text: //===--- LoopConvertCheck.cpp - clang-tidy---------------------------------===//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  
  #include "LoopConvertCheck.h"
  #include "clang/AST/ASTContext.h"
  #include "clang/ASTMatchers/ASTMatchFinder.h"
  #include "clang/Basic/LLVM.h"
  #include "clang/Basic/LangOptions.h"
  #include "clang/Basic/SourceLocation.h"
  #include "clang/Basic/SourceManager.h"
  #include "clang/Lex/Lexer.h"
  #include "llvm/ADT/ArrayRef.h"
  #include "llvm/ADT/SmallVector.h"
  #include "llvm/ADT/StringRef.h"
  #include "llvm/ADT/StringSwitch.h"
  #include "llvm/Support/Casting.h"
  #include <cassert>
  #include <cstring>
  #include <utility>
  
  using namespace clang::ast_matchers;
  using namespace llvm;
  
  namespace clang {
  namespace tidy {
  namespace modernize {
  
  static const char LoopNameArray[] = "forLoopArray";
  static const char LoopNameIterator[] = "forLoopIterator";
  static const char LoopNamePseudoArray[] = "forLoopPseudoArray";
  static const char ConditionBoundName[] = "conditionBound";
  static const char ConditionVarName[] = "conditionVar";
  static const char IncrementVarName[] = "incrementVar";
  static const char InitVarName[] = "initVar";
  static const char BeginCallName[] = "beginCall";
  static const char EndCallName[] = "endCall";
  static const char ConditionEndVarName[] = "conditionEndVar";
  static const char EndVarName[] = "endVar";
  static const char DerefByValueResultName[] = "derefByValueResult";
  static const char DerefByRefResultName[] = "derefByRefResult";
  
  static ArrayRef<std::pair<StringRef, Confidence::Level>>
  getConfidenceMapping() {
    static constexpr std::pair<StringRef, Confidence::Level> Mapping[] = {
        {"reasonable", Confidence::CL_Reasonable},
        {"safe", Confidence::CL_Safe},
        {"risky", Confidence::CL_Risky}};
    return makeArrayRef(Mapping);
  }
  
  static ArrayRef<std::pair<StringRef, VariableNamer::NamingStyle>>
  getStyleMapping() {
    static constexpr std::pair<StringRef, VariableNamer::NamingStyle> Mapping[] =
        {{"CamelCase", VariableNamer::NS_CamelCase},
         {"camelBack", VariableNamer::NS_CamelBack},
         {"lower_case", VariableNamer::NS_LowerCase},
         {"UPPER_CASE", VariableNamer::NS_UpperCase}};
    return makeArrayRef(Mapping);
  }
  
  // shared matchers
  static const TypeMatcher AnyType() { return anything(); }
  
  static const StatementMatcher IntegerComparisonMatcher() {
    return expr(ignoringParenImpCasts(
        declRefExpr(to(varDecl(hasType(isInteger())).bind(ConditionVarName)))));
  }
  
  static const DeclarationMatcher InitToZeroMatcher() {
    return varDecl(
               hasInitializer(ignoringParenImpCasts(integerLiteral(equals(0)))))
        .bind(InitVarName);
  }
  
  static const StatementMatcher IncrementVarMatcher() {
    return declRefExpr(to(varDecl(hasType(isInteger())).bind(IncrementVarName)));
  }
  
  /// The matcher for loops over arrays.
  ///
  /// In this general example, assuming 'j' and 'k' are of integral type:
  /// \code
  ///   for (int i = 0; j < 3 + 2; ++k) { ... }
  /// \endcode
  /// The following string identifiers are bound to these parts of the AST:
  ///   ConditionVarName: 'j' (as a VarDecl)
  ///   ConditionBoundName: '3 + 2' (as an Expr)
  ///   InitVarName: 'i' (as a VarDecl)
  ///   IncrementVarName: 'k' (as a VarDecl)
  ///   LoopName: The entire for loop (as a ForStmt)
  ///
  /// Client code will need to make sure that:
  ///   - The three index variables identified by the matcher are the same
  ///     VarDecl.
  ///   - The index variable is only used as an array index.
  ///   - All arrays indexed by the loop are the same.
  StatementMatcher makeArrayLoopMatcher() {
    StatementMatcher ArrayBoundMatcher =
        expr(hasType(isInteger())).bind(ConditionBoundName);
  
    return forStmt(
               unless(isInTemplateInstantiation()),
               hasLoopInit(declStmt(hasSingleDecl(InitToZeroMatcher()))),
               hasCondition(anyOf(
                   binaryOperator(hasOperatorName("<"),
                                  hasLHS(IntegerComparisonMatcher()),
                                  hasRHS(ArrayBoundMatcher)),
                   binaryOperator(hasOperatorName(">"), hasLHS(ArrayBoundMatcher),
                                  hasRHS(IntegerComparisonMatcher())))),
               hasIncrement(unaryOperator(hasOperatorName("++"),
                                          hasUnaryOperand(IncrementVarMatcher()))))
        .bind(LoopNameArray);
  }
  
