clang-tools  10.0.0git
RedundantStringCStrCheck.cpp
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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 
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 tooling::fixit::getText(*Op->getSubExpr()->IgnoreParens(),
50  *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 } // end namespace
65 
66 void RedundantStringCStrCheck::registerMatchers(
67  ast_matchers::MatchFinder *Finder) {
68  // Only register the matchers for C++; the functionality currently does not
69  // provide any benefit to other languages, despite being benign.
70  if (!getLangOpts().CPlusPlus)
71  return;
72 
73  // Match expressions of type 'string' or 'string*'.
74  const auto StringDecl = type(hasUnqualifiedDesugaredType(recordType(
75  hasDeclaration(cxxRecordDecl(hasName("::std::basic_string"))))));
76  const auto StringExpr =
77  expr(anyOf(hasType(StringDecl), hasType(qualType(pointsTo(StringDecl)))));
78 
79  // Match string constructor.
80  const auto StringConstructorExpr = expr(anyOf(
81  cxxConstructExpr(argumentCountIs(1),
82  hasDeclaration(cxxMethodDecl(hasName("basic_string")))),
83  cxxConstructExpr(
84  argumentCountIs(2),
85  hasDeclaration(cxxMethodDecl(hasName("basic_string"))),
86  // If present, the second argument is the alloc object which must not
87  // be present explicitly.
88  hasArgument(1, cxxDefaultArgExpr()))));
89 
90  // Match a call to the string 'c_str()' method.
91  const auto StringCStrCallExpr =
92  cxxMemberCallExpr(on(StringExpr.bind("arg")),
93  callee(memberExpr().bind("member")),
94  callee(cxxMethodDecl(hasAnyName("c_str", "data"))))
95  .bind("call");
96 
97  // Detect redundant 'c_str()' calls through a string constructor.
98  Finder->addMatcher(cxxConstructExpr(StringConstructorExpr,
99  hasArgument(0, StringCStrCallExpr)),
100  this);
101 
102  // Detect: 's == str.c_str()' -> 's == str'
103  Finder->addMatcher(
104  cxxOperatorCallExpr(
105  anyOf(
106  hasOverloadedOperatorName("<"), hasOverloadedOperatorName(">"),
107  hasOverloadedOperatorName(">="), hasOverloadedOperatorName("<="),
108  hasOverloadedOperatorName("!="), hasOverloadedOperatorName("=="),
109  hasOverloadedOperatorName("+")),
110  anyOf(allOf(hasArgument(0, StringExpr),
111  hasArgument(1, StringCStrCallExpr)),
112  allOf(hasArgument(0, StringCStrCallExpr),
113  hasArgument(1, StringExpr)))),
114  this);
115 
116  // Detect: 'dst += str.c_str()' -> 'dst += str'
117  // Detect: 's = str.c_str()' -> 's = str'
118  Finder->addMatcher(cxxOperatorCallExpr(anyOf(hasOverloadedOperatorName("="),
119  hasOverloadedOperatorName("+=")),
120  hasArgument(0, StringExpr),
121  hasArgument(1, StringCStrCallExpr)),
122  this);
123 
124  // Detect: 'dst.append(str.c_str())' -> 'dst.append(str)'
125  Finder->addMatcher(
126  cxxMemberCallExpr(on(StringExpr), callee(decl(cxxMethodDecl(hasAnyName(
127  "append", "assign", "compare")))),
128  argumentCountIs(1), hasArgument(0, StringCStrCallExpr)),
129  this);
130 
131  // Detect: 'dst.compare(p, n, str.c_str())' -> 'dst.compare(p, n, str)'
132  Finder->addMatcher(
133  cxxMemberCallExpr(on(StringExpr),
134  callee(decl(cxxMethodDecl(hasName("compare")))),
135  argumentCountIs(3), hasArgument(2, StringCStrCallExpr)),
136  this);
137 
138  // Detect: 'dst.find(str.c_str())' -> 'dst.find(str)'
139  Finder->addMatcher(
140  cxxMemberCallExpr(on(StringExpr),
141  callee(decl(cxxMethodDecl(hasAnyName(
142  "find", "find_first_not_of", "find_first_of",
143  "find_last_not_of", "find_last_of", "rfind")))),
144  anyOf(argumentCountIs(1), argumentCountIs(2)),
145  hasArgument(0, StringCStrCallExpr)),
146  this);
147 
148  // Detect: 'dst.insert(pos, str.c_str())' -> 'dst.insert(pos, str)'
149  Finder->addMatcher(
150  cxxMemberCallExpr(on(StringExpr),
151  callee(decl(cxxMethodDecl(hasName("insert")))),
152  argumentCountIs(2), hasArgument(1, StringCStrCallExpr)),
153  this);
154 
155  // Detect redundant 'c_str()' calls through a StringRef constructor.
156  Finder->addMatcher(
157  cxxConstructExpr(
158  // Implicit constructors of these classes are overloaded
159  // wrt. string types and they internally make a StringRef
160  // referring to the argument. Passing a string directly to
161  // them is preferred to passing a char pointer.
162  hasDeclaration(cxxMethodDecl(hasAnyName(
163  "::llvm::StringRef::StringRef", "::llvm::Twine::Twine"))),
164  argumentCountIs(1),
165  // The only argument must have the form x.c_str() or p->c_str()
166  // where the method is string::c_str(). StringRef also has
167  // a constructor from string which is more efficient (avoids
168  // strlen), so we can construct StringRef from the string
169  // directly.
170  hasArgument(0, StringCStrCallExpr)),
171  this);
172 }
173 
174 void RedundantStringCStrCheck::check(const MatchFinder::MatchResult &Result) {
175  const auto *Call = Result.Nodes.getNodeAs<CallExpr>("call");
176  const auto *Arg = Result.Nodes.getNodeAs<Expr>("arg");
177  const auto *Member = Result.Nodes.getNodeAs<MemberExpr>("member");
178  bool Arrow = Member->isArrow();
179  // Replace the "call" node with the "arg" node, prefixed with '*'
180  // if the call was using '->' rather than '.'.
181  std::string ArgText =
182  Arrow ? formatDereference(Result, *Arg)
183  : tooling::fixit::getText(*Arg, *Result.Context).str();
184  if (ArgText.empty())
185  return;
186 
187  diag(Call->getBeginLoc(), "redundant call to %0")
188  << Member->getMemberDecl()
189  << FixItHint::CreateReplacement(Call->getSourceRange(), ArgText);
190 }
191 
192 } // namespace readability
193 } // namespace tidy
194 } // namespace clang
std::string Text
===– Representation.cpp - ClangDoc Representation --------—*- C++ -*-===//