From 9a098efd6b82b4b70582e6f5dad085c52850d33d Mon Sep 17 00:00:00 2001
From: Maff Glover <78152252+mo-mglover@users.noreply.github.com>
Date: Fri, 9 Jan 2026 13:46:00 +0000
Subject: [PATCH] Workaround for compiler bug: don't pass local_tag if not
 allocated.

---
 src/f/vernier_mod.F90 | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/f/vernier_mod.F90 b/src/f/vernier_mod.F90
index db0d3302..ad217691 100644
--- a/src/f/vernier_mod.F90
+++ b/src/f/vernier_mod.F90
@@ -109,13 +109,18 @@ subroutine vernier_init(client_comm_handle, tag)
       !Local variables
       character(len=:), allocatable :: local_tag
 
+      ! NB: Dual calls to interface_vernier_init() ought to be unnecessary,
+      ! since unallocated actual arguments passed to optional dummy arguments
+      ! count as not present in downstream code. We separate the calls here
+      ! (with and without local_tag) to accommodate a compiler bug. 
       if (present(tag)) then
         allocate(character(len=len_trim(tag)+1) :: local_tag)
         call append_null_char(tag, local_tag, len_trim(tag))
+        call interface_vernier_init(client_comm_handle, local_tag)
+      else
+        call interface_vernier_init(client_comm_handle)
       end if
 
-      call interface_vernier_init(client_comm_handle, local_tag)
-
     end subroutine vernier_init
 
     !> @brief  Start profiling a code region.