  /// The matcher used for iterator-based for loops.
  ///
  /// This matcher is more flexible than array-based loops. It will match
  /// catch loops of the following textual forms (regardless of whether the
  /// iterator type is actually a pointer type or a class type):
  ///
  /// Assuming f, g, and h are of type containerType::iterator,
  /// \code
  ///   for (containerType::iterator it = container.begin(),
  ///        e = createIterator(); f != g; ++h) { ... }
  ///   for (containerType::iterator it = container.begin();
  ///        f != anotherContainer.end(); ++h) { ... }
  /// \endcode
  /// The following string identifiers are bound to the parts of the AST:
  ///   InitVarName: 'it' (as a VarDecl)
  ///   ConditionVarName: 'f' (as a VarDecl)
  ///   LoopName: The entire for loop (as a ForStmt)
  ///   In the first example only:
  ///     EndVarName: 'e' (as a VarDecl)
  ///     ConditionEndVarName: 'g' (as a VarDecl)
  ///   In the second example only:
  ///     EndCallName: 'container.end()' (as a CXXMemberCallExpr)
  ///
  /// Client code will need to make sure that:
  ///   - The iterator variables 'it', 'f', and 'h' are the same.
  ///   - The two containers on which 'begin' and 'end' are called are the same.
  ///   - If the end iterator variable 'g' is defined, it is the same as 'f'.
  StatementMatcher makeIteratorLoopMatcher() {
    StatementMatcher BeginCallMatcher =
        cxxMemberCallExpr(
            argumentCountIs(0),
            callee(cxxMethodDecl(anyOf(hasName("begin"), hasName("cbegin")))))
            .bind(BeginCallName);
  
    DeclarationMatcher InitDeclMatcher =
        varDecl(hasInitializer(anyOf(ignoringParenImpCasts(BeginCallMatcher),
                                     materializeTemporaryExpr(
                                         ignoringParenImpCasts(BeginCallMatcher)),
                                     hasDescendant(BeginCallMatcher))))
            .bind(InitVarName);
  
    DeclarationMatcher EndDeclMatcher =
        varDecl(hasInitializer(anything())).bind(EndVarName);
  
    StatementMatcher EndCallMatcher = cxxMemberCallExpr(
        argumentCountIs(0),
        callee(cxxMethodDecl(anyOf(hasName("end"), hasName("cend")))));
  
    StatementMatcher IteratorBoundMatcher =
        expr(anyOf(ignoringParenImpCasts(
                       declRefExpr(to(varDecl().bind(ConditionEndVarName)))),
                   ignoringParenImpCasts(expr(EndCallMatcher).bind(EndCallName)),
                   materializeTemporaryExpr(ignoringParenImpCasts(
                       expr(EndCallMatcher).bind(EndCallName)))));
  
    StatementMatcher IteratorComparisonMatcher = expr(
        ignoringParenImpCasts(declRefExpr(to(varDecl().bind(ConditionVarName)))));
  
    auto OverloadedNEQMatcher = ignoringImplicit(
        cxxOperatorCallExpr(hasOverloadedOperatorName("!="), argumentCountIs(2),
                            hasArgument(0, IteratorComparisonMatcher),
                            hasArgument(1, IteratorBoundMatcher)));
  
    // This matcher tests that a declaration is a CXXRecordDecl that has an
    // overloaded operator*(). If the operator*() returns by value instead of by
    // reference then the return type is tagged with DerefByValueResultName.
    internal::Matcher<VarDecl> TestDerefReturnsByValue =
        hasType(hasUnqualifiedDesugaredType(
            recordType(hasDeclaration(cxxRecordDecl(hasMethod(cxxMethodDecl(
                hasOverloadedOperatorName("*"),
                anyOf(
                    // Tag the return type if it's by value.
                    returns(qualType(unless(hasCanonicalType(referenceType())))
                                .bind(DerefByValueResultName)),
                    returns(
                        // Skip loops where the iterator's operator* returns an
                        // rvalue reference. This is just weird.
                        qualType(unless(hasCanonicalType(rValueReferenceType())))
                            .bind(DerefByRefResultName))))))))));
  
    return forStmt(
               unless(isInTemplateInstantiation()),
               hasLoopInit(anyOf(declStmt(declCountIs(2),
                                          containsDeclaration(0, InitDeclMatcher),
                                          containsDeclaration(1, EndDeclMatcher)),
                                 declStmt(hasSingleDecl(InitDeclMatcher)))),
               hasCondition(
                   anyOf(binaryOperator(hasOperatorName("!="),
                                        hasLHS(IteratorComparisonMatcher),
                                        hasRHS(IteratorBoundMatcher)),
                         binaryOperator(hasOperatorName("!="),
                                        hasLHS(IteratorBoundMatcher),
                                        hasRHS(IteratorComparisonMatcher)),
                         OverloadedNEQMatcher)),
               hasIncrement(anyOf(
                   unaryOperator(hasOperatorName("++"),
                                 hasUnaryOperand(declRefExpr(
                                     to(varDecl(hasType(pointsTo(AnyType())))
                                            .bind(IncrementVarName))))),
                   cxxOperatorCallExpr(
                       hasOverloadedOperatorName("++"),
                       hasArgument(
                           0, declRefExpr(to(varDecl(TestDerefReturnsByValue)
                                                 .bind(IncrementVarName))))))))
        .bind(LoopNameIterator);
  }
  
