1 files changed, 34 insertions, 12 deletions

diff --git a/clang/lib/Sema/SemaModule.cpp b/clang/lib/Sema/SemaModule.cpp
index 85e5864..9bed3cb 100644
--- a/clang/lib/Sema/SemaModule.cpp
+++ b/clang/lib/Sema/SemaModule.cpp
@@ -80,12 +80,20 @@ Sema::ActOnGlobalModuleFragmentDecl(SourceLocation ModuleLoc) {
   return nullptr;
 }
 
-Sema::DeclGroupPtrTy
-Sema::ActOnModuleDecl(SourceLocation StartLoc, SourceLocation ModuleLoc,
-                      ModuleDeclKind MDK, ModuleIdPath Path, bool IsFirstDecl) {
+Sema::DeclGroupPtrTy Sema::ActOnModuleDecl(SourceLocation StartLoc,
+                                           SourceLocation ModuleLoc,
+                                           ModuleDeclKind MDK,
+                                           ModuleIdPath Path,
+                                           ModuleImportState &ImportState) {
   assert((getLangOpts().ModulesTS || getLangOpts().CPlusPlusModules) &&
          "should only have module decl in Modules TS or C++20");
 
+  bool IsFirstDecl = ImportState == ModuleImportState::FirstDecl;
+  bool SeenGMF = ImportState == ModuleImportState::GlobalFragment;
+  // If any of the steps here fail, we count that as invalidating C++20
+  // module state;
+  ImportState = ModuleImportState::NotACXX20Module;
+
   // A module implementation unit requires that we are not compiling a module
   // of any kind. A module interface unit requires that we are not compiling a
   // module map.
@@ -134,9 +142,13 @@ Sema::ActOnModuleDecl(SourceLocation StartLoc, SourceLocation ModuleLoc,
       ModuleScopes.back().Module->Kind == Module::GlobalModuleFragment)
     GlobalModuleFragment = ModuleScopes.back().Module;
 
+  assert((!getLangOpts().CPlusPlusModules ||
+          SeenGMF == (bool)GlobalModuleFragment) &&
+         "mismatched global module state");
+
   // In C++20, the module-declaration must be the first declaration if there
   // is no global module fragment.
-  if (getLangOpts().CPlusPlusModules && !IsFirstDecl && !GlobalModuleFragment) {
+  if (getLangOpts().CPlusPlusModules && !IsFirstDecl && !SeenGMF) {
     Diag(ModuleLoc, diag::err_module_decl_not_at_start);
     SourceLocation BeginLoc =
         ModuleScopes.empty()
@@ -231,6 +243,10 @@ Sema::ActOnModuleDecl(SourceLocation StartLoc, SourceLocation ModuleLoc,
   TU->setModuleOwnershipKind(Decl::ModuleOwnershipKind::ModulePrivate);
   TU->setLocalOwningModule(Mod);
 
+  // We are in the module purview, but before any other (non import)
+  // statements, so imports are allowed.
+  ImportState = ModuleImportState::ImportAllowed;
+
   // FIXME: Create a ModuleDecl.
   return nullptr;
 }
@@ -301,10 +317,10 @@ DeclResult Sema::ActOnModuleImport(SourceLocation StartLoc,
                                    SourceLocation ExportLoc,
                                    SourceLocation ImportLoc,
                                    ModuleIdPath Path) {
-  // Flatten the module path for a Modules TS module name.
+  // Flatten the module path for a C++20 or Modules TS module name.
   std::pair<IdentifierInfo *, SourceLocation> ModuleNameLoc;
-  if (getLangOpts().ModulesTS) {
-    std::string ModuleName;
+  std::string ModuleName;
+  if (getLangOpts().CPlusPlusModules || getLangOpts().ModulesTS) {
     for (auto &Piece : Path) {
       if (!ModuleName.empty())
         ModuleName += ".";
@@ -314,6 +330,14 @@ DeclResult Sema::ActOnModuleImport(SourceLocation StartLoc,
     Path = ModuleIdPath(ModuleNameLoc);
   }
 
+  // Diagnose self-import before attempting a load.
+  if (getLangOpts().CPlusPlusModules && isCurrentModulePurview() &&
+      getCurrentModule()->Name == ModuleName) {
+    Diag(ImportLoc, diag::err_module_self_import)
+        << ModuleName << getLangOpts().CurrentModule;
+    return true;
+  }
+
   Module *Mod =
       getModuleLoader().loadModule(ImportLoc, Path, Module::AllVisible,
                                    /*IsInclusionDirective=*/false);
@@ -342,11 +366,9 @@ DeclResult Sema::ActOnModuleImport(SourceLocation StartLoc,
   // FIXME: we should support importing a submodule within a different submodule
   // of the same top-level module. Until we do, make it an error rather than
   // silently ignoring the import.
-  // Import-from-implementation is valid in the Modules TS. FIXME: Should we
-  // warn on a redundant import of the current module?
-  // FIXME: Import of a module from an implementation partition of the same
-  // module is permitted.
-  if (Mod->getTopLevelModuleName() == getLangOpts().CurrentModule &&
+  // FIXME: Should we warn on a redundant import of the current module?
+  if (!getLangOpts().CPlusPlusModules &&
+      Mod->getTopLevelModuleName() == getLangOpts().CurrentModule &&
       (getLangOpts().isCompilingModule() || !getLangOpts().ModulesTS)) {
     Diag(ImportLoc, getLangOpts().isCompilingModule()
                         ? diag::err_module_self_import