[gcc r15-1223] c++: module std and exception_ptr

[Jason Merrill]

https://gcc.gnu.org/g:f8356d66cfbda1e65536016d3049342a43f6af63

commit r15-1223-gf8356d66cfbda1e65536016d3049342a43f6af63
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Jun 12 00:13:45 2024 -0400

    c++: module std and exception_ptr
    
    exception_ptr.h contains
    
      namespace __exception_ptr
      {
        class exception_ptr;
      }
      using __exception_ptr::exception_ptr;
    
    so when module std tries to 'export using std::exception_ptr', it names
    another using-directive rather than the class directly, so __exception_ptr
    is never explicitly opened in module purview.
    
    gcc/cp/ChangeLog:
    
            * module.cc (depset::hash::add_binding_entity): Set
            DECL_MODULE_PURVIEW_P instead of asserting.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/modules/using-20_a.C: New test.

Diff:
---
 gcc/cp/module.cc                          |  7 +++++--
 gcc/testsuite/g++.dg/modules/using-20_a.C | 14 ++++++++++++++
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index 21fc85150c9e..72e876cec187 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -13253,8 +13253,11 @@ depset::hash::add_binding_entity (tree decl, WMB_Flags flags, void *data_)
       data->met_namespace = true;
       if (data->hash->add_namespace_entities (decl, data->partitions))
 	{
-	  /* It contains an exported thing, so it is exported.  */
-	  gcc_checking_assert (DECL_MODULE_PURVIEW_P (decl));
+	  /* It contains an exported thing, so it is exported.
+	     We used to assert DECL_MODULE_PURVIEW_P, but that fails for a
+	     namespace like std::__exception_ptr which is never opened in
+	     module purview; the exporting using finds another using.  */
+	  DECL_MODULE_PURVIEW_P (decl) = true;
 	  DECL_MODULE_EXPORT_P (decl) = true;
 	}
 
diff --git a/gcc/testsuite/g++.dg/modules/using-20_a.C b/gcc/testsuite/g++.dg/modules/using-20_a.C
new file mode 100644
index 000000000000..bb3bb6160f8b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/using-20_a.C
@@ -0,0 +1,14 @@
+// { dg-additional-options "-fmodules-ts -fdump-lang-module -Wno-global-module" }
+// { dg-final { scan-lang-dump {Writing definition '::foo::bar::baz'} module } }
+
+module;
+namespace foo {
+  namespace bar {
+    struct baz { };
+  }
+  using bar::baz;
+}
+export module foo;
+namespace foo {
+  export using foo::baz;
+}