  /// The matcher used for array-like containers (pseudoarrays).
  ///
  /// This matcher is more flexible than array-based loops. It will match
  /// loops of the following textual forms (regardless of whether the
  /// iterator type is actually a pointer type or a class type):
  ///
  /// Assuming f, g, and h are of type containerType::iterator,
  /// \code
  ///   for (int i = 0, j = container.size(); f < g; ++h) { ... }
  ///   for (int i = 0; f < container.size(); ++h) { ... }
  /// \endcode
  /// The following string identifiers are bound to the parts of the AST:
  ///   InitVarName: 'i' (as a VarDecl)
  ///   ConditionVarName: 'f' (as a VarDecl)
  ///   LoopName: The entire for loop (as a ForStmt)
  ///   In the first example only:
  ///     EndVarName: 'j' (as a VarDecl)
  ///     ConditionEndVarName: 'g' (as a VarDecl)
  ///   In the second example only:
  ///     EndCallName: 'container.size()' (as a CXXMemberCallExpr)
  ///
  /// Client code will need to make sure that:
  ///   - The index variables 'i', 'f', and 'h' are the same.
  ///   - The containers on which 'size()' is called is the container indexed.
  ///   - The index variable is only used in overloaded operator[] or
  ///     container.at().
  ///   - If the end iterator variable 'g' is defined, it is the same as 'j'.
  ///   - The container's iterators would not be invalidated during the loop.
  StatementMatcher makePseudoArrayLoopMatcher() {
    // Test that the incoming type has a record declaration that has methods
    // called 'begin' and 'end'. If the incoming type is const, then make sure
    // these methods are also marked const.
    //
    // FIXME: To be completely thorough this matcher should also ensure the
    // return type of begin/end is an iterator that dereferences to the same as
    // what operator[] or at() returns. Such a test isn't likely to fail except
    // for pathological cases.
    //
    // FIXME: Also, a record doesn't necessarily need begin() and end(). Free
    // functions called begin() and end() taking the container as an argument
    // are also allowed.
    TypeMatcher RecordWithBeginEnd = qualType(anyOf(
        qualType(
            isConstQualified(),
            hasUnqualifiedDesugaredType(recordType(hasDeclaration(cxxRecordDecl(
                hasMethod(cxxMethodDecl(hasName("begin"), isConst())),
                hasMethod(cxxMethodDecl(hasName("end"),
                                        isConst()))))   // hasDeclaration
                                                   ))), // qualType
        qualType(unless(isConstQualified()),
                 hasUnqualifiedDesugaredType(recordType(hasDeclaration(
                     cxxRecordDecl(hasMethod(hasName("begin")),
                                   hasMethod(hasName("end"))))))) // qualType
        ));
  
    StatementMatcher SizeCallMatcher = cxxMemberCallExpr(
        argumentCountIs(0),
        callee(cxxMethodDecl(anyOf(hasName("size"), hasName("length")))),
        on(anyOf(hasType(pointsTo(RecordWithBeginEnd)),
                 hasType(RecordWithBeginEnd))));
  
    StatementMatcher EndInitMatcher =
        expr(anyOf(ignoringParenImpCasts(expr(SizeCallMatcher).bind(EndCallName)),
                   explicitCastExpr(hasSourceExpression(ignoringParenImpCasts(
                       expr(SizeCallMatcher).bind(EndCallName))))));
  
    DeclarationMatcher EndDeclMatcher =
        varDecl(hasInitializer(EndInitMatcher)).bind(EndVarName);
  
    StatementMatcher IndexBoundMatcher =
        expr(anyOf(ignoringParenImpCasts(declRefExpr(to(
                       varDecl(hasType(isInteger())).bind(ConditionEndVarName)))),
                   EndInitMatcher));
  
    return forStmt(
               unless(isInTemplateInstantiation()),
               hasLoopInit(
                   anyOf(declStmt(declCountIs(2),
                                  containsDeclaration(0, InitToZeroMatcher()),
                                  containsDeclaration(1, EndDeclMatcher)),
                         declStmt(hasSingleDecl(InitToZeroMatcher())))),
               hasCondition(anyOf(
                   binaryOperator(hasOperatorName("<"),
                                  hasLHS(IntegerComparisonMatcher()),
                                  hasRHS(IndexBoundMatcher)),
                   binaryOperator(hasOperatorName(">"), hasLHS(IndexBoundMatcher),
                                  hasRHS(IntegerComparisonMatcher())))),
               hasIncrement(unaryOperator(hasOperatorName("++"),
                                          hasUnaryOperand(IncrementVarMatcher()))))
        .bind(LoopNamePseudoArray);
  }
  
  /// Determine whether Init appears to be an initializing an iterator.
  ///
  /// If it is, returns the object whose begin() or end() method is called, and
  /// the output parameter isArrow is set to indicate whether the initialization
  /// is called via . or ->.
  static const Expr *getContainerFromBeginEndCall(const Expr *Init, bool IsBegin,
                                                  bool *IsArrow) {
    // FIXME: Maybe allow declaration/initialization outside of the for loop.
    const auto *TheCall =
        dyn_cast_or_null<CXXMemberCallExpr>(digThroughConstructors(Init));
    if (!TheCall || TheCall->getNumArgs() != 0)
      return nullptr;
  
    const auto *Member = dyn_cast<MemberExpr>(TheCall->getCallee());
    if (!Member)
      return nullptr;
    StringRef Name = Member->getMemberDecl()->getName();
    StringRef TargetName = IsBegin ? "begin" : "end";
    StringRef ConstTargetName = IsBegin ? "cbegin" : "cend";
    if (Name != TargetName && Name != ConstTargetName)
      return nullptr;
  
    const Expr *SourceExpr = Member->getBase();
    if (!SourceExpr)
      return nullptr;
  
