//===--- PreferMemberInitializerCheck.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 "PreferMemberInitializerCheck.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/Decl.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
#include "clang/Lex/Lexer.h"
#include "llvm/ADT/DenseMap.h"

using namespace clang::ast_matchers;

namespace clang::tidy::cppcoreguidelines {

static bool isControlStatement(const Stmt *S) {
  return isa<IfStmt, SwitchStmt, ForStmt, WhileStmt, DoStmt, ReturnStmt,
             GotoStmt, CXXTryStmt, CXXThrowExpr>(S);
}

static bool isNoReturnCallStatement(const Stmt *S) {
  const auto *Call = dyn_cast<CallExpr>(S);
  if (!Call)
    return false;

  const FunctionDecl *Func = Call->getDirectCallee();
  if (!Func)
    return false;

  return Func->isNoReturn();
}

static bool isLiteral(const Expr *E) {
  return isa<StringLiteral, CharacterLiteral, IntegerLiteral, FloatingLiteral,
             CXXBoolLiteralExpr, CXXNullPtrLiteralExpr>(E);
}

static bool isUnaryExprOfLiteral(const Expr *E) {
  if (const auto *UnOp = dyn_cast<UnaryOperator>(E))
    return isLiteral(UnOp->getSubExpr());
  return false;
}

static bool shouldBeDefaultMemberInitializer(const Expr *Value) {
  if (isLiteral(Value) || isUnaryExprOfLiteral(Value))
    return true;

  if (const auto *DRE = dyn_cast<DeclRefExpr>(Value))
    return isa<EnumConstantDecl>(DRE->getDecl());

  return false;
}

namespace {

AST_MATCHER_P(FieldDecl, indexNotLessThan, unsigned, Index) {
  return Node.getFieldIndex() >= Index;
}

enum class AssignedLevel {
  // Field is not assigned.
  None,
  // Field is assigned.
  Default,
  // Assignment of field has side effect:
  // - assign to reference.
  // FIXME: support other side effect.
  HasSideEffect,
  // Assignment of field has data dependence.
  HasDependence,
};

} // namespace

static bool canAdvanceAssignment(AssignedLevel Level) {
  return Level == AssignedLevel::None || Level == AssignedLevel::Default;
}

// Checks if Field is initialised using a field that will be initialised after
// it.
// TODO: Probably should guard against function calls that could have side
// effects or if they do reference another field that's initialized before
// this field, but is modified before the assignment.
static void updateAssignmentLevel(
    const FieldDecl *Field, const Expr *Init, const CXXConstructorDecl *Ctor,
    llvm::DenseMap<const FieldDecl *, AssignedLevel> &AssignedFields) {
  auto It = AssignedFields.find(Field);
  if (It == AssignedFields.end())
    It = AssignedFields.insert({Field, AssignedLevel::None}).first;

  if (!canAdvanceAssignment(It->second))
    // fast path for already decided field.
    return;

  if (Field->getType().getCanonicalType()->isReferenceType()) {
    // assign to reference type twice cannot be simplified to once.
    It->second = AssignedLevel::HasSideEffect;
    return;
  }

  auto MemberMatcher =
      memberExpr(hasObjectExpression(cxxThisExpr()),
                 member(fieldDecl(indexNotLessThan(Field->getFieldIndex()))));
  auto DeclMatcher = declRefExpr(
      to(varDecl(unless(parmVarDecl()), hasDeclContext(equalsNode(Ctor)))));
  const bool HasDependence = !match(expr(anyOf(MemberMatcher, DeclMatcher,
                                               hasDescendant(MemberMatcher),
                                               hasDescendant(DeclMatcher))),
                                    *Init, Field->getASTContext())
                                  .empty();
  if (HasDependence) {
    It->second = AssignedLevel::HasDependence;
    return;
  }
}

struct AssignmentPair {
  const FieldDecl *Field;
  const Expr *Init;
};

static std::optional<AssignmentPair>
isAssignmentToMemberOf(const CXXRecordDecl *Rec, const Stmt *S,
                       const CXXConstructorDecl *Ctor) {
  if (const auto *BO = dyn_cast<BinaryOperator>(S)) {
    if (BO->getOpcode() != BO_Assign)
      return {};

    const auto *ME = dyn_cast<MemberExpr>(BO->getLHS()->IgnoreParenImpCasts());
    if (!ME)
      return {};

    const auto *Field = dyn_cast<FieldDecl>(ME->getMemberDecl());
    if (!Field)
      return {};

