view CONTRIBUTING @ 34272:53fb09c73ba8

revset: remove "small" argument from "_optimize"

`_optimize` calculates weights of subtrees. "small" affects some weight
calculation (either 1 or 0.5). The weights are now only useful in `and`
optimization where we might swap two arguments and use `andsmally`.

In the real world, it seems unlikely that revsets with weight of 0.5 or 1
matters the `and` order optimization. I think the important thing is to get
weights of expensive revsets right (ex. `contains`).

This patch removes the `small` argument to simplify the interface.

As for choosing between 0.5 vs 1, things returning a single revision
(`ancestor`, `string`) has a weight of 0.5. Things returning multiple
revisions returns 1. This could be sometimes useful in the `andsmally`
optimization, ex.

  (((:)-2) & expensive()) & ((1-2) & expensive())
    ^^^                       ^
   ^^^^^^^                   ^^^^^
  ^^^^^^^^^^^^^^^^^^^^^^^   ^^^^^^^^^^^^^^^^^^^^^
    weight=1                 weight=0.5

would have an `andsmally` optimization so `1-2` gets executed first, which
seems to be desirable.

Differential Revision: https://phab.mercurial-scm.org/D656

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