c++ modules: lazy loading from within template [PR99377]

Here when lazily loading the binding for f due to its first use from the
template g, processing_template_decl is set which causes the call to
note_vague_linkage_fn from module_state::read_cluster to have no effect,
and thus we never push f onto deferred_fns and end up never emitting its
definition despite needing it.

The behavior of the lazy loading machinery shouldn't be sensitive to
whether we're inside a template, so to that end this patch makes us
clear processing_template_decl in the entrypoints lazy_load_binding and
lazy_load_pendings.

	PR c++/99377

gcc/cp/ChangeLog:

	* module.cc (lazy_load_binding): Clear processing_template_decl.
	(lazy_load_pendings): Likewise.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/pr99377-2_a.C: New test.
	* g++.dg/modules/pr99377-2_b.C: New test.

3 files changed, 22 insertions, 0 deletions

diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index 4d27ceb..7ffeefa 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -19083,6 +19083,10 @@ lazy_load_binding (unsigned mod, tree ns, tree id, binding_slot *mslot)
 
   timevar_start (TV_MODULE_IMPORT);
 
+  /* Make sure lazy loading from a template context behaves as if
+     from a non-template context.  */
+  processing_template_decl_sentinel ptds;
+
   /* Stop GC happening, even in outermost loads (because our caller
      could well be building up a lookup set).  */
   function_depth++;
@@ -19131,6 +19135,10 @@ lazy_load_binding (unsigned mod, tree ns, tree id, binding_slot *mslot)
 void
 lazy_load_pendings (tree decl)
 {
+  /* Make sure lazy loading from a template context behaves as if
+     from a non-template context.  */
+  processing_template_decl_sentinel ptds;
+
   tree key_decl;
   pending_key key;
   key.ns = find_pending_key (decl, &key_decl);
diff --git a/gcc/testsuite/g++.dg/modules/pr99377-2_a.C b/gcc/testsuite/g++.dg/modules/pr99377-2_a.C
new file mode 100644
index 0000000..98d1854
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/pr99377-2_a.C
@@ -0,0 +1,6 @@
+// PR c++/99377
+// { dg-additional-options -fmodules-ts }
+// { dg-module-cmi pr99377_2 }
+export module pr99377_2;
+
+export inline void f() { }
diff --git a/gcc/testsuite/g++.dg/modules/pr99377-2_b.C b/gcc/testsuite/g++.dg/modules/pr99377-2_b.C
new file mode 100644
index 0000000..1d5d79c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/pr99377-2_b.C
@@ -0,0 +1,8 @@
+// PR c++/99377
+// { dg-additional-options -fmodules-ts }
+// { dg-do link }
+import pr99377_2;
+
+template<class> void g() { f(); }
+
+int main() { f(); }