clang-tidy module: add #pragma once check

Co-Authored-by: Kyle Edwards <kyle.edwards@kitware.com>

4 files changed, 389 insertions, 0 deletions

diff --git a/Utilities/ClangTidyModule/CMakeLists.txt b/Utilities/ClangTidyModule/CMakeLists.txt
index c51f43a6a6..6fc54b1e74 100644
--- a/Utilities/ClangTidyModule/CMakeLists.txt
+++ b/Utilities/ClangTidyModule/CMakeLists.txt
@@ -22,6 +22,8 @@ add_library(cmake-clang-tidy-module MODULE
   UseCmstrlenCheck.h
   UseCmsysFstreamCheck.cxx
   UseCmsysFstreamCheck.h
+  UsePragmaOnceCheck.cxx
+  UsePragmaOnceCheck.h
   )
 target_include_directories(cmake-clang-tidy-module PRIVATE ${CLANG_INCLUDE_DIRS})
 target_link_libraries(cmake-clang-tidy-module PRIVATE clang-tidy)
diff --git a/Utilities/ClangTidyModule/Module.cxx b/Utilities/ClangTidyModule/Module.cxx
index 7ef8e7dabe..c747cee0fb 100644
--- a/Utilities/ClangTidyModule/Module.cxx
+++ b/Utilities/ClangTidyModule/Module.cxx
@@ -7,6 +7,7 @@
 #include "UseBespokeEnumClassCheck.h"
 #include "UseCmstrlenCheck.h"
 #include "UseCmsysFstreamCheck.h"
+#include "UsePragmaOnceCheck.h"
 
 namespace clang {
 namespace tidy {
@@ -23,6 +24,7 @@ public:
       "cmake-use-bespoke-enum-class");
     CheckFactories.registerCheck<OstringstreamUseCmstrcatCheck>(
       "cmake-ostringstream-use-cmstrcat");
+    CheckFactories.registerCheck<UsePragmaOnceCheck>("cmake-use-pragma-once");
   }
 };
 
diff --git a/Utilities/ClangTidyModule/UsePragmaOnceCheck.cxx b/Utilities/ClangTidyModule/UsePragmaOnceCheck.cxx
new file mode 100644
index 0000000000..7a42798a6d
--- /dev/null
+++ b/Utilities/ClangTidyModule/UsePragmaOnceCheck.cxx
@@ -0,0 +1,325 @@
+/* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+   file Copyright.txt or https://cmake.org/licensing for details.  */
+
+/* This code was originally taken from part of the Clang-Tidy LLVM project and
+ * modified for use with CMake under the following original license: */
+
+//===--- HeaderGuard.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 "UsePragmaOnceCheck.h"
+
+#include <algorithm>
+#include <cassert>
+
+#include <clang/Frontend/CompilerInstance.h>
+#include <clang/Lex/PPCallbacks.h>
+#include <clang/Lex/Preprocessor.h>
+#include <clang/Tooling/Tooling.h>
+#include <llvm/Support/Path.h>
+
+namespace clang {
+namespace tidy {
+namespace cmake {
+
+/// canonicalize a path by removing ./ and ../ components.
+static std::string cleanPath(StringRef Path)
+{
+  SmallString<256> Result = Path;
+  llvm::sys::path::remove_dots(Result, true);
+  return std::string(Result.str());
+}
+
+namespace {
+// This class is a workaround for the fact that PPCallbacks doesn't give us the
+// location of the hash for an #ifndef, #define, or #endif, so we have to find
+// it ourselves. We can't lex backwards, and attempting to turn on the
+// preprocessor's backtracking functionality wreaks havoc, so we have to
+// instantiate a second lexer and lex all the way from the beginning of the
+// file. Cache the results of this lexing so that we don't have to do it more
+// times than needed.
+//
+// TODO: Upstream a change to LLVM to give us the location of the hash in
+// PPCallbacks so we don't have to do this workaround.
