[PATCH 10 of 10] effectflag: detect when diff changed

[Jun Wu]

It's not very clear to me that what do we plan to use the effectflags.

I guess the most useful case is divergent resolution, like Alice changes
message, Bob changes content, so we know what to do. But a chain of changes
could cancel effects with each other, like:

  A0 - (amend by Alice) -> A1 - (amend by Alice) -> A2
   \
    -- (a chain of rewrites by Bob) -> A9

"A0 -> A1" changes diff content, "A1 -> A2" changes diff content. But
"A0 -> A2" does not necessarily change diff content.

This is a divergent case where A0 has two visible successors: A2 and A9. A2
does not have diff content change but with effectflags, A2 might be treated
as having diff content change.

I think we should store the hash of actual diff text as metadata to detect
diff changes across a chain of rewrites. That hash could be stored in a
cache.

For other information like branch, desc, meta, parents. Since reading them
is very fast using changelog, I'm not sure about the benefit of storing them
in obsmarkers. It might be helpful to provide extra information for nodes
unknown to local changelog (I'd also argue those markers are meaningless and
should be hidden from the user, but that's another topic), but I don't think
this feature is useful for an end-user.


Excerpts from Boris Feld's message of 2017-07-07 14:38:39 +0200:
> # HG changeset patch
> # User Boris Feld <boris.feld at octobus.net>
> # Date 1499346007 -7200
> #      Thu Jul 06 15:00:07 2017 +0200
> # Node ID 449fc1c748c6e058e892a4c940e20137e52e7808
> # Parent  6a40d87dfedcce4064eb4bcdb131ed4d427fd4de
> # EXP-Topic effectflag
> effectflag: detect when diff changed
> 
> Store in effect flag when the diff changed between the predecessor and
> its successors.
> 
> Comparing the diff is not easy because we do not want to incorrectly detect a
> diff modification when the changeset has only been rebased.
> 
> diff -r 6a40d87dfedc -r 449fc1c748c6 mercurial/obsutil.py
> --- a/mercurial/obsutil.py    Thu Jul 06 14:58:44 2017 +0200
> +++ b/mercurial/obsutil.py    Thu Jul 06 15:00:07 2017 +0200
> @@ -542,6 +542,7 @@
>  DESCCHANGED = 1 << 0 # action changed the description
>  METACHANGED = 1 << 1 # action change the meta
>  PARENTCHANGED = 1 << 2 # action change the parent
> +DIFFCHANGED = 1 << 3 # action change diff introduced by the changeset
>  USERCHANGED = 1 << 4 # the user changed
>  DATECHANGED = 1 << 5 # the date changed
>  BRANCHCHANGED = 1 << 6 # the branch changed
> @@ -565,6 +566,46 @@
>  
>      return True
>  
> +def _prepare_hunk(hunk):
> +    """Drop all information but the username and patch"""
> +    cleanunk = []
> +    for line in hunk.splitlines():
> +        if line.startswith(b'# User') or not line.startswith(b'#'):
> +            if line.startswith(b'@@'):
> +                line = b'@@\n'
> +            cleanunk.append(line)
> +    return cleanunk
> +
> +def _getdifflines(iterdiff):
> +    """return a cleaned up lines"""
> +    try:
> +        lines = next(iterdiff)
> +    except StopIteration:
> +        return None
> +    return _prepare_hunk(lines)
> +
> +def _cmpdiff(leftctx, rightctx):
> +    """return True if both ctx introduce the "same diff"
> +
> +    This is a first and basic implementation, with many shortcoming.
> +    """
> +
> +    # Leftctx or right ctx might be filtered, so we need to use the contexts
> +    # with an unfiltered repository to safely compute the diff
> +    leftunfi = leftctx._repo.unfiltered()[leftctx.rev()]
> +    leftdiff = leftunfi.diff(git=1)
> +    rightunfi = rightctx._repo.unfiltered()[rightctx.rev()]
> +    rightdiff = rightunfi.diff(git=1)
> +
> +    left, right = (0, 0)
> +    while None not in (left, right):
> +        left = _getdifflines(leftdiff)
> +        right = _getdifflines(rightdiff)
> +
> +        if left != right:
> +            return False
> +    return True
> +
>  def geteffectflag(relation):
>      """ From an obs-marker relation, compute what changed between the
>      predecessor and the successor.
> @@ -604,4 +645,12 @@
>          if ctxmeta != srcmeta:
>              effects |= METACHANGED
>  
> +        # Check if at least one of the parent has changed
> +        if changectx.parents() != source.parents():
> +            effects |= PARENTCHANGED
> +
> +        # Check if the diff has changed
> +        if not _cmpdiff(source, changectx):
> +            effects |= DIFFCHANGED
> +
>      return effects
> diff -r 6a40d87dfedc -r 449fc1c748c6 tests/test-obsmarkers-effectflag.t
> --- a/tests/test-obsmarkers-effectflag.t    Thu Jul 06 14:58:44 2017 +0200
> +++ b/tests/test-obsmarkers-effectflag.t    Thu Jul 06 15:00:07 2017 +0200
> @@ -95,7 +95,7 @@
>  
>    $ hg debugobsolete --rev .
>    d6f4d8b8d3c8cde990f13915bced7f92ce1cc54f 0 {ebfe0333e0d96f68a917afd97c0a0af87f1c3b5f} (Thu Jan 01 00:00:00 1970 +0000) {'ef1': '0', 'user': 'test'}
> -  ebfe0333e0d96f68a917afd97c0a0af87f1c3b5f 75781fdbdbf58a987516b00c980bccda1e9ae588 0 (Thu Jan 01 00:00:00 1970 +0000) {'ef1': '0', 'user': 'test'}
> +  ebfe0333e0d96f68a917afd97c0a0af87f1c3b5f 75781fdbdbf58a987516b00c980bccda1e9ae588 0 (Thu Jan 01 00:00:00 1970 +0000) {'ef1': '8', 'user': 'test'}
>  
>  amend with multiple effect (desc and meta)