    *IsArrow = Member->isArrow();
    return SourceExpr;
  }
  
  /// Determines the container whose begin() and end() functions are called
  /// for an iterator-based loop.
  ///
  /// BeginExpr must be a member call to a function named "begin()", and EndExpr
  /// must be a member.
  static const Expr *findContainer(ASTContext *Context, const Expr *BeginExpr,
                                   const Expr *EndExpr,
                                   bool *ContainerNeedsDereference) {
    // Now that we know the loop variable and test expression, make sure they are
    // valid.
    bool BeginIsArrow = false;
    bool EndIsArrow = false;
    const Expr *BeginContainerExpr =
        getContainerFromBeginEndCall(BeginExpr, /*IsBegin=*/true, &BeginIsArrow);
    if (!BeginContainerExpr)
      return nullptr;
  
    const Expr *EndContainerExpr =
        getContainerFromBeginEndCall(EndExpr, /*IsBegin=*/false, &EndIsArrow);
    // Disallow loops that try evil things like this (note the dot and arrow):
    //  for (IteratorType It = Obj.begin(), E = Obj->end(); It != E; ++It) { }
    if (!EndContainerExpr || BeginIsArrow != EndIsArrow ||
        !areSameExpr(Context, EndContainerExpr, BeginContainerExpr))
      return nullptr;
  
    *ContainerNeedsDereference = BeginIsArrow;
    return BeginContainerExpr;
  }
  
  /// Obtain the original source code text from a SourceRange.
  static StringRef getStringFromRange(SourceManager &SourceMgr,
                                      const LangOptions &LangOpts,
                                      SourceRange Range) {
    if (SourceMgr.getFileID(Range.getBegin()) !=
        SourceMgr.getFileID(Range.getEnd())) {
      return StringRef(); // Empty string.
    }
  
    return Lexer::getSourceText(CharSourceRange(Range, true), SourceMgr,
                                LangOpts);
  }
  
  /// If the given expression is actually a DeclRefExpr or a MemberExpr,
  /// find and return the underlying ValueDecl; otherwise, return NULL.
  static const ValueDecl *getReferencedVariable(const Expr *E) {
    if (const DeclRefExpr *DRE = getDeclRef(E))
      return dyn_cast<VarDecl>(DRE->getDecl());
    if (const auto *Mem = dyn_cast<MemberExpr>(E->IgnoreParenImpCasts()))
      return dyn_cast<FieldDecl>(Mem->getMemberDecl());
    return nullptr;
  }
  
  /// Returns true when the given expression is a member expression
  /// whose base is `this` (implicitly or not).
  static bool isDirectMemberExpr(const Expr *E) {
    if (const auto *Member = dyn_cast<MemberExpr>(E->IgnoreParenImpCasts()))
      return isa<CXXThisExpr>(Member->getBase()->IgnoreParenImpCasts());
    return false;
  }
  
  /// Given an expression that represents an usage of an element from the
  /// containter that we are iterating over, returns false when it can be
  /// guaranteed this element cannot be modified as a result of this usage.
  static bool canBeModified(ASTContext *Context, const Expr *E) {
    if (E->getType().isConstQualified())
      return false;
    auto Parents = Context->getParents(*E);
    if (Parents.size() != 1)
      return true;
    if (const auto *Cast = Parents[0].get<ImplicitCastExpr>()) {
      if ((Cast->getCastKind() == CK_NoOp &&
           Cast->getType() == E->getType().withConst()) ||
          (Cast->getCastKind() == CK_LValueToRValue &&
           !Cast->getType().isNull() && Cast->getType()->isFundamentalType()))
        return false;
    }
    // FIXME: Make this function more generic.
    return true;
  }
  
  /// Returns true when it can be guaranteed that the elements of the
  /// container are not being modified.
  static bool usagesAreConst(ASTContext *Context, const UsageResult &Usages) {
    for (const Usage &U : Usages) {
      // Lambda captures are just redeclarations (VarDecl) of the same variable,
      // not expressions. If we want to know if a variable that is captured by
      // reference can be modified in an usage inside the lambda's body, we need
      // to find the expression corresponding to that particular usage, later in
      // this loop.
      if (U.Kind != Usage::UK_CaptureByCopy && U.Kind != Usage::UK_CaptureByRef &&
          canBeModified(Context, U.Expression))
        return false;
    }
    return true;
  }
  
  /// Returns true if the elements of the container are never accessed
  /// by reference.
  static bool usagesReturnRValues(const UsageResult &Usages) {
    for (const auto &U : Usages) {
      if (U.Expression && !U.Expression->isRValue())
        return false;
    }
    return true;
  }
  
  /// Returns true if the container is const-qualified.
  static bool containerIsConst(const Expr *ContainerExpr, bool Dereference) {
    if (const auto *VDec = getReferencedVariable(ContainerExpr)) {
      QualType CType = VDec->getType();
      if (Dereference) {
        if (!CType->isPointerType())
          return false;
        CType = CType->getPointeeType();
      }
      // If VDec is a reference to a container, Dereference is false,
      // but we still need to check the const-ness of the underlying container
      // type.
      CType = CType.getNonReferenceType();
      return CType.isConstQualified();
    }
    return false;
  }
  
