[PR fortran/60091, patch] - Misleading error messages in rank-2 pointer assignment to rank-1 target

[Dominique d'Humières]

> Le 13 mars 2019 à 13:39, Harald Anlauf <anlauf@gmx.de> a écrit :
> 
> Hi Thomas,
> 
> I am not so convinced that "plain english" messages are the way to go,
> even if they appear better readable at first sight, if conciseness is
> lost.

Well, "Syntax error" is concise, but not really helpful!

>  The main reason is that there three variants of the messages,
> depending on context.  One of them refers to expecting either a
> bounds-specification-list or a bounds-remapping-list.
> 
> Do you prefer sth. like
> 
> "All lower bounds and all or none of the upper bounds must be specified"

This is what I expect for p(:,:)=>a and I won’t complain if "use the later for bound remapping" is added
when the target is a rank 1 array.

For mat(2, 6)   => arr I would prefer the above error rather than "Expected bounds specification ».

For p(1:,1:)=>a where a is a rank 1 target, I’ll go with

"all the upper bounds must be specified for bound remapping"

> or
> 
> "Either all or none of the upper bounds must be specified at (1)"

This is what I expect for p(1:3,1:)=>a with the same remark as above about bound remapping.

> (which we currently print in another context where it is wrong),
> 
> while other compilers print:
> 
> E.g. Crayftn:
> 
>  p(1 ,2:3) => t
>    ^            
> ftn-1768 crayftn: ERROR SUB, File = ptr-remap.f90, Line = 3, Column = 5 
>  Invalid bounds-spec-list or bounds-remapping-list for this pointer assignment.
> 
> E.g. Intel:
> 
> ptr-remap.f90(3): error #8524: The syntax of this data pointer assignment is incorrect: either 'bound spec' or 'bound remapping' is expected in this context.   [1]
>  p(1 ,2:3) => t
> ----^
> 
> Pointer remapping belongs IMHO to the 'more advanced’ features

Agreed

> and requires
> some technical insight to get it right, which is why I think the related
> error messages should be more technical and concise.

Here I disagree, the error message should try to tell the user what is wrong
without requiring any access to the standard.

> 
> I'll think for another day or two.
> 
> Thanks,
> Harald

These defines should probably be swapped

+#define BOUNDS_SPEC_LIST "list of %<lower-bound-expr:upper-bound-expr%>"
+#define BOUNDS_REMAPPING_LIST "list of %<lower-bound-expr:%>"

to match

> R1035 bounds-spec is lower-bound-expr :
> R1036 bounds-remapping is lower-bound-expr : upper-bound-exp

Dominique