clang-tools-extra/clang-tidy/modernize/UseAutoCheck.cpp - rust-lang/llvm-project - Git at Google

 //===--- UseAutoCheck.cpp - clang-tidy-------------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//

 #include "UseAutoCheck.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
 #include "clang/ASTMatchers/ASTMatchers.h"
 #include "clang/Basic/CharInfo.h"
 #include "clang/Tooling/FixIt.h"

 using namespace clang;
 using namespace clang::ast_matchers;
 using namespace clang::ast_matchers::internal;

 namespace clang {
 namespace tidy {
 namespace modernize {
 namespace {

 const char IteratorDeclStmtId[] = "iterator_decl";
 const char DeclWithNewId[] = "decl_new";
 const char DeclWithCastId[] = "decl_cast";
 const char DeclWithTemplateCastId[] = "decl_template";

 size_t GetTypeNameLength(bool RemoveStars, StringRef Text) {
   enum CharType { Space, Alpha, Punctuation };
   CharType LastChar = Space, BeforeSpace = Punctuation;
   size_t NumChars = 0;
   int TemplateTypenameCntr = 0;
   for (const unsigned char C : Text) {
     if (C == '<')
       ++TemplateTypenameCntr;
     else if (C == '>')
       --TemplateTypenameCntr;
     const CharType NextChar =
         isAlphanumeric(C)
             ? Alpha
             : (isWhitespace(C) ||
                (!RemoveStars && TemplateTypenameCntr == 0 && C == '*'))
                   ? Space
                   : Punctuation;
     if (NextChar != Space) {
       ++NumChars; // Count the non-space character.
       if (LastChar == Space && NextChar == Alpha && BeforeSpace == Alpha)
         ++NumChars; // Count a single space character between two words.
       BeforeSpace = NextChar;
     }
     LastChar = NextChar;
   }
   return NumChars;
 }

 /// \brief Matches variable declarations that have explicit initializers that
 /// are not initializer lists.
 ///
 /// Given
 /// \code
 ///   iterator I = Container.begin();
 ///   MyType A(42);
 ///   MyType B{2};
 ///   MyType C;
 /// \endcode
 ///
 /// varDecl(hasWrittenNonListInitializer()) maches \c I and \c A but not \c B
 /// or \c C.
 AST_MATCHER(VarDecl, hasWrittenNonListInitializer) {
   const Expr *Init = Node.getAnyInitializer();
   if (!Init)
     return false;

   Init = Init->IgnoreImplicit();

   // The following test is based on DeclPrinter::VisitVarDecl() to find if an
   // initializer is implicit or not.
   if (const auto *Construct = dyn_cast<CXXConstructExpr>(Init)) {
     return !Construct->isListInitialization() && Construct->getNumArgs() > 0 &&
            !Construct->getArg(0)->isDefaultArgument();
   }
   return Node.getInitStyle() != VarDecl::ListInit;
 }

 /// \brief Matches QualTypes that are type sugar for QualTypes that match \c
 /// SugarMatcher.
 ///
 /// Given
 /// \code
 ///   class C {};
 ///   typedef C my_type;
 ///   typedef my_type my_other_type;
 /// \endcode
 ///
 /// qualType(isSugarFor(recordType(hasDeclaration(namedDecl(hasName("C"))))))
 /// matches \c my_type and \c my_other_type.
 AST_MATCHER_P(QualType, isSugarFor, Matcher<QualType>, SugarMatcher) {
   QualType QT = Node;
   while (true) {
     if (SugarMatcher.matches(QT, Finder, Builder))
       return true;

     QualType NewQT = QT.getSingleStepDesugaredType(Finder->getASTContext());
     if (NewQT == QT)
       return false;
     QT = NewQT;
   }
 }

 /// \brief Matches named declarations that have one of the standard iterator
 /// names: iterator, reverse_iterator, const_iterator, const_reverse_iterator.
 ///
 /// Given
 /// \code
 ///   iterator I;
 ///   const_iterator CI;
 /// \endcode
 ///
 /// namedDecl(hasStdIteratorName()) matches \c I and \c CI.
 AST_MATCHER(NamedDecl, hasStdIteratorName) {
   static const char *const IteratorNames[] = {"iterator", "reverse_iterator",
                                               "const_iterator",
                                               "const_reverse_iterator"};

   for (const char *Name : IteratorNames) {
     if (hasName(Name).matches(Node, Finder, Builder))
       return true;
   }
   return false;
 }

 /// \brief Matches named declarations that have one of the standard container
 /// names.
 ///
 /// Given
 /// \code
 ///   class vector {};
 ///   class forward_list {};
 ///   class my_ver{};
 /// \endcode
 ///
 /// recordDecl(hasStdContainerName()) matches \c vector and \c forward_list
 /// but not \c my_vec.
 AST_MATCHER(NamedDecl, hasStdContainerName) {
   static const char *const ContainerNames[] = {
       "array",         "deque",
       "forward_list",  "list",
       "vector",

