[gcc r13-6758] Fortran: Allow external function from in an associate block [PR87127]

[Paul Thomas <pault@gcc.gnu.org>]

https://gcc.gnu.org/g:5889c7bd46a45dc07ffb77ec0d698e18e0b99840

commit r13-6758-g5889c7bd46a45dc07ffb77ec0d698e18e0b99840
Author: Paul Thomas <pault@gcc.gnu.org>
Date:   Mon Mar 20 06:13:54 2023 +0000

    Fortran: Allow external function from in an associate block [PR87127]
    
    2023-03-20  Paul Thomas  <pault@gcc.gnu.org>
    
    gcc/fortran
            PR fortran/87127
            * resolve.cc (check_host_association): If an external function
            is typed but not declared explicitly to be external, change the
            old symbol from a variable to an external function.
    
    gcc/testsuite/
            PR fortran/87127
            * gfortran.dg/external_procedures_4.f90: New test.

Diff:
---
 gcc/fortran/resolve.cc                             | 34 ++++++++++++++++++----
 .../gfortran.dg/external_procedures_4.f90          | 28 ++++++++++++++++++
 2 files changed, 57 insertions(+), 5 deletions(-)

diff --git a/gcc/fortran/resolve.cc b/gcc/fortran/resolve.cc
index f3f3051eb47..1d973d12ff1 100644
--- a/gcc/fortran/resolve.cc
+++ b/gcc/fortran/resolve.cc
@@ -6079,11 +6079,14 @@ resolve_procedure:
 
 
 /* Checks to see that the correct symbol has been host associated.
-   The only situation where this arises is that in which a twice
-   contained function is parsed after the host association is made.
-   Therefore, on detecting this, change the symbol in the expression
-   and convert the array reference into an actual arglist if the old
-   symbol is a variable.  */
+   The only situations where this arises are:
+	(i)  That in which a twice contained function is parsed after
+	     the host association is made. On detecting this, change
+	     the symbol in the expression and convert the array reference
+	     into an actual arglist if the old symbol is a variable; or
+	(ii) That in which an external function is typed but not declared
+	     explcitly to be external. Here, the old symbol is changed
+	     from a variable to an external function.  */
 static bool
 check_host_association (gfc_expr *e)
 {
@@ -6185,6 +6188,27 @@ check_host_association (gfc_expr *e)
 	  gfc_resolve_expr (e);
 	  sym->refs++;
 	}
+      /* This case corresponds to a call, from a block or a contained
+	 procedure, to an external function, which has not been declared
+	 as being external in the main program but has been typed.  */
+      else if (sym && old_sym != sym
+	       && !e->ref
+	       && sym->ts.type == BT_UNKNOWN
+	       && old_sym->ts.type != BT_UNKNOWN
+	       && sym->attr.flavor == FL_PROCEDURE
+	       && old_sym->attr.flavor == FL_VARIABLE
+	       && sym->ns->parent == old_sym->ns
+	       && sym->ns->proc_name
+	       && sym->ns->proc_name->attr.proc != PROC_MODULE
+	       && (sym->ns->proc_name->attr.flavor == FL_LABEL
+		   || sym->ns->proc_name->attr.flavor == FL_PROCEDURE))
+	{
+	  old_sym->attr.flavor = FL_PROCEDURE;
+	  old_sym->attr.external = 1;
+	  old_sym->attr.function = 1;
+	  old_sym->result = old_sym;
+	  gfc_resolve_expr (e);
+	}
     }
   /* This might have changed!  */
   return e->expr_type == EXPR_FUNCTION;
diff --git a/gcc/testsuite/gfortran.dg/external_procedures_4.f90 b/gcc/testsuite/gfortran.dg/external_procedures_4.f90
new file mode 100644
index 00000000000..252bae580d1
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/external_procedures_4.f90
@@ -0,0 +1,28 @@
+! { dg-do run }
+!
+! Test the fix for PR87127 in which the references to exfunc cause
+! the error "exfunc at (1) is not a function".
+!
+! Contributed by Gerhard Steinmetz  <gscfq@t-online.de>
+!
+function exfunc(i)
+  implicit none
+  integer :: exfunc,i
+  exfunc = 2*i
+end function
+
+! contents of test.f90
+program test
+  implicit none
+  integer :: exfunc,i
+  integer,parameter :: array(2)=[6,7]
+  associate(i=>array(2))            ! Original bug
+    if (exfunc(i) .ne. 2*i) stop 1
+  end associate
+  i = 99
+  call foo
+contains
+  subroutine foo()                  ! Comment #3
+    if (exfunc(i) .ne. 2*i) stop 2
+  end subroutine foo
+end program