[NFC] [C++20] [Modules] Refactor the warning to '-fmodule-file=<BMIPath>' for C++20 modules

Previous implementation of the warning to use `-fmodule-file=<BMIPath>`
for C++20 Modules is not straightforward and it is problematic in case
we read the BMIPath by writing tools based clang components. This patch
refactors it with a simple and direct style.

7 files changed, 40 insertions, 20 deletions

diff --git a/clang/include/clang/Basic/DiagnosticFrontendKinds.td b/clang/include/clang/Basic/DiagnosticFrontendKinds.td
index c950a2d..715e0c0d 100644
--- a/clang/include/clang/Basic/DiagnosticFrontendKinds.td
+++ b/clang/include/clang/Basic/DiagnosticFrontendKinds.td
@@ -261,6 +261,11 @@ def err_test_module_file_extension_version : Error<
   "test module file extension '%0' has different version (%1.%2) than expected "
   "(%3.%4)">;
 
+def warn_eagerly_load_for_standard_cplusplus_modules : Warning<
+  "the form '-fmodule-file=<BMI-path>' is deprecated for standard C++ named modules;"
+  "consider to use '-fmodule-file=<module-name>=<BMI-path>' instead">,
+  InGroup<DiagGroup<"eager-load-cxx-named-modules">>;
+
 def err_missing_vfs_overlay_file : Error<
   "virtual filesystem overlay file '%0' not found">, DefaultFatal;
 def err_invalid_vfs_overlay : Error<
diff --git a/clang/include/clang/Basic/DiagnosticSerializationKinds.td b/clang/include/clang/Basic/DiagnosticSerializationKinds.td
index 5197aa1..a1ae23a 100644
--- a/clang/include/clang/Basic/DiagnosticSerializationKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSerializationKinds.td
@@ -129,11 +129,6 @@ def warn_module_system_bit_conflict : Warning<
   "as a non-system module; any difference in diagnostic options will be ignored">,
   InGroup<ModuleConflict>;
 
-def warn_eagerly_load_for_standard_cplusplus_modules : Warning<
-  "the form '-fmodule-file=<BMI-path>' is deprecated for standard C++ named modules;"
-  "consider to use '-fmodule-file=<module-name>=<BMI-path>' instead">,
-  InGroup<DiagGroup<"eager-load-cxx-named-modules">>;
-
 def warn_reading_std_cxx_module_by_implicit_paths : Warning<
   "it is deprecated to read module '%0' implicitly; it is going to be removed in clang 18; "
   "consider to specify the dependencies explicitly">,
diff --git a/clang/include/clang/Frontend/CompilerInstance.h b/clang/include/clang/Frontend/CompilerInstance.h
index 1255d2c..d26a452 100644
--- a/clang/include/clang/Frontend/CompilerInstance.h
+++ b/clang/include/clang/Frontend/CompilerInstance.h
@@ -40,6 +40,11 @@ class TimerGroup;
 namespace clang {
 class ASTContext;
 class ASTReader;
+
+namespace serialization {
+class ModuleFile;
+}
+
 class CodeCompleteConsumer;
 class DiagnosticsEngine;
 class DiagnosticConsumer;
@@ -794,7 +799,8 @@ public:
 
   void createASTReader();
 
-  bool loadModuleFile(StringRef FileName);
+  bool loadModuleFile(StringRef FileName,
+                      serialization::ModuleFile *&LoadedModuleFile);
 
 private:
   /// Find a module, potentially compiling it, before reading its AST.  This is
diff --git a/clang/include/clang/Serialization/ASTReader.h b/clang/include/clang/Serialization/ASTReader.h
index 2d114fc..dc1eb21 100644
--- a/clang/include/clang/Serialization/ASTReader.h
+++ b/clang/include/clang/Serialization/ASTReader.h
@@ -1632,9 +1632,18 @@ public:
   /// \param ClientLoadCapabilities The set of client load-failure
   /// capabilities, represented as a bitset of the enumerators of
   /// LoadFailureCapabilities.
+  ///
+  /// \param LoadedModuleFile The optional out-parameter refers to the new
+  /// loaded modules. In case the module specified by FileName is already
+  /// loaded, the module file pointer referred by NewLoadedModuleFile wouldn't
+  /// change. Otherwise if the AST file get loaded successfully,
+  /// NewLoadedModuleFile would refer to the address of the new loaded top level
+  /// module. The state of NewLoadedModuleFile is unspecified if the AST file
+  /// isn't loaded successfully.
   ASTReadResult ReadAST(StringRef FileName, ModuleKind Type,
                         SourceLocation ImportLoc,
-                        unsigned ClientLoadCapabilities);
+                        unsigned ClientLoadCapabilities,
+                        ModuleFile **NewLoadedModuleFile = nullptr);
 