       "map",           "multimap",
       "set",           "multiset",

       "unordered_map", "unordered_multimap",
       "unordered_set", "unordered_multiset",

       "queue",         "priority_queue",
       "stack"};

   for (const char *Name : ContainerNames) {
     if (hasName(Name).matches(Node, Finder, Builder))
       return true;
   }
   return false;
 }

 /// Matches declarations whose declaration context is the C++ standard library
 /// namespace std.
 ///
 /// Note that inline namespaces are silently ignored during the lookup since
 /// both libstdc++ and libc++ are known to use them for versioning purposes.
 ///
 /// Given:
 /// \code
 ///   namespace ns {
 ///     struct my_type {};
 ///     using namespace std;
 ///   }
 ///
 ///   using std::vector;
 ///   using ns:my_type;
 ///   using ns::list;
 /// \code
 ///
 /// usingDecl(hasAnyUsingShadowDecl(hasTargetDecl(isFromStdNamespace())))
 /// matches "using std::vector" and "using ns::list".
 AST_MATCHER(Decl, isFromStdNamespace) {
   const DeclContext *D = Node.getDeclContext();

   while (D->isInlineNamespace())
     D = D->getParent();

   if (!D->isNamespace() || !D->getParent()->isTranslationUnit())
     return false;

   const IdentifierInfo *Info = cast<NamespaceDecl>(D)->getIdentifier();

   return (Info && Info->isStr("std"));
 }

 /// Matches declaration reference or member expressions with explicit template
 /// arguments.
 AST_POLYMORPHIC_MATCHER(hasExplicitTemplateArgs,
                         AST_POLYMORPHIC_SUPPORTED_TYPES(DeclRefExpr,
                                                         MemberExpr)) {
   return Node.hasExplicitTemplateArgs();
 }

 /// \brief Returns a DeclarationMatcher that matches standard iterators nested
 /// inside records with a standard container name.
 DeclarationMatcher standardIterator() {
   return decl(
       namedDecl(hasStdIteratorName()),
       hasDeclContext(recordDecl(hasStdContainerName(), isFromStdNamespace())));
 }

 /// \brief Returns a TypeMatcher that matches typedefs for standard iterators
 /// inside records with a standard container name.
 TypeMatcher typedefIterator() {
   return typedefType(hasDeclaration(standardIterator()));
 }

 /// \brief Returns a TypeMatcher that matches records named for standard
 /// iterators nested inside records named for standard containers.
 TypeMatcher nestedIterator() {
   return recordType(hasDeclaration(standardIterator()));
 }

 /// \brief Returns a TypeMatcher that matches types declared with using
 /// declarations and which name standard iterators for standard containers.
 TypeMatcher iteratorFromUsingDeclaration() {
   auto HasIteratorDecl = hasDeclaration(namedDecl(hasStdIteratorName()));
   // Types resulting from using declarations are represented by elaboratedType.
   return elaboratedType(
       // Unwrap the nested name specifier to test for one of the standard
       // containers.
       hasQualifier(specifiesType(templateSpecializationType(hasDeclaration(
           namedDecl(hasStdContainerName(), isFromStdNamespace()))))),
       // the named type is what comes after the final '::' in the type. It
       // should name one of the standard iterator names.
       namesType(
           anyOf(typedefType(HasIteratorDecl), recordType(HasIteratorDecl))));
 }

 /// \brief This matcher returns declaration statements that contain variable
 /// declarations with written non-list initializer for standard iterators.
 StatementMatcher makeIteratorDeclMatcher() {
   return declStmt(unless(has(
                       varDecl(anyOf(unless(hasWrittenNonListInitializer()),
                                     unless(hasType(isSugarFor(anyOf(
                                         typedefIterator(), nestedIterator(),
                                         iteratorFromUsingDeclaration())))))))))
       .bind(IteratorDeclStmtId);
 }

 StatementMatcher makeDeclWithNewMatcher() {
   return declStmt(
              unless(has(varDecl(anyOf(
                  unless(hasInitializer(ignoringParenImpCasts(cxxNewExpr()))),
                  // FIXME: TypeLoc information is not reliable where CV
                  // qualifiers are concerned so these types can't be
                  // handled for now.
                  hasType(pointerType(
                      pointee(hasCanonicalType(hasLocalQualifiers())))),

                  // FIXME: Handle function pointers. For now we ignore them
                  // because the replacement replaces the entire type
                  // specifier source range which includes the identifier.
                  hasType(pointsTo(
                      pointsTo(parenType(innerType(functionType()))))))))))
       .bind(DeclWithNewId);
 }

