clang-tidy/modernize/AvoidCArraysCheck.cpp

//===----------------------------------------------------------------------===//
//
// 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 "AvoidCArraysCheck.h"
#include "clang/AST/ASTContext.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
#include "clang/ASTMatchers/ASTMatchers.h"

using namespace clang::ast_matchers;

namespace clang::tidy::modernize {

namespace {

AST_MATCHER(clang::TypeLoc, hasValidBeginLoc) {
  return Node.getBeginLoc().isValid();
}

AST_MATCHER_P(clang::TypeLoc, hasType,
              clang::ast_matchers::internal::Matcher<clang::Type>,
              InnerMatcher) {
  const clang::Type *TypeNode = Node.getTypePtr();
  return TypeNode != nullptr &&
         InnerMatcher.matches(*TypeNode, Finder, Builder);
}

AST_MATCHER(clang::RecordDecl, isExternCContext) {
  return Node.isExternCContext();
}

AST_MATCHER(clang::ParmVarDecl, isArgvOfMain) {
  const clang::DeclContext *DC = Node.getDeclContext();
  const auto *FD = llvm::dyn_cast<clang::FunctionDecl>(DC);
  return FD ? FD->isMain() : false;
}

template <typename TargetType, typename NodeType>
const TargetType *getAs(const NodeType *Node) {
  if constexpr (std::is_same_v<NodeType, clang::DynTypedNode>)
    return Node->template get<TargetType>();
  else
    return llvm::dyn_cast<TargetType>(Node);
}

AST_MATCHER(clang::TypeLoc, isWithinImplicitTemplateInstantiation) {
  const auto IsImplicitTemplateInstantiation = [](const auto *Node) {
    const auto IsImplicitInstantiation = [](const auto *Node) {
      return (Node != nullptr) && (Node->getTemplateSpecializationKind() ==
                                   TSK_ImplicitInstantiation);
    };
    return (IsImplicitInstantiation(getAs<clang::CXXRecordDecl>(Node)) ||
            IsImplicitInstantiation(getAs<clang::FunctionDecl>(Node)) ||
            IsImplicitInstantiation(getAs<clang::VarDecl>(Node)));
  };

  DynTypedNodeList ParentNodes = Finder->getASTContext().getParents(Node);
  const clang::NamedDecl *ParentDecl = nullptr;
  while (!ParentNodes.empty()) {
    const DynTypedNode &ParentNode = ParentNodes[0];
    if (IsImplicitTemplateInstantiation(&ParentNode))
      return true;

    // in case of a `NamedDecl` as parent node, it is more efficient to proceed
    // with the upward traversal via DeclContexts (see below) instead of via
    // parent nodes
    if ((ParentDecl = ParentNode.template get<clang::NamedDecl>()))
      break;

    ParentNodes = Finder->getASTContext().getParents(ParentNode);
  }

  if (ParentDecl != nullptr) {
    const clang::DeclContext *DeclContext = ParentDecl->getDeclContext();
    while (DeclContext != nullptr) {
      if (IsImplicitTemplateInstantiation(DeclContext))
        return true;
      DeclContext = DeclContext->getParent();
    }
  }

  return false;
}

} // namespace

AvoidCArraysCheck::AvoidCArraysCheck(StringRef Name, ClangTidyContext *Context)
    : ClangTidyCheck(Name, Context),
      AllowStringArrays(Options.get("AllowStringArrays", false)) {}

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

void AvoidCArraysCheck::registerMatchers(MatchFinder *Finder) {
  ast_matchers::internal::Matcher<TypeLoc> IgnoreStringArrayIfNeededMatcher =
      anything();
  if (AllowStringArrays)
    IgnoreStringArrayIfNeededMatcher =
        unless(typeLoc(loc(hasCanonicalType(incompleteArrayType(
                           hasElementType(isAnyCharacter())))),
                       hasParent(varDecl(hasInitializer(stringLiteral()),
                                         unless(parmVarDecl())))));

  Finder->addMatcher(
      typeLoc(hasValidBeginLoc(), hasType(arrayType()),
              optionally(hasParent(parmVarDecl().bind("param_decl"))),
              unless(anyOf(hasParent(parmVarDecl(isArgvOfMain())),
                           hasParent(varDecl(isExternC())),
                           hasParent(fieldDecl(
                               hasParent(recordDecl(isExternCContext())))),
                           hasAncestor(functionDecl(isExternC())),
                           isWithinImplicitTemplateInstantiation())),
              IgnoreStringArrayIfNeededMatcher)
          .bind("typeloc"),
      this);

  Finder->addMatcher(
      templateArgumentLoc(hasTypeLoc(
          typeLoc(hasType(arrayType())).bind("template_arg_array_typeloc"))),
      this);
}

void AvoidCArraysCheck::check(const MatchFinder::MatchResult &Result) {
  TypeLoc ArrayTypeLoc{};

  if (const auto *MatchedTypeLoc = Result.Nodes.getNodeAs<TypeLoc>("typeloc"))
    ArrayTypeLoc = *MatchedTypeLoc;

  if (const auto *TemplateArgArrayTypeLoc =
          Result.Nodes.getNodeAs<TypeLoc>("template_arg_array_typeloc"))
    ArrayTypeLoc = *TemplateArgArrayTypeLoc;

  assert(!ArrayTypeLoc.isNull());

  const bool IsInParam =
      Result.Nodes.getNodeAs<ParmVarDecl>("param_decl") != nullptr;
  const bool IsVLA = ArrayTypeLoc.getTypePtr()->isVariableArrayType();
  enum class RecommendType { Array, Vector, Span };
  llvm::SmallVector<const char *> RecommendTypes{};
  if (IsVLA) {
    RecommendTypes.push_back("'std::vector'");
  } else if (ArrayTypeLoc.getTypePtr()->isIncompleteArrayType() && IsInParam) {
    // in function parameter, we also don't know the size of
    // IncompleteArrayType.
    if (Result.Context->getLangOpts().CPlusPlus20)
      RecommendTypes.push_back("'std::span'");
    else {
      RecommendTypes.push_back("'std::array'");
      RecommendTypes.push_back("'std::vector'");
    }
  } else {
    RecommendTypes.push_back("'std::array'");
  }

  diag(ArrayTypeLoc.getBeginLoc(),
       "do not declare %select{C-style|C VLA}0 arrays, use %1 instead")
      << IsVLA << llvm::join(RecommendTypes, " or ")
      << ArrayTypeLoc.getSourceRange();
}

} // namespace clang::tidy::modernize