  LoopConvertCheck::RangeDescriptor::RangeDescriptor()
      : ContainerNeedsDereference(false), DerefByConstRef(false),
        DerefByValue(false) {}
  
  LoopConvertCheck::LoopConvertCheck(StringRef Name, ClangTidyContext *Context)
      : ClangTidyCheck(Name, Context), TUInfo(new TUTrackingInfo),
        MaxCopySize(std::stoull(Options.get("MaxCopySize", "16"))),
        MinConfidence(Options.get("MinConfidence", getConfidenceMapping(),
                                  Confidence::CL_Reasonable)),
        NamingStyle(Options.get("NamingStyle", getStyleMapping(),
                                VariableNamer::NS_CamelCase)) {}
  
  void LoopConvertCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
    Options.store(Opts, "MaxCopySize", std::to_string(MaxCopySize));
    Options.store(Opts, "MinConfidence", MinConfidence, getConfidenceMapping());
    Options.store(Opts, "NamingStyle", NamingStyle, getStyleMapping());
  }
  
  void LoopConvertCheck::registerMatchers(MatchFinder *Finder) {
    Finder->addMatcher(traverse(ast_type_traits::TK_AsIs, makeArrayLoopMatcher()),
                       this);
    Finder->addMatcher(
        traverse(ast_type_traits::TK_AsIs, makeIteratorLoopMatcher()), this);
    Finder->addMatcher(
        traverse(ast_type_traits::TK_AsIs, makePseudoArrayLoopMatcher()), this);
  }
  
  /// Given the range of a single declaration, such as:
  /// \code
  ///   unsigned &ThisIsADeclarationThatCanSpanSeveralLinesOfCode =
  ///       InitializationValues[I];
  ///   next_instruction;
  /// \endcode
  /// Finds the range that has to be erased to remove this declaration without
  /// leaving empty lines, by extending the range until the beginning of the
  /// next instruction.
  ///
  /// We need to delete a potential newline after the deleted alias, as
  /// clang-format will leave empty lines untouched. For all other formatting we
  /// rely on clang-format to fix it.
  void LoopConvertCheck::getAliasRange(SourceManager &SM, SourceRange &Range) {
    bool Invalid = false;
    const char *TextAfter =
        SM.getCharacterData(Range.getEnd().getLocWithOffset(1), &Invalid);
    if (Invalid)
      return;
    unsigned Offset = std::strspn(TextAfter, " \t\r\n");
    Range =
        SourceRange(Range.getBegin(), Range.getEnd().getLocWithOffset(Offset));
  }
  
  /// Computes the changes needed to convert a given for loop, and
  /// applies them.
  void LoopConvertCheck::doConversion(
      ASTContext *Context, const VarDecl *IndexVar,
      const ValueDecl *MaybeContainer, const UsageResult &Usages,
      const DeclStmt *AliasDecl, bool AliasUseRequired, bool AliasFromForInit,
      const ForStmt *Loop, RangeDescriptor Descriptor) {
    std::string VarName;
    bool VarNameFromAlias = (Usages.size() == 1) && AliasDecl;
    bool AliasVarIsRef = false;
    bool CanCopy = true;
    std::vector<FixItHint> FixIts;
    if (VarNameFromAlias) {
      const auto *AliasVar = cast<VarDecl>(AliasDecl->getSingleDecl());
      VarName = AliasVar->getName().str();
  
      // Use the type of the alias if it's not the same
      QualType AliasVarType = AliasVar->getType();
      assert(!AliasVarType.isNull() && "Type in VarDecl is null");
      if (AliasVarType->isReferenceType()) {
        AliasVarType = AliasVarType.getNonReferenceType();
        AliasVarIsRef = true;
      }
      if (Descriptor.ElemType.isNull() ||
          !Context->hasSameUnqualifiedType(AliasVarType, Descriptor.ElemType))
        Descriptor.ElemType = AliasVarType;
  
      // We keep along the entire DeclStmt to keep the correct range here.
      SourceRange ReplaceRange = AliasDecl->getSourceRange();
  
      std::string ReplacementText;
      if (AliasUseRequired) {
        ReplacementText = VarName;
      } else if (AliasFromForInit) {
        // FIXME: Clang includes the location of the ';' but only for DeclStmt's
        // in a for loop's init clause. Need to put this ';' back while removing
        // the declaration of the alias variable. This is probably a bug.
        ReplacementText = ";";
      } else {
        // Avoid leaving empty lines or trailing whitespaces.
        getAliasRange(Context->getSourceManager(), ReplaceRange);
      }
  
