Detected with "type" instead of "class" :


$ cat za1.f90
type(t) function f()
   allocatable :: f
end


$ cat za2.f90
type(t) function f()
   pointer :: f
end


$ gfortran-12-20210905 -c za1.f90
za1.f90:1:0:

    1 | type(t) function f()
      |
Error: The type for function 'f' at (1) is not accessible

The following patch fixes the problem.  It has not been regression tested.

diff --git a/gcc/fortran/decl.c b/gcc/fortran/decl.c
index 05081c40f1e..85c95cea17f 100644
--- a/gcc/fortran/decl.c
+++ b/gcc/fortran/decl.c
@@ -8695,7 +8695,9 @@ attr_decl1 (void)
   /* Update symbol table.  DIMENSION attribute is set in
      gfc_set_array_spec().  For CLASS variables, this must be applied
      to the first component, or '_data' field.  */
-  if (sym->ts.type == BT_CLASS && sym->ts.u.derived->attr.is_class)
+  if (sym->ts.type == BT_CLASS
+      && sym->ts.u.derived
+      && sym->ts.u.derived->attr.is_class)
     {
       /* gfc_set_array_spec sets sym->attr not CLASS_DATA(sym)->attr.  Check
 	 for duplicate attribute here.  */
diff --git a/gcc/fortran/parse.c b/gcc/fortran/parse.c
index 6d7845e8517..8d6d4f4e98f 100644
--- a/gcc/fortran/parse.c
+++ b/gcc/fortran/parse.c
@@ -3813,7 +3813,7 @@ match_deferred_characteristics (gfc_typespec * ts)
   m = gfc_match_prefix (ts);
   gfc_buffer_error (false);
 
-  if (ts->type == BT_DERIVED)
+  if (ts->type == BT_DERIVED || ts->type == BT_CLASS)
     {
       ts->kind = 0;
 
@@ -4094,7 +4094,7 @@ declSt:
   if (bad_characteristic)
     {
       ts = &gfc_current_block ()->result->ts;
-      if (ts->type != BT_DERIVED)
+      if (ts->type != BT_DERIVED && ts->type != BT_CLASS)
 	gfc_error ("Bad kind expression for function %qs at %L",
 		   gfc_current_block ()->name,
 		   &gfc_current_block ()->declared_at);

(In reply to kargl from comment #2)
> The following patch fixes the problem.  It has not been regression tested.

This restores the error, but for CLASS I now get:

pr102331.f90:2:3:

    2 |   allocatable :: f
      |   1
Error: Unclassifiable statement at (1)
pr102331.f90:1:0:

    1 | class(t) function f()
      | 
Error: The type for function 'f' at (1) is not accessible

while the error message for line 2 does not show up for TYPE.
Maybe there are a few more places that need fixing.
(Not only the obvious one after the second hunk for parse.c).

On Wed, Sep 15, 2021 at 08:57:45PM +0000, anlauf at gcc dot gnu.org wrote:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102331
> 
> --- Comment #3 from anlauf at gcc dot gnu.org ---
> (In reply to kargl from comment #2)
> > The following patch fixes the problem.  It has not been regression tested.
> 
> This restores the error, but for CLASS I now get:
> 
> pr102331.f90:2:3:
> 
>     2 |   allocatable :: f
>       |   1
> Error: Unclassifiable statement at (1)
> pr102331.f90:1:0:
> 
>     1 | class(t) function f()
>       | 
> Error: The type for function 'f' at (1) is not accessible
> 
> while the error message for line 2 does not show up for TYPE.
> Maybe there are a few more places that need fixing.
> (Not only the obvious one after the second hunk for parse.c).
> 

Yes, likely, 'ts.type == BT_CLASS' needs to be sprinkled in
other places.  Unfortunately, the 'Unclassifiable statement' 
error is a last resort catch-all error.  I know little about
the CLASS implementation.  I suspect BT_CLASS takes a much
different path through the compiler.

After exploring a while and looking for other places I have concluded that for invalid code Steve's patch is adequate.

I will regression test it next.

Regression testing looks good. The patch wiggles on the error messages given for:

pr85779.f90

class_result_4.f90

In both cases they are reasonable.  I don't think we need any new test cases since we are obviously exercising the patch.  If anyone insists I add the z1 and z2 cases to the testsuite, let me know and i will do so.

 I biffed the PR number on this commit. It should have been here. I will have to look into amending the ChangeLog correctly.

The master branch has been updated by Jerry DeLisle <jvdelisle@gcc.gnu.org>:

https://gcc.gnu.org/g:cdc6bf44eec295805ae29a8aaddafd111de01c8e

commit r13-4934-gcdc6bf44eec295805ae29a8aaddafd111de01c8e
Author: Steve Kargl <kargl@gcc.gnu.org>
Date:   Mon Dec 26 14:07:04 2022 -0800

    Modify checks to avoid referencing NULL pointer.
    
    Update test cases with error messages that changed as a result.
    
    gcc/fortran/ChangeLog:
    
            PR fortran/102595
            * decl.cc (attr_decl1): Guard against NULL pointer.
            * parse.cc (match_deferred_characteristics): Include BT_CLASS in check for
            derived being undefined.
    
    gcc/testsuite/ChangeLog:
    
            PR fortran/102595
            * gfortran.dg/class_result_4.f90: Update error message check.
            * gfortran.dg/pr85779_3.f90: Update error message check.

Fixed ChangeLogs PR number referenced.

commit 04d7cc165387d19e1433a4b2157d2bde7b95305b (HEAD -> master, origin/master, origin/HEAD)
Author: Jerry DeLisle <jvdelisle@gcc.gnu.org>
Date:   Tue Jan 17 17:30:49 2023 -0800

    Fix bug number reference in Changelogs

For:

    gcc/fortran/ChangeLog-2022:
  
    gcc/testsuite/ChangeLog-2022:

The releases/gcc-12 branch has been updated by Jerry DeLisle <jvdelisle@gcc.gnu.org>:

https://gcc.gnu.org/g:82ec75a726b3f8f874dacb0cb342c9bbd1233cc0

commit r12-9320-g82ec75a726b3f8f874dacb0cb342c9bbd1233cc0
Author: Jerry DeLisle <jvdelisle@gcc.gnu.org>
Date:   Sun Mar 26 18:44:35 2023 -0700

    Fortran: Modify checks to avoid referencing NULL pointer.
    
    Backport from mainline.
    
    gcc/fortran/ChangeLog:
    
            PR fortran/102331
            * decl.cc (attr_decl1): Guard against NULL pointer.
            * parse.cc (match_deferred_characteristics): Include BT_CLASS in check
            for derived being undefined.
    
    gcc/testsuite/ChangeLog:
    
            PR fortran/102331
            * gfortran.dg/class_result_4.f90: Update error message check.
            * gfortran.dg/pr85779_3.f90: Update error message check.

fixed on 12, 13, and master.