 StatementMatcher makeDeclWithCastMatcher() {
   return declStmt(
              unless(has(varDecl(unless(hasInitializer(explicitCastExpr()))))))
       .bind(DeclWithCastId);
 }

 StatementMatcher makeDeclWithTemplateCastMatcher() {
   auto ST =
       substTemplateTypeParmType(hasReplacementType(equalsBoundNode("arg")));

   auto ExplicitCall =
       anyOf(has(memberExpr(hasExplicitTemplateArgs())),
             has(ignoringImpCasts(declRefExpr(hasExplicitTemplateArgs()))));

   auto TemplateArg =
       hasTemplateArgument(0, refersToType(qualType().bind("arg")));

   auto TemplateCall = callExpr(
       ExplicitCall,
       callee(functionDecl(TemplateArg,
                           returns(anyOf(ST, pointsTo(ST), references(ST))))));

   return declStmt(unless(has(varDecl(
                       unless(hasInitializer(ignoringImplicit(TemplateCall)))))))
       .bind(DeclWithTemplateCastId);
 }

 StatementMatcher makeCombinedMatcher() {
   return declStmt(
       // At least one varDecl should be a child of the declStmt to ensure
       // it's a declaration list and avoid matching other declarations,
       // e.g. using directives.
       has(varDecl(unless(isImplicit()))),
       // Skip declarations that are already using auto.
       unless(has(varDecl(anyOf(hasType(autoType()),
                                hasType(qualType(hasDescendant(autoType()))))))),
       anyOf(makeIteratorDeclMatcher(), makeDeclWithNewMatcher(),
             makeDeclWithCastMatcher(), makeDeclWithTemplateCastMatcher()));
 }

 } // namespace

 UseAutoCheck::UseAutoCheck(StringRef Name, ClangTidyContext *Context)
     : ClangTidyCheck(Name, Context),
       MinTypeNameLength(Options.get("MinTypeNameLength", 5)),
       RemoveStars(Options.get("RemoveStars", 0)) {}

 void UseAutoCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
   Options.store(Opts, "MinTypeNameLength", MinTypeNameLength);
   Options.store(Opts, "RemoveStars", RemoveStars ? 1 : 0);
 }

 void UseAutoCheck::registerMatchers(MatchFinder *Finder) {
   // Only register the matchers for C++; the functionality currently does not
   // provide any benefit to other languages, despite being benign.
   if (getLangOpts().CPlusPlus) {
     Finder->addMatcher(makeCombinedMatcher(), this);
   }
 }

 void UseAutoCheck::replaceIterators(const DeclStmt *D, ASTContext *Context) {
   for (const auto *Dec : D->decls()) {
     const auto *V = cast<VarDecl>(Dec);
     const Expr *ExprInit = V->getInit();

     // Skip expressions with cleanups from the intializer expression.
     if (const auto *E = dyn_cast<ExprWithCleanups>(ExprInit))
       ExprInit = E->getSubExpr();

     const auto *Construct = dyn_cast<CXXConstructExpr>(ExprInit);
     if (!Construct)
       continue;

     // Ensure that the constructor receives a single argument.
     if (Construct->getNumArgs() != 1)
       return;

     // Drill down to the as-written initializer.
     const Expr *E = (*Construct->arg_begin())->IgnoreParenImpCasts();
     if (E != E->IgnoreConversionOperator()) {
       // We hit a conversion operator. Early-out now as they imply an implicit
       // conversion from a different type. Could also mean an explicit
       // conversion from the same type but that's pretty rare.
       return;
     }

     if (const auto *NestedConstruct = dyn_cast<CXXConstructExpr>(E)) {
       // If we ran into an implicit conversion contructor, can't convert.
       //
       // FIXME: The following only checks if the constructor can be used
       // implicitly, not if it actually was. Cases where the converting
       // constructor was used explicitly won't get converted.
       if (NestedConstruct->getConstructor()->isConvertingConstructor(false))
         return;
     }
     if (!Context->hasSameType(V->getType(), E->getType()))
       return;
   }

   // Get the type location using the first declaration.
   const auto *V = cast<VarDecl>(*D->decl_begin());

   // WARNING: TypeLoc::getSourceRange() will include the identifier for things
   // like function pointers. Not a concern since this action only works with
   // iterators but something to keep in mind in the future.

