clang-tools-extra/clang-tidy/performance/ImplicitConversionInLoopCheck.cpp

   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::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.
  25 static bool isNonTrivialImplicitCast(const Stmt *ST) {
  26   if (const auto *ICE = dyn_cast<ImplicitCastExpr>(ST)) {
  27     return (ICE->getCastKind() != CK_NoOp) ||
  28            isNonTrivialImplicitCast(ICE->getSubExpr());
  29   }
  30   return false;
  31 }
  32
  33 void 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       traverse(
  49           TK_AsIs,
  50           cxxForRangeStmt(hasLoopVariable(
  51               varDecl(
  52                   hasType(qualType(references(qualType(isConstQualified())))),
  53                   hasInitializer(
  54                       expr(anyOf(
  55                                hasDescendant(
  56                                    cxxOperatorCallExpr().bind("operator-call")),
  57                                hasDescendant(unaryOperator(hasOperatorName("*"))
  58                                                  .bind("operator-call"))))
  59                           .bind("init")))
  60                   .bind("faulty-var")))),
  61       this);
  62 }
  63
  64 void ImplicitConversionInLoopCheck::check(
  65     const MatchFinder::MatchResult &Result) {
  66   const auto *VD = Result.Nodes.getNodeAs<VarDecl>("faulty-var");
  67   const auto *Init = Result.Nodes.getNodeAs<Expr>("init");
  68   const auto *OperatorCall =
  69       Result.Nodes.getNodeAs<Expr>("operator-call");
  70
  71   if (const auto *Cleanup = dyn_cast<ExprWithCleanups>(Init))
  72     Init = Cleanup->getSubExpr();
  73
  74   const auto *Materialized = dyn_cast<MaterializeTemporaryExpr>(Init);
  75   if (!Materialized)
  76     return;
  77
  78   // We ignore NoOp casts. Those are generated if the * operator on the
  79   // iterator returns a value instead of a reference, and the loop variable
  80   // is a reference. This situation is fine (it probably produces the same
  81   // code at the end).
  82   if (isNonTrivialImplicitCast(Materialized->getSubExpr()))
  83     reportAndFix(Result.Context, VD, OperatorCall);
  84 }
  85
  86 void ImplicitConversionInLoopCheck::reportAndFix(const ASTContext *Context,
  87                                                  const VarDecl *VD,
  88                                                  const Expr *OperatorCall) {
  89   // We only match on const ref, so we should print a const ref version of the
  90   // type.
  91   QualType ConstType = OperatorCall->getType().withConst();
  92   QualType ConstRefType = Context->getLValueReferenceType(ConstType);
  93   const char Message[] =
  94       "the type of the loop variable %0 is different from the one returned "
  95       "by the iterator and generates an implicit conversion; you can either "
  96       "change the type to the matching one (%1 but 'const auto&' is always a "
  97       "valid option) or remove the reference to make it explicit that you are "
  98       "creating a new value";
  99   diag(VD->getBeginLoc(), Message) << VD << ConstRefType;
 100 }
 101
 102 } // namespace clang::tidy::performance