Expr &ExprNode) {
46   if (const auto *Op = dyn_cast<clang::UnaryOperator>(&ExprNode)) {
47     if (Op->getOpcode() == UO_AddrOf) {
48       // Strip leading '&'.
49       return std::string(tooling::fixit::getText(
50           *Op->getSubExpr()->IgnoreParens(), *Result.Context));
51     }
52   }
53   StringRef Text = tooling::fixit::getText(ExprNode, *Result.Context);
54 
55   if (Text.empty())
56     return std::string();
57   // Add leading '*'.
58   if (needParensAfterUnaryOperator(ExprNode)) {
59     return (llvm::Twine("*(") + Text + ")").str();
60   }
61   return (llvm::Twine("*") + Text).str();
62 }
63 
64 AST_MATCHER(MaterializeTemporaryExpr, isBoundToLValue) {
65   return Node.isBoundToLvalueReference();
66 }
67 
68 } // end namespace
69 
70 void RedundantStringCStrCheck::registerMatchers(
71     ast_matchers::MatchFinder *Finder) {
72   // Match expressions of type 'string' or 'string*'.
73   const auto StringDecl = type(hasUnqualifiedDesugaredType(recordType(
74       hasDeclaration(cxxRecordDecl(hasName("::std::basic_string"))))));
75   const auto StringExpr =
76       expr(anyOf(hasType(StringDecl), hasType(qualType(pointsTo(StringDecl)))));
77 
78   // Match string constructor.
79   const auto StringConstructorExpr = expr(anyOf(
80       cxxConstructExpr(argumentCountIs(1),
81                        hasDeclaration(cxxMethodDecl(hasName("basic_string")))),
82       cxxConstructExpr(
83           argumentCountIs(2),
84           hasDeclaration(cxxMethodDecl(hasName("basic_string"))),
85           // If present, the second argument is the alloc object which must not
86           // be present explicitly.
87           hasArgument(1, cxxDefaultArgExpr()))));
88 
89   // Match a call to the string 'c_str()' method.
90   const auto StringCStrCallExpr =
91       cxxMemberCallExpr(on(StringExpr.bind("arg")),
92                         callee(memberExpr().bind("member")),
93                         callee(cxxMethodDecl(hasAnyName("c_str", "data"))))
94           .bind("call");
95   const auto HasRValueTempParent =
96       hasParent(materializeTemporaryExpr(unless(isBoundToLValue())));
97   // Detect redundant 'c_str()' calls through a string constructor.
98   // If CxxConstructExpr is the part of some CallExpr we need to
99   // check that matched ParamDecl of the ancestor CallExpr is not rvalue.
100   Finder->addMatcher(
101       traverse(
102           TK_AsIs,
103           cxxConstructExpr(
104               StringConstructorExpr, hasArgument(0, StringCStrCallExpr),
105               unless(anyOf(HasRValueTempParent, hasParent(cxxBindTemporaryExpr(
106                                                     HasRValueTempParent)))))),
107       this);
108 
109   // Detect: 's == str.c_str()'  ->  's == str'
110   Finder->addMatcher(
111       cxxOperatorCallExpr(
112           hasAnyOverloadedOperatorName("<", ">", ">=", "<=", "!=", "==", "+"),
113           anyOf(allOf(hasArgument(0, StringExpr),
114                       hasArgument(1, StringCStrCallExpr)),
115                 allOf(hasArgument(0, StringCStrCallExpr),
116                       hasArgument(1, StringExpr)))),
117       this);
118 
119   // Detect: 'dst += str.c_str()'  ->  'dst += str'
120   // Detect: 's = str.c_str()'  ->  's = str'
121   Finder->addMatcher(
122       cxxOperatorCallExpr(hasAnyOverloadedOperatorName("=", "+="),
123                           hasArgument(0, StringExpr),
124                           hasArgument(1, StringCStrCallExpr)),
125       this);
126 
127   // Detect: 'dst.append(str.c_str())'  ->  'dst.append(str)'
128   Finder->addMatcher(
129       cxxMemberCallExpr(on(StringExpr), callee(decl(cxxMethodDecl(hasAnyName(
130                                             "append", "assign", "compare")))),
131                         argumentCountIs(1), hasArgument(0, StringCStrCallExpr)),
132       this);
133 
134   // Detect: 'dst.compare(p, n, str.c_str())'  ->  'dst.compare(p, n, str)'
135   Finder->addMatcher(
136       cxxMemberCallExpr(on(StringExpr),
137                         callee(decl(cxxMethodDecl(hasName("compare")))),
138                         argumentCountIs(3), hasArgument(2, StringCStrCallExpr)),
139       this);
140 
141   // Detect: 'dst.find(str.c_str())'  ->  'dst.find(str)'
142   Finder->addMatcher(
143       cxxMemberCallExpr(on(StringExpr),
144                         callee(decl(cxxMethodDecl(hasAnyName(
145                             "find", "find_first_not_of", "find_first_of",
146                             "find_last_not_of", "find_last_of", "rfind")))),
147                         anyOf(argumentCountIs(1), argumentCountIs(2)),
148                         hasArgument(0, StringCStrCallExpr)),
149       this);
150 
151   // Detect: 'dst.insert(pos, str.c_str())'  ->  'dst.insert(pos, str)'
152   Finder->addMatcher(
153       cxxMemberCallExpr(on(StringExpr),
154                         callee(decl(cxxMethodDecl(hasName("insert")))),
155                         argumentCountIs(2), hasArgument(1, StringCStrCallExpr)),
156       this);
157 
158   // Detect redundant 'c_str()' calls through a StringRef constructor.
159   Finder->addMatcher(
160       traverse(
161           TK_AsIs,
162           cxxConstructExpr(
163               // Implicit constructors of these classes are overloaded
164               // wrt. string types and they internally make a StringRef
165               // referring to the argument.  Passing a string directly to
166               // them is preferred to passing a char pointer.
167               hasDeclaration(cxxMethodDecl(hasAnyName(
168                   "::llvm::StringRef::StringRef", "::llvm::Twine::Twine"))),
169               argumentCountIs(1),
170               // The only argument must have the form x.c_str() or p->c_str()
171               // where the method is string::c_str().  StringRef also has
172               // a constructor from string which is more efficient (avoids
173               // strlen), so we can construct StringRef from the string
174               // directly.
175               hasArgument(0, StringCStrCallExpr))),
176       this);
177 }
178 
179 void RedundantStringCStrCheck::check(const MatchFinder::MatchResult &Result) {
180   const auto *Call = Result.Nodes.getNodeAs<CallExpr>("call");
181   const auto *Arg = Result.Nodes.getNodeAs<Expr>("arg");
182   const auto *Member = Result.Nodes.getNodeAs<MemberExpr>("member");
183   bool Arrow = Member->isArrow();
184   // Replace the "call" node with the "arg" node, prefixed with '*'
185   // if the call was using '->' rather than '.'.
186   std::string ArgText =
187       Arrow ? formatDereference(Result, *Arg)
188             : tooling::fixit::getText(*Arg, *Result.Context).str();
189   if (ArgText.empty())
190     return;
191 
192   diag(Call->getBeginLoc(), "redundant call to %0")
193       << Member->getMemberDecl()
194       << FixItHint::CreateReplacement(Call->getSourceRange(), ArgText);
195 }
196 
197 } // namespace readability
198 } // namespace tidy
199 } // namespace clang
200