UseStringViewCheck.cpp

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//===----------------------------------------------------------------------===//
//
// 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 "UseStringViewCheck.h"
#include "../utils/Matchers.h"
#include "../utils/OptionsUtils.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/ASTDiagnostic.h"
#include "clang/AST/Stmt.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
#include "clang/ASTMatchers/ASTMatchers.h"
#include "clang/Basic/Diagnostic.h"
#include "llvm/ADT/StringMap.h"
 
using namespace clang::ast_matchers;
 
namespace clang::tidy::modernize {
 
namespace {
AST_MATCHER(Expr, isStringLiteralOrTernary) {
  const auto Matches = [](const auto &Self, const Expr &Expression) -> bool {
    const Expr *Unwrapped = Expression.IgnoreParenImpCasts();
    if (const auto *Ternary = dyn_cast<ConditionalOperator>(Unwrapped))
      return Self(Self, *Ternary->getTrueExpr()) &&
             Self(Self, *Ternary->getFalseExpr());
    return isa<StringLiteral>(Unwrapped);
  };
  return Matches(Matches, Node);
}
 
AST_MATCHER(FunctionDecl, isOverloaded) {
  const DeclarationName Name = Node.getDeclName();
  // Sanity check
  if (Name.isEmpty())
    return false;
  const DeclContext *DC = Node.getDeclContext();
  auto LookupResult = DC->lookup(Name);
  size_t UniqueSignatures = 0;
  llvm::SmallPtrSet<const FunctionDecl *, 2> SeenFunctions;
  for (NamedDecl *ND : LookupResult) {
    const FunctionDecl *FD = nullptr;
    if (const auto *Func = dyn_cast<FunctionDecl>(ND)) {
      // Regular functions
      FD = Func;
    } else if (const auto *USD = dyn_cast<UsingShadowDecl>(ND)) {
      // Overloads via "using ns::func_name"
      FD = dyn_cast<FunctionDecl>(USD->getTargetDecl());
    } else if (const auto *FTD = dyn_cast<FunctionTemplateDecl>(ND)) {
      // Templated functions
      FD = FTD->getTemplatedDecl();
    }
    if (FD && SeenFunctions.insert(FD->getCanonicalDecl()).second) {
      UniqueSignatures++;
      if (UniqueSignatures > 1)
        return true;
    }
  }
  return false;
}
} // namespace
 
static constexpr StringRef StringViewClassKey = "string";
static constexpr StringRef WStringViewClassKey = "wstring";
static constexpr StringRef U8StringViewClassKey = "u8string";
static constexpr StringRef U16StringViewClassKey = "u16string";
static constexpr StringRef U32StringViewClassKey = "u32string";
 
static auto getStringTypeMatcher(StringRef CharType) {
  return hasCanonicalType(hasDeclaration(cxxRecordDecl(hasName(CharType))));
}
 
static void fixReturns(const FunctionDecl *FuncDecl,
                       const DiagnosticBuilder &Diag, ASTContext &Context) {
  auto Matches = match(
      findAll(returnStmt(hasReturnValue(ignoringParenImpCasts(
          cxxTemporaryObjectExpr(argumentCountIs(0)).bind("temp_obj_expr"))))),
      *FuncDecl->getBody(), Context);
 
  for (const auto &Match : Matches)
    if (const auto *TempObjExpr =
            Match.getNodeAs<CXXTemporaryObjectExpr>("temp_obj_expr");
        TempObjExpr && TempObjExpr->getSourceRange().isValid())
      Diag << FixItHint::CreateReplacement(TempObjExpr->getSourceRange(), "{}");
}
 
UseStringViewCheck::UseStringViewCheck(StringRef Name,
                                       ClangTidyContext *Context)
    : ClangTidyCheck(Name, Context),
      CheckOverloadedFunctions(Options.get("CheckOverloadedFunctions", false)),
      IgnoredFunctions(utils::options::parseStringList(
          Options.get("IgnoredFunctions", "toString$;ToString$;to_string$"))) {
  parseReplacementStringViewClass(
      Options.get("ReplacementStringViewClass", ""));
}
 
void UseStringViewCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
  Options.store(Opts, "CheckOverloadedFunctions", CheckOverloadedFunctions);
  Options.store(Opts, "IgnoredFunctions",
                utils::options::serializeStringList(IgnoredFunctions));
  Options.store(Opts, "ReplacementStringViewClass",
                (Twine("") + StringViewClassKey + "=" + StringViewClass + ";" +
                 WStringViewClassKey + "=" + WStringViewClass + ";" +
                 U8StringViewClassKey + "=" + U8StringViewClass + ";" +
                 U16StringViewClassKey + "=" + U16StringViewClass + ";" +
                 U32StringViewClassKey + "=" + U32StringViewClass)
                    .str());
}
 
void UseStringViewCheck::registerMatchers(MatchFinder *Finder) {
  const auto IsStdString = getStringTypeMatcher("::std::basic_string");
  // TODO: also consider *StringViewClass types
  const auto IsStdStringView = getStringTypeMatcher("::std::basic_string_view");
  const auto IgnoredFunctionsMatcher =
      matchers::matchesAnyListedRegexName(IgnoredFunctions);
  const auto VirtualOrOperator =
      cxxMethodDecl(anyOf(cxxConversionDecl(), isVirtual()));
  const auto CheckOverloaded =
      CheckOverloadedFunctions ? unless(anything()) : isOverloaded();
  Finder->addMatcher(
      functionDecl(
          isDefinition(),
          unless(anyOf(VirtualOrOperator, IgnoredFunctionsMatcher,
                       CheckOverloaded,
                       ast_matchers::isExplicitTemplateSpecialization())),
          returns(IsStdString), hasDescendant(returnStmt()),
          unless(hasDescendant(returnStmt(hasReturnValue(unless(
              anyOf(stringLiteral(), hasType(IsStdStringView),
                    isStringLiteralOrTernary(),
                    cxxConstructExpr(anyOf(
                        allOf(hasType(IsStdString), argumentCountIs(0)),
                        allOf(isListInitialization(),
                              unless(cxxTemporaryObjectExpr()),
                              hasArgument(0, ignoringParenImpCasts(
                                                 stringLiteral()))))))))))))
          .bind("func"),
      this);
}
 
void UseStringViewCheck::check(const MatchFinder::MatchResult &Result) {
  const auto *MatchedDecl = Result.Nodes.getNodeAs<FunctionDecl>("func");
  assert(MatchedDecl);
  bool ShouldAKA = false;
  const std::string DesugaredTypeStr =
      desugarForDiagnostic(*Result.Context,
                           QualType(MatchedDecl->getReturnType()), ShouldAKA)
          .getAsString();
  const StringRef DestReturnTypeStr = toStringViewTypeStr(DesugaredTypeStr);
 
  auto Diag =
      diag(MatchedDecl->getTypeSpecStartLoc(),
           "consider using '%0' to avoid unnecessary copying and allocations")
      << DestReturnTypeStr;
 
  fixReturns(MatchedDecl, Diag, *Result.Context);
 
  for (const auto *FuncDecl : MatchedDecl->redecls())
    if (const SourceRange ReturnTypeRange =
            FuncDecl->getReturnTypeSourceRange();
        ReturnTypeRange.isValid())
      Diag << FixItHint::CreateReplacement(ReturnTypeRange, DestReturnTypeStr);
}
 
StringRef UseStringViewCheck::toStringViewTypeStr(StringRef Type) const {
  if (Type.contains("wchar_t"))
    return WStringViewClass;
  if (Type.contains("char8_t"))
    return U8StringViewClass;
  if (Type.contains("char16_t"))
    return U16StringViewClass;
  if (Type.contains("char32_t"))
    return U32StringViewClass;
  return StringViewClass;
}
 
void UseStringViewCheck::parseReplacementStringViewClass(StringRef Options) {
  if (Options.empty())
    return;
  const llvm::StringMap<StringRef *> StringClassesMap{
      {StringViewClassKey, &StringViewClass},
      {WStringViewClassKey, &WStringViewClass},
      {U8StringViewClassKey, &U8StringViewClass},
      {U16StringViewClassKey, &U16StringViewClass},
      {U32StringViewClassKey, &U32StringViewClass}};
  for (const auto &Option : utils::options::parseStringList(Options)) {
    const auto Split = Option.split('=');
    if (auto It = StringClassesMap.find(Split.first);
        It != StringClassesMap.end())
      *It->second = Split.second;
  }
}
 
} // namespace clang::tidy::modernize