[PATCH, Fortran] Regression Fix PR121743

The following regression tested on x86_64. The oneliner was provided by the 
reporter. Jakub gave the reduced test case in the PR.

OK to commit to mailine and then will backport to 15 in a few days.

Best regards,

Jerry

commit 49ca17dea6de4e01b068a678b36f1c7caa578cc2
Author: Jerry DeLisle <[email protected]>
Date:   Thu Mar 12 10:23:47 2026 -0700

     Fortran: [PR121743] ICE in build_function_decl.

             PR fortran/121743

     gcc/fortran/ChangeLog:

             * trans-decl.cc (build_function_decl): Adjust the
             gcc_assert condition to avoid the ICE.

     gcc/testsuite/ChangeLog:

             * gfortran.dg/pr121743.f90: New test.

     Co-Authored-By: Gilles Gouaillardet <[email protected]>

diff --git a/gcc/fortran/trans-decl.cc b/gcc/fortran/trans-decl.cc
index 8649d0fbc81..0080e83fc36 100644
--- a/gcc/fortran/trans-decl.cc
+++ b/gcc/fortran/trans-decl.cc
@@ -2550,6 +2550,8 @@ build_function_decl (gfc_symbol * sym, bool global)
    /* Allow only one nesting level.  Allow public declarations.  */
    gcc_assert (current_function_decl == NULL_TREE
  	      || DECL_FILE_SCOPE_P (current_function_decl)
+	      || (TREE_CODE (DECL_CONTEXT (current_function_decl))
+		  == FUNCTION_DECL)
  	      || (TREE_CODE (DECL_CONTEXT (current_function_decl))
  		  == NAMESPACE_DECL));

diff --git a/gcc/testsuite/gfortran.dg/pr121743.f90 
b/gcc/testsuite/gfortran.dg/pr121743.f90
new file mode 100644
index 00000000000..29a1cdec2ac
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/pr121743.f90
@@ -0,0 +1,11 @@
+! PR fortran/121743
+! { dg-do compile }
+! { dg-options "-fcoarray=lib" }
+
+program pr121743
+end program pr121743
+subroutine foo ()
+  integer, allocatable, dimension(:), codimension[:] :: s
+  integer :: i
+  i = s(1)[1]
+end