      FixIts.push_back(FixItHint::CreateReplacement(
          CharSourceRange::getTokenRange(ReplaceRange), ReplacementText));
      // No further replacements are made to the loop, since the iterator or index
      // was used exactly once - in the initialization of AliasVar.
    } else {
      VariableNamer Namer(&TUInfo->getGeneratedDecls(),
                          &TUInfo->getParentFinder().getStmtToParentStmtMap(),
                          Loop, IndexVar, MaybeContainer, Context, NamingStyle);
      VarName = Namer.createIndexName();
      // First, replace all usages of the array subscript expression with our new
      // variable.
      for (const auto &Usage : Usages) {
        std::string ReplaceText;
        SourceRange Range = Usage.Range;
        if (Usage.Expression) {
          // If this is an access to a member through the arrow operator, after
          // the replacement it must be accessed through the '.' operator.
          ReplaceText = Usage.Kind == Usage::UK_MemberThroughArrow ? VarName + "."
                                                                   : VarName;
          auto Parents = Context->getParents(*Usage.Expression);
          if (Parents.size() == 1) {
            if (const auto *Paren = Parents[0].get<ParenExpr>()) {
              // Usage.Expression will be replaced with the new index variable,
              // and parenthesis around a simple DeclRefExpr can always be
              // removed.
              Range = Paren->getSourceRange();
            } else if (const auto *UOP = Parents[0].get<UnaryOperator>()) {
              // If we are taking the address of the loop variable, then we must
              // not use a copy, as it would mean taking the address of the loop's
              // local index instead.
              // FIXME: This won't catch cases where the address is taken outside
              // of the loop's body (for instance, in a function that got the
              // loop's index as a const reference parameter), or where we take
              // the address of a member (like "&Arr[i].A.B.C").
              if (UOP->getOpcode() == UO_AddrOf)
                CanCopy = false;
            }
          }
        } else {
          // The Usage expression is only null in case of lambda captures (which
          // are VarDecl). If the index is captured by value, add '&' to capture
          // by reference instead.
          ReplaceText =
              Usage.Kind == Usage::UK_CaptureByCopy ? "&" + VarName : VarName;
        }
        TUInfo->getReplacedVars().insert(std::make_pair(Loop, IndexVar));
        FixIts.push_back(FixItHint::CreateReplacement(
            CharSourceRange::getTokenRange(Range), ReplaceText));
      }
    }
  
    // Now, we need to construct the new range expression.
    SourceRange ParenRange(Loop->getLParenLoc(), Loop->getRParenLoc());
  
    QualType Type = Context->getAutoDeductType();
    if (!Descriptor.ElemType.isNull() && Descriptor.ElemType->isFundamentalType())
      Type = Descriptor.ElemType.getUnqualifiedType();
    Type = Type.getDesugaredType(*Context);
  
    // If the new variable name is from the aliased variable, then the reference
    // type for the new variable should only be used if the aliased variable was
    // declared as a reference.
    bool IsCheapToCopy =
        !Descriptor.ElemType.isNull() &&
        Descriptor.ElemType.isTriviallyCopyableType(*Context) &&
        // TypeInfo::Width is in bits.
        Context->getTypeInfo(Descriptor.ElemType).Width <= 8 * MaxCopySize;
    bool UseCopy = CanCopy && ((VarNameFromAlias && !AliasVarIsRef) ||
                               (Descriptor.DerefByConstRef && IsCheapToCopy));
  
    if (!UseCopy) {
      if (Descriptor.DerefByConstRef) {
        Type = Context->getLValueReferenceType(Context->getConstType(Type));
      } else if (Descriptor.DerefByValue) {
        if (!IsCheapToCopy)
          Type = Context->getRValueReferenceType(Type);
      } else {
        Type = Context->getLValueReferenceType(Type);
      }
    }
  
    StringRef MaybeDereference = Descriptor.ContainerNeedsDereference ? "*" : "";
    std::string TypeString = Type.getAsString(getLangOpts());
    std::string Range = ("(" + TypeString + " " + VarName + " : " +
                         MaybeDereference + Descriptor.ContainerString + ")")
                            .str();
    FixIts.push_back(FixItHint::CreateReplacement(
        CharSourceRange::getTokenRange(ParenRange), Range));
    diag(Loop->getForLoc(), "use range-based for loop instead") << FixIts;
    TUInfo->getGeneratedDecls().insert(make_pair(Loop, VarName));
  }
  
  /// Returns a string which refers to the container iterated over.
  StringRef LoopConvertCheck::getContainerString(ASTContext *Context,
                                                 const ForStmt *Loop,
                                                 const Expr *ContainerExpr) {
    StringRef ContainerString;
    ContainerExpr = ContainerExpr->IgnoreParenImpCasts();
    if (isa<CXXThisExpr>(ContainerExpr)) {
      ContainerString = "this";
    } else {
      // For CXXOperatorCallExpr (e.g. vector_ptr->size()), its first argument is
      // the class object (vector_ptr) we are targeting.
      if (const auto* E = dyn_cast<CXXOperatorCallExpr>(ContainerExpr))
        ContainerExpr = E->getArg(0);
      ContainerString =
          getStringFromRange(Context->getSourceManager(), Context->getLangOpts(),
                             ContainerExpr->getSourceRange());
    }
  
    return ContainerString;
  }
  
  /// Determines what kind of 'auto' must be used after converting a for
  /// loop that iterates over an array or pseudoarray.
  void LoopConvertCheck::getArrayLoopQualifiers(ASTContext *Context,
                                                const BoundNodes &Nodes,
                                                const Expr *ContainerExpr,
                                                const UsageResult &Usages,
                                                RangeDescriptor &Descriptor) {
    // On arrays and pseudoarrays, we must figure out the qualifiers from the
    // usages.
    if (usagesAreConst(Context, Usages) ||
        containerIsConst(ContainerExpr, Descriptor.ContainerNeedsDereference)) {
      Descriptor.DerefByConstRef = true;
    }
    if (usagesReturnRValues(Usages)) {
      // If the index usages (dereference, subscript, at, ...) return rvalues,
      // then we should not use a reference, because we need to keep the code
      // correct if it mutates the returned objects.
      Descriptor.DerefByValue = true;
    }
    // Try to find the type of the elements on the container, to check if
    // they are trivially copyable.
    for (const Usage &U : Usages) {
      if (!U.Expression || U.Expression->getType().isNull())
        continue;
      QualType Type = U.Expression->getType().getCanonicalType();
      if (U.Kind == Usage::UK_MemberThroughArrow) {
        if (!Type->isPointerType()) {
          continue;
        }
        Type = Type->getPointeeType();
      }
      Descriptor.ElemType = Type;
    }
  }
  
