llvm-project/clang-tools-extra/clang-tidy/modernize/PassByValueCheck.cpp

//===--- PassByValueCheck.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 "PassByValueCheck.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/RecursiveASTVisitor.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
#include "clang/ASTMatchers/ASTMatchers.h"
#include "clang/Frontend/CompilerInstance.h"
#include "clang/Lex/Lexer.h"
#include "clang/Lex/Preprocessor.h"

using namespace clang::ast_matchers;
using namespace llvm;

namespace clang {
namespace tidy {
namespace modernize {

/// \brief Matches move-constructible classes.
///
/// Given
/// \code
///   // POD types are trivially move constructible.
///   struct Foo { int a; };
///
///   struct Bar {
///     Bar(Bar &&) = deleted;
///     int a;
///   };
/// \endcode
/// recordDecl(isMoveConstructible())
///   matches "Foo".
AST_MATCHER(CXXRecordDecl, isMoveConstructible) {
  for (const CXXConstructorDecl *Ctor : Node.ctors()) {
    if (Ctor->isMoveConstructor() && !Ctor->isDeleted())
      return true;
  }
  return false;
}

static TypeMatcher constRefType() {
  return lValueReferenceType(pointee(isConstQualified()));
}

static TypeMatcher nonConstValueType() {
  return qualType(unless(anyOf(referenceType(), isConstQualified())));
}

/// \brief Whether or not \p ParamDecl is used exactly one time in \p Ctor.
///
/// Checks both in the init-list and the body of the constructor.
static bool paramReferredExactlyOnce(const CXXConstructorDecl *Ctor,
                                     const ParmVarDecl *ParamDecl) {
  /// \brief \c clang::RecursiveASTVisitor that checks that the given
  /// \c ParmVarDecl is used exactly one time.
  ///
  /// \see ExactlyOneUsageVisitor::hasExactlyOneUsageIn()
  class ExactlyOneUsageVisitor
      : public RecursiveASTVisitor<ExactlyOneUsageVisitor> {
    friend class RecursiveASTVisitor<ExactlyOneUsageVisitor>;

  public:
    ExactlyOneUsageVisitor(const ParmVarDecl *ParamDecl)
        : ParamDecl(ParamDecl) {}

    /// \brief Whether or not the parameter variable is referred only once in
    /// the
    /// given constructor.
    bool hasExactlyOneUsageIn(const CXXConstructorDecl *Ctor) {
      Count = 0;
      TraverseDecl(const_cast<CXXConstructorDecl *>(Ctor));
      return Count == 1;
    }

  private:
    /// \brief Counts the number of references to a variable.
    ///
    /// Stops the AST traversal if more than one usage is found.
    bool VisitDeclRefExpr(DeclRefExpr *D) {
      if (const ParmVarDecl *To = dyn_cast<ParmVarDecl>(D->getDecl())) {
        if (To == ParamDecl) {
          ++Count;
          if (Count > 1) {
            // No need to look further, used more than once.
            return false;
          }
        }
      }
      return true;
    }

    const ParmVarDecl *ParamDecl;
    unsigned Count;
  };

  return ExactlyOneUsageVisitor(ParamDecl).hasExactlyOneUsageIn(Ctor);
}

/// \brief Find all references to \p ParamDecl across all of the
/// redeclarations of \p Ctor.
static SmallVector<const ParmVarDecl *, 2>
collectParamDecls(const CXXConstructorDecl *Ctor,
                  const ParmVarDecl *ParamDecl) {
  SmallVector<const ParmVarDecl *, 2> Results;
  unsigned ParamIdx = ParamDecl->getFunctionScopeIndex();

  for (const FunctionDecl *Redecl : Ctor->redecls())
    Results.push_back(Redecl->getParamDecl(ParamIdx));
  return Results;
}

PassByValueCheck::PassByValueCheck(StringRef Name, ClangTidyContext *Context)
    : ClangTidyCheck(Name, Context),
      IncludeStyle(utils::IncludeSorter::parseIncludeStyle(
          Options.get("IncludeStyle", "llvm"))),
      ValuesOnly(Options.get("ValuesOnly", 0) != 0) {}

void PassByValueCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
  Options.store(Opts, "IncludeStyle",
                utils::IncludeSorter::toString(IncludeStyle));
  Options.store(Opts, "ValuesOnly", ValuesOnly);
}

void PassByValueCheck::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)
    return;

