clang-tools  3.9.0
RedundantStringCStrCheck.cpp
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1 //===- RedundantStringCStrCheck.cpp - Check for redundant c_str calls -----===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements a check for redundant calls of c_str() on strings.
11 //
12 //===----------------------------------------------------------------------===//
13 
15 #include "clang/Lex/Lexer.h"
16 
17 using namespace clang::ast_matchers;
18 
19 namespace clang {
20 namespace tidy {
21 namespace readability {
22 
23 namespace {
24 
25 template <typename T>
26 StringRef getText(const ast_matchers::MatchFinder::MatchResult &Result,
27  T const &Node) {
28  return Lexer::getSourceText(
29  CharSourceRange::getTokenRange(Node.getSourceRange()),
30  *Result.SourceManager, Result.Context->getLangOpts());
31 }
32 
33 // Return true if expr needs to be put in parens when it is an argument of a
34 // prefix unary operator, e.g. when it is a binary or ternary operator
35 // syntactically.
36 bool needParensAfterUnaryOperator(const Expr &ExprNode) {
37  if (isa<clang::BinaryOperator>(&ExprNode) ||
38  isa<clang::ConditionalOperator>(&ExprNode)) {
39  return true;
40  }
41  if (const auto *Op = dyn_cast<CXXOperatorCallExpr>(&ExprNode)) {
42  return Op->getNumArgs() == 2 && Op->getOperator() != OO_PlusPlus &&
43  Op->getOperator() != OO_MinusMinus && Op->getOperator() != OO_Call &&
44  Op->getOperator() != OO_Subscript;
45  }
46  return false;
47 }
48 
49 // Format a pointer to an expression: prefix with '*' but simplify
50 // when it already begins with '&'. Return empty string on failure.
51 std::string
52 formatDereference(const ast_matchers::MatchFinder::MatchResult &Result,
53  const Expr &ExprNode) {
54  if (const auto *Op = dyn_cast<clang::UnaryOperator>(&ExprNode)) {
55  if (Op->getOpcode() == UO_AddrOf) {
56  // Strip leading '&'.
57  return getText(Result, *Op->getSubExpr()->IgnoreParens());
58  }
59  }
60  StringRef Text = getText(Result, ExprNode);
61  if (Text.empty())
62  return std::string();
63  // Add leading '*'.
64  if (needParensAfterUnaryOperator(ExprNode)) {
65  return (llvm::Twine("*(") + Text + ")").str();
66  }
67  return (llvm::Twine("*") + Text).str();
68 }
69 
70 } // end namespace
71 
72 void RedundantStringCStrCheck::registerMatchers(
73  ast_matchers::MatchFinder *Finder) {
74  // Only register the matchers for C++; the functionality currently does not
75  // provide any benefit to other languages, despite being benign.
76  if (!getLangOpts().CPlusPlus)
77  return;
78 
79  // Match expressions of type 'string' or 'string*'.
80  const auto StringDecl =
81  cxxRecordDecl(hasName("::std::basic_string"));
82  const auto StringExpr =
83  expr(anyOf(hasType(StringDecl),
84  hasType(qualType(pointsTo(StringDecl)))));
85 
86  // Match string constructor.
87  const auto StringConstructorExpr = expr(anyOf(
88  cxxConstructExpr(
89  argumentCountIs(1),
90  hasDeclaration(cxxMethodDecl(hasName("basic_string")))),
91  cxxConstructExpr(
92  argumentCountIs(2),
93  hasDeclaration(cxxMethodDecl(hasName("basic_string"))),
94  // If present, the second argument is the alloc object which must not
95  // be present explicitly.
96  hasArgument(1, cxxDefaultArgExpr()))));
97 
98  // Match a call to the string 'c_str()' method.
99  const auto StringCStrCallExpr =
100  cxxMemberCallExpr(on(StringExpr.bind("arg")),
101  callee(memberExpr().bind("member")),
102  callee(cxxMethodDecl(hasName("c_str"))))
103  .bind("call");
104 
105  // Detect redundant 'c_str()' calls through a string constructor.
