[Bug fortran/108921] New: ICE: using the result of an impure function in automatic character allocation

[Bug fortran/108921] New: ICE: using the result of an impure function in automatic character allocation

[vterzi1996 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108921

            Bug ID: 108921
           Summary: ICE: using the result of an impure function in
                    automatic character allocation
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vterzi1996 at gmail dot com
  Target Milestone: ---

Created attachment 54527
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54527&action=edit
Complete backtrace

Consider the following minimal working example:
```
module lib
    type t
    contains
        procedure::f,g
    end type
contains
    integer function f(this)
        class(t),intent(in)::this
        f=10
    end
    function g(this)result(r)
        class(t),intent(in)::this
        character(len=this%f())::r  ! problem appears here
        r='42'
    end
end

program prog
    use lib
    type(t)::o
    print*,o%g()
end
```

This example was already discussed here:
https://stackoverflow.com/questions/75544072/using-function-result-as-character-length-in-fortran

The compilation of this code with the GNU compiler (gfortran 12.2.0 on Rocky
Linux 8.7) fails with the message `f951: internal compiler error: Segmentation
fault` (full output is in the attachment). It also fails with 7.5.0, 9.4.0, and
11.1.0 on Ubuntu 18.04.2 LTS. The reason for this problem is the unallowed
usage of the result of an impure function (here: `f`) in the automatic
allocation of the CHARACTER variable, but the compiler fails to identify the
mistake in the code.

[Bug fortran/108921] ICE: using the result of an impure function in automatic character allocation

[kargl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108921

kargl at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P4
           Keywords|                            |ice-on-invalid-code
                 CC|                            |kargl at gcc dot gnu.org

--- Comment #1 from kargl at gcc dot gnu.org ---
The ever popular NULL pointer dereference from
parsing invalid code.
With this patch

diff --git a/gcc/fortran/class.cc b/gcc/fortran/class.cc
index ae653e74437..9ece4482f76 100644
--- a/gcc/fortran/class.cc
+++ b/gcc/fortran/class.cc
@@ -2491,7 +2491,7 @@ gfc_find_derived_vtab (gfc_symbol *derived)
                  /* This is elemental so that arrays are automatically
                     treated correctly by the scalarizer.  */
                  copy->attr.elemental = 1;
-                 if (ns->proc_name->attr.flavor == FL_MODULE)
+                 if (ns->proc_name && ns->proc_name->attr.flavor == FL_MODULE)
                    copy->module = ns->proc_name->name;
                  gfc_set_sym_referenced (copy);
                  /* Set up formal arguments.  */
diff --git a/gcc/fortran/symbol.cc b/gcc/fortran/symbol.cc
index 2ce0f3e4df7..54c9441d7fd 100644
--- a/gcc/fortran/symbol.cc
+++ b/gcc/fortran/symbol.cc
@@ -2499,7 +2499,7 @@ gfc_find_component (gfc_symbol *sym, const char *name,
   if (sym->attr.flavor == FL_DERIVED)
     sym = gfc_use_derived (sym);
   else
-    gcc_assert (gfc_fl_struct (sym->attr.flavor));
+    return NULL;

   if (sym == NULL)
     return NULL;

I get 
% gfcx -c a.f90
a.f90:13:34:

   13 |         character(len=this%f())::r  ! problem appears here
      |                                  1
Error: Symbol 'r' at (1) already has basic type of REAL
a.f90:13:22:

   13 |         character(len=this%f())::r  ! problem appears here
      |                      1
Error: Function 'this' at (1) must be PURE
a.f90:14:10:

   14 |         r='42'
      |          1
Error: Cannot convert CHARACTER(2) to REAL(4) at (1)
a.f90:19:9:

   19 |     use lib
      |         1
Fatal Error: Cannot open module file 'lib.mod' for reading at (1): No such file
or directory
compilation terminated.

The first and last errors appear to be run on errors.  The second error appears
to be the relevant one, but the 'name' of the function is munged.

Anywhoo, the patch fixes the ICE