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
17using namespace clang::ast_matchers;
18
19namespace clang::tidy::performance {
20
21// Checks if the stmt is a ImplicitCastExpr with a CastKind that is not a NoOp.
22// The subtlety is that in some cases (user defined conversions), we can
23// get to ImplicitCastExpr inside each other, with the outer one a NoOp. In this
24// case we skip the first cast expr.
25static bool isNonTrivialImplicitCast(const Stmt *ST) {
26 if (const auto *ICE = dyn_cast<ImplicitCastExpr>(Val: ST)) {
27 return (ICE->getCastKind() != CK_NoOp) ||
28 isNonTrivialImplicitCast(ICE->getSubExpr());
29 }
30 return false;
31}
32
33void ImplicitConversionInLoopCheck::registerMatchers(MatchFinder *Finder) {
34 // We look for const ref loop variables that (optionally inside an
35 // ExprWithCleanup) materialize a temporary, and contain a implicit
36 // conversion. The check on the implicit conversion is done in check() because
37 // we can't access implicit conversion subnode via matchers: has() skips casts
38 // and materialize! We also bind on the call to operator* to get the proper
39 // type in the diagnostic message. We use both cxxOperatorCallExpr for user
40 // defined operator and unaryOperator when the iterator is a pointer, like
41 // for arrays or std::array.
42 //
43 // Note that when the implicit conversion is done through a user defined
44 // conversion operator, the node is a CXXMemberCallExpr, not a
45 // CXXOperatorCallExpr, so it should not get caught by the
46 // cxxOperatorCallExpr() matcher.
47 Finder->addMatcher(
48 NodeMatch: traverse(
49 TK: TK_AsIs,
50 InnerMatcher: cxxForRangeStmt(hasLoopVariable(
51 InnerMatcher: varDecl(
52 hasType(InnerMatcher: qualType(references(InnerMatcher: qualType(isConstQualified())))),
53 hasInitializer(
54 InnerMatcher: expr(anyOf(
55 hasDescendant(
56 cxxOperatorCallExpr().bind(ID: "operator-call")),
57 hasDescendant(unaryOperator(hasOperatorName(Name: "*"))
58 .bind(ID: "operator-call"))))
59 .bind(ID: "init")))
60 .bind(ID: "faulty-var")))),
61 Action: this);
62}
63
64void ImplicitConversionInLoopCheck::check(
65 const MatchFinder::MatchResult &Result) {
66 const auto *VD = Result.Nodes.getNodeAs<VarDecl>(ID: "faulty-var");
67 const auto *Init = Result.Nodes.getNodeAs<Expr>(ID: "init");
68 const auto *OperatorCall = Result.Nodes.getNodeAs<Expr>(ID: "operator-call");
69
70 if (const auto *Cleanup = dyn_cast<ExprWithCleanups>(Val: Init))
71 Init = Cleanup->getSubExpr();
72
73 const auto *Materialized = dyn_cast<MaterializeTemporaryExpr>(Val: 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(Context: Result.Context, VD, OperatorCall);
83}
84
85void ImplicitConversionInLoopCheck::reportAndFix(const ASTContext *Context,
86 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(T: 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 clang::tidy::performance
102

source code of clang-tools-extra/clang-tidy/performance/ImplicitConversionInLoopCheck.cpp