Re: [RFA v2 00/13] various frame filter fixes and cleanups

Pedro Alves
2017-08-14T13:20:25Z

On 08/14/2017 04:40 AM, Tom Tromey wrote:

>> So "bt elide" means "elide the elided frames", not "show me the
>> elided frames too". It's fine with me, though I mildly wonder whether
>> users will be confused by the "double negative".
>
> "Elide" means "drop", so really "bt elide" should mean "drop whatever
> frames are droppable". Having "bt elide" mean "show the dropped
> frames" would be confusing. But maybe another word would be better
> here, I don't know.

Maybe "bt no-elided", to go with "bt no-filters".

Because "elided frames" are a preexisting concept, and "elide" is
actually referring to that concept.

Let me try to clarify what I meant. Note how the patch has the
confusing (to me) "elide the elided" "double negative":

+ if ((flags & PRINT_ELIDE) == 0)
+ {
+ /* Finally recursively print elided frames, if any. */
+ gdbpy_ref<> elided (get_py_iter_from_func (filter, "elided"));
+ if (elided == NULL)
+ return EXT_LANG_BT_ERROR;

I.e., if "bt elide" is NOT in effect, frames returned by the
"elided" function are printed:

If PRINT_ELIDE => don't print elided frames
If not PRINT_ELIDE => print elided frames

I think my brain wants to read PRINT_ELIDE as PRINT_ELIDED, and
then it it becomes really clearly backwards:

If PRINT_ELIDED => don't print elided frames
If not PRINT_ELIDED => print elided frames

The "bt elide" switch name confuses me in the same way. Looking at the
proposed manual change:

+@item backtrace elide
+A Python frame filter might decide to ``elide'' some frames. Normally
+such elided frames are still printed, but they are indented relative
+to the filtered frames that cause them to be elided. The @code{elide}
+option causes elided frames to not be printed at all.
@end table

A filter elides a frames. And then the elide switch elides those
elided frames from view. So there's two levels of elision, what I
was calling "double negative".

It would seem more natural to me to have a "bt no-elided" switch
meaning "don't print frames marked as elided":

@item backtrace no-elided
A Python frame filter might decide to ``elide'' some frames. Normally
such elided frames are still printed, but they are indented relative
to the filtered frames that cause them to be elided. The @code{no-elided}
option causes elided frames to not be printed at all.

Or alternatively, to make gdb not print elided frames by default and
add a "bt elided" switch to print them:

@item backtrace elided
A Python frame filter might decide to ``elide'' some frames. Normally
such elided frames are not printed. The @code{elided} option causes
elided frames to be printed, indented relative to the filtered frames
that cause them to be elided.

Maybe it's just me and/or a case of "lost in translation", and I'm
fine with that. Please do feel free to ignore.

Thanks,
Pedro Alves