[MERGE] Add --no-pending to status to not show the pending merges. (#202830)

[John Arbash Meinel]

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James Westby wrote:
> Hi,
> 
> It was requested that there be an option to turn off the display
> of pending merges, as doing that is slow on large histories. This
> patch does that.
> 
> It is just showing the summaries etc. that is slow, so it is possible
> that we could give some notification that there are pending merges 
> still. Does anyone have an opinion on doing that? Even showing just
> the summaries of the tips of the merged branches would be pretty cheap,
> it's showing the rest of the revisions that you will be getting that
> is the slowest part.
> 
> Thanks,
> 
> James

I think it should be done with a flag called "--pending" which has
"pending=True" as the default. As we will get "--no-pending" "for free"
from our parameters infrastructure and then you don't get stuff like:

"not no_pending".

Though more importantly, if you look at the original bug, I'd rather
just fix the speed issue, rather than hack around it with --no-pending.

I also think we should add a "find_unique()" api rather than
"find_differences()". find_differences is symmetric, which means we need
to keep searching on one side even after we've found all the unique ones
on the other side.

I'd have to think about it a little bit more, but it sounds like I might
want to either brush off my "graph_optimizations" branch, or convince
someone else to do so. I think at its core it will be faster for a lot
of "common" cases, even if it isn't faster in some edge ones.

so.... I won't block on a "--no-pending" flag as it is a prudent hack
for something that is currently *much* slower than it should to be. I
just would really wish we could fix the bug rather than adding a
band-aid. (As having good graph ops will allow us to use them in other
functions that are also slow.)

BB:comment

John
=:->

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