[PATCH STABLE] sparse-revlog: fix delta validity computation

[Gregory Szorc]

On Thu, Aug 16, 2018 at 2:01 AM, Boris Feld <boris.feld at octobus.net> wrote:

> # HG changeset patch
> # User Boris Feld <boris.feld at octobus.net>
> # Date 1534337020 -7200
> #      Wed Aug 15 14:43:40 2018 +0200
> # Branch stable
> # Node ID 1b78bebb7a8793b4b858d335b11f4deaf57dd128
> # Parent  7e023ce26c7f5e800c778fb4ff76c6d7726666b3
> # EXP-Topic fix-sparse
> # Available At https://bitbucket.org/octobus/mercurial-devel/
> #              hg pull https://bitbucket.org/octobus/mercurial-devel/ -r
> 1b78bebb7a87
> sparse-revlog: fix delta validity computation
>
> When considering the validity of a delta with sparse-revlog, we check the
> size
> of the largest read. To do so, we use some regular logic with the extra
> delta
> information. Some of this logic was not handling this extra delta properly,
> confusing it with "nullrev". This confusion with nullrev lead to wrong
> results
> for this computation but preventing a crash.
>
> Changeset 781b2720d2ac on default revealed this error, crashing. This
> changeset fixes the logic on stable so that the computation is correct (and
> the crash is averted).
>
> The fix is made on stable as this will impact 4.7 clients interacting with
> sparse-revlog repositories (eg: created by later version).
>

Queued for stable.


>
> diff --git a/mercurial/revlog.py b/mercurial/revlog.py
> --- a/mercurial/revlog.py
> +++ b/mercurial/revlog.py
> @@ -262,13 +262,17 @@ def _trimchunk(revlog, revs, startidx, e
>      if endidx is None:
>          endidx = len(revs)
>
> -    # Trim empty revs at the end, but never the very first revision of a
> chain
> -    while endidx > 1 and endidx > startidx and length(revs[endidx - 1])
> == 0:
> -        endidx -= 1
> +    # If we have a non-emtpy delta candidate, there are nothing to trim
> +    if revs[endidx - 1] < len(revlog):
> +        # Trim empty revs at the end, except the very first revision of a
> chain
> +        while (endidx > 1
> +                and endidx > startidx
> +                and length(revs[endidx - 1]) == 0):
> +            endidx -= 1
>
>      return revs[startidx:endidx]
>
> -def _segmentspan(revlog, revs):
> +def _segmentspan(revlog, revs, deltainfo=None):
>      """Get the byte span of a segment of revisions
>
>      revs is a sorted array of revision numbers
> @@ -294,7 +298,14 @@ def _segmentspan(revlog, revs):
>      """
>      if not revs:
>          return 0
> -    return revlog.end(revs[-1]) - revlog.start(revs[0])
> +    if deltainfo is not None and len(revlog) <= revs[-1]:
> +        if len(revs) == 1:
> +            return deltainfo.deltalen
> +        offset = revlog.end(len(revlog) - 1)
> +        end = deltainfo.deltalen + offset
> +    else:
> +        end = revlog.end(revs[-1])
> +    return end - revlog.start(revs[0])
>
>  def _slicechunk(revlog, revs, deltainfo=None, targetsize=None):
>      """slice revs to reduce the amount of unrelated data to be read from
> disk.
> @@ -526,7 +537,7 @@ def _slicechunktodensity(revlog, revs, d
>          yield revs
>          return
>
> -    if deltainfo is not None:
> +    if deltainfo is not None and deltainfo.deltalen:
>          revs = list(revs)
>          revs.append(nextrev)
>
> @@ -2444,7 +2455,8 @@ class revlog(object):
>                  deltachain = []
>
>              chunks = _slicechunk(self, deltachain, deltainfo)
> -            distance = max(map(lambda revs:_segmentspan(self, revs),
> chunks))
> +            all_span = [_segmentspan(self, revs, deltainfo) for revs in
> chunks]
> +            distance = max(all_span)
>          else:
>              distance = deltainfo.distance
>
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