--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/clang-tools-extra/clang-tidy/modernize/UseEqualsDefaultCheck.cpp	Thu Feb 13 15:10:13 2020 +0900
@@ -0,0 +1,320 @@
+//===--- UseEqualsDefaultCheck.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 "UseEqualsDefaultCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Lex/Lexer.h"
+#include "../utils/LexerUtils.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace modernize {
+
+static const char SpecialFunction[] = "SpecialFunction";
+
+/// Finds all the named non-static fields of \p Record.
+static std::set<const FieldDecl *>
+getAllNamedFields(const CXXRecordDecl *Record) {
+  std::set<const FieldDecl *> Result;
+  for (const auto *Field : Record->fields()) {
+    // Static data members are not in this range.
+    if (Field->isUnnamedBitfield())
+      continue;
+    Result.insert(Field);
+  }
+  return Result;
+}
+
+/// Returns the names of the direct bases of \p Record, both virtual and
+/// non-virtual.
+static std::set<const Type *> getAllDirectBases(const CXXRecordDecl *Record) {
+  std::set<const Type *> Result;
+  for (auto Base : Record->bases()) {
+    // CXXBaseSpecifier.
+    const auto *BaseType = Base.getTypeSourceInfo()->getType().getTypePtr();
+    Result.insert(BaseType);
+  }
+  return Result;
+}
+
+/// Returns a matcher that matches member expressions where the base is
+/// the variable declared as \p Var and the accessed member is the one declared
+/// as \p Field.
+internal::Matcher<Expr> accessToFieldInVar(const FieldDecl *Field,
+                                           const ValueDecl *Var) {
+  return ignoringImpCasts(
+      memberExpr(hasObjectExpression(declRefExpr(to(varDecl(equalsNode(Var))))),
+                 member(fieldDecl(equalsNode(Field)))));
+}
+
+/// Check that the given constructor has copy signature and that it
+/// copy-initializes all its bases and members.
+static bool isCopyConstructorAndCanBeDefaulted(ASTContext *Context,
+                                               const CXXConstructorDecl *Ctor) {
+  // An explicitly-defaulted constructor cannot have default arguments.
+  if (Ctor->getMinRequiredArguments() != 1)
+    return false;
+
+  const auto *Record = Ctor->getParent();
+  const auto *Param = Ctor->getParamDecl(0);
+
+  // Base classes and members that have to be copied.
+  auto BasesToInit = getAllDirectBases(Record);
+  auto FieldsToInit = getAllNamedFields(Record);
+
+  // Ensure that all the bases are copied.
+  for (const auto *Base : BasesToInit) {
+    // The initialization of a base class should be a call to a copy
+    // constructor of the base.
+    if (match(
+            cxxConstructorDecl(forEachConstructorInitializer(cxxCtorInitializer(
+                isBaseInitializer(),
+                withInitializer(cxxConstructExpr(
+                    hasType(equalsNode(Base)),
+                    hasDeclaration(cxxConstructorDecl(isCopyConstructor())),
+                    argumentCountIs(1),
+                    hasArgument(
+                        0, declRefExpr(to(varDecl(equalsNode(Param)))))))))),
+            *Ctor, *Context)
+            .empty())
+      return false;
+  }
+
+  // Ensure that all the members are copied.
+  for (const auto *Field : FieldsToInit) {
+    auto AccessToFieldInParam = accessToFieldInVar(Field, Param);
+    // The initialization is a CXXConstructExpr for class types.
+    if (match(
+            cxxConstructorDecl(forEachConstructorInitializer(cxxCtorInitializer(
+                isMemberInitializer(), forField(equalsNode(Field)),
+                withInitializer(anyOf(
+                    AccessToFieldInParam,
+                    initListExpr(has(AccessToFieldInParam)),
+                    cxxConstructExpr(
+                        hasDeclaration(cxxConstructorDecl(isCopyConstructor())),
+                        argumentCountIs(1),
+                        hasArgument(0, AccessToFieldInParam))))))),
+            *Ctor, *Context)
+            .empty())
+      return false;
+  }
+
+  // Ensure that we don't do anything else, like initializing an indirect base.
+  return Ctor->getNumCtorInitializers() ==
+         BasesToInit.size() + FieldsToInit.size();
+}
+
+/// Checks that the given method is an overloading of the assignment
+/// operator, has copy signature, returns a reference to "*this" and copies
+/// all its members and subobjects.
