[modules] When a #include is mapped to a module import and appears somewhere

other than the top level, we issue an error. This breaks a fair amount of C++
code wrapping C libraries, where the C library is #included within a namespace
/ extern "C" combination, because the C library (probably) includes C++
standard library headers which may be within modules.

Without modules, this setup is harmless if (and *only* if) the corresponding
standard library module was already included outside the namespace, so
downgrade the error to a default-error extension in that case, so that it can
be selectively disabled for such misbehaving libraries.

llvm-svn: 253398

1 files changed, 6 insertions, 4 deletions

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index e4e48a69ab8..4e2616ebe20 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -14500,8 +14500,8 @@ Decl *Sema::ActOnFileScopeAsmDecl(Expr *expr,
 }
 
 static void checkModuleImportContext(Sema &S, Module *M,
-                                     SourceLocation ImportLoc,
-                                     DeclContext *DC) {
+                                     SourceLocation ImportLoc, DeclContext *DC,
+                                     bool FromInclude = false) {
   SourceLocation ExternCLoc;
 
   if (auto *LSD = dyn_cast<LinkageSpecDecl>(DC)) {
@@ -14520,7 +14520,9 @@ static void checkModuleImportContext(Sema &S, Module *M,
     DC = DC->getParent();
 
   if (!isa<TranslationUnitDecl>(DC)) {
-    S.Diag(ImportLoc, diag::err_module_import_not_at_top_level_fatal)
+    S.Diag(ImportLoc, (FromInclude && S.isModuleVisible(M))
+                          ? diag::ext_module_import_not_at_top_level_noop
+                          : diag::err_module_import_not_at_top_level_fatal)
         << M->getFullModuleName() << DC;
     S.Diag(cast<Decl>(DC)->getLocStart(),
            diag::note_module_import_not_at_top_level) << DC;
@@ -14579,7 +14581,7 @@ DeclResult Sema::ActOnModuleImport(SourceLocation AtLoc,
 }
 
 void Sema::ActOnModuleInclude(SourceLocation DirectiveLoc, Module *Mod) {
-  checkModuleImportContext(*this, Mod, DirectiveLoc, CurContext);
+  checkModuleImportContext(*this, Mod, DirectiveLoc, CurContext, true);
 
   // Determine whether we're in the #include buffer for a module. The #includes
   // in that buffer do not qualify as module imports; they're just an