+class DirectiveCache
+{
+public:
+  DirectiveCache(Preprocessor* PP, FileID FID)
+    : PP(PP)
+    , FID(FID)
+  {
+    SourceManager& SM = this->PP->getSourceManager();
+    const FileEntry* Entry = SM.getFileEntryForID(FID);
+    assert(Entry && "Invalid FileID given");
+
+    Lexer MyLexer(FID, SM.getMemoryBufferForFileOrFake(Entry), SM,
+                  this->PP->getLangOpts());
+    Token Tok;
+
+    while (!MyLexer.LexFromRawLexer(Tok)) {
+      if (Tok.getKind() == tok::hash) {
+        assert(SM.getFileID(Tok.getLocation()) == this->FID &&
+               "Token FileID does not match passed FileID");
+        if (!this->HashLocs.empty()) {
+          assert(SM.getFileOffset(this->HashLocs.back()) <
+                   SM.getFileOffset(Tok.getLocation()) &&
+                 "Tokens in file are not in order");
+        }
+
+        this->HashLocs.push_back(Tok.getLocation());
+      }
+    }
+  }
+
+  SourceRange createRangeForIfndef(SourceLocation IfndefMacroTokLoc)
+  {
+    // The #ifndef of an include guard is likely near the beginning of the
+    // file, so search from the front.
+    return SourceRange(this->findPreviousHashFromFront(IfndefMacroTokLoc),
+                       IfndefMacroTokLoc);
+  }
+
+  SourceRange createRangeForDefine(SourceLocation DefineMacroTokLoc)
+  {
+    // The #define of an include guard is likely near the beginning of the
+    // file, so search from the front.
+    return SourceRange(this->findPreviousHashFromFront(DefineMacroTokLoc),
+                       DefineMacroTokLoc);
+  }
+
+  SourceRange createRangeForEndif(SourceLocation EndifLoc)
+  {
+    // The #endif of an include guard is likely near the end of the file, so
+    // search from the back.
+    return SourceRange(this->findPreviousHashFromBack(EndifLoc), EndifLoc);
+  }
+
+private:
+  Preprocessor* PP;
+  FileID FID;
+  SmallVector<SourceLocation> HashLocs;
+
+  SourceLocation findPreviousHashFromFront(SourceLocation Loc)
+  {
+    SourceManager& SM = this->PP->getSourceManager();
+    Loc = SM.getExpansionLoc(Loc);
+    assert(SM.getFileID(Loc) == this->FID &&
+           "Loc FileID does not match our FileID");
+
+    auto It = std::find_if(
+      this->HashLocs.begin(), this->HashLocs.end(),
+      [&SM, &Loc](const SourceLocation& OtherLoc) -> bool {
+        return SM.getFileOffset(OtherLoc) >= SM.getFileOffset(Loc);
+      });
+    assert(It != this->HashLocs.begin() &&
+           "No hash associated with passed Loc");
+    return *--It;
+  }
+
+  SourceLocation findPreviousHashFromBack(SourceLocation Loc)
+  {
+    SourceManager& SM = this->PP->getSourceManager();
+    Loc = SM.getExpansionLoc(Loc);
+    assert(SM.getFileID(Loc) == this->FID &&
+           "Loc FileID does not match our FileID");
+
+    auto It =
+      std::find_if(this->HashLocs.rbegin(), this->HashLocs.rend(),
+                   [&SM, &Loc](const SourceLocation& OtherLoc) -> bool {
+                     return SM.getFileOffset(OtherLoc) < SM.getFileOffset(Loc);
+                   });
+    assert(It != this->HashLocs.rend() &&
+           "No hash associated with passed Loc");
+    return *It;
+  }
+};
+
+class UsePragmaOncePPCallbacks : public PPCallbacks
+{
+public:
+  UsePragmaOncePPCallbacks(Preprocessor* PP, UsePragmaOnceCheck* Check)
+    : PP(PP)
+    , Check(Check)
+  {
+  }
+
+  void FileChanged(SourceLocation Loc, FileChangeReason Reason,
+                   SrcMgr::CharacteristicKind FileType,
+                   FileID PrevFID) override
+  {
+    // Record all files we enter. We'll need them to diagnose headers without
+    // guards.
+    SourceManager& SM = this->PP->getSourceManager();
+    if (Reason == EnterFile && FileType == SrcMgr::C_User) {
+      if (const FileEntry* FE = SM.getFileEntryForID(SM.getFileID(Loc))) {
+        std::string FileName = cleanPath(FE->getName());
+        this->Files[FileName] = FE;
+      }
+    }
+  }
+
+  void Ifndef(SourceLocation Loc, const Token& MacroNameTok,
+              const MacroDefinition& MD) override
+  {
+    if (MD) {
+      return;
+    }
+
+    // Record #ifndefs that succeeded. We also need the Location of the Name.
