sparse-revlog: only refine delta candidates in the sparse case (issue6006)
Starting with 5aef5afa8654, a valid delta parent might be "refined". This
allows repository using sparse-revlog to produce better delta chain by using
better intermediate snapshot base.
However, this refining step was performed in all cases, including for
repository not using sparse-revlog. This could produce a strange chain in the
general delta case and corrupted repository in the non-general delta case.
We now skip this step unless sparse-revlog is in use.
In issue 6006, Yuya Nishihara provided a test case using an external
repository, so we did not include it. Finding "laboratory" condition to
reproduce this case and implementing an efficient test reproducing it is a bit
tricky. We do not foresee to have the time to provide one by the release date.
Differential Revision: https://phab.mercurial-scm.org/D5197
% lazy ancestor set for [], stoprev = 0, inclusive = False
membership: []
iteration: []
% lazy ancestor set for [11, 13], stoprev = 0, inclusive = False
membership: [7, 8, 3, 4, 1, 0]
iteration: [8, 7, 4, 3, 2, 1, 0]
% lazy ancestor set for [1, 3], stoprev = 0, inclusive = False
membership: [1, 0]
iteration: [1, 0]
% lazy ancestor set for [11, 13], stoprev = 0, inclusive = True
membership: [11, 13, 7, 8, 3, 4, 1, 0]
iteration: [13, 11, 8, 7, 4, 3, 2, 1, 0]
% lazy ancestor set for [11, 13], stoprev = 6, inclusive = False
membership: [7, 8]
iteration: [8, 7]
% lazy ancestor set for [11, 13], stoprev = 6, inclusive = True
membership: [11, 13, 7, 8]
iteration: [13, 11, 8, 7]
% lazy ancestor set for [11, 13], stoprev = 11, inclusive = True
membership: [11, 13]
iteration: [13, 11]
% lazy ancestor set for [11, 13], stoprev = 12, inclusive = True
membership: [13]
iteration: [13]
% lazy ancestor set for [10, 1], stoprev = 0, inclusive = True
membership: [2, 10, 4, 5, 0, 1]
iteration: [10, 5, 4, 2, 1, 0]