clang-tools  7.0.0
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 = type(hasUnqualifiedDesugaredType(recordType(
81  hasDeclaration(cxxRecordDecl(hasName("::std::basic_string"))))));
82  const auto StringExpr =
83  expr(anyOf(hasType(StringDecl), hasType(qualType(pointsTo(StringDecl)))));
84 
85  // Match string constructor.
86  const auto StringConstructorExpr = expr(anyOf(
87  cxxConstructExpr(argumentCountIs(1),
88  hasDeclaration(cxxMethodDecl(hasName("basic_string")))),
89  cxxConstructExpr(
90  argumentCountIs(2),
91  hasDeclaration(cxxMethodDecl(hasName("basic_string"))),
92  // If present, the second argument is the alloc object which must not
93  // be present explicitly.
94  hasArgument(1, cxxDefaultArgExpr()))));
95 
96  // Match a call to the string 'c_str()' method.
97  const auto StringCStrCallExpr =
98  cxxMemberCallExpr(on(StringExpr.bind("arg")),
99  callee(memberExpr().bind("member")),
100  callee(cxxMethodDecl(hasAnyName("c_str", "data"))))
101  .bind("call");
102 
103  // Detect redundant 'c_str()' calls through a string constructor.
104  Finder->addMatcher(cxxConstructExpr(StringConstructorExpr,
105  hasArgument(0, StringCStrCallExpr)),
106  this);
107 
108  // Detect: 's == str.c_str()' -> 's == str'
109  Finder->addMatcher(
110  cxxOperatorCallExpr(
111  anyOf(
112  hasOverloadedOperatorName("<"), hasOverloadedOperatorName(">"),
113  hasOverloadedOperatorName(">="), hasOverloadedOperatorName("<="),
114  hasOverloadedOperatorName("!="), hasOverloadedOperatorName("=="),
115  hasOverloadedOperatorName("+")),
116  anyOf(allOf(hasArgument(0, StringExpr),
117  hasArgument(1, StringCStrCallExpr)),
118  allOf(hasArgument(0, StringCStrCallExpr),
119  hasArgument(1, StringExpr)))),
120  this);
121 
122  // Detect: 'dst += str.c_str()' -> 'dst += str'
123  // Detect: 's = str.c_str()' -> 's = str'
124  Finder->addMatcher(cxxOperatorCallExpr(anyOf(hasOverloadedOperatorName("="),
125  hasOverloadedOperatorName("+=")),
126  hasArgument(0, StringExpr),
127  hasArgument(1, StringCStrCallExpr)),
128  this);
129 
130  // Detect: 'dst.append(str.c_str())' -> 'dst.append(str)'
131  Finder->addMatcher(
132  cxxMemberCallExpr(on(StringExpr), callee(decl(cxxMethodDecl(hasAnyName(
133  "append", "assign", "compare")))),
134  argumentCountIs(1), hasArgument(0, StringCStrCallExpr)),
135  this);
136 
137  // Detect: 'dst.compare(p, n, str.c_str())' -> 'dst.compare(p, n, str)'
138  Finder->addMatcher(
139  cxxMemberCallExpr(on(StringExpr),
140  callee(decl(cxxMethodDecl(hasName("compare")))),
141  argumentCountIs(3), hasArgument(2, StringCStrCallExpr)),
142  this);
143 
144  // Detect: 'dst.find(str.c_str())' -> 'dst.find(str)'
145  Finder->addMatcher(
146  cxxMemberCallExpr(on(StringExpr),
147  callee(decl(cxxMethodDecl(hasAnyName(
148  "find", "find_first_not_of", "find_first_of",
149  "find_last_not_of", "find_last_of", "rfind")))),
150  anyOf(argumentCountIs(1), argumentCountIs(2)),
151  hasArgument(0, StringCStrCallExpr)),
152  this);
153 
154  // Detect: 'dst.insert(pos, str.c_str())' -> 'dst.insert(pos, str)'
155  Finder->addMatcher(
156  cxxMemberCallExpr(on(StringExpr),
157  callee(decl(cxxMethodDecl(hasName("insert")))),
158  argumentCountIs(2), hasArgument(1, StringCStrCallExpr)),
159  this);
160 
161  // Detect redundant 'c_str()' calls through a StringRef constructor.
162  Finder->addMatcher(
163  cxxConstructExpr(
164  // Implicit constructors of these classes are overloaded
165  // wrt. string types and they internally make a StringRef
166  // referring to the argument. Passing a string directly to
167  // them is preferred to passing a char pointer.
168  hasDeclaration(cxxMethodDecl(hasAnyName(
169  "::llvm::StringRef::StringRef", "::llvm::Twine::Twine"))),
170  argumentCountIs(1),
171  // The only argument must have the form x.c_str() or p->c_str()
172  // where the method is string::c_str(). StringRef also has
173  // a constructor from string which is more efficient (avoids
174  // strlen), so we can construct StringRef from the string
175  // directly.
176  hasArgument(0, StringCStrCallExpr)),
177  this);
178 }
179 
180 void RedundantStringCStrCheck::check(const MatchFinder::MatchResult &Result) {
181  const auto *Call = Result.Nodes.getNodeAs<CallExpr>("call");
182  const auto *Arg = Result.Nodes.getNodeAs<Expr>("arg");
183  const auto *Member = Result.Nodes.getNodeAs<MemberExpr>("member");
184  bool Arrow = Member->isArrow();
185  // Replace the "call" node with the "arg" node, prefixed with '*'
186  // if the call was using '->' rather than '.'.
187  std::string ArgText =
188  Arrow ? formatDereference(Result, *Arg) : getText(Result, *Arg).str();
189  if (ArgText.empty())
190  return;
191 
192  diag(Call->getLocStart(), "redundant call to %0")
193  << Member->getMemberDecl()
194  << FixItHint::CreateReplacement(Call->getSourceRange(), ArgText);
195 }
196 
197 } // namespace readability
198 } // namespace tidy
199 } // namespace clang
===– Representation.cpp - ClangDoc Representation --------—*- C++ -*-===//