   SourceRange Range(V->getTypeSourceInfo()->getTypeLoc().getSourceRange());
   diag(Range.getBegin(), "use auto when declaring iterators")
       << FixItHint::CreateReplacement(Range, "auto");
 }

 void UseAutoCheck::replaceExpr(
     const DeclStmt *D, ASTContext *Context,
     llvm::function_ref<QualType(const Expr *)> GetType, StringRef Message) {
   const auto *FirstDecl = dyn_cast<VarDecl>(*D->decl_begin());
   // Ensure that there is at least one VarDecl within the DeclStmt.
   if (!FirstDecl)
     return;

   const QualType FirstDeclType = FirstDecl->getType().getCanonicalType();

   std::vector<FixItHint> StarRemovals;
   for (const auto *Dec : D->decls()) {
     const auto *V = cast<VarDecl>(Dec);
     // Ensure that every DeclStmt child is a VarDecl.
     if (!V)
       return;

     const auto *Expr = V->getInit()->IgnoreParenImpCasts();
     // Ensure that every VarDecl has an initializer.
     if (!Expr)
       return;

     // If VarDecl and Initializer have mismatching unqualified types.
     if (!Context->hasSameUnqualifiedType(V->getType(), GetType(Expr)))
       return;

     // All subsequent variables in this declaration should have the same
     // canonical type.  For example, we don't want to use `auto` in
     // `T *p = new T, **pp = new T*;`.
     if (FirstDeclType != V->getType().getCanonicalType())
       return;

     if (RemoveStars) {
       // Remove explicitly written '*' from declarations where there's more than
       // one declaration in the declaration list.
       if (Dec == *D->decl_begin())
         continue;

       auto Q = V->getTypeSourceInfo()->getTypeLoc().getAs<PointerTypeLoc>();
       while (!Q.isNull()) {
         StarRemovals.push_back(FixItHint::CreateRemoval(Q.getStarLoc()));
         Q = Q.getNextTypeLoc().getAs<PointerTypeLoc>();
       }
     }
   }

   // FIXME: There is, however, one case we can address: when the VarDecl pointee
   // is the same as the initializer, just more CV-qualified. However, TypeLoc
   // information is not reliable where CV qualifiers are concerned so we can't
   // do anything about this case for now.
   TypeLoc Loc = FirstDecl->getTypeSourceInfo()->getTypeLoc();
   if (!RemoveStars) {
     while (Loc.getTypeLocClass() == TypeLoc::Pointer ||
            Loc.getTypeLocClass() == TypeLoc::Qualified)
       Loc = Loc.getNextTypeLoc();
   }
   while (Loc.getTypeLocClass() == TypeLoc::LValueReference ||
          Loc.getTypeLocClass() == TypeLoc::RValueReference ||
          Loc.getTypeLocClass() == TypeLoc::Qualified) {
     Loc = Loc.getNextTypeLoc();
   }
   SourceRange Range(Loc.getSourceRange());

   if (MinTypeNameLength != 0 &&
       GetTypeNameLength(RemoveStars,
                         tooling::fixit::getText(Loc.getSourceRange(),
                                                 FirstDecl->getASTContext())) <
           MinTypeNameLength)
     return;

   auto Diag = diag(Range.getBegin(), Message);

   // Space after 'auto' to handle cases where the '*' in the pointer type is
   // next to the identifier. This avoids changing 'int *p' into 'autop'.
   // FIXME: This doesn't work for function pointers because the variable name
   // is inside the type.
   Diag << FixItHint::CreateReplacement(Range, RemoveStars ? "auto " : "auto")
        << StarRemovals;
 }

 void UseAutoCheck::check(const MatchFinder::MatchResult &Result) {
   if (const auto *Decl = Result.Nodes.getNodeAs<DeclStmt>(IteratorDeclStmtId)) {
     replaceIterators(Decl, Result.Context);
   } else if (const auto *Decl =
                  Result.Nodes.getNodeAs<DeclStmt>(DeclWithNewId)) {
     replaceExpr(Decl, Result.Context,
                 [](const Expr *Expr) { return Expr->getType(); },
                 "use auto when initializing with new to avoid "
                 "duplicating the type name");
   } else if (const auto *Decl =
                  Result.Nodes.getNodeAs<DeclStmt>(DeclWithCastId)) {
     replaceExpr(
         Decl, Result.Context,
         [](const Expr *Expr) {
           return cast<ExplicitCastExpr>(Expr)->getTypeAsWritten();
         },
         "use auto when initializing with a cast to avoid duplicating the type "
         "name");
   } else if (const auto *Decl =
                  Result.Nodes.getNodeAs<DeclStmt>(DeclWithTemplateCastId)) {
     replaceExpr(
         Decl, Result.Context,
         [](const Expr *Expr) {
           return cast<CallExpr>(Expr->IgnoreImplicit())
               ->getDirectCallee()
               ->getReturnType();
         },
         "use auto when initializing with a template cast to avoid duplicating "
         "the type name");
   } else {
     llvm_unreachable("Bad Callback. No node provided.");
   }
 }

