[clang-tidy] Add --enable-module-headers-parsing option

Change default behavior in Clang-tidy and skip by default
module headers parsing. That functionality is buggy and
slow in C++20, and provide tiny benefit.

Reviewed By: carlosgalvezp

Differential Revision: https://reviews.llvm.org/D156161

clang-tools-extra/clang-tidy/ClangTidy.cpp

@@ -418,7 +418,8 @@ ClangTidyASTConsumerFactory::createASTConsumer(
   Preprocessor *PP = &Compiler.getPreprocessor();
   Preprocessor *ModuleExpanderPP = PP;
 
-  if (Context.getLangOpts().Modules && OverlayFS != nullptr) {
+  if (Context.canEnableModuleHeadersParsing() &&
+      Context.getLangOpts().Modules && OverlayFS != nullptr) {
     auto ModuleExpander = std::make_unique<ExpandModularHeadersPPCallbacks>(
         &Compiler, OverlayFS);
     ModuleExpanderPP = ModuleExpander->getPreprocessor();

clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.cpp

@@ -161,10 +161,11 @@ ClangTidyError::ClangTidyError(StringRef CheckName,
 
 ClangTidyContext::ClangTidyContext(
     std::unique_ptr<ClangTidyOptionsProvider> OptionsProvider,
-    bool AllowEnablingAnalyzerAlphaCheckers)
+    bool AllowEnablingAnalyzerAlphaCheckers, bool EnableModuleHeadersParsing)
     : DiagEngine(nullptr), OptionsProvider(std::move(OptionsProvider)),
       Profile(false),
       AllowEnablingAnalyzerAlphaCheckers(AllowEnablingAnalyzerAlphaCheckers),
+      EnableModuleHeadersParsing(EnableModuleHeadersParsing),
       SelfContainedDiags(false) {
   // Before the first translation unit we can get errors related to command-line
   // parsing, use empty string for the file name in this case.

clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.h

@@ -70,7 +70,8 @@ class ClangTidyContext {
 public:
   /// Initializes \c ClangTidyContext instance.
   ClangTidyContext(std::unique_ptr<ClangTidyOptionsProvider> OptionsProvider,
-                   bool AllowEnablingAnalyzerAlphaCheckers = false);
+                   bool AllowEnablingAnalyzerAlphaCheckers = false,
+                   bool EnableModuleHeadersParsing = false);
   /// Sets the DiagnosticsEngine that diag() will emit diagnostics to.
   // FIXME: this is required initialization, and should be a constructor param.
   // Fix the context -> diag engine -> consumer -> context initialization cycle.
@@ -198,6 +199,12 @@ class ClangTidyContext {
     return AllowEnablingAnalyzerAlphaCheckers;
   }
 
+  // This method determines whether preprocessor-level module header parsing is
+  // enabled using the `--experimental-enable-module-headers-parsing` option.
+  bool canEnableModuleHeadersParsing() const {
+    return EnableModuleHeadersParsing;
+  }
+
   void setSelfContainedDiags(bool Value) { SelfContainedDiags = Value; }
 
   bool areDiagsSelfContained() const { return SelfContainedDiags; }
@@ -245,6 +252,7 @@ class ClangTidyContext {
   std::string ProfilePrefix;
 
   bool AllowEnablingAnalyzerAlphaCheckers;
+  bool EnableModuleHeadersParsing;
 
   bool SelfContainedDiags;
 

clang-tools-extra/clang-tidy/tool/ClangTidyMain.cpp

@@ -263,6 +263,17 @@ static cl::opt<bool>
                                        cl::init(false), cl::Hidden,
                                        cl::cat(ClangTidyCategory));
 
+static cl::opt<bool> EnableModuleHeadersParsing("enable-module-headers-parsing",
+                                                desc(R"(
+Enables preprocessor-level module header parsing
+for C++20 and above, empowering specific checks
+to detect macro definitions within modules. This
+feature may cause performance and parsing issues
+and is therefore considered experimental.
+)"),
+                                                cl::init(false),
+                                                cl::cat(ClangTidyCategory));
+
 static cl::opt<std::string> ExportFixes("export-fixes", desc(R"(
 YAML file to store suggested fixes in. The
 stored fixes can be applied to the input source
@@ -659,7 +670,8 @@ int clangTidyMain(int argc, const char **argv) {
   llvm::InitializeAllAsmParsers();
 
   ClangTidyContext Context(std::move(OwningOptionsProvider),
-                           AllowEnablingAnalyzerAlphaCheckers);
+                           AllowEnablingAnalyzerAlphaCheckers,
+                           EnableModuleHeadersParsing);
   std::vector<ClangTidyError> Errors =
       runClangTidy(Context, OptionsParser->getCompilations(), PathList, BaseFS,
                    FixNotes, EnableCheckProfile, ProfilePrefix);

clang-tools-extra/docs/ReleaseNotes.rst

@@ -94,6 +94,20 @@ The improvements are...
 Improvements to clang-tidy
 --------------------------
 
+- Preprocessor-level module header parsing is now disabled by default due to
+  the problems it caused in C++20 and above, leading to performance and code
+  parsing issues regardless of whether modules were used or not. This change
+  will impact only the following checks:
+  :doc:`modernize-replace-disallow-copy-and-assign-macro
+  <clang-tidy/checks/modernize/replace-disallow-copy-and-assign-macro>`,
+  :doc:`bugprone-reserved-identifier
+  <clang-tidy/checks/bugprone/reserved-identifier>`, and
+  :doc:`readability-identifier-naming
+  <clang-tidy/checks/readability/identifier-naming>`. Those checks will no
+  longer see macros defined in modules. Users can still enable this
+  functionality using the newly added command line option
+  `--enable-module-headers-parsing`.
+
 New checks
 ^^^^^^^^^^