    if (!isa<CXXThisExpr>(ME->getBase()))
      return {};
    const Expr *Init = BO->getRHS()->IgnoreParenImpCasts();
    return AssignmentPair{Field, Init};
  }
  if (const auto *COCE = dyn_cast<CXXOperatorCallExpr>(S)) {
    if (COCE->getOperator() != OO_Equal)
      return {};

    const auto *ME =
        dyn_cast<MemberExpr>(COCE->getArg(0)->IgnoreParenImpCasts());
    if (!ME)
      return {};

    const auto *Field = dyn_cast<FieldDecl>(ME->getMemberDecl());
    if (!Field)
      return {};

    if (!isa<CXXThisExpr>(ME->getBase()))
      return {};
    const Expr *Init = COCE->getArg(1)->IgnoreParenImpCasts();
    return AssignmentPair{Field, Init};
  }
  return {};
}

PreferMemberInitializerCheck::PreferMemberInitializerCheck(
    StringRef Name, ClangTidyContext *Context)
    : ClangTidyCheck(Name, Context),
      IsUseDefaultMemberInitEnabled(
          Context->isCheckEnabled("modernize-use-default-member-init")),
      UseAssignment(
          Options.get("UseAssignment",
                      OptionsView("modernize-use-default-member-init",
                                  Context->getOptions().CheckOptions, Context)
                          .get("UseAssignment", false))) {}

void PreferMemberInitializerCheck::storeOptions(
    ClangTidyOptions::OptionMap &Opts) {
  Options.store(Opts, "UseAssignment", UseAssignment);
}

void PreferMemberInitializerCheck::registerMatchers(MatchFinder *Finder) {
  Finder->addMatcher(cxxConstructorDecl(hasBody(compoundStmt()),
                                        unless(isInstantiated()),
                                        unless(isDelegatingConstructor()))
                         .bind("ctor"),
                     this);
}

void PreferMemberInitializerCheck::check(
    const MatchFinder::MatchResult &Result) {
  const auto *Ctor = Result.Nodes.getNodeAs<CXXConstructorDecl>("ctor");
  const auto *Body = cast<CompoundStmt>(Ctor->getBody());

  const CXXRecordDecl *Class = Ctor->getParent();
  bool FirstToCtorInits = true;

  llvm::DenseMap<const FieldDecl *, AssignedLevel> AssignedFields{};

  for (const CXXCtorInitializer *Init : Ctor->inits())
    if (FieldDecl *Field = Init->getMember())
      updateAssignmentLevel(Field, Init->getInit(), Ctor, AssignedFields);

  for (const Stmt *S : Body->body()) {
    if (S->getBeginLoc().isMacroID()) {
      StringRef MacroName = Lexer::getImmediateMacroName(
          S->getBeginLoc(), *Result.SourceManager, getLangOpts());
      if (MacroName.contains_insensitive("assert"))
        return;
    }
    if (isControlStatement(S))
      return;

    if (isNoReturnCallStatement(S))
      return;

    if (const auto *CondOp = dyn_cast<ConditionalOperator>(S)) {
      if (isNoReturnCallStatement(CondOp->getLHS()) ||
          isNoReturnCallStatement(CondOp->getRHS()))
        return;
    }

    std::optional<AssignmentPair> AssignmentToMember =
        isAssignmentToMemberOf(Class, S, Ctor);
    if (!AssignmentToMember)
      continue;
    const FieldDecl *Field = AssignmentToMember->Field;
    const Expr *InitValue = AssignmentToMember->Init;
    updateAssignmentLevel(Field, InitValue, Ctor, AssignedFields);
    if (!canAdvanceAssignment(AssignedFields[Field]))
      continue;
    const bool IsInDefaultMemberInitializer =
        IsUseDefaultMemberInitEnabled && getLangOpts().CPlusPlus11 &&
        Ctor->isDefaultConstructor() &&
        (getLangOpts().CPlusPlus20 || !Field->isBitField()) &&
        !Field->hasInClassInitializer() &&
        (!isa<RecordDecl>(Class->getDeclContext()) ||
         !cast<RecordDecl>(Class->getDeclContext())->isUnion()) &&
        shouldBeDefaultMemberInitializer(InitValue);
    if (IsInDefaultMemberInitializer) {
      bool InvalidFix = false;
      SourceLocation FieldEnd =
          Lexer::getLocForEndOfToken(Field->getSourceRange().getEnd(), 0,
                                     *Result.SourceManager, getLangOpts());
      InvalidFix |= FieldEnd.isInvalid() || FieldEnd.isMacroID();
      SourceLocation SemiColonEnd;
      if (auto NextToken = Lexer::findNextToken(
              S->getEndLoc(), *Result.SourceManager, getLangOpts()))
        SemiColonEnd = NextToken->getEndLoc();
      else
        InvalidFix = true;
      auto Diag =
          diag(S->getBeginLoc(), "%0 should be initialized in an in-class"
                                 " default member initializer")
          << Field;
      if (InvalidFix)
        continue;
      CharSourceRange StmtRange =
          CharSourceRange::getCharRange(S->getBeginLoc(), SemiColonEnd);