+    this->Ifndefs[MacroNameTok.getIdentifierInfo()] =
+      std::make_pair(Loc, MacroNameTok.getLocation());
+  }
+
+  void MacroDefined(const Token& MacroNameTok,
+                    const MacroDirective* MD) override
+  {
+    // Record all defined macros. We store the whole token to get info on the
+    // name later.
+    this->Macros.emplace_back(MacroNameTok, MD->getMacroInfo());
+  }
+
+  void Endif(SourceLocation Loc, SourceLocation IfLoc) override
+  {
+    // Record all #endif and the corresponding #ifs (including #ifndefs).
+    this->EndIfs[IfLoc] = Loc;
+  }
+
+  void EndOfMainFile() override
+  {
+    // Now that we have all this information from the preprocessor, use it!
+    SourceManager& SM = this->PP->getSourceManager();
+
+    for (const auto& MacroEntry : this->Macros) {
+      const MacroInfo* MI = MacroEntry.second;
+
+      // We use clang's header guard detection. This has the advantage of also
+      // emitting a warning for cases where a pseudo header guard is found but
+      // preceded by something blocking the header guard optimization.
+      if (!MI->isUsedForHeaderGuard()) {
+        continue;
+      }
+
+      const FileEntry* FE =
+        SM.getFileEntryForID(SM.getFileID(MI->getDefinitionLoc()));
+      std::string FileName = cleanPath(FE->getName());
+      this->Files.erase(FileName);
+
+      // Look up Locations for this guard.
+      SourceLocation Ifndef =
+        this->Ifndefs[MacroEntry.first.getIdentifierInfo()].second;
+      SourceLocation Define = MacroEntry.first.getLocation();
+      SourceLocation EndIf =
+        this
+          ->EndIfs[this->Ifndefs[MacroEntry.first.getIdentifierInfo()].first];
+
+      StringRef CurHeaderGuard =
+        MacroEntry.first.getIdentifierInfo()->getName();
+      std::vector<FixItHint> FixIts;
+
+      HeaderSearch& HeaderInfo = this->PP->getHeaderSearchInfo();
+
+      HeaderFileInfo& Info = HeaderInfo.getFileInfo(FE);
+
+      DirectiveCache Cache(this->PP, SM.getFileID(MI->getDefinitionLoc()));
+      SourceRange IfndefSrcRange = Cache.createRangeForIfndef(Ifndef);
+      SourceRange DefineSrcRange = Cache.createRangeForDefine(Define);
+      SourceRange EndifSrcRange = Cache.createRangeForEndif(EndIf);
+
+      if (Info.isPragmaOnce) {
+        FixIts.push_back(FixItHint::CreateRemoval(IfndefSrcRange));
+      } else {
+        FixIts.push_back(
+          FixItHint::CreateReplacement(IfndefSrcRange, "#pragma once"));
+      }
+
+      FixIts.push_back(FixItHint::CreateRemoval(DefineSrcRange));
+      FixIts.push_back(FixItHint::CreateRemoval(EndifSrcRange));
+
+      this->Check->diag(IfndefSrcRange.getBegin(), "use #pragma once")
+        << FixIts;
+    }
+
+    // Emit warnings for headers that are missing guards.
+    checkGuardlessHeaders();
+    clearAllState();
+  }
+
+  /// Looks for files that were visited but didn't have a header guard.
+  /// Emits a warning with fixits suggesting adding one.
+  void checkGuardlessHeaders()
+  {
+    // Look for header files that didn't have a header guard. Emit a warning
+    // and fix-its to add the guard.
+    // TODO: Insert the guard after top comments.
