Fortran: error recovery on invalid array reference of non-array [PR103590]

  Dear all,

I intend to commit the attached patch as obvious to mainline
within the next 24h unless someone complains.  It replaces a
lazy gfc_internal_error by an explicit error message and an
error recovery path.

As a side-effect, we now diagnose a previously missed error
in testcase gfortran.dg/associate_54.f90 similarly to Intel.

Regtested on x86_64-pc-linux-gnu.

Thanks,
Harald
  

Hello,

the principle looks good, but...

Le 18/07/2022 à 22:43, Harald Anlauf via Fortran a écrit :

> diff --git a/gcc/fortran/resolve.cc b/gcc/fortran/resolve.cc
> index 2ebf076f730..dacd33561d0 100644
> --- a/gcc/fortran/resolve.cc
> +++ b/gcc/fortran/resolve.cc
> @@ -5004,7 +5004,11 @@ find_array_spec (gfc_expr *e)
>        {
>        case REF_ARRAY:
>  	if (as == NULL)
> -	  gfc_internal_error ("find_array_spec(): Missing spec");
> +	  {
> +	    gfc_error ("Symbol %qs at %L has not been declared as an array",
> +		       e->symtree->n.sym->name, &e->where);

... the error here only makes sense if the array reference follows a 
variable reference.  If it follows a derived type component reference, a 
slightly different error message would be more appropriate.
  

Hi Mikael,

Am 19.07.22 um 11:03 schrieb Mikael Morin:
> Hello,
>
> the principle looks good, but...
>
> Le 18/07/2022 à 22:43, Harald Anlauf via Fortran a écrit :
>
>> diff --git a/gcc/fortran/resolve.cc b/gcc/fortran/resolve.cc
>> index 2ebf076f730..dacd33561d0 100644
>> --- a/gcc/fortran/resolve.cc
>> +++ b/gcc/fortran/resolve.cc
>> @@ -5004,7 +5004,11 @@ find_array_spec (gfc_expr *e)
>>        {
>>        case REF_ARRAY:
>>      if (as == NULL)
>> -      gfc_internal_error ("find_array_spec(): Missing spec");
>> +      {
>> +        gfc_error ("Symbol %qs at %L has not been declared as an array",
>> +               e->symtree->n.sym->name, &e->where);
>
> ... the error here only makes sense if the array reference follows a
> variable reference.  If it follows a derived type component reference, a
> slightly different error message would be more appropriate.

how detailed or tailored should the error message be, or can
we just have a more generic message, like "Name at %L ...",
or "Invalid subscript reference at %L"?  We seem to not hit
that internal error very often...

I have played only little with invalid code in the present context,
but often hit another code path that shows up in associate_54.f90
and gives

Error: Associate-name 'state' at (1) is used as array

For the testcase in the PR, Intel says:

associate_59.f90(7): error #6410: This name has not been declared as an
array or a function.   [A]
     print *, [character(a(1)) :: '1'] ! { dg-error "Scalar INTEGER
expression" }
------------------------^

Crayftn 14.0 says:

   Improper ir tree in expr_semantics.

     print *, [character(a(1)) :: '1'] ! { dg-error "Scalar INTEGER
expression" }
                          ^

ftn-873 crayftn: ERROR P, File = associate_59.f90, Line = 7, Column = 26
   Invalid subscripted reference of a scalar ASSOCIATE name.


gfortran's behavior during error handling is difficult to understand.
While the proposed new error message is emitted for associate_54.f90,
it never makes it far enough for the testcase of the present PR
(associate_59.f90).

Thanks,
Harald
  

Le 19/07/2022 à 21:09, Harald Anlauf via Fortran a écrit :
> Hi Mikael,
> 
> Am 19.07.22 um 11:03 schrieb Mikael Morin:
>> Hello,
>>
>> the principle looks good, but...
>>
>> Le 18/07/2022 à 22:43, Harald Anlauf via Fortran a écrit :
>>
>>> diff --git a/gcc/fortran/resolve.cc b/gcc/fortran/resolve.cc
>>> index 2ebf076f730..dacd33561d0 100644
>>> --- a/gcc/fortran/resolve.cc
>>> +++ b/gcc/fortran/resolve.cc
>>> @@ -5004,7 +5004,11 @@ find_array_spec (gfc_expr *e)
>>>        {
>>>        case REF_ARRAY:
>>>      if (as == NULL)
>>> -      gfc_internal_error ("find_array_spec(): Missing spec");
>>> +      {
>>> +        gfc_error ("Symbol %qs at %L has not been declared as an 
>>> array",
>>> +               e->symtree->n.sym->name, &e->where);
>>
>> ... the error here only makes sense if the array reference follows a 
>> variable reference.  If it follows a derived type component reference, 
>> a slightly different error message would be more appropriate.
> 
> how detailed or tailored should the error message be, or can
> we just have a more generic message, like "Name at %L ...",
> or "Invalid subscript reference at %L"?  We seem to not hit
> that internal error very often...
> 
It could be anything better than the (unhelpfull) internal error it is 
replacing.
I suggest for example "Invalid array reference of a non-array entity at 
%L".  Cray’s words, or Intel’s, or your other propositions work as well.

> 
> gfortran's behavior during error handling is difficult to understand.
> While the proposed new error message is emitted for associate_54.f90,
> it never makes it far enough for the testcase of the present PR
> (associate_59.f90).
> 
Indeed.  We try to match several types of statement one after the other, 
and each failed match can possibly register an error.  But it is emitted 
only if all have failed (see gfc_error_check).  There is no choice of 
the best error; the last one registered wins.

This buffering behavior is controlled by calls to gfc_buffer_error(...). 
  Error handling during resolution doesn’t need to delay error reporting 
as far as I know, and the calls to gfc_buffer_error (false) seem to 
correctly disable buffering at the end of every call to next_statement. 
  I don’t know why it remains active in this case.
  

Hi Mikael,

Am 19.07.22 um 22:53 schrieb Mikael Morin:
> It could be anything better than the (unhelpfull) internal error it is
> replacing.
> I suggest for example "Invalid array reference of a non-array entity at
> %L".

yes, that's much better!  The attached updated patch uses this.

Committed: r13-1757-gf838d15641d256e21ffc126c3277b290ed743928


>> gfortran's behavior during error handling is difficult to understand.
>> While the proposed new error message is emitted for associate_54.f90,
>> it never makes it far enough for the testcase of the present PR
>> (associate_59.f90).
>>
> Indeed.  We try to match several types of statement one after the other,
> and each failed match can possibly register an error.  But it is emitted
> only if all have failed (see gfc_error_check).  There is no choice of
> the best error; the last one registered wins.
>
> This buffering behavior is controlled by calls to gfc_buffer_error(...).
>   Error handling during resolution doesn’t need to delay error reporting
> as far as I know, and the calls to gfc_buffer_error (false) seem to
> correctly disable buffering at the end of every call to next_statement.
>   I don’t know why it remains active in this case.
>

Alright, I should try to remember this and take a closer look next time
I get confused about not getting the error message I wanted...

Thanks,
Harald
  

Le 19/07/2022 à 23:34, Harald Anlauf a écrit :
> 
> Committed: r13-1757-gf838d15641d256e21ffc126c3277b290ed743928
> 
Thanks.