      SmallString<128> Insertion(
          {UseAssignment ? " = " : "{",
           Lexer::getSourceText(
               CharSourceRange(InitValue->getSourceRange(), true),
               *Result.SourceManager, getLangOpts()),
           UseAssignment ? "" : "}"});

      Diag << FixItHint::CreateInsertion(FieldEnd, Insertion)
           << FixItHint::CreateRemoval(StmtRange);

    } else {
      StringRef InsertPrefix = "";
      bool HasInitAlready = false;
      SourceLocation InsertPos;
      SourceRange ReplaceRange;
      bool AddComma = false;
      bool InvalidFix = false;
      unsigned Index = Field->getFieldIndex();
      const CXXCtorInitializer *LastInListInit = nullptr;
      for (const CXXCtorInitializer *Init : Ctor->inits()) {
        if (!Init->isWritten() || Init->isInClassMemberInitializer())
          continue;
        if (Init->getMember() == Field) {
          HasInitAlready = true;
          if (isa<ImplicitValueInitExpr>(Init->getInit()))
            InsertPos = Init->getRParenLoc();
          else {
            ReplaceRange = Init->getInit()->getSourceRange();
          }
          break;
        }
        if (Init->isMemberInitializer() &&
            Index < Init->getMember()->getFieldIndex()) {
          InsertPos = Init->getSourceLocation();
          // There are initializers after the one we are inserting, so add a
          // comma after this insertion in order to not break anything.
          AddComma = true;
          break;
        }
        LastInListInit = Init;
      }
      if (HasInitAlready) {
        if (InsertPos.isValid())
          InvalidFix |= InsertPos.isMacroID();
        else
          InvalidFix |= ReplaceRange.getBegin().isMacroID() ||
                        ReplaceRange.getEnd().isMacroID();
      } else {
        if (InsertPos.isInvalid()) {
          if (LastInListInit) {
            InsertPos = Lexer::getLocForEndOfToken(
                LastInListInit->getRParenLoc(), 0, *Result.SourceManager,
                getLangOpts());
            // Inserting after the last constructor initializer, so we need a
            // comma.
            InsertPrefix = ", ";
          } else {
            InsertPos = Lexer::getLocForEndOfToken(
                Ctor->getTypeSourceInfo()
                    ->getTypeLoc()
                    .getAs<clang::FunctionTypeLoc>()
                    .getLocalRangeEnd(),
                0, *Result.SourceManager, getLangOpts());

            // If this is first time in the loop, there are no initializers so
            // `:` declares member initialization list. If this is a
            // subsequent pass then we have already inserted a `:` so continue
            // with a comma.
            InsertPrefix = FirstToCtorInits ? " : " : ", ";
          }
        }
        InvalidFix |= InsertPos.isMacroID();
      }

      SourceLocation SemiColonEnd;
      if (auto NextToken = Lexer::findNextToken(
              S->getEndLoc(), *Result.SourceManager, getLangOpts()))
        SemiColonEnd = NextToken->getEndLoc();
      else
        InvalidFix = true;

      auto Diag = diag(S->getBeginLoc(), "%0 should be initialized in a member"
                                         " initializer of the constructor")
                  << Field;
      if (InvalidFix)
        continue;
      StringRef NewInit = Lexer::getSourceText(
          CharSourceRange(InitValue->getSourceRange(), true),
          *Result.SourceManager, getLangOpts());
      if (HasInitAlready) {
        if (InsertPos.isValid())
          Diag << FixItHint::CreateInsertion(InsertPos, NewInit);
        else
          Diag << FixItHint::CreateReplacement(ReplaceRange, NewInit);
      } else {
        SmallString<128> Insertion({InsertPrefix, Field->getName(), "(",
                                    NewInit, AddComma ? "), " : ")"});
        Diag << FixItHint::CreateInsertion(InsertPos, Insertion,
                                           FirstToCtorInits);
        FirstToCtorInits = areDiagsSelfContained();
      }
      Diag << FixItHint::CreateRemoval(
          CharSourceRange::getCharRange(S->getBeginLoc(), SemiColonEnd));
    }
  }
}

} // namespace clang::tidy::cppcoreguidelines