clang-tools  3.8.0
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 namespace clang {
18 
19 using namespace ast_matchers;
20 
21 namespace {
22 
23 template <typename T>
24 StringRef getText(const ast_matchers::MatchFinder::MatchResult &Result,
25  T const &Node) {
26  return Lexer::getSourceText(
27  CharSourceRange::getTokenRange(Node.getSourceRange()),
28  *Result.SourceManager, Result.Context->getLangOpts());
29 }
30 
31 // Return true if expr needs to be put in parens when it is an argument of a
32 // prefix unary operator, e.g. when it is a binary or ternary operator
33 // syntactically.
34 bool needParensAfterUnaryOperator(const Expr &ExprNode) {
35  if (isa<clang::BinaryOperator>(&ExprNode) ||
36  isa<clang::ConditionalOperator>(&ExprNode)) {
37  return true;
38  }
39  if (const auto *Op = dyn_cast<CXXOperatorCallExpr>(&ExprNode)) {
40  return Op->getNumArgs() == 2 && Op->getOperator() != OO_PlusPlus &&
41  Op->getOperator() != OO_MinusMinus && Op->getOperator() != OO_Call &&
42  Op->getOperator() != OO_Subscript;
43  }
44  return false;
45 }
46 
47 // Format a pointer to an expression: prefix with '*' but simplify
48 // when it already begins with '&'. Return empty string on failure.
49 std::string
50 formatDereference(const ast_matchers::MatchFinder::MatchResult &Result,
51  const Expr &ExprNode) {
52  if (const auto *Op = dyn_cast<clang::UnaryOperator>(&ExprNode)) {
53  if (Op->getOpcode() == UO_AddrOf) {
54  // Strip leading '&'.
55  return getText(Result, *Op->getSubExpr()->IgnoreParens());
56  }
57  }
58  StringRef Text = getText(Result, ExprNode);
59  if (Text.empty())
60  return std::string();
61  // Add leading '*'.
62  if (needParensAfterUnaryOperator(ExprNode)) {
63  return (llvm::Twine("*(") + Text + ")").str();
64  }
65  return (llvm::Twine("*") + Text).str();
66 }
67 
68 const char StringConstructor[] =
69  "::std::basic_string<char, std::char_traits<char>, std::allocator<char> >"
70  "::basic_string";
71 
72 const char StringCStrMethod[] =
73  "::std::basic_string<char, std::char_traits<char>, std::allocator<char> >"
74  "::c_str";
75 
76 } // end namespace
77 
78 namespace tidy {
79 namespace readability {
80 
81 void RedundantStringCStrCheck::registerMatchers(
82  ast_matchers::MatchFinder *Finder) {
83  // Only register the matchers for C++; the functionality currently does not
84  // provide any benefit to other languages, despite being benign.
85  if (!getLangOpts().CPlusPlus)
86  return;
87 
88  Finder->addMatcher(
89  cxxConstructExpr(
90  hasDeclaration(cxxMethodDecl(hasName(StringConstructor))),
91  argumentCountIs(2),
92  // The first argument must have the form x.c_str() or p->c_str()
93  // where the method is string::c_str(). We can use the copy
94  // constructor of string instead (or the compiler might share
95  // the string object).
96  hasArgument(0, cxxMemberCallExpr(
97  callee(memberExpr().bind("member")),
98  callee(cxxMethodDecl(hasName(StringCStrMethod))),
99  on(expr().bind("arg")))
100  .bind("call")),
101  // The second argument is the alloc object which must not be
102  // present explicitly.
103  hasArgument(1, cxxDefaultArgExpr())),
104  this);
105  Finder->addMatcher(
106  cxxConstructExpr(
107  // Implicit constructors of these classes are overloaded
108  // wrt. string types and they internally make a StringRef
109  // referring to the argument. Passing a string directly to
110  // them is preferred to passing a char pointer.
111  hasDeclaration(
112  cxxMethodDecl(anyOf(hasName("::llvm::StringRef::StringRef"),
113  hasName("::llvm::Twine::Twine")))),
114  argumentCountIs(1),
115  // The only argument must have the form x.c_str() or p->c_str()
116  // where the method is string::c_str(). StringRef also has
117  // a constructor from string which is more efficient (avoids
118  // strlen), so we can construct StringRef from the string
119  // directly.
120  hasArgument(0, cxxMemberCallExpr(
121  callee(memberExpr().bind("member")),
122  callee(cxxMethodDecl(hasName(StringCStrMethod))),
123  on(expr().bind("arg")))
124  .bind("call"))),
125  this);
126 }
127 
128 void RedundantStringCStrCheck::check(const MatchFinder::MatchResult &Result) {
129  const auto *Call = Result.Nodes.getStmtAs<CallExpr>("call");
130  const auto *Arg = Result.Nodes.getStmtAs<Expr>("arg");
131  bool Arrow = Result.Nodes.getStmtAs<MemberExpr>("member")->isArrow();
132  // Replace the "call" node with the "arg" node, prefixed with '*'
133  // if the call was using '->' rather than '.'.
134  std::string ArgText =
135  Arrow ? formatDereference(Result, *Arg) : getText(Result, *Arg).str();
136  if (ArgText.empty())
137  return;
138 
139  diag(Call->getLocStart(), "redundant call to `c_str()`")
140  << FixItHint::CreateReplacement(Call->getSourceRange(), ArgText);
141 }
142 
143 } // namespace readability
144 } // namespace tidy
145 } // namespace clang
std::unique_ptr< ast_matchers::MatchFinder > Finder
Definition: ClangTidy.cpp:188
const NamedDecl * Result
Definition: USRFinder.cpp:121