  /// Determines what kind of 'auto' must be used after converting an
  /// iterator based for loop.
  void LoopConvertCheck::getIteratorLoopQualifiers(ASTContext *Context,
                                                   const BoundNodes &Nodes,
                                                   RangeDescriptor &Descriptor) {
    // The matchers for iterator loops provide bound nodes to obtain this
    // information.
    const auto *InitVar = Nodes.getNodeAs<VarDecl>(InitVarName);
    QualType CanonicalInitVarType = InitVar->getType().getCanonicalType();
    const auto *DerefByValueType =
        Nodes.getNodeAs<QualType>(DerefByValueResultName);
    Descriptor.DerefByValue = DerefByValueType;
  
    if (Descriptor.DerefByValue) {
      // If the dereference operator returns by value then test for the
      // canonical const qualification of the init variable type.
      Descriptor.DerefByConstRef = CanonicalInitVarType.isConstQualified();
      Descriptor.ElemType = *DerefByValueType;
    } else {
      if (const auto *DerefType =
              Nodes.getNodeAs<QualType>(DerefByRefResultName)) {
        // A node will only be bound with DerefByRefResultName if we're dealing
        // with a user-defined iterator type. Test the const qualification of
        // the reference type.
        auto ValueType = DerefType->getNonReferenceType();
  
        Descriptor.DerefByConstRef = ValueType.isConstQualified();
        Descriptor.ElemType = ValueType;
      } else {
        // By nature of the matcher this case is triggered only for built-in
        // iterator types (i.e. pointers).
        assert(isa<PointerType>(CanonicalInitVarType) &&
               "Non-class iterator type is not a pointer type");
  
        // We test for const qualification of the pointed-at type.
        Descriptor.DerefByConstRef =
            CanonicalInitVarType->getPointeeType().isConstQualified();
        Descriptor.ElemType = CanonicalInitVarType->getPointeeType();
      }
    }
  }
  
  /// Determines the parameters needed to build the range replacement.
  void LoopConvertCheck::determineRangeDescriptor(
      ASTContext *Context, const BoundNodes &Nodes, const ForStmt *Loop,
      LoopFixerKind FixerKind, const Expr *ContainerExpr,
      const UsageResult &Usages, RangeDescriptor &Descriptor) {
    Descriptor.ContainerString =
        std::string(getContainerString(Context, Loop, ContainerExpr));
  
    if (FixerKind == LFK_Iterator)
      getIteratorLoopQualifiers(Context, Nodes, Descriptor);
    else
      getArrayLoopQualifiers(Context, Nodes, ContainerExpr, Usages, Descriptor);
  }
  
  /// Check some of the conditions that must be met for the loop to be
  /// convertible.
  bool LoopConvertCheck::isConvertible(ASTContext *Context,
                                       const ast_matchers::BoundNodes &Nodes,
                                       const ForStmt *Loop,
                                       LoopFixerKind FixerKind) {
    // If we already modified the range of this for loop, don't do any further
    // updates on this iteration.
    if (TUInfo->getReplacedVars().count(Loop))
      return false;
  
    // Check that we have exactly one index variable and at most one end variable.
    const auto *LoopVar = Nodes.getNodeAs<VarDecl>(IncrementVarName);
    const auto *CondVar = Nodes.getNodeAs<VarDecl>(ConditionVarName);
    const auto *InitVar = Nodes.getNodeAs<VarDecl>(InitVarName);
    if (!areSameVariable(LoopVar, CondVar) || !areSameVariable(LoopVar, InitVar))
      return false;
    const auto *EndVar = Nodes.getNodeAs<VarDecl>(EndVarName);
    const auto *ConditionEndVar = Nodes.getNodeAs<VarDecl>(ConditionEndVarName);
    if (EndVar && !areSameVariable(EndVar, ConditionEndVar))
      return false;
  
    // FIXME: Try to put most of this logic inside a matcher.
    if (FixerKind == LFK_Iterator) {
      QualType InitVarType = InitVar->getType();
      QualType CanonicalInitVarType = InitVarType.getCanonicalType();
  
      const auto *BeginCall = Nodes.getNodeAs<CXXMemberCallExpr>(BeginCallName);
      assert(BeginCall && "Bad Callback. No begin call expression");
      QualType CanonicalBeginType =
          BeginCall->getMethodDecl()->getReturnType().getCanonicalType();
      if (CanonicalBeginType->isPointerType() &&
          CanonicalInitVarType->isPointerType()) {
        // If the initializer and the variable are both pointers check if the
        // un-qualified pointee types match, otherwise we don't use auto.
        if (!Context->hasSameUnqualifiedType(
                CanonicalBeginType->getPointeeType(),
                CanonicalInitVarType->getPointeeType()))
          return false;
      }
    } else if (FixerKind == LFK_PseudoArray) {
      // This call is required to obtain the container.
      const auto *EndCall = Nodes.getNodeAs<CXXMemberCallExpr>(EndCallName);
      if (!EndCall || !dyn_cast<MemberExpr>(EndCall->getCallee()))
        return false;
    }
    return true;
  }
  
