clang-tools  12.0.0git
ImplicitConversionInLoopCheck.cpp
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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 
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.
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 
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  traverse(
51  ast_type_traits::TK_AsIs,
52  cxxForRangeStmt(hasLoopVariable(
53  varDecl(
54  hasType(qualType(references(qualType(isConstQualified())))),
55  hasInitializer(
56  expr(anyOf(
57  hasDescendant(
58  cxxOperatorCallExpr().bind("operator-call")),
59  hasDescendant(unaryOperator(hasOperatorName("*"))
60  .bind("operator-call"))))
61  .bind("init")))
62  .bind("faulty-var")))),
63  this);
64 }
65 
66 void ImplicitConversionInLoopCheck::check(
67  const MatchFinder::MatchResult &Result) {
68  const auto *VD = Result.Nodes.getNodeAs<VarDecl>("faulty-var");
69  const auto *Init = Result.Nodes.getNodeAs<Expr>("init");
70  const auto *OperatorCall =
71  Result.Nodes.getNodeAs<Expr>("operator-call");
72 
73  if (const auto *Cleanup = dyn_cast<ExprWithCleanups>(Init))
74  Init = Cleanup->getSubExpr();
75 
76  const auto *Materialized = dyn_cast<MaterializeTemporaryExpr>(Init);
77  if (!Materialized)
78  return;
79 
80  // We ignore NoOp casts. Those are generated if the * operator on the
81  // iterator returns a value instead of a reference, and the loop variable
82  // is a reference. This situation is fine (it probably produces the same
83  // code at the end).
84  if (IsNonTrivialImplicitCast(Materialized->getSubExpr()))
85  ReportAndFix(Result.Context, VD, OperatorCall);
86 }
87 
88 void ImplicitConversionInLoopCheck::ReportAndFix(
89  const ASTContext *Context, const VarDecl *VD,
90  const Expr *OperatorCall) {
91  // We only match on const ref, so we should print a const ref version of the
92  // type.
93  QualType ConstType = OperatorCall->getType().withConst();
94  QualType ConstRefType = Context->getLValueReferenceType(ConstType);
95  const char Message[] =
96  "the type of the loop variable %0 is different from the one returned "
97  "by the iterator and generates an implicit conversion; you can either "
98  "change the type to the matching one (%1 but 'const auto&' is always a "
99  "valid option) or remove the reference to make it explicit that you are "
100  "creating a new value";
101  diag(VD->getBeginLoc(), Message) << VD << ConstRefType;
102 }
103 
104 } // namespace performance
105 } // namespace tidy
106 } // namespace clang
static bool IsNonTrivialImplicitCast(const Stmt *ST)
===– Representation.cpp - ClangDoc Representation --------—*- C++ -*-===//