push: rework the computation of fallbackheads to be correct The previous computation tried to be smart but ended up being wrong. This was caught by phase movement test while reworking the phase discovery logic to be faster. The previous logic was failing to catch case where the pushed set was not based on a common heads (i.e. when the discovery seemed to have "over discovered" content, outside the pushed set) In the following graph, `e` is a common head and we `hg push -r f`. We need to detect `c` as a fallback heads and we previous failed to do so:: e | d f |/ c | b | a The performance impact of the change seems minimal. On the most impacted repository at hand (mozilla-try), the slowdown seems mostly mixed in the overall noise `hg push` but seems to be in the hundred of milliseconds order of magnitude. When using rust, we seems to be a bit faster, probably because we leverage more accelaratd internals. I added a couple of performance related common for further investigation later on.

     1

Set up

     2

     3

  $ hg init repo

     4

  $ cd repo

     5

  $ echo a > a

     6

  $ hg add a

     7

  $ hg commit -m a

     8

     9

Try to import an empty patch

    10

    11

  $ hg import --no-commit - <<EOF

    12

  > EOF

    13

  applying patch from stdin

    14

  abort: stdin: no diffs found

    15

  [10]

    16

    17

No dirstate backups are left behind

    18

    19

  $ ls .hg/dirstate* | sort

    20

  .hg/dirstate

    21