+static bool isCopyAssignmentAndCanBeDefaulted(ASTContext *Context,
+                                              const CXXMethodDecl *Operator) {
+  const auto *Record = Operator->getParent();
+  const auto *Param = Operator->getParamDecl(0);
+
+  // Base classes and members that have to be copied.
+  auto BasesToInit = getAllDirectBases(Record);
+  auto FieldsToInit = getAllNamedFields(Record);
+
+  const auto *Compound = cast<CompoundStmt>(Operator->getBody());
+
+  // The assignment operator definition has to end with the following return
+  // statement:
+  //   return *this;
+  if (Compound->body_empty() ||
+      match(returnStmt(has(ignoringParenImpCasts(unaryOperator(
+                hasOperatorName("*"), hasUnaryOperand(cxxThisExpr()))))),
+            *Compound->body_back(), *Context)
+          .empty())
+    return false;
+
+  // Ensure that all the bases are copied.
+  for (const auto *Base : BasesToInit) {
+    // Assignment operator of a base class:
+    //   Base::operator=(Other);
+    //
+    // Clang translates this into:
+    //   ((Base*)this)->operator=((Base)Other);
+    //
+    // So we are looking for a member call that fulfills:
+    if (match(
+            compoundStmt(has(ignoringParenImpCasts(cxxMemberCallExpr(
+                // - The object is an implicit cast of 'this' to a pointer to
+                //   a base class.
+                onImplicitObjectArgument(
+                    implicitCastExpr(hasImplicitDestinationType(
+                                         pointsTo(type(equalsNode(Base)))),
+                                     hasSourceExpression(cxxThisExpr()))),
+                // - The called method is the operator=.
+                callee(cxxMethodDecl(isCopyAssignmentOperator())),
+                // - The argument is (an implicit cast to a Base of) the
+                // argument taken by "Operator".
+                argumentCountIs(1),
+                hasArgument(0, declRefExpr(to(varDecl(equalsNode(Param))))))))),
+            *Compound, *Context)
+            .empty())
+      return false;
+  }
+
+  // Ensure that all the members are copied.
+  for (const auto *Field : FieldsToInit) {
+    // The assignment of data members:
+    //   Field = Other.Field;
+    // Is a BinaryOperator in non-class types, and a CXXOperatorCallExpr
+    // otherwise.
+    auto LHS = memberExpr(hasObjectExpression(cxxThisExpr()),
+                          member(fieldDecl(equalsNode(Field))));
+    auto RHS = accessToFieldInVar(Field, Param);
+    if (match(
+            compoundStmt(has(ignoringParenImpCasts(stmt(anyOf(
+                binaryOperator(hasOperatorName("="), hasLHS(LHS), hasRHS(RHS)),
+                cxxOperatorCallExpr(hasOverloadedOperatorName("="),
+                                    argumentCountIs(2), hasArgument(0, LHS),
+                                    hasArgument(1, RHS))))))),
+            *Compound, *Context)
+            .empty())
+      return false;
+  }
+
+  // Ensure that we don't do anything else.
+  return Compound->size() == BasesToInit.size() + FieldsToInit.size() + 1;
+}
+
+/// Returns false if the body has any non-whitespace character.
+static bool bodyEmpty(const ASTContext *Context, const CompoundStmt *Body) {
+  bool Invalid = false;
+  StringRef Text = Lexer::getSourceText(
+      CharSourceRange::getCharRange(Body->getLBracLoc().getLocWithOffset(1),
+                                    Body->getRBracLoc()),
+      Context->getSourceManager(), Context->getLangOpts(), &Invalid);
+  return !Invalid && std::strspn(Text.data(), " \t\r\n") == Text.size();
+}
+
+UseEqualsDefaultCheck::UseEqualsDefaultCheck(StringRef Name,
+                                             ClangTidyContext *Context)
+    : ClangTidyCheck(Name, Context),
+      IgnoreMacros(Options.getLocalOrGlobal("IgnoreMacros", true) != 0) {}
+
+void UseEqualsDefaultCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
+  Options.store(Opts, "IgnoreMacros", IgnoreMacros);
+}
+
+void UseEqualsDefaultCheck::registerMatchers(MatchFinder *Finder) {
+  if (!getLangOpts().CPlusPlus)
+    return;
+
+  // Destructor.
+  Finder->addMatcher(cxxDestructorDecl(isDefinition()).bind(SpecialFunction),
+                     this);
+  Finder->addMatcher(
+      cxxConstructorDecl(
+          isDefinition(),
+          anyOf(
+              // Default constructor.
