1 //===--- ImplicitConversionInLoopCheck.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 "ImplicitConversionInLoopCheck.h"
10
11 #include "clang/AST/ASTContext.h"
12 #include "clang/AST/Decl.h"
13 #include "clang/ASTMatchers/ASTMatchFinder.h"
14 #include "clang/ASTMatchers/ASTMatchers.h"
15 #include "clang/Lex/Lexer.h"
16
17 using namespace clang::ast_matchers;
18
19 namespace clang {
20 namespace tidy {
21 namespace performance {
22
23 // Checks if the stmt is a ImplicitCastExpr with a CastKind that is not a NoOp.
24 // The subtelty is that in some cases (user defined conversions), we can
25 // get to ImplicitCastExpr inside each other, with the outer one a NoOp. In this
26 // case we skip the first cast expr.
IsNonTrivialImplicitCast(const Stmt * ST)27 static bool IsNonTrivialImplicitCast(const Stmt *ST) {
28 if (const auto *ICE = dyn_cast<ImplicitCastExpr>(ST)) {
29 return (ICE->getCastKind() != CK_NoOp) ||
30 IsNonTrivialImplicitCast(ICE->getSubExpr());
31 }
32 return false;
33 }
34
registerMatchers(MatchFinder * Finder)35 void ImplicitConversionInLoopCheck::registerMatchers(MatchFinder *Finder) {
36 // We look for const ref loop variables that (optionally inside an
37 // ExprWithCleanup) materialize a temporary, and contain a implicit
38 // conversion. The check on the implicit conversion is done in check() because
39 // we can't access implicit conversion subnode via matchers: has() skips casts
40 // and materialize! We also bind on the call to operator* to get the proper
41 // type in the diagnostic message. We use both cxxOperatorCallExpr for user
42 // defined operator and unaryOperator when the iterator is a pointer, like
43 // for arrays or std::array.
44 //
45 // Note that when the implicit conversion is done through a user defined
46 // conversion operator, the node is a CXXMemberCallExpr, not a
47 // CXXOperatorCallExpr, so it should not get caught by the
48 // cxxOperatorCallExpr() matcher.
49 Finder->addMatcher(
50 cxxForRangeStmt(hasLoopVariable(
51 varDecl(
52 hasType(qualType(references(qualType(isConstQualified())))),
53 hasInitializer(
54 expr(anyOf(hasDescendant(
55 cxxOperatorCallExpr().bind("operator-call")),
56 hasDescendant(unaryOperator(hasOperatorName("*"))
57 .bind("operator-call"))))
58 .bind("init")))
59 .bind("faulty-var"))),
60 this);
61 }
62
check(const MatchFinder::MatchResult & Result)63 void ImplicitConversionInLoopCheck::check(
64 const MatchFinder::MatchResult &Result) {
65 const auto *VD = Result.Nodes.getNodeAs<VarDecl>("faulty-var");
66 const auto *Init = Result.Nodes.getNodeAs<Expr>("init");
67 const auto *OperatorCall =
68 Result.Nodes.getNodeAs<Expr>("operator-call");
69
70 if (const auto *Cleanup = dyn_cast<ExprWithCleanups>(Init))
71 Init = Cleanup->getSubExpr();
72
73 const auto *Materialized = dyn_cast<MaterializeTemporaryExpr>(Init);
74 if (!Materialized)
75 return;
76
77 // We ignore NoOp casts. Those are generated if the * operator on the
78 // iterator returns a value instead of a reference, and the loop variable
79 // is a reference. This situation is fine (it probably produces the same
80 // code at the end).
81 if (IsNonTrivialImplicitCast(Materialized->getSubExpr()))
82 ReportAndFix(Result.Context, VD, OperatorCall);
83 }
84
ReportAndFix(const ASTContext * Context,const VarDecl * VD,const Expr * OperatorCall)85 void ImplicitConversionInLoopCheck::ReportAndFix(
86 const ASTContext *Context, const VarDecl *VD,
87 const Expr *OperatorCall) {
88 // We only match on const ref, so we should print a const ref version of the
89 // type.
90 QualType ConstType = OperatorCall->getType().withConst();
91 QualType ConstRefType = Context->getLValueReferenceType(ConstType);
92 const char Message[] =
93 "the type of the loop variable %0 is different from the one returned "
94 "by the iterator and generates an implicit conversion; you can either "
95 "change the type to the matching one (%1 but 'const auto&' is always a "
96 "valid option) or remove the reference to make it explicit that you are "
97 "creating a new value";
98 diag(VD->getBeginLoc(), Message) << VD << ConstRefType;
99 }
100
101 } // namespace performance
102 } // namespace tidy
103 } // namespace clang
104