[clang] fix assert in ADL finding entity in the implicit global module

clang/docs/ReleaseNotes.rst

@@ -43,7 +43,7 @@ code bases.
   still supporting SPARC V8 CPUs need to specify ``-mcpu=v8`` with a
   `config file
   <https://clang.llvm.org/docs/UsersManual.html#configuration-files>`_.
-  
+
 - The ``clang-rename`` tool has been removed.
 
 C/C++ Language Potentially Breaking Changes
@@ -115,7 +115,7 @@ C++ Language Changes
 - Allow single element access of GCC vector/ext_vector_type object to be
   constant expression. Supports the `V.xyzw` syntax and other tidbits
   as seen in OpenCL. Selecting multiple elements is left as a future work.
-- Implement `CWG1815 <https://wg21.link/CWG1815>`_. Support lifetime extension 
+- Implement `CWG1815 <https://wg21.link/CWG1815>`_. Support lifetime extension
   of temporary created by aggregate initialization using a default member
   initializer.
 
@@ -452,6 +452,9 @@ Miscellaneous Clang Crashes Fixed
 
 - Fixed ``-ast-dump`` crashes on codes involving ``concept`` with ``-ast-dump-decl-types``. (#GH94928)
 
+- Fixed internal assertion firing when a declaration in the implicit global
+  module is found through ADL. (GH#109879)
+
 OpenACC Specific Changes
 ------------------------
 

clang/lib/Sema/SemaLookup.cpp

@@ -3850,8 +3850,9 @@ void Sema::ArgumentDependentLookup(DeclarationName Name, SourceLocation Loc,
             // exports are only valid in module purview and outside of any
             // PMF (although a PMF should not even be present in a module
             // with an import).
-            assert(FM && FM->isNamedModule() && !FM->isPrivateModule() &&
-                   "bad export context");
+            assert(FM &&
+                   (FM->isNamedModule() || FM->isImplicitGlobalModule()) &&
+                   !FM->isPrivateModule() && "bad export context");
             // .. are attached to a named module M, do not appear in the
             // translation unit containing the point of the lookup..
             if (D->isInAnotherModuleUnit() &&

clang/test/Modules/GH109879-1.cpp

@@ -0,0 +1,25 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+//
+// RUN: %clang_cc1 -std=c++20 %t/A.cppm -emit-module-interface -o %t/A.pcm
+// RUN: %clang_cc1 -std=c++20 %t/B.cppm -fprebuilt-module-path=%t -emit-module-interface -o %t/B.pcm
+// RUN: %clang_cc1 -fsyntax-only -std=c++20 -fprebuilt-module-path=%t -verify %t/C.cpp
+
+//--- A.cppm
+export module A;
+export extern "C" void foo(struct Bar);
+
+//--- B.cppm
+module;
+import A;
+export module B;
+
+//--- C.cpp
+import B;
+struct Bar {};
+void test() {
+  foo(Bar());
+  // expected-error@-1 {{declaration of 'foo' must be imported}}
+  // [email protected]:2 {{declaration here is not visible}}
+}

clang/test/Modules/GH109879-2.cpp

@@ -0,0 +1,29 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+//
+// RUN: %clang_cc1 -std=c++20 %t/A.cppm -emit-module-interface -o %t/A.pcm
+// RUN: %clang_cc1 -std=c++20 %t/B.cppm -fprebuilt-module-path=%t -emit-module-interface -o %t/B.pcm
+// RUN: %clang_cc1 -fsyntax-only -std=c++20 -fprebuilt-module-path=%t -verify %t/C.cpp
+
+//--- foo.h
+struct Bar {};
+extern "C" void foo(struct Bar);
+
+//--- A.cppm
+module;
+#include "foo.h"
+export module A;
+export extern "C" using ::foo;
+//--- B.cppm
+module;
+import A;
+export module B;
+
+//--- C.cpp
+// expected-no-diagnostics
+import B;
+#include "foo.h"
+void test() {
+  foo(Bar());
+}