Re: [Patch, Fortran] PR fortran/83522 – reject array-valued substrings

[Jakub Jelinek <jakub@redhat.com>]

On Mon, Oct 08, 2018 at 09:44:57PM +0200, Tobias Burnus wrote:
> as the PR (and the attached testcase) shows, gfortran doesn't handle
> noncontiguous access with substrings. Namely, "str_array(:)(1:5)" is
> mishandled (segfault while building the "tree" as expr == NULL).
> 
> As Jerry has dug up in the standard (F2008, R610 alias F2018, R908),
> substrings are only permitted on scalars (or array elements). – [gfortran
> has some partial support for noncontiguous memory as actual argument the now
> rejected test cases show.]
> 
> In words of the standard (here: F2018):
> 
> 9.4.1  Substrings
> 
> A substring is a contiguous portion of a character string (7.4.4).
> 
> R908   substring   is   parent-string  ( substring-range )
> 
> R909   parent-string
>             is   scalar-variable-name
>             or  array-element
>             or  coindexed-named-object
>             or  scalar-structure-component
>             or  scalar-constant
> 
> The patch adds a check to the variable resolving – it comes too late to
> print a nice error message for "string(:)(:)"; that statement gets matched
> unsuccessfully and at the end the buffered error message of match_variable
> (unexpected character "(") gets printed. – One could reject it earlier but
> the code doesn't seem to be that nice. (See PR for a variant.)
> 
> Build and regtested on x86_64-linux.
> OK for the trunk?

As I wrote in the PR, I believe it is incorrect and should be reverted.
While for
  character(kind=1,length=4) :: f(4,5)
e.g.
  f(:,:)(1:2)
is not matching the substring non-terminal, it is IMNSHO matching the
array-section non-terminal:
R918   array-section
            is data-ref [ ( substring-range ) ]
            or complex-part-designator
C925   (R918) Exactly one part-ref shall have nonzero rank, and either the final
	      part-ref shall have a section-subscript-list with nonzero rank, another
	      part-ref shall have nonzero rank, or the complex-part-designator
	      shall be an array.
C926   (R918) If a substring-range appears, the rightmost part-name shall be of type
	      character.
and in that case:

An array element is a scalar. An array section is an array. If a substring-range
appears in an array-section, each element is the designated substring of the
corresponding element of the array section.

applies.

	Jakub