106  Finder->addMatcher(
107  cxxConstructExpr(StringConstructorExpr,
108  hasArgument(0, StringCStrCallExpr)),
109  this);
110 
111  // Detect: 's == str.c_str()' -> 's == str'
112  Finder->addMatcher(
113  cxxOperatorCallExpr(
114  anyOf(hasOverloadedOperatorName("<"),
115  hasOverloadedOperatorName(">"),
116  hasOverloadedOperatorName(">="),
117  hasOverloadedOperatorName("<="),
118  hasOverloadedOperatorName("!="),
119  hasOverloadedOperatorName("=="),
120  hasOverloadedOperatorName("+")),
121  anyOf(allOf(hasArgument(0, StringExpr),
122  hasArgument(1, StringCStrCallExpr)),
123  allOf(hasArgument(0, StringCStrCallExpr),
124  hasArgument(1, StringExpr)))),
125  this);
126 
127  // Detect: 'dst += str.c_str()' -> 'dst += str'
128  // Detect: 's = str.c_str()' -> 's = str'
129  Finder->addMatcher(
130  cxxOperatorCallExpr(
131  anyOf(hasOverloadedOperatorName("="),
132  hasOverloadedOperatorName("+=")),
133  hasArgument(0, StringExpr),
134  hasArgument(1, StringCStrCallExpr)),
135  this);
136 
137  // Detect: 'dst.append(str.c_str())' -> 'dst.append(str)'
138  Finder->addMatcher(
139  cxxMemberCallExpr(on(StringExpr),
140  callee(decl(cxxMethodDecl(
141  hasAnyName("append", "assign", "compare")))),
142  argumentCountIs(1),
143  hasArgument(0, StringCStrCallExpr)),
144  this);
145 
146  // Detect: 'dst.compare(p, n, str.c_str())' -> 'dst.compare(p, n, str)'
147  Finder->addMatcher(
148  cxxMemberCallExpr(on(StringExpr),
149  callee(decl(cxxMethodDecl(hasName("compare")))),
150  argumentCountIs(3),
151  hasArgument(2, StringCStrCallExpr)),
152  this);
153 
154  // Detect: 'dst.find(str.c_str())' -> 'dst.find(str)'
155  Finder->addMatcher(
156  cxxMemberCallExpr(on(StringExpr),
157  callee(decl(cxxMethodDecl(
158  hasAnyName("find", "find_first_not_of", "find_first_of",
159  "find_last_not_of", "find_last_of", "rfind")))),
160  anyOf(argumentCountIs(1), argumentCountIs(2)),
161  hasArgument(0, StringCStrCallExpr)),
162  this);
163 
164  // Detect: 'dst.insert(pos, str.c_str())' -> 'dst.insert(pos, str)'
165  Finder->addMatcher(
166  cxxMemberCallExpr(on(StringExpr),
167  callee(decl(cxxMethodDecl(hasName("insert")))),
168  argumentCountIs(2),
169  hasArgument(1, StringCStrCallExpr)),
170  this);
171 
172  // Detect redundant 'c_str()' calls through a StringRef constructor.
173  Finder->addMatcher(
174  cxxConstructExpr(
175  // Implicit constructors of these classes are overloaded
176  // wrt. string types and they internally make a StringRef
177  // referring to the argument. Passing a string directly to
178  // them is preferred to passing a char pointer.
179  hasDeclaration(
180  cxxMethodDecl(hasAnyName("::llvm::StringRef::StringRef",
181  "::llvm::Twine::Twine"))),
182  argumentCountIs(1),
183  // The only argument must have the form x.c_str() or p->c_str()
184  // where the method is string::c_str(). StringRef also has
185  // a constructor from string which is more efficient (avoids
186  // strlen), so we can construct StringRef from the string
187  // directly.
188  hasArgument(0, StringCStrCallExpr)),
189  this);
190 }
191 
192 void RedundantStringCStrCheck::check(const MatchFinder::MatchResult &Result) {
193  const auto *Call = Result.Nodes.getStmtAs<CallExpr>("call");
194  const auto *Arg = Result.Nodes.getStmtAs<Expr>("arg");
195  bool Arrow = Result.Nodes.getStmtAs<MemberExpr>("member")->isArrow();
196  // Replace the "call" node with the "arg" node, prefixed with '*'
197  // if the call was using '->' rather than '.'.
198  std::string ArgText =
199  Arrow ? formatDereference(Result, *Arg) : getText(Result, *Arg).str();
200  if (ArgText.empty())
201  return;
202 
203  diag(Call->getLocStart(), "redundant call to `c_str()`")
204  << FixItHint::CreateReplacement(Call->getSourceRange(), ArgText);
205 }
206 
207 } // namespace readability
208 } // namespace tidy
209 } // namespace clang
std::unique_ptr< ast_matchers::MatchFinder > Finder
Definition: ClangTidy.cpp:210
const NamedDecl * Result
Definition: USRFinder.cpp:137