[Bug python/18567] Frame filters apply to 'backtrace' but not 'frame' command

["adinn at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=18567

Andrew Dinn <adinn at redhat dot com> changed:

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                 CC|                            |adinn at redhat dot com

--- Comment #4 from Andrew Dinn <adinn at redhat dot com> ---
(In reply to Phil Muldoon from comment #2)
> Yes, that's a design intent. They only apply (at the moment) to backtraces
> (in MI and CLI). That being said, let's revisit that decision.
> 
> I'm not sure how a frame filter can apply to a single line of output? Frame
> filters receive and return an iterator of frame decorators that are printed
> out when the frame filter chain is exausted. If one frame is only ever
> printed (regardless, say, if the iterator had more than one), then a frame
> filter is not needed: there's nothing to filter. Perhaps we could apply a
> single frame decorator? 

Can you not achieve this by subclassing the frame_iter so that only produces
one frame at the required index in the frame list? That way when you only need
one frame decorated you can pass a subclassed iter to the frame filter and get
a single frame decorator back but for the case where you want all frames
decorated (under bt) you can pass the current iter.

> However, that would be a pain as previously written frame filters that would
> apply to backtraces would have to adapt to just returning one frame for
> these and other commands. I suppose we could, in fact, take a frame filter
> here and just print the first frame as a compromise; this would allow
> existing frame filters to just work.

I think it would be better for performance if only the one frame were presented
to the filter.

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