   /// Make the entities in the given module and any of its (non-explicit)
   /// submodules visible to name lookup.
diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index e500675..49c1d8e 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -1717,7 +1717,8 @@ void CompilerInstance::createASTReader() {
     Listener->attachToASTReader(*TheASTReader);
 }
 
-bool CompilerInstance::loadModuleFile(StringRef FileName) {
+bool CompilerInstance::loadModuleFile(
+    StringRef FileName, serialization::ModuleFile *&LoadedModuleFile) {
   llvm::Timer Timer;
   if (FrontendTimerGroup)
     Timer.init("preloading." + FileName.str(), "Preloading " + FileName.str(),
@@ -1743,7 +1744,8 @@ bool CompilerInstance::loadModuleFile(StringRef FileName) {
   // Try to load the module file.
   switch (TheASTReader->ReadAST(
       FileName, serialization::MK_ExplicitModule, SourceLocation(),
-      ConfigMismatchIsRecoverable ? ASTReader::ARR_ConfigurationMismatch : 0)) {
+      ConfigMismatchIsRecoverable ? ASTReader::ARR_ConfigurationMismatch : 0,
+      &LoadedModuleFile)) {
   case ASTReader::Success:
     // We successfully loaded the module file; remember the set of provided
     // modules so that we don't try to load implicit modules for them.
diff --git a/clang/lib/Frontend/FrontendAction.cpp b/clang/lib/Frontend/FrontendAction.cpp
index 2da25be..e016b94 100644
--- a/clang/lib/Frontend/FrontendAction.cpp
+++ b/clang/lib/Frontend/FrontendAction.cpp
@@ -1023,10 +1023,16 @@ bool FrontendAction::BeginSourceFile(CompilerInstance &CI,
   }
 
   // If we were asked to load any module files, do so now.
-  for (const auto &ModuleFile : CI.getFrontendOpts().ModuleFiles)
-    if (!CI.loadModuleFile(ModuleFile))
+  for (const auto &ModuleFile : CI.getFrontendOpts().ModuleFiles) {
+    serialization::ModuleFile *Loaded = nullptr;
+    if (!CI.loadModuleFile(ModuleFile, Loaded))
       return false;
 
+    if (Loaded && Loaded->StandardCXXModule)
+      CI.getDiagnostics().Report(
+          diag::warn_eagerly_load_for_standard_cplusplus_modules);
+  }
+
   // If there is a layout overrides file, attach an external AST source that
   // provides the layouts from that file.
   if (!CI.getFrontendOpts().OverrideRecordLayoutsFile.empty() &&
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index faeea66..8ece979 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -4311,10 +4311,10 @@ static bool SkipCursorToBlock(BitstreamCursor &Cursor, unsigned BlockID) {
   }
 }
 
-ASTReader::ASTReadResult ASTReader::ReadAST(StringRef FileName,
-                                            ModuleKind Type,
+ASTReader::ASTReadResult ASTReader::ReadAST(StringRef FileName, ModuleKind Type,
                                             SourceLocation ImportLoc,
-                                            unsigned ClientLoadCapabilities) {
+                                            unsigned ClientLoadCapabilities,
+                                            ModuleFile **NewLoadedModuleFile) {
   llvm::TimeTraceScope scope("ReadAST", FileName);
 
   llvm::SaveAndRestore SetCurImportLocRAII(CurrentImportLoc, ImportLoc);
@@ -4344,6 +4344,9 @@ ASTReader::ASTReadResult ASTReader::ReadAST(StringRef FileName,
     return ReadResult;
   }
 
+  if (NewLoadedModuleFile && !Loaded.empty())
+    *NewLoadedModuleFile = Loaded.back().Mod;
+
   // Here comes stuff that we only do once the entire chain is loaded. Do *not*
   // remove modules from this point. Various fields are updated during reading
   // the AST block and removing the modules would result in dangling pointers.
@@ -5709,12 +5712,6 @@ llvm::Error ASTReader::ReadSubmoduleBlock(ModuleFile &F,
       if (DeserializationListener)
         DeserializationListener->ModuleRead(GlobalID, CurrentModule);
 
-      // If we're loading a module before we initialize the sema, it implies
-      // we're performing eagerly loading.
-      if (!getSema() && CurrentModule->isModulePurview() &&
-          !getContext().getLangOpts().isCompilingModule())
-        Diag(clang::diag::warn_eagerly_load_for_standard_cplusplus_modules);
-
       SubmodulesLoaded[GlobalIndex] = CurrentModule;
 
       // Clear out data that will be replaced by what is in the module file.