 } // namespace modernize
 } // namespace tidy
 } // namespace clang
	//===--- UseAutoCheck.cpp - clang-tidy-------------------------------------===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//

	#include "UseAutoCheck.h"
	#include "clang/AST/ASTContext.h"
	#include "clang/ASTMatchers/ASTMatchFinder.h"
	#include "clang/ASTMatchers/ASTMatchers.h"
	#include "clang/Basic/CharInfo.h"
	#include "clang/Tooling/FixIt.h"

	using namespace clang;
	using namespace clang::ast_matchers;
	using namespace clang::ast_matchers::internal;

	namespace clang {
	namespace tidy {
	namespace modernize {
	namespace {

	const char IteratorDeclStmtId[] = "iterator_decl";
	const char DeclWithNewId[] = "decl_new";
	const char DeclWithCastId[] = "decl_cast";
	const char DeclWithTemplateCastId[] = "decl_template";

	size_t GetTypeNameLength(bool RemoveStars, StringRef Text) {
	enum CharType { Space, Alpha, Punctuation };
	CharType LastChar = Space, BeforeSpace = Punctuation;
	size_t NumChars = 0;
	int TemplateTypenameCntr = 0;
	for (const unsigned char C : Text) {
	if (C == '<')
	++TemplateTypenameCntr;
	else if (C == '>')
	--TemplateTypenameCntr;
	const CharType NextChar =
	isAlphanumeric(C)
	? Alpha
	: (isWhitespace(C) \|\|
	(!RemoveStars && TemplateTypenameCntr == 0 && C == '*'))
	? Space
	: Punctuation;
	if (NextChar != Space) {
	++NumChars; // Count the non-space character.
	if (LastChar == Space && NextChar == Alpha && BeforeSpace == Alpha)
	++NumChars; // Count a single space character between two words.
	BeforeSpace = NextChar;
	}
	LastChar = NextChar;
	}
	return NumChars;
	}

	/// \brief Matches variable declarations that have explicit initializers that
	/// are not initializer lists.
	///
	/// Given
	/// \code
	/// iterator I = Container.begin();
	/// MyType A(42);
	/// MyType B{2};
	/// MyType C;
	/// \endcode
	///
	/// varDecl(hasWrittenNonListInitializer()) maches \c I and \c A but not \c B
	/// or \c C.
	AST_MATCHER(VarDecl, hasWrittenNonListInitializer) {
	const Expr *Init = Node.getAnyInitializer();
	if (!Init)
	return false;

	Init = Init->IgnoreImplicit();

	// The following test is based on DeclPrinter::VisitVarDecl() to find if an
	// initializer is implicit or not.
	if (const auto *Construct = dyn_cast<CXXConstructExpr>(Init)) {
	return !Construct->isListInitialization() && Construct->getNumArgs() > 0 &&
	!Construct->getArg(0)->isDefaultArgument();
	}
	return Node.getInitStyle() != VarDecl::ListInit;
	}

	/// \brief Matches QualTypes that are type sugar for QualTypes that match \c
	/// SugarMatcher.
	///
	/// Given
	/// \code
	/// class C {};
	/// typedef C my_type;
	/// typedef my_type my_other_type;
	/// \endcode
	///
	/// qualType(isSugarFor(recordType(hasDeclaration(namedDecl(hasName("C"))))))
	/// matches \c my_type and \c my_other_type.
	AST_MATCHER_P(QualType, isSugarFor, Matcher<QualType>, SugarMatcher) {
	QualType QT = Node;
	while (true) {
	if (SugarMatcher.matches(QT, Finder, Builder))
	return true;

	QualType NewQT = QT.getSingleStepDesugaredType(Finder->getASTContext());
	if (NewQT == QT)
	return false;
	QT = NewQT;
	}
	}

	/// \brief Matches named declarations that have one of the standard iterator
	/// names: iterator, reverse_iterator, const_iterator, const_reverse_iterator.
	///
	/// Given
	/// \code
	/// iterator I;
	/// const_iterator CI;
	/// \endcode
	///
	/// namedDecl(hasStdIteratorName()) matches \c I and \c CI.
	AST_MATCHER(NamedDecl, hasStdIteratorName) {
	static const char *const IteratorNames[] = {"iterator", "reverse_iterator",
	"const_iterator",
	"const_reverse_iterator"};

	for (const char *Name : IteratorNames) {
	if (hasName(Name).matches(Node, Finder, Builder))
	return true;
	}
	return false;
	}

