Re: warnings shut off in ov.cc?

[John W. Eaton]

On 10/15/19 2:21 PM, Rik wrote:
> jwe,
>
> Can you try the attached patch which implements a warning when non-scalar
> arguments are used with the colon operator?  Everything looks correct, and
> the printf debugging that I started using when I got confused shows that
> the code is executing, but no warnings are printed.  The code is exactly
> the same format as the warning for complex values using in colon
> expressions, however that warning fires.  Is there something that disables
> warnings temporarily in the interpreter when calling operators?
>
> Sample session:
>
> 1:[3,4]
> running do_colon_op
> Got here
> Got here2
> ans =
>
>     1   2   3
>
> whereas
>
> octave:1> 1:3*i
> running do_colon_op
> warning: imaginary part of complex colon arguments is ignored
> ans = [](1x0)
>
> Maybe this is a red herring, but occasionally warnings seem to be turned
> off for the complex code path as well.
>
> octave:2> 1:(3i)
> running do_colon_op
> ans = [](1x0)
>
> The last example should also have produced a warning.

I think you are seeing the effect of constant folding in the parser:


http://hg.savannah.gnu.org/hgweb/octave/file/5a0543de1e47/libinterp/parse-tree/oct-parse.yy#l2493

Warnings are intentionally disabled when doing constant folding 
operations.  The original idea may have been the same as what we should 
be doing for errors, which is to be silent about them when attempting 
constant folding, but if there is an error (or warning), fail to 
generate a constant value so that the expression will generate an error 
(or warning) later at run time.  This is clearly not happening for warnings.

Unfortunately, I don't think that skipping the message but detecting the 
warning is an easy thing to do.

Maybe we should just eliminate the constant folding operations in the 
parser?  I'm not sure that they really provide that much advantage.

jwe