[Bug fortran/64678] Expected association error on dependent associate statements

["kargl at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64678

kargl at gcc dot gnu.org changed:

           What    |Removed                     |Added
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                 CC|                            |kargl at gcc dot gnu.org

--- Comment #1 from kargl at gcc dot gnu.org ---
(In reply to Antony Lewis from comment #0)
> In trunk
> 
> module X
>   Type T
>    integer :: map
>   end Type T
> contains
> 
> subroutine DoBug
> Type(T) TT
>   
>  associate(A=>TT, B=>A%map)
>  end associate
>   
> end subroutine
> end module X
> 
> gives:
> 
> testbug.f90:10:17:
> 
>   associate(A=>TT, B=>A%map)
>                  1
> Error: Expected association at (1)
> testbug.f90:11:4:
> 
>   end associate
>     1
> 
> It's not entirely clear to me from the standard if this is allowed, but I
> don't see why not (useful when you are breaking up complicated array/class
> structures into associate names, where the second name refers to the first).
> It compiles in ifort. Obviously low priority as can be worked around easily
> enough

I believe gfortran is correct in issuing an error; although I admit
it seems to be a subtle distinction in language.  For F2003 standard

  8.1.4  ASSOCIATE construct

  The ASSOCIATE construct associates named entities with expressions
  or variables during the execution of its block. These named construct
  entities (16.3) are associating entities (16.4.1.5).  The names are
  associate names.

The BNF shows

  R818   association   is   associate-name => selector
  R819   selector      is   expr
                       or   variable


In your code, 'A' and 'B' are associate-names.  The target
of an associate-name is a selector, which is an expr or variable.
The target for 'B' is 'A%map'.  So, the question becomes whether 'A%map'
is now a variable or expression even though 'A' is an associate-name.

The BNF for 'variable is

  R601 variable                  is designator
  C601 (R601) designator shall not be a constant or a subobject of a constant.
  R602 variable-name             is  name
  C602 (R602) A variable-name shall be the name of a variable.
  R603 designator                is object-name
                                 or array-element
                                 or array-section
                                 or structure-component
                                 or substring

  R505 object-name     is   name
  C505 (R505) The object-name shall be the name of a data object.

  A data object (often abbreviated to object) is a constant (4.1.2),
  a variable (6), or a subobject of a constant. The type and type
  parameters of a named data object may be specified explicitly (5.1)
  or implicitly (5.3).

'A%map' as a data object is certainly not a constant or subobject of
a constant, so it must be a variable.  But, we've already established
that 'A' is an associate-name not a variable-name.  So, 'A%map' is
not an object-name.

array-element, array-section, and substring are of no consequence here.

So, now, structure-component

  R614 structure-component is data-ref

  R612 data-ref is part-ref [ % part-ref ] ...
  R613 part-ref is part-name [ ( section-subscript-list ) ]

  C612 (R612) The leftmost part-name shall be the name of a data object.

We've already established 'A' is not a data object.  So, now we
are left with 'expr'.  I have no interest in reproducing Section 7
of Fortran 2003 standard.  I suspect you'll find that 'A%map' is not
an 'expr'.

Note, I could be wrong.  You may want to post to comp.lang.fortran.
There are numerous people, who contribute to c.l.f, that are much
more in-tune with the nuances of the Fortran standard.