+    for (const auto& FE : this->Files) {
+      StringRef FileName = FE.getKey();
+      if (!Check->shouldSuggestToAddPragmaOnce(FileName)) {
+        continue;
+      }
+
+      SourceManager& SM = this->PP->getSourceManager();
+      FileID FID = SM.translateFile(FE.getValue());
+      SourceLocation StartLoc = SM.getLocForStartOfFile(FID);
+      if (StartLoc.isInvalid()) {
+        continue;
+      }
+
+      HeaderSearch& HeaderInfo = this->PP->getHeaderSearchInfo();
+
+      HeaderFileInfo& Info = HeaderInfo.getFileInfo(FE.second);
+      if (Info.isPragmaOnce) {
+        continue;
+      }
+
+      this->Check->diag(StartLoc, "use #pragma once")
+        << FixItHint::CreateInsertion(StartLoc, "#pragma once\n");
+    }
+  }
+
+private:
+  void clearAllState()
+  {
+    this->Macros.clear();
+    this->Files.clear();
+    this->Ifndefs.clear();
+    this->EndIfs.clear();
+  }
+
+  std::vector<std::pair<Token, const MacroInfo*>> Macros;
+  llvm::StringMap<const FileEntry*> Files;
+  std::map<const IdentifierInfo*, std::pair<SourceLocation, SourceLocation>>
+    Ifndefs;
+  std::map<SourceLocation, SourceLocation> EndIfs;
+
+  Preprocessor* PP;
+  UsePragmaOnceCheck* Check;
+};
+} // namespace
+
+void UsePragmaOnceCheck::storeOptions(ClangTidyOptions::OptionMap& Opts)
+{
+  this->Options.store(Opts, "HeaderFileExtensions",
+                      RawStringHeaderFileExtensions);
+}
+
+void UsePragmaOnceCheck::registerPPCallbacks(const SourceManager& SM,
+                                             Preprocessor* PP,
+                                             Preprocessor* ModuleExpanderPP)
+{
+  PP->addPPCallbacks(std::make_unique<UsePragmaOncePPCallbacks>(PP, this));
+}
+
+bool UsePragmaOnceCheck::shouldSuggestToAddPragmaOnce(StringRef FileName)
+{
+  return utils::isFileExtension(FileName, this->HeaderFileExtensions);
+}
+
+} // namespace cmake
+} // namespace tidy
+} // namespace clang
diff --git a/Utilities/ClangTidyModule/UsePragmaOnceCheck.h b/Utilities/ClangTidyModule/UsePragmaOnceCheck.h
new file mode 100644
index 0000000000..08c2099a9f
--- /dev/null
+++ b/Utilities/ClangTidyModule/UsePragmaOnceCheck.h
@@ -0,0 +1,60 @@
+/* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+   file Copyright.txt or https://cmake.org/licensing for details.  */
+
+/* This code was originally taken from part of the Clang-Tidy LLVM project and
+ * modified for use with CMake under the following original license: */
+
+//===--- HeaderGuard.h - clang-tidy -----------------------------*- C++
+//-*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#pragma once
+
+#include <clang-tidy/ClangTidyCheck.h>
+#include <clang-tidy/utils/FileExtensionsUtils.h>
+
+namespace clang {
+namespace tidy {
+namespace cmake {
+
+/// Finds and replaces header guards with pragma once.
+/// The check supports these options:
+///   - `HeaderFileExtensions`: a semicolon-separated list of filename
+///     extensions of header files (The filename extension should not contain
+///     "." prefix). ";h;hh;hpp;hxx" by default.
+///
+///     For extension-less header files, using an empty string or leaving an
+///     empty string between ";" if there are other filename extensions.
+class UsePragmaOnceCheck : public ClangTidyCheck
+{
+public:
+  UsePragmaOnceCheck(StringRef Name, ClangTidyContext* Context)
+    : ClangTidyCheck(Name, Context)
+    , RawStringHeaderFileExtensions(Options.getLocalOrGlobal(
+        "HeaderFileExtensions", utils::defaultHeaderFileExtensions()))
+  {
+    utils::parseFileExtensions(RawStringHeaderFileExtensions,
+                               HeaderFileExtensions,
+                               utils::defaultFileExtensionDelimiters());
+  }
+  void storeOptions(ClangTidyOptions::OptionMap& Opts) override;
+  void registerPPCallbacks(const SourceManager& SM, Preprocessor* PP,
+                           Preprocessor* ModuleExpanderPP) override;
+
+  /// Returns ``true`` if the check should add pragma once to the file
+  /// if it has none.
+  virtual bool shouldSuggestToAddPragmaOnce(StringRef Filename);
+
+private:
+  std::string RawStringHeaderFileExtensions;
+  utils::FileExtensionsSet HeaderFileExtensions;
+};
+
+} // namespace cmake
+} // namespace tidy
+} // namespace clang