RedundantPreprocessorCheck.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 "RedundantPreprocessorCheck.h"
#include "clang/Frontend/CompilerInstance.h"
#include "clang/Lex/Lexer.h"
#include "clang/Lex/PPCallbacks.h"
#include "clang/Lex/Preprocessor.h"
 
namespace clang::tidy::readability {
 
static StringRef getConditionText(SourceLocation Loc, const SourceManager &SM,
                                  const LangOptions &LangOpts) {
  bool Invalid = false;
  const FileID FID = SM.getFileID(Loc);
  const StringRef Buffer = SM.getBufferData(FID, &Invalid);
  if (Invalid)
    return {};
 
  // Initialize a raw lexer starting exactly at the condition's location
  Lexer RawLexer(SM.getLocForStartOfFile(FID), LangOpts, Buffer.begin(),
                 SM.getCharacterData(Loc), Buffer.end());
  RawLexer.SetCommentRetentionState(true);
 
  Token Tok;
  // Lex the 'if' token itself
  RawLexer.LexFromRawLexer(Tok);
 
  const unsigned StartOffset = SM.getFileOffset(Tok.getEndLoc());
  unsigned EndOffset = StartOffset;
 
  // Lex tokens until we hit the start of a new line or EOF.
  // The lexer handles backslash line continuations automatically.
  while (!RawLexer.LexFromRawLexer(Tok)) {
    if (Tok.isAtStartOfLine() || Tok.is(tok::eof))
      break;
    EndOffset = SM.getFileOffset(Tok.getLocation()) + Tok.getLength();
  }
 
  if (EndOffset <= StartOffset)
    return {};
 
  // Extract the raw text from the buffer to preserve original spacing
  return Buffer.substr(StartOffset, EndOffset - StartOffset).trim();
}
 
namespace {
 
/// Information about an opening preprocessor directive.
struct PreprocessorEntry {
  SourceLocation Loc;
  /// Condition used after the preprocessor directive.
  std::string Condition;
};
 
const char WarningDescription[] =
    "nested redundant %select{#if|#ifdef|#ifndef}0; consider removing it";
const char NoteDescription[] = "previous %select{#if|#ifdef|#ifndef}0 was here";
 
class RedundantPreprocessorCallbacks : public PPCallbacks {
  enum DirectiveKind { DK_If = 0, DK_Ifdef = 1, DK_Ifndef = 2 };
 
public:
  explicit RedundantPreprocessorCallbacks(ClangTidyCheck &Check,
                                          Preprocessor &PP)
      : Check(Check), PP(PP) {}
 
  void If(SourceLocation Loc, SourceRange ConditionRange,
          ConditionValueKind ConditionValue) override {
    const StringRef Condition =
        getConditionText(Loc, PP.getSourceManager(), PP.getLangOpts());
    checkMacroRedundancy(Loc, Condition, IfStack, DK_If, DK_If, true);
  }
 
  void Ifdef(SourceLocation Loc, const Token &MacroNameTok,
             const MacroDefinition &MacroDefinition) override {
    const std::string MacroName = PP.getSpelling(MacroNameTok);
    checkMacroRedundancy(Loc, MacroName, IfdefStack, DK_Ifdef, DK_Ifdef, true);
    checkMacroRedundancy(Loc, MacroName, IfndefStack, DK_Ifdef, DK_Ifndef,
                         false);
  }
 
  void Ifndef(SourceLocation Loc, const Token &MacroNameTok,
              const MacroDefinition &MacroDefinition) override {
    const std::string MacroName = PP.getSpelling(MacroNameTok);
    checkMacroRedundancy(Loc, MacroName, IfndefStack, DK_Ifndef, DK_Ifndef,
                         true);
    checkMacroRedundancy(Loc, MacroName, IfdefStack, DK_Ifndef, DK_Ifdef,
                         false);
  }
 
  void Endif(SourceLocation Loc, SourceLocation IfLoc) override {
    if (!IfStack.empty() && IfLoc == IfStack.back().Loc)
      IfStack.pop_back();
    if (!IfdefStack.empty() && IfLoc == IfdefStack.back().Loc)
      IfdefStack.pop_back();
    if (!IfndefStack.empty() && IfLoc == IfndefStack.back().Loc)
      IfndefStack.pop_back();
  }
 
private:
  void checkMacroRedundancy(SourceLocation Loc, StringRef MacroName,
                            SmallVector<PreprocessorEntry, 4> &Stack,
                            DirectiveKind WarningKind, DirectiveKind NoteKind,
                            bool Store) {
    if (PP.getSourceManager().isInMainFile(Loc)) {
      for (const auto &Entry : Stack) {
        if (Entry.Condition == MacroName) {
          Check.diag(Loc, WarningDescription) << WarningKind;
          Check.diag(Entry.Loc, NoteDescription, DiagnosticIDs::Note)
              << NoteKind;
        }
      }
    }
 
    if (Store)
      // This is an actual directive to be remembered.
      Stack.push_back({Loc, std::string(MacroName)});
  }
 
  ClangTidyCheck &Check;
  Preprocessor &PP;
  SmallVector<PreprocessorEntry, 4> IfStack;
  SmallVector<PreprocessorEntry, 4> IfdefStack;
  SmallVector<PreprocessorEntry, 4> IfndefStack;
};
} // namespace
 
void RedundantPreprocessorCheck::registerPPCallbacks(
    const SourceManager &SM, Preprocessor *PP, Preprocessor *ModuleExpanderPP) {
  PP->addPPCallbacks(
      ::std::make_unique<RedundantPreprocessorCallbacks>(*this, *PP));
}
 
} // namespace clang::tidy::readability