1 //===--- ImplicitConversionInLoopCheck.cpp - clang-tidy--------------------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 10 #include "ImplicitConversionInLoopCheck.h" 11 12 #include "clang/AST/ASTContext.h" 13 #include "clang/AST/Decl.h" 14 #include "clang/ASTMatchers/ASTMatchFinder.h" 15 #include "clang/ASTMatchers/ASTMatchers.h" 16 #include "clang/Lex/Lexer.h" 17 18 using namespace clang::ast_matchers; 19 20 namespace clang { 21 namespace tidy { 22 namespace performance { 23 24 // Checks if the stmt is a ImplicitCastExpr with a CastKind that is not a NoOp. 25 // The subtelty is that in some cases (user defined conversions), we can 26 // get to ImplicitCastExpr inside each other, with the outer one a NoOp. In this 27 // case we skip the first cast expr. 28 static bool IsNonTrivialImplicitCast(const Stmt *ST) { 29 if (const auto *ICE = dyn_cast<ImplicitCastExpr>(ST)) { 30 return (ICE->getCastKind() != CK_NoOp) || 31 IsNonTrivialImplicitCast(ICE->getSubExpr()); 32 } 33 return false; 34 } 35 36 void ImplicitConversionInLoopCheck::registerMatchers(MatchFinder *Finder) { 37 // We look for const ref loop variables that (optionally inside an 38 // ExprWithCleanup) materialize a temporary, and contain a implicit 39 // conversion. The check on the implicit conversion is done in check() because 40 // we can't access implicit conversion subnode via matchers: has() skips casts 41 // and materialize! We also bind on the call to operator* to get the proper 42 // type in the diagnostic message. 43 // 44 // Note that when the implicit conversion is done through a user defined 45 // conversion operator, the node is a CXXMemberCallExpr, not a 46 // CXXOperatorCallExpr, so it should not get caught by the 47 // cxxOperatorCallExpr() matcher. 48 Finder->addMatcher( 49 cxxForRangeStmt(hasLoopVariable( 50 varDecl(hasType(qualType(references(qualType(isConstQualified())))), 51 hasInitializer(expr(hasDescendant(cxxOperatorCallExpr().bind( 52 "operator-call"))) 53 .bind("init"))) 54 .bind("faulty-var"))), 55 this); 56 } 57 58 void ImplicitConversionInLoopCheck::check( 59 const MatchFinder::MatchResult &Result) { 60 const auto *VD = Result.Nodes.getNodeAs<VarDecl>("faulty-var"); 61 const auto *Init = Result.Nodes.getNodeAs<Expr>("init"); 62 const auto *OperatorCall = 63 Result.Nodes.getNodeAs<CXXOperatorCallExpr>("operator-call"); 64 65 if (const auto *Cleanup = dyn_cast<ExprWithCleanups>(Init)) 66 Init = Cleanup->getSubExpr(); 67 68 const auto *Materialized = dyn_cast<MaterializeTemporaryExpr>(Init); 69 if (!Materialized) 70 return; 71 72 // We ignore NoOp casts. Those are generated if the * operator on the 73 // iterator returns a value instead of a reference, and the loop variable 74 // is a reference. This situation is fine (it probably produces the same 75 // code at the end). 76 if (IsNonTrivialImplicitCast(Materialized->getTemporary())) 77 ReportAndFix(Result.Context, VD, OperatorCall); 78 } 79 80 void ImplicitConversionInLoopCheck::ReportAndFix( 81 const ASTContext *Context, const VarDecl *VD, 82 const CXXOperatorCallExpr *OperatorCall) { 83 // We only match on const ref, so we should print a const ref version of the 84 // type. 85 QualType ConstType = OperatorCall->getType().withConst(); 86 QualType ConstRefType = Context->getLValueReferenceType(ConstType); 87 const char Message[] = 88 "the type of the loop variable %0 is different from the one returned " 89 "by the iterator and generates an implicit conversion; you can either " 90 "change the type to the matching one (%1 but 'const auto&' is always a " 91 "valid option) or remove the reference to make it explicit that you are " 92 "creating a new value"; 93 diag(VD->getLocStart(), Message) << VD << ConstRefType; 94 } 95 96 } // namespace performance 97 } // namespace tidy 98 } // namespace clang 99