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 {
18 namespace tidy {
19 namespace bugprone {
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 void SwappedArgumentsCheck::check(const MatchFinder::MatchResult &Result) {
50   const ASTContext &Ctx = *Result.Context;
51   const auto *Call = Result.Nodes.getNodeAs<CallExpr>("call");
52 
53   llvm::SmallPtrSet<const Expr *, 4> UsedArgs;
54   for (unsigned I = 1, E = Call->getNumArgs(); I < E; ++I) {
55     const Expr *LHS = Call->getArg(I - 1);
56     const Expr *RHS = Call->getArg(I);
57 
58     // Only need to check RHS, as LHS has already been covered. We don't want to
59     // emit two warnings for a single argument.
60     if (UsedArgs.count(RHS))
61       continue;
62 
63     const auto *LHSCast = dyn_cast<ImplicitCastExpr>(ignoreNoOpCasts(LHS));
64     const auto *RHSCast = dyn_cast<ImplicitCastExpr>(ignoreNoOpCasts(RHS));
65 
66     // Look if this is a potentially swapped argument pair. First look for
67     // implicit casts.
68     if (!LHSCast || !RHSCast || !isImplicitCastCandidate(LHSCast) ||
69         !isImplicitCastCandidate(RHSCast))
70       continue;
71 
72     // If the types that go into the implicit casts match the types of the other
73     // argument in the declaration there is a high probability that the
74     // arguments were swapped.
75     // TODO: We could make use of the edit distance between the argument name
76     // and the name of the passed variable in addition to this type based
77     // heuristic.
78     const Expr *LHSFrom = ignoreNoOpCasts(LHSCast->getSubExpr());
79     const Expr *RHSFrom = ignoreNoOpCasts(RHSCast->getSubExpr());
80     if (LHS->getType() == RHS->getType() ||
81         LHS->getType() != RHSFrom->getType() ||
82         RHS->getType() != LHSFrom->getType())
83       continue;
84 
85     // Emit a warning and fix-its that swap the arguments.
86     diag(Call->getBeginLoc(), "argument with implicit conversion from %0 "
87                               "to %1 followed by argument converted from "
88                               "%2 to %3, potentially swapped arguments.")
89         << LHS->getType() << LHSFrom->getType() << RHS->getType()
90         << RHSFrom->getType()
91         << tooling::fixit::createReplacement(*LHS, *RHS, Ctx)
92         << tooling::fixit::createReplacement(*RHS, *LHS, Ctx);
93 
94     // Remember that we emitted a warning for this argument.
95     UsedArgs.insert(RHSCast);
96   }
97 }
98 
99 } // namespace bugprone
100 } // namespace tidy
101 } // namespace clang
102