	/// \brief Matches named declarations that have one of the standard container
	/// names.
	///
	/// Given
	/// \code
	/// class vector {};
	/// class forward_list {};
	/// class my_ver{};
	/// \endcode
	///
	/// recordDecl(hasStdContainerName()) matches \c vector and \c forward_list
	/// but not \c my_vec.
	AST_MATCHER(NamedDecl, hasStdContainerName) {
	static const char *const ContainerNames[] = {
	"array", "deque",
	"forward_list", "list",
	"vector",

	"map", "multimap",
	"set", "multiset",

	"unordered_map", "unordered_multimap",
	"unordered_set", "unordered_multiset",

	"queue", "priority_queue",
	"stack"};

	for (const char *Name : ContainerNames) {
	if (hasName(Name).matches(Node, Finder, Builder))
	return true;
	}
	return false;
	}

	/// Matches declarations whose declaration context is the C++ standard library
	/// namespace std.
	///
	/// Note that inline namespaces are silently ignored during the lookup since
	/// both libstdc++ and libc++ are known to use them for versioning purposes.
	///
	/// Given:
	/// \code
	/// namespace ns {
	/// struct my_type {};
	/// using namespace std;
	/// }
	///
	/// using std::vector;
	/// using ns:my_type;
	/// using ns::list;
	/// \code
	///
	/// usingDecl(hasAnyUsingShadowDecl(hasTargetDecl(isFromStdNamespace())))
	/// matches "using std::vector" and "using ns::list".
	AST_MATCHER(Decl, isFromStdNamespace) {
	const DeclContext *D = Node.getDeclContext();

	while (D->isInlineNamespace())
	D = D->getParent();

	if (!D->isNamespace() \|\| !D->getParent()->isTranslationUnit())
	return false;

	const IdentifierInfo *Info = cast<NamespaceDecl>(D)->getIdentifier();

	return (Info && Info->isStr("std"));
	}

	/// Matches declaration reference or member expressions with explicit template
	/// arguments.
	AST_POLYMORPHIC_MATCHER(hasExplicitTemplateArgs,
	AST_POLYMORPHIC_SUPPORTED_TYPES(DeclRefExpr,
	MemberExpr)) {
	return Node.hasExplicitTemplateArgs();
	}

	/// \brief Returns a DeclarationMatcher that matches standard iterators nested
	/// inside records with a standard container name.
	DeclarationMatcher standardIterator() {
	return decl(
	namedDecl(hasStdIteratorName()),
	hasDeclContext(recordDecl(hasStdContainerName(), isFromStdNamespace())));
	}

	/// \brief Returns a TypeMatcher that matches typedefs for standard iterators
	/// inside records with a standard container name.
	TypeMatcher typedefIterator() {
	return typedefType(hasDeclaration(standardIterator()));
	}

	/// \brief Returns a TypeMatcher that matches records named for standard
	/// iterators nested inside records named for standard containers.
	TypeMatcher nestedIterator() {
	return recordType(hasDeclaration(standardIterator()));
	}

	/// \brief Returns a TypeMatcher that matches types declared with using
	/// declarations and which name standard iterators for standard containers.
	TypeMatcher iteratorFromUsingDeclaration() {
	auto HasIteratorDecl = hasDeclaration(namedDecl(hasStdIteratorName()));
	// Types resulting from using declarations are represented by elaboratedType.
	return elaboratedType(
	// Unwrap the nested name specifier to test for one of the standard
	// containers.
	hasQualifier(specifiesType(templateSpecializationType(hasDeclaration(
	namedDecl(hasStdContainerName(), isFromStdNamespace()))))),
	// the named type is what comes after the final '::' in the type. It
	// should name one of the standard iterator names.
	namesType(
	anyOf(typedefType(HasIteratorDecl), recordType(HasIteratorDecl))));
	}

	/// \brief This matcher returns declaration statements that contain variable
	/// declarations with written non-list initializer for standard iterators.
	StatementMatcher makeIteratorDeclMatcher() {
	return declStmt(unless(has(
	varDecl(anyOf(unless(hasWrittenNonListInitializer()),
	unless(hasType(isSugarFor(anyOf(
	typedefIterator(), nestedIterator(),
	iteratorFromUsingDeclaration())))))))))
	.bind(IteratorDeclStmtId);
	}

	StatementMatcher makeDeclWithNewMatcher() {
	return declStmt(
	unless(has(varDecl(anyOf(
	unless(hasInitializer(ignoringParenImpCasts(cxxNewExpr()))),
	// FIXME: TypeLoc information is not reliable where CV
	// qualifiers are concerned so these types can't be
	// handled for now.
	hasType(pointerType(
	pointee(hasCanonicalType(hasLocalQualifiers())))),

	// FIXME: Handle function pointers. For now we ignore them
	// because the replacement replaces the entire type
	// specifier source range which includes the identifier.
	hasType(pointsTo(
	pointsTo(parenType(innerType(functionType()))))))))))
	.bind(DeclWithNewId);
	}