  Finder->addMatcher(
      cxxConstructorDecl(
          forEachConstructorInitializer(
              cxxCtorInitializer(
                  unless(isBaseInitializer()),
                  // Clang builds a CXXConstructExpr only when it knows which
                  // constructor will be called. In dependent contexts a
                  // ParenListExpr is generated instead of a CXXConstructExpr,
                  // filtering out templates automatically for us.
                  withInitializer(cxxConstructExpr(
                      has(ignoringParenImpCasts(declRefExpr(to(
                          parmVarDecl(
                              hasType(qualType(
                                  // Match only const-ref or a non-const value
                                  // parameters. Rvalues and const-values
                                  // shouldn't be modified.
                                  ValuesOnly ? nonConstValueType()
                                             : anyOf(constRefType(),
                                                     nonConstValueType()))))
                              .bind("Param"))))),
                      hasDeclaration(cxxConstructorDecl(
                          isCopyConstructor(), unless(isDeleted()),
                          hasDeclContext(
                              cxxRecordDecl(isMoveConstructible())))))))
                  .bind("Initializer")))
          .bind("Ctor"),
      this);
}

void PassByValueCheck::registerPPCallbacks(CompilerInstance &Compiler) {
  // Only register the preprocessor callbacks for C++; the functionality
  // currently does not provide any benefit to other languages, despite being
  // benign.
  if (getLangOpts().CPlusPlus) {
    Inserter.reset(new utils::IncludeInserter(
        Compiler.getSourceManager(), Compiler.getLangOpts(), IncludeStyle));
    Compiler.getPreprocessor().addPPCallbacks(Inserter->CreatePPCallbacks());
  }
}

void PassByValueCheck::check(const MatchFinder::MatchResult &Result) {
  const auto *Ctor = Result.Nodes.getNodeAs<CXXConstructorDecl>("Ctor");
  const auto *ParamDecl = Result.Nodes.getNodeAs<ParmVarDecl>("Param");
  const auto *Initializer =
      Result.Nodes.getNodeAs<CXXCtorInitializer>("Initializer");
  SourceManager &SM = *Result.SourceManager;

  // If the parameter is used or anything other than the copy, do not apply
  // the changes.
  if (!paramReferredExactlyOnce(Ctor, ParamDecl))
    return;

  // If the parameter is trivial to copy, don't move it. Moving a trivivally
  // copyable type will cause a problem with misc-move-const-arg
  if (ParamDecl->getType().getNonReferenceType().isTriviallyCopyableType(
          *Result.Context))
    return;

  auto Diag = diag(ParamDecl->getLocStart(), "pass by value and use std::move");

  // Iterate over all declarations of the constructor.
  for (const ParmVarDecl *ParmDecl : collectParamDecls(Ctor, ParamDecl)) {
    auto ParamTL = ParmDecl->getTypeSourceInfo()->getTypeLoc();
    auto RefTL = ParamTL.getAs<ReferenceTypeLoc>();

    // Do not replace if it is already a value, skip.
    if (RefTL.isNull())
      continue;

    TypeLoc ValueTL = RefTL.getPointeeLoc();
    auto TypeRange = CharSourceRange::getTokenRange(ParmDecl->getLocStart(),
                                                    ParamTL.getLocEnd());
    std::string ValueStr = Lexer::getSourceText(CharSourceRange::getTokenRange(
                                                    ValueTL.getSourceRange()),
                                                SM, getLangOpts())
                               .str();
    ValueStr += ' ';
    Diag << FixItHint::CreateReplacement(TypeRange, ValueStr);
  }

  // Use std::move in the initialization list.
  Diag << FixItHint::CreateInsertion(Initializer->getRParenLoc(), ")")
       << FixItHint::CreateInsertion(
              Initializer->getLParenLoc().getLocWithOffset(1), "std::move(");

  if (auto IncludeFixit = Inserter->CreateIncludeInsertion(
          Result.SourceManager->getFileID(Initializer->getSourceLocation()),
          "utility",
          /*IsAngled=*/true)) {
    Diag << *IncludeFixit;
  }
}

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