[Patch, fortran] PR63205 - [OOP] Wrongly rejects type = class (for identical declared type)

[Paul Richard Thomas <paul dot richard dot thomas at gmail dot com>]

Dear All,

This patch enables the passing of an allocatable class object, scalar
or array, to a derived type of the declared type, either in an
assignment or as an actual argument. Much of the effort went into
sorting out the finalization call so that the 'left over' allocatable
components added by the dynamic type do not leak memory. At the
moment, the existence of the finalization function is tested for. A
check to see if the dynamic type is the same as the declared type
could be added.

Note that adding the 'must_finalize' field to gfc_expr will be useful
in enabling the missing mandatory finalization calls.

There are still interrogation marks about the patch; especially in
build_class_array_ref, where I do not understand why the added code
does not work in general, except for hidden function results.
Nonetheless, the code does not leak memory, apart perhaps from the
compound derived type constructors, with allocatable components that
already show leaks elsewhere. It is also well ringfenced and so should
not cause any regressions... touch wood!

Bootstraps and regtests on x86_64/FC21 - OK for trunk?

Paul

2015-01-27  Paul Thomas  <pault@gcc.gnu.org>

    PR fortran/63205
    * gfortran.h: Add 'must finalize' field to gfc_expr and
    prototypes for gfc_is_alloc_class_scalar_function and for
    gfc_is_alloc_class_array_function.
    * expr.c (gfc_is_alloc_class_scalar_function,
    gfc_is_alloc_class_array_function): New functions.
    * trans-array.c (gfc_add_loop_ss_code): Do not move the
    expression for allocatable class scalar functions outside the
    loop.
    (conv_array_index_offset): Cope with deltas being NULL_TREE.
    (build_class_array_ref): Do not return with allocatable class
    array functions. Add code to pick out the returned class array.
    Dereference if necessary and return if not a class object.
    (gfc_conv_scalarized_array_ref): Cope with offsets being NULL.
    (gfc_walk_function_expr): Return an array ss for the result of
    an allocatable class array function.
    * trans-expr.c (gfc_conv_subref_array_arg): Remove the assert
    that the argument should be a variable. If an allocatable class
    array function, set the offset to zero and skip the write-out
    loop in this case.
    (gfc_conv_procedure_call): Add allocatable class array function
    to the assert. Call gfc_conv_subref_array_arg for allocatable
    class array function arguments with derived type formal arg..
    Add the code for handling allocatable class functions, including
    finalization calls to prevent memory leaks.
    (arrayfunc_assign_needs_temporary): Return if an allocatable
    class array function.
    (gfc_trans_assignment_1): Set must_finalize to rhs expression
    for allocatable class functions. Set scalar_to_array as needed
    for scalar class allocatable functions assigned to an array.
    Nullify the allocatable components corresponding the the lhs
    derived type so that the finalization does not free them.

2015-01-27  Paul Thomas  <pault@gcc.gnu.org>

    PR fortran/63205
    * gfortran.dg/class_to_type_4.f90: New test

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