+              allOf(unless(hasAnyConstructorInitializer(isWritten())),
+                    parameterCountIs(0)),
+              // Copy constructor.
+              allOf(isCopyConstructor(),
+                    // Discard constructors that can be used as a copy
+                    // constructor because all the other arguments have
+                    // default values.
+                    parameterCountIs(1))))
+          .bind(SpecialFunction),
+      this);
+  // Copy-assignment operator.
+  Finder->addMatcher(
+      cxxMethodDecl(isDefinition(), isCopyAssignmentOperator(),
+                    // isCopyAssignmentOperator() allows the parameter to be
+                    // passed by value, and in this case it cannot be
+                    // defaulted.
+                    hasParameter(0, hasType(lValueReferenceType())))
+          .bind(SpecialFunction),
+      this);
+}
+
+void UseEqualsDefaultCheck::check(const MatchFinder::MatchResult &Result) {
+  std::string SpecialFunctionName;
+
+  // Both CXXConstructorDecl and CXXDestructorDecl inherit from CXXMethodDecl.
+  const auto *SpecialFunctionDecl =
+      Result.Nodes.getNodeAs<CXXMethodDecl>(SpecialFunction);
+
+  if (IgnoreMacros && SpecialFunctionDecl->getLocation().isMacroID())
+    return;
+
+  // Discard explicitly deleted/defaulted special member functions and those
+  // that are not user-provided (automatically generated).
+  if (SpecialFunctionDecl->isDeleted() ||
+      SpecialFunctionDecl->isExplicitlyDefaulted() ||
+      SpecialFunctionDecl->isLateTemplateParsed() ||
+      SpecialFunctionDecl->isTemplateInstantiation() ||
+      !SpecialFunctionDecl->isUserProvided() || !SpecialFunctionDecl->hasBody())
+    return;
+
+  const auto *Body = dyn_cast<CompoundStmt>(SpecialFunctionDecl->getBody());
+  if (!Body)
+    return;
+
+  // If there is code inside the body, don't warn.
+  if (!SpecialFunctionDecl->isCopyAssignmentOperator() && !Body->body_empty())
+    return;
+
+  // If there are comments inside the body, don't do the change.
+  bool ApplyFix = SpecialFunctionDecl->isCopyAssignmentOperator() ||
+                  bodyEmpty(Result.Context, Body);
+
+  std::vector<FixItHint> RemoveInitializers;
+
+  if (const auto *Ctor = dyn_cast<CXXConstructorDecl>(SpecialFunctionDecl)) {
+    if (Ctor->getNumParams() == 0) {
+      SpecialFunctionName = "default constructor";
+    } else {
+      if (!isCopyConstructorAndCanBeDefaulted(Result.Context, Ctor))
+        return;
+      SpecialFunctionName = "copy constructor";
+      // If there are constructor initializers, they must be removed.
+      for (const auto *Init : Ctor->inits()) {
+        RemoveInitializers.emplace_back(
+            FixItHint::CreateRemoval(Init->getSourceRange()));
+      }
+    }
+  } else if (isa<CXXDestructorDecl>(SpecialFunctionDecl)) {
+    SpecialFunctionName = "destructor";
+  } else {
+    if (!isCopyAssignmentAndCanBeDefaulted(Result.Context, SpecialFunctionDecl))
+      return;
+    SpecialFunctionName = "copy-assignment operator";
+  }
+
+  // The location of the body is more useful inside a macro as spelling and
+  // expansion locations are reported.
+  SourceLocation Location = SpecialFunctionDecl->getLocation();
+  if (Location.isMacroID())
+    Location = Body->getBeginLoc();
+
+  auto Diag = diag(Location, "use '= default' to define a trivial " +
+                                 SpecialFunctionName);
+
+  if (ApplyFix) {
+    // Skipping comments, check for a semicolon after Body->getSourceRange()
+    Optional<Token> Token = utils::lexer::findNextTokenSkippingComments(
+        Body->getSourceRange().getEnd().getLocWithOffset(1),
+        Result.Context->getSourceManager(), Result.Context->getLangOpts());
+    StringRef Replacement =
+        Token && Token->is(tok::semi) ? "= default" : "= default;";
+    Diag << FixItHint::CreateReplacement(Body->getSourceRange(), Replacement)
+         << RemoveInitializers;
+  }
+}
+
+} // namespace modernize
+} // namespace tidy
+} // namespace clang