	StatementMatcher makeDeclWithCastMatcher() {
	return declStmt(
	unless(has(varDecl(unless(hasInitializer(explicitCastExpr()))))))
	.bind(DeclWithCastId);
	}

	StatementMatcher makeDeclWithTemplateCastMatcher() {
	auto ST =
	substTemplateTypeParmType(hasReplacementType(equalsBoundNode("arg")));

	auto ExplicitCall =
	anyOf(has(memberExpr(hasExplicitTemplateArgs())),
	has(ignoringImpCasts(declRefExpr(hasExplicitTemplateArgs()))));

	auto TemplateArg =
	hasTemplateArgument(0, refersToType(qualType().bind("arg")));

	auto TemplateCall = callExpr(
	ExplicitCall,
	callee(functionDecl(TemplateArg,
	returns(anyOf(ST, pointsTo(ST), references(ST))))));

	return declStmt(unless(has(varDecl(
	unless(hasInitializer(ignoringImplicit(TemplateCall)))))))
	.bind(DeclWithTemplateCastId);
	}

	StatementMatcher makeCombinedMatcher() {
	return declStmt(
	// At least one varDecl should be a child of the declStmt to ensure
	// it's a declaration list and avoid matching other declarations,
	// e.g. using directives.
	has(varDecl(unless(isImplicit()))),
	// Skip declarations that are already using auto.
	unless(has(varDecl(anyOf(hasType(autoType()),
	hasType(qualType(hasDescendant(autoType()))))))),
	anyOf(makeIteratorDeclMatcher(), makeDeclWithNewMatcher(),
	makeDeclWithCastMatcher(), makeDeclWithTemplateCastMatcher()));
	}

	} // namespace

	UseAutoCheck::UseAutoCheck(StringRef Name, ClangTidyContext *Context)
	: ClangTidyCheck(Name, Context),
	MinTypeNameLength(Options.get("MinTypeNameLength", 5)),
	RemoveStars(Options.get("RemoveStars", 0)) {}

	void UseAutoCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
	Options.store(Opts, "MinTypeNameLength", MinTypeNameLength);
	Options.store(Opts, "RemoveStars", RemoveStars ? 1 : 0);
	}

	void UseAutoCheck::registerMatchers(MatchFinder *Finder) {
	// Only register the matchers for C++; the functionality currently does not
	// provide any benefit to other languages, despite being benign.
	if (getLangOpts().CPlusPlus) {
	Finder->addMatcher(makeCombinedMatcher(), this);
	}
	}

	void UseAutoCheck::replaceIterators(const DeclStmt D, ASTContext Context) {
	for (const auto *Dec : D->decls()) {
	const auto *V = cast<VarDecl>(Dec);
	const Expr *ExprInit = V->getInit();

	// Skip expressions with cleanups from the intializer expression.
	if (const auto *E = dyn_cast<ExprWithCleanups>(ExprInit))
	ExprInit = E->getSubExpr();

	const auto *Construct = dyn_cast<CXXConstructExpr>(ExprInit);
	if (!Construct)
	continue;

	// Ensure that the constructor receives a single argument.
	if (Construct->getNumArgs() != 1)
	return;

	// Drill down to the as-written initializer.
	const Expr E = (Construct->arg_begin())->IgnoreParenImpCasts();
	if (E != E->IgnoreConversionOperator()) {
	// We hit a conversion operator. Early-out now as they imply an implicit
	// conversion from a different type. Could also mean an explicit
	// conversion from the same type but that's pretty rare.
	return;
	}

	if (const auto *NestedConstruct = dyn_cast<CXXConstructExpr>(E)) {
	// If we ran into an implicit conversion contructor, can't convert.
	//
	// FIXME: The following only checks if the constructor can be used
	// implicitly, not if it actually was. Cases where the converting
	// constructor was used explicitly won't get converted.
	if (NestedConstruct->getConstructor()->isConvertingConstructor(false))
	return;
	}
	if (!Context->hasSameType(V->getType(), E->getType()))
	return;
	}

	// Get the type location using the first declaration.
	const auto V = cast<VarDecl>(D->decl_begin());

	// WARNING: TypeLoc::getSourceRange() will include the identifier for things
	// like function pointers. Not a concern since this action only works with
	// iterators but something to keep in mind in the future.