  void LoopConvertCheck::check(const MatchFinder::MatchResult &Result) {
    const BoundNodes &Nodes = Result.Nodes;
    Confidence ConfidenceLevel(Confidence::CL_Safe);
    ASTContext *Context = Result.Context;
  
    const ForStmt *Loop;
    LoopFixerKind FixerKind;
    RangeDescriptor Descriptor;
  
    if ((Loop = Nodes.getNodeAs<ForStmt>(LoopNameArray))) {
      FixerKind = LFK_Array;
    } else if ((Loop = Nodes.getNodeAs<ForStmt>(LoopNameIterator))) {
      FixerKind = LFK_Iterator;
    } else {
      Loop = Nodes.getNodeAs<ForStmt>(LoopNamePseudoArray);
      assert(Loop && "Bad Callback. No for statement");
      FixerKind = LFK_PseudoArray;
    }
  
    if (!isConvertible(Context, Nodes, Loop, FixerKind))
      return;
  
    const auto *LoopVar = Nodes.getNodeAs<VarDecl>(IncrementVarName);
    const auto *EndVar = Nodes.getNodeAs<VarDecl>(EndVarName);
  
    // If the loop calls end()/size() after each iteration, lower our confidence
    // level.
    if (FixerKind != LFK_Array && !EndVar)
      ConfidenceLevel.lowerTo(Confidence::CL_Reasonable);
  
    // If the end comparison isn't a variable, we can try to work with the
    // expression the loop variable is being tested against instead.
    const auto *EndCall = Nodes.getNodeAs<CXXMemberCallExpr>(EndCallName);
    const auto *BoundExpr = Nodes.getNodeAs<Expr>(ConditionBoundName);
  
    // Find container expression of iterators and pseudoarrays, and determine if
    // this expression needs to be dereferenced to obtain the container.
    // With array loops, the container is often discovered during the
    // ForLoopIndexUseVisitor traversal.
    const Expr *ContainerExpr = nullptr;
    if (FixerKind == LFK_Iterator) {
      ContainerExpr = findContainer(Context, LoopVar->getInit(),
                                    EndVar ? EndVar->getInit() : EndCall,
                                    &Descriptor.ContainerNeedsDereference);
    } else if (FixerKind == LFK_PseudoArray) {
      ContainerExpr = EndCall->getImplicitObjectArgument();
      Descriptor.ContainerNeedsDereference =
          dyn_cast<MemberExpr>(EndCall->getCallee())->isArrow();
    }
  
    // We must know the container or an array length bound.
    if (!ContainerExpr && !BoundExpr)
      return;
  
    ForLoopIndexUseVisitor Finder(Context, LoopVar, EndVar, ContainerExpr,
                                  BoundExpr,
                                  Descriptor.ContainerNeedsDereference);
  
    // Find expressions and variables on which the container depends.
    if (ContainerExpr) {
      ComponentFinderASTVisitor ComponentFinder;
      ComponentFinder.findExprComponents(ContainerExpr->IgnoreParenImpCasts());
      Finder.addComponents(ComponentFinder.getComponents());
    }
  
    // Find usages of the loop index. If they are not used in a convertible way,
    // stop here.
    if (!Finder.findAndVerifyUsages(Loop->getBody()))
      return;
    ConfidenceLevel.lowerTo(Finder.getConfidenceLevel());
  
    // Obtain the container expression, if we don't have it yet.
    if (FixerKind == LFK_Array) {
      ContainerExpr = Finder.getContainerIndexed()->IgnoreParenImpCasts();
  
      // Very few loops are over expressions that generate arrays rather than
      // array variables. Consider loops over arrays that aren't just represented
      // by a variable to be risky conversions.
      if (!getReferencedVariable(ContainerExpr) &&
          !isDirectMemberExpr(ContainerExpr))
        ConfidenceLevel.lowerTo(Confidence::CL_Risky);
    }
  
    // Find out which qualifiers we have to use in the loop range.
    TraversalKindScope RAII(*Context, ast_type_traits::TK_AsIs);
    const UsageResult &Usages = Finder.getUsages();
    determineRangeDescriptor(Context, Nodes, Loop, FixerKind, ContainerExpr,
                             Usages, Descriptor);
  
    // Ensure that we do not try to move an expression dependent on a local
    // variable declared inside the loop outside of it.
    // FIXME: Determine when the external dependency isn't an expression converted
    // by another loop.
    TUInfo->getParentFinder().gatherAncestors(*Context);
    DependencyFinderASTVisitor DependencyFinder(
        &TUInfo->getParentFinder().getStmtToParentStmtMap(),
        &TUInfo->getParentFinder().getDeclToParentStmtMap(),
        &TUInfo->getReplacedVars(), Loop);
  
    if (DependencyFinder.dependsOnInsideVariable(ContainerExpr) ||
        Descriptor.ContainerString.empty() || Usages.empty() ||
        ConfidenceLevel.getLevel() < MinConfidence)
      return;
  
    doConversion(Context, LoopVar, getReferencedVariable(ContainerExpr), Usages,
                 Finder.getAliasDecl(), Finder.aliasUseRequired(),
                 Finder.aliasFromForInit(), Loop, Descriptor);
  }
  
  } // namespace modernize
  } // namespace tidy
  } // namespace clang
  