1 //===--- SwappedArgumentsCheck.cpp - clang-tidy ---------------------------===//
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 #include "SwappedArgumentsCheck.h"
10 #include "clang/AST/ASTContext.h"
11 #include "clang/Lex/Lexer.h"
12 #include "clang/Tooling/FixIt.h"
13 #include "llvm/ADT/SmallPtrSet.h"
14
15 using namespace clang::ast_matchers;
16
17 namespace clang::tidy::bugprone {
18
registerMatchers(MatchFinder * Finder)19 void SwappedArgumentsCheck::registerMatchers(MatchFinder *Finder) {
20 Finder->addMatcher(callExpr(unless(isInTemplateInstantiation())).bind("call"),
21 this);
22 }
23
24 /// Look through lvalue to rvalue and nop casts. This filters out
25 /// implicit conversions that have no effect on the input but block our view for
26 /// other implicit casts.
ignoreNoOpCasts(const Expr * E)27 static const Expr *ignoreNoOpCasts(const Expr *E) {
28 if (auto *Cast = dyn_cast<CastExpr>(E))
29 if (Cast->getCastKind() == CK_LValueToRValue ||
30 Cast->getCastKind() == CK_NoOp)
31 return ignoreNoOpCasts(Cast->getSubExpr());
32 return E;
33 }
34
35 /// Restrict the warning to implicit casts that are most likely
36 /// accidental. User defined or integral conversions fit in this category,
37 /// lvalue to rvalue or derived to base does not.
isImplicitCastCandidate(const CastExpr * Cast)38 static bool isImplicitCastCandidate(const CastExpr *Cast) {
39 return Cast->getCastKind() == CK_UserDefinedConversion ||
40 Cast->getCastKind() == CK_FloatingToBoolean ||
41 Cast->getCastKind() == CK_FloatingToIntegral ||
42 Cast->getCastKind() == CK_IntegralToBoolean ||
43 Cast->getCastKind() == CK_IntegralToFloating ||
44 Cast->getCastKind() == CK_MemberPointerToBoolean ||
45 Cast->getCastKind() == CK_PointerToBoolean ||
46 (Cast->getCastKind() == CK_IntegralCast &&
47 Cast->getSubExpr()->getType()->isBooleanType());
48 }
49
areTypesSemiEqual(const QualType L,const QualType R)50 static bool areTypesSemiEqual(const QualType L, const QualType R) {
51 if (L == R)
52 return true;
53
54 if (!L->isBuiltinType() || !R->isBuiltinType())
55 return false;
56
57 return (L->isFloatingType() && R->isFloatingType()) ||
58 (L->isIntegerType() && R->isIntegerType()) ||
59 (L->isBooleanType() && R->isBooleanType());
60 }
61
areArgumentsPotentiallySwapped(const QualType LTo,const QualType RTo,const QualType LFrom,const QualType RFrom)62 static bool areArgumentsPotentiallySwapped(const QualType LTo,
63 const QualType RTo,
64 const QualType LFrom,
65 const QualType RFrom) {
66 if (LTo == RTo || LFrom == RFrom)
67 return false;
68
69 const bool REq = areTypesSemiEqual(RTo, LFrom);
70 if (LTo == RFrom && REq)
71 return true;
72
73 bool LEq = areTypesSemiEqual(LTo, RFrom);
74 if (RTo == LFrom && LEq)
75 return true;
76
77 if (REq && LEq && !areTypesSemiEqual(RTo, LTo))
78 return true;
79
80 return false;
81 }
82
check(const MatchFinder::MatchResult & Result)83 void SwappedArgumentsCheck::check(const MatchFinder::MatchResult &Result) {
84 const ASTContext &Ctx = *Result.Context;
85 const auto *Call = Result.Nodes.getNodeAs<CallExpr>("call");
86
87 llvm::SmallPtrSet<const Expr *, 4> UsedArgs;
88 for (unsigned I = 1, E = Call->getNumArgs(); I < E; ++I) {
89 const Expr *LHS = Call->getArg(I - 1);
90 const Expr *RHS = Call->getArg(I);
91
92 // Only need to check RHS, as LHS has already been covered. We don't want to
93 // emit two warnings for a single argument.
94 if (UsedArgs.count(RHS))
95 continue;
96
97 const auto *LHSCast = dyn_cast<ImplicitCastExpr>(ignoreNoOpCasts(LHS));
98 const auto *RHSCast = dyn_cast<ImplicitCastExpr>(ignoreNoOpCasts(RHS));
99
100 // Look if this is a potentially swapped argument pair. First look for
101 // implicit casts.
102 if (!LHSCast || !RHSCast || !isImplicitCastCandidate(LHSCast) ||
103 !isImplicitCastCandidate(RHSCast))
104 continue;
105
106 // If the types that go into the implicit casts match the types of the other
107 // argument in the declaration there is a high probability that the
108 // arguments were swapped.
109 // TODO: We could make use of the edit distance between the argument name
110 // and the name of the passed variable in addition to this type based
111 // heuristic.
112 const Expr *LHSFrom = ignoreNoOpCasts(LHSCast->getSubExpr());
113 const Expr *RHSFrom = ignoreNoOpCasts(RHSCast->getSubExpr());
114 if (!areArgumentsPotentiallySwapped(LHS->getType(), RHS->getType(),
115 LHSFrom->getType(), RHSFrom->getType()))
116 continue;
117
118 // Emit a warning and fix-its that swap the arguments.
119 diag(Call->getBeginLoc(), "argument with implicit conversion from %0 "
120 "to %1 followed by argument converted from "
121 "%2 to %3, potentially swapped arguments.")
122 << LHSFrom->getType() << LHS->getType() << RHSFrom->getType()
123 << RHS->getType() << tooling::fixit::createReplacement(*LHS, *RHS, Ctx)
124 << tooling::fixit::createReplacement(*RHS, *LHS, Ctx);
125
126 // Remember that we emitted a warning for this argument.
127 UsedArgs.insert(RHSCast);
128 }
129 }
130
131 } // namespace clang::tidy::bugprone
132