c++/modules: ICEs with modular fmtlib

Building modular fmtlib triggered two small modules bugs in C++23 and
C++26 mode respectively (due to libstdc++ header differences).

The first is that a TEMPLATE_DECL having DECL_LANG_SPECIFIC doesn't
necessarily imply that its DECL_TEMPLATE_RESULT has DECL_LANG_SPECIFIC.
So in add_specializations we need to use STRIP_TEMPLATE consistently;
this is a follow-up to r12-7187-gdb84f382ae3dc2.

The second is that get_originating_module_decl was ICEing on class-scope
enumerators injected via using-enum.  I suppose we should handle them
like a class-scope entity rather than a non-using-enum enumerator.

gcc/cp/ChangeLog:

	* module.cc (depset::hash::add_specializations): Use
	STRIP_TEMPLATE consistently.
	(get_originating_module_decl): Handle class-scope CONST_DECL.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/friend-6_a.C: New test.
	* g++.dg/modules/using-enum-3_a.C: New test.
	* g++.dg/modules/using-enum-3_b.C: New test.

Reviewed-by: Jason Merill <jason@redhat.com>

4 files changed, 31 insertions, 2 deletions

diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index 560d8f3..34fafe7 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -13256,7 +13256,7 @@ depset::hash::add_specializations (bool decl_p)
       if (use_tpl == 1)
 	/* Implicit instantiations only walked if we reach them.  */
 	needs_reaching = true;
-      else if (!DECL_LANG_SPECIFIC (spec)
+      else if (!DECL_LANG_SPECIFIC (STRIP_TEMPLATE (spec))
 	       || !DECL_MODULE_PURVIEW_P (STRIP_TEMPLATE (spec)))
 	/* Likewise, GMF explicit or partial specializations.  */
 	needs_reaching = true;
@@ -18716,7 +18716,8 @@ get_originating_module_decl (tree decl)
       && (TREE_CODE (DECL_CONTEXT (decl)) == ENUMERAL_TYPE))
     decl = TYPE_NAME (DECL_CONTEXT (decl));
   else if (TREE_CODE (decl) == FIELD_DECL
-	   || TREE_CODE (decl) == USING_DECL)
+	   || TREE_CODE (decl) == USING_DECL
+	   || CONST_DECL_USING_P (decl))
     {
       decl = DECL_CONTEXT (decl);
       if (TREE_CODE (decl) != FUNCTION_DECL)
diff --git a/gcc/testsuite/g++.dg/modules/friend-6_a.C b/gcc/testsuite/g++.dg/modules/friend-6_a.C
new file mode 100644
index 0000000..7493e8f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/friend-6_a.C
@@ -0,0 +1,11 @@
+// { dg-additional-options "-fmodules-ts -Wno-pedantic" }
+// { dg-module-cmi friend_6 }
+
+module;
+# 1 "" 1
+template <typename> struct Trans_NS___cxx11_basic_string {
+  template <typename> friend class basic_stringbuf;
+};
+template struct Trans_NS___cxx11_basic_string<char>;
+# 6 "" 2
+export module friend_6;
diff --git a/gcc/testsuite/g++.dg/modules/using-enum-3_a.C b/gcc/testsuite/g++.dg/modules/using-enum-3_a.C
new file mode 100644
index 0000000..10671ee
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/using-enum-3_a.C
@@ -0,0 +1,11 @@
+// { dg-do compile { target c++20 } }
+// { dg-additional-options "-fmodules-ts" }
+// { dg-module-cmi using_enum_3 }
+
+export module using_enum_3;
+
+export
+struct text_encoding {
+  enum class id { CP50220 };
+  using enum id;
+};
diff --git a/gcc/testsuite/g++.dg/modules/using-enum-3_b.C b/gcc/testsuite/g++.dg/modules/using-enum-3_b.C
new file mode 100644
index 0000000..8ac6e39
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/using-enum-3_b.C
@@ -0,0 +1,6 @@
+// { dg-do compile { target c++20 } }
+// { dg-additional-options "-fmodules-ts" }
+
+import using_enum_3;
+
+static_assert(text_encoding::id::CP50220 == text_encoding::CP50220);