[PATCH] c++/modules: handle templates in exported using-declarations [PR106849]

[Nathaniel Shead <nathanieloshead@gmail.com>]

Bootstrapped and regtested on x86_64-pc-linux-gnu.

-- >8 --

A TEMPLATE_DECL does not have module attachment flags associated with
it, so this patch extracts the result from the template to read the
flags from there instead.

As a drive-by fix we also group the error with its informative note.

	PR c++/106849

gcc/cp/ChangeLog:

	* name-lookup.cc (do_nonmember_using_decl): Handle
	TEMPLATE_DECLs when checking module attachment.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/using-9.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
---
 gcc/cp/name-lookup.cc                  | 14 ++++++++++----
 gcc/testsuite/g++.dg/modules/using-9.C | 13 +++++++++++++
 2 files changed, 23 insertions(+), 4 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/modules/using-9.C

diff --git a/gcc/cp/name-lookup.cc b/gcc/cp/name-lookup.cc
index a8b9229b29e..512dc1be87f 100644
--- a/gcc/cp/name-lookup.cc
+++ b/gcc/cp/name-lookup.cc
@@ -4846,12 +4846,18 @@ do_nonmember_using_decl (name_lookup &lookup, bool fn_scope_p,
 	  bool exporting = revealing_p && module_exporting_p ();
 	  if (exporting)
 	    {
+	      /* Module flags for templates are on the template_result.  */
+	      tree decl = new_fn;
+	      if (TREE_CODE (decl) == TEMPLATE_DECL)
+		decl = DECL_TEMPLATE_RESULT (decl);
+
 	      /* If the using decl is exported, the things it refers
-		 to must also be exported (or not habve module attachment).  */
-	      if (!DECL_MODULE_EXPORT_P (new_fn)
-		  && (DECL_LANG_SPECIFIC (new_fn)
-		      && DECL_MODULE_ATTACH_P (new_fn)))
+		 to must also be exported (or not have module attachment).  */
+	      if (!DECL_MODULE_EXPORT_P (decl)
+		  && (DECL_LANG_SPECIFIC (decl)
+		      && DECL_MODULE_ATTACH_P (decl)))
 		{
+		  auto_diagnostic_group d;
 		  error ("%q#D does not have external linkage", new_fn);
 		  inform (DECL_SOURCE_LOCATION (new_fn),
 			  "%q#D declared here", new_fn);
diff --git a/gcc/testsuite/g++.dg/modules/using-9.C b/gcc/testsuite/g++.dg/modules/using-9.C
new file mode 100644
index 00000000000..4290280d897
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/using-9.C
@@ -0,0 +1,13 @@
+// PR c++/106849
+// { dg-additional-options "-fmodules-ts" }
+// { dg-module-cmi !lib }
+
+export module lib;
+
+namespace outer {
+  template<typename T> void any_of(T) { }  // { dg-note "declared here" }
+}
+
+export using outer::any_of;  // { dg-error "does not have external linkage" }
+
+// { dg-prune-output "not writing module" }
-- 
2.42.0