clang-tools  3.8.0
SwappedArgumentsCheck.cpp
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1 //===--- SwappedArgumentsCheck.cpp - clang-tidy ---------------------------===//
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 #include "SwappedArgumentsCheck.h"
11 #include "clang/AST/ASTContext.h"
12 #include "clang/Lex/Lexer.h"
13 #include "llvm/ADT/SmallPtrSet.h"
14 
15 using namespace clang::ast_matchers;
16 
17 namespace clang {
18 namespace tidy {
19 namespace misc {
20 
21 void SwappedArgumentsCheck::registerMatchers(MatchFinder *Finder) {
22  Finder->addMatcher(callExpr().bind("call"), this);
23 }
24 
25 /// \brief Look through lvalue to rvalue and nop casts. This filters out
26 /// implicit conversions that have no effect on the input but block our view for
27 /// other implicit casts.
28 static const Expr *ignoreNoOpCasts(const Expr *E) {
29  if (auto *Cast = dyn_cast<CastExpr>(E))
30  if (Cast->getCastKind() == CK_LValueToRValue ||
31  Cast->getCastKind() == CK_NoOp)
32  return ignoreNoOpCasts(Cast->getSubExpr());
33  return E;
34 }
35 
36 /// \brief Restrict the warning to implicit casts that are most likely
37 /// accidental. User defined or integral conversions fit in this category,
38 /// lvalue to rvalue or derived to base does not.
39 static bool isImplicitCastCandidate(const CastExpr *Cast) {
40  return Cast->getCastKind() == CK_UserDefinedConversion ||
41  Cast->getCastKind() == CK_FloatingToBoolean ||
42  Cast->getCastKind() == CK_FloatingToIntegral ||
43  Cast->getCastKind() == CK_IntegralToBoolean ||
44  Cast->getCastKind() == CK_IntegralToFloating ||
45  Cast->getCastKind() == CK_MemberPointerToBoolean ||
46  Cast->getCastKind() == CK_PointerToBoolean;
47 }
48 
49 /// \brief Get a StringRef representing a SourceRange.
50 static StringRef getAsString(const MatchFinder::MatchResult &Result,
51  SourceRange R) {
52  const SourceManager &SM = *Result.SourceManager;
53  // Don't even try to resolve macro or include contraptions. Not worth emitting
54  // a fixit for.
55  if (R.getBegin().isMacroID() ||
56  !SM.isWrittenInSameFile(R.getBegin(), R.getEnd()))
57  return StringRef();
58 
59  const char *Begin = SM.getCharacterData(R.getBegin());
60  const char *End = SM.getCharacterData(Lexer::getLocForEndOfToken(
61  R.getEnd(), 0, SM, Result.Context->getLangOpts()));
62 
63  return StringRef(Begin, End - Begin);
64 }
65 
66 void SwappedArgumentsCheck::check(const MatchFinder::MatchResult &Result) {
67  auto *Call = Result.Nodes.getStmtAs<CallExpr>("call");
68 
69  llvm::SmallPtrSet<const Expr *, 4> UsedArgs;
70  for (unsigned I = 1, E = Call->getNumArgs(); I < E; ++I) {
71  const Expr *LHS = Call->getArg(I - 1);
72  const Expr *RHS = Call->getArg(I);
73 
74  // Only need to check RHS, as LHS has already been covered. We don't want to
75  // emit two warnings for a single argument.
76  if (UsedArgs.count(RHS))
77  continue;
78 
79  const auto *LHSCast = dyn_cast<ImplicitCastExpr>(ignoreNoOpCasts(LHS));
80  const auto *RHSCast = dyn_cast<ImplicitCastExpr>(ignoreNoOpCasts(RHS));
81 
82  // Look if this is a potentially swapped argument pair. First look for
83  // implicit casts.
84  if (!LHSCast || !RHSCast || !isImplicitCastCandidate(LHSCast) ||
85  !isImplicitCastCandidate(RHSCast))
86  continue;
87 
88  // If the types that go into the implicit casts match the types of the other
89  // argument in the declaration there is a high probability that the
90  // arguments were swapped.
91  // TODO: We could make use of the edit distance between the argument name
92  // and the name of the passed variable in addition to this type based
93  // heuristic.
94  const Expr *LHSFrom = ignoreNoOpCasts(LHSCast->getSubExpr());
95  const Expr *RHSFrom = ignoreNoOpCasts(RHSCast->getSubExpr());
96  if (LHS->getType() == RHS->getType() ||
97  LHS->getType() != RHSFrom->getType() ||
98  RHS->getType() != LHSFrom->getType())
99  continue;
100 
101  // Emit a warning and fix-its that swap the arguments.
102  SourceRange LHSRange = LHS->getSourceRange(),
103  RHSRange = RHS->getSourceRange();
104  auto D =
105  diag(Call->getLocStart(), "argument with implicit conversion from %0 "
106  "to %1 followed by argument converted from "
107  "%2 to %3, potentially swapped arguments.")
108  << LHS->getType() << LHSFrom->getType() << RHS->getType()
109  << RHSFrom->getType() << LHSRange << RHSRange;
110 
111  StringRef RHSString = getAsString(Result, RHSRange);
112  StringRef LHSString = getAsString(Result, LHSRange);
113  if (!LHSString.empty() && !RHSString.empty()) {
114  D << FixItHint::CreateReplacement(
115  CharSourceRange::getTokenRange(LHSRange), RHSString)
116  << FixItHint::CreateReplacement(
117  CharSourceRange::getTokenRange(RHSRange), LHSString);
118  }
119 
120  // Remember that we emitted a warning for this argument.
121  UsedArgs.insert(RHSCast);
122  }
123 }
124 
125 } // namespace misc
126 } // namespace tidy
127 } // namespace clang
static const Expr * ignoreNoOpCasts(const Expr *E)
Look through lvalue to rvalue and nop casts.
std::unique_ptr< ast_matchers::MatchFinder > Finder
Definition: ClangTidy.cpp:188
SourceManager & SM
static StringRef getAsString(const MatchFinder::MatchResult &Result, SourceRange R)
Get a StringRef representing a SourceRange.
static bool isImplicitCastCandidate(const CastExpr *Cast)
Restrict the warning to implicit casts that are most likely accidental.
const NamedDecl * Result
Definition: USRFinder.cpp:121