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

[Patrick Palka <ppalka@redhat.com>]

Here when lazily loading the binding for f at parse time from the
template g, processing_template_decl is set and thus the call to
note_vague_linkage_fn from module_state::read_cluster has no effect,
and we never push f onto deferred_fns and end up never emitting its
definition.

ISTM the behavior of the lazy loading machinery shouldn't be sensitive
to whether we're inside a template, and therefore we should probably be
clearing processing_template_decl somewhere e.g in lazy_load_binding.
This is sufficient to fix the testcase.

But it also seems the processing_template_decl test in
note_vague_linkage_fn, added by r8-7539-g977bc3ee11383e for PR84973, is
perhaps too strong: if the intent is to avoid deferring output for
uninstantiated templates, we should make sure that DECL in question is
an uninstantiated template by checking e.g. value_dependent_expression_p.
This too is sufficient to fix the testcase (since f isn't a template)
and survives bootstrap and regtest.

Does one or the other approach look like the correct fix for this PR?

	PR c++/99377

gcc/cp/ChangeLog:

	* decl2.cc (note_vague_linkage_fn): Relax processing_template_decl
	test to value_dependent_expression_p.
	* module.cc (lazy_load_binding): Clear processing_template_decl.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/pr99377-2_a.C: New test.
	* g++.dg/modules/pr99377-2_b.C: New test.
---
 gcc/cp/decl2.cc                            | 2 +-
 gcc/cp/module.cc                           | 2 ++
 gcc/testsuite/g++.dg/modules/pr99377-2_a.C | 5 +++++
 gcc/testsuite/g++.dg/modules/pr99377-2_b.C | 6 ++++++
 4 files changed, 14 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/modules/pr99377-2_a.C
 create mode 100644 gcc/testsuite/g++.dg/modules/pr99377-2_b.C

diff --git a/gcc/cp/decl2.cc b/gcc/cp/decl2.cc
index 9f18466192f..5af4d17ee3b 100644
--- a/gcc/cp/decl2.cc
+++ b/gcc/cp/decl2.cc
@@ -876,7 +876,7 @@ check_classfn (tree ctype, tree function, tree template_parms)
 void
 note_vague_linkage_fn (tree decl)
 {
-  if (processing_template_decl)
+  if (value_dependent_expression_p (decl))
     return;
 
   DECL_DEFER_OUTPUT (decl) = 1;
diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index 500ac06563a..79cbb346ffa 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -19074,6 +19074,8 @@ lazy_load_binding (unsigned mod, tree ns, tree id, binding_slot *mslot)
 
   timevar_start (TV_MODULE_IMPORT);
 
+  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++;
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 00000000000..26e2bccbbbe
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/pr99377-2_a.C
@@ -0,0 +1,5 @@
+// PR c++/99377
+// { dg-additional-options -fmodules-ts }
+// { dg-module-cmi pr99377 }
+export module pr99377;
+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 00000000000..69571952c8a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/pr99377-2_b.C
@@ -0,0 +1,6 @@
+// PR c++/99377
+// { dg-additional-options -fmodules-ts }
+// { dg-do link }
+import pr99377;
+template<class> void g() { f(); }
+int main() { g<int>(); }
-- 
2.38.0.rc2