	SourceRange Range(V->getTypeSourceInfo()->getTypeLoc().getSourceRange());
	diag(Range.getBegin(), "use auto when declaring iterators")
	<< FixItHint::CreateReplacement(Range, "auto");
	}

	void UseAutoCheck::replaceExpr(
	const DeclStmt D, ASTContext Context,
	llvm::function_ref<QualType(const Expr *)> GetType, StringRef Message) {
	const auto FirstDecl = dyn_cast<VarDecl>(D->decl_begin());
	// Ensure that there is at least one VarDecl within the DeclStmt.
	if (!FirstDecl)
	return;

	const QualType FirstDeclType = FirstDecl->getType().getCanonicalType();

	std::vector<FixItHint> StarRemovals;
	for (const auto *Dec : D->decls()) {
	const auto *V = cast<VarDecl>(Dec);
	// Ensure that every DeclStmt child is a VarDecl.
	if (!V)
	return;

	const auto *Expr = V->getInit()->IgnoreParenImpCasts();
	// Ensure that every VarDecl has an initializer.
	if (!Expr)
	return;

	// If VarDecl and Initializer have mismatching unqualified types.
	if (!Context->hasSameUnqualifiedType(V->getType(), GetType(Expr)))
	return;

	// All subsequent variables in this declaration should have the same
	// canonical type. For example, we don't want to use `auto` in
	// `T p = new T, pp = new T;`.
	if (FirstDeclType != V->getType().getCanonicalType())
	return;

	if (RemoveStars) {
	// Remove explicitly written '*' from declarations where there's more than
	// one declaration in the declaration list.
	if (Dec == *D->decl_begin())
	continue;

	auto Q = V->getTypeSourceInfo()->getTypeLoc().getAs<PointerTypeLoc>();
	while (!Q.isNull()) {
	StarRemovals.push_back(FixItHint::CreateRemoval(Q.getStarLoc()));
	Q = Q.getNextTypeLoc().getAs<PointerTypeLoc>();
	}
	}
	}

	// FIXME: There is, however, one case we can address: when the VarDecl pointee
	// is the same as the initializer, just more CV-qualified. However, TypeLoc
	// information is not reliable where CV qualifiers are concerned so we can't
	// do anything about this case for now.
	TypeLoc Loc = FirstDecl->getTypeSourceInfo()->getTypeLoc();
	if (!RemoveStars) {
	while (Loc.getTypeLocClass() == TypeLoc::Pointer \|\|
	Loc.getTypeLocClass() == TypeLoc::Qualified)
	Loc = Loc.getNextTypeLoc();
	}
	while (Loc.getTypeLocClass() == TypeLoc::LValueReference \|\|
	Loc.getTypeLocClass() == TypeLoc::RValueReference \|\|
	Loc.getTypeLocClass() == TypeLoc::Qualified) {
	Loc = Loc.getNextTypeLoc();
	}
	SourceRange Range(Loc.getSourceRange());

	if (MinTypeNameLength != 0 &&
	GetTypeNameLength(RemoveStars,
	tooling::fixit::getText(Loc.getSourceRange(),
	FirstDecl->getASTContext())) <
	MinTypeNameLength)
	return;

	auto Diag = diag(Range.getBegin(), Message);

	// Space after 'auto' to handle cases where the '*' in the pointer type is
	// next to the identifier. This avoids changing 'int *p' into 'autop'.
	// FIXME: This doesn't work for function pointers because the variable name
	// is inside the type.
	Diag << FixItHint::CreateReplacement(Range, RemoveStars ? "auto " : "auto")
	<< StarRemovals;
	}

	void UseAutoCheck::check(const MatchFinder::MatchResult &Result) {
	if (const auto *Decl = Result.Nodes.getNodeAs<DeclStmt>(IteratorDeclStmtId)) {
	replaceIterators(Decl, Result.Context);
	} else if (const auto *Decl =
	Result.Nodes.getNodeAs<DeclStmt>(DeclWithNewId)) {
	replaceExpr(Decl, Result.Context,
	[](const Expr *Expr) { return Expr->getType(); },
	"use auto when initializing with new to avoid "
	"duplicating the type name");
	} else if (const auto *Decl =
	Result.Nodes.getNodeAs<DeclStmt>(DeclWithCastId)) {
	replaceExpr(
	Decl, Result.Context,
	[](const Expr *Expr) {
	return cast<ExplicitCastExpr>(Expr)->getTypeAsWritten();
	},
	"use auto when initializing with a cast to avoid duplicating the type "
	"name");
	} else if (const auto *Decl =
	Result.Nodes.getNodeAs<DeclStmt>(DeclWithTemplateCastId)) {
	replaceExpr(
	Decl, Result.Context,
	[](const Expr *Expr) {
	return cast<CallExpr>(Expr->IgnoreImplicit())
	->getDirectCallee()
	->getReturnType();
	},
	"use auto when initializing with a template cast to avoid duplicating "
	"the type name");
	} else {
	llvm_unreachable("Bad Callback. No node provided.");
	}
	}

	} // namespace modernize
	} // namespace tidy
	} // namespace clang