[Monotone-devel] Updated Issue 65 - When the left and right descendants contain the same change, merge into ancestor (monotone)

[code]

Hello,

The following issue has been updated:

65 - When the left and right descendants contain the same change, merge into 
ancestor
Project: monotone
Status: Invalid
Reported by: Unknown User
URL: https://code.monotone.ca/p/monotone/issues/65/
Labels:
 Type:Feature Request
 Component:Merge Algorithm
 Priority:Medium

Comments (last first):

# By Stephen Leake, Jun 24, 2012:



 Status: Invalid

# By Unknown User, Jul  1, 2007:

OK. Bottom line: Fix meld. Understood. I wasn't sure whose scope this change 
was in. Thanks for making it clear.

# By Unknown User, Jul  1, 2007:

Not sure how we would fix this.

The way (file content) merging works is, we attempt to do our textual merge, 
and if the whole files merge cleanly, then great.  However, even if most of the 
file merges cleanly (including clean merges resulting from identical edits on 
both sides), even one conflicting hunk will cause this stage to fail.

If that stage fails, then we call the user's preferred merge tool, and just 
give it the left/right/ancestor files, and it gets to do the whole merge again 
from scratch, using whatever algorithms, heuristics, user interaction, 
whatever, that it is programmed with.  It sounds like meld's are sucky when it 
comes to automatically resolving easy hunks so you can find the hard hunks that 
need your attention.  There isn't any way for us to reach into meld's innards 
and tell it to automatically resolve certain hunks for you.

The only way we could do that would be by somehow programmatically generating 
some made-up "ancestor" file, in such a way that typical 3-way line-by-line 
merge tools that happened to use the same diff algorithm as monotone would 
magically find fewer conflicts.  This is obviously complex, error prone, and it 
would workaround the limitations of dumb merge tools at the cost of making it 
impossible to create reliable smart merge tools (that really do just want to be 
told the facts on the ground, and then do whatever clever thing they know how 
to do).

Maybe it would be easier to fix meld so it could effectively "do the mindless 
clicking for you", automatically?  I'm pretty sure both xxdiff and emacs' 
ediff-mode get this right, for instance.

# By Unknown User, Jul  1, 2007:

added attachment meld-screenshot.png

Attachments:
- meld-screenshot.png - 136.33 kB
  
https://code.monotone.ca/p/monotone/issues/view/attachment/6/meld-screenshot.png


# By Unknown User, Jul  1, 2007:

(This entry was imported from the savannah tracker, original location: 
https://savannah.nongnu.org/bugs/index.php?20309)

Perhaps this is an artifact of my using meld for all my manual merging, however:

Whenever monotone presents me with 3 versions of a file I need to merge 
manually, one scenario occurs with great frequency, and its resolution requires 
absolutely no decision making on my part. This is the scenario:

The left descendant and the right descendant both have a change which has to go 
into the ancestor. However, the 2 versions of the change are identical in 
content.

Thus, I mindlessly click through 10s of such hunks. I cannot envision a 
scenario where you wouldn't want to merge something into the ancestor that both 
descendants have identically. After all, if, in the course of working on one of 
the descendants it is decided that the hunk is unnecessary, it will be removed, 
in which case the left and right descendants will no longer be "symmetrically 
different" from the ancestor.

My suggestion is that, before monotone offers the 3 versions of the file up for 
merging, all such "symmetrical differences" be automatically merged into the 
ancestor.

I was saying earlier that this may be an artifact of my using meld, because 
only in meld do I have to merge left and right descendant into the ancestor 
(this is a warning issued by monotone before running meld). Nonetheless, if the 
changes introduced in both the left and right descendant are identical to one 
another, IMO they can be merged before asking the user to decide on the rest of 
the changes.

monotone version:
-----------------
monotone 0.35 (base revision: f92dd754bf5c1e6eddc9c462b8d68691cfeb7f8b)
Running on          : Linux 2.6.21.5 #4 SMP Sun Jun 24 13:28:49 EEST 2007 i686
C++ compiler        : GNU C++ version 4.1.1 (Gentoo 4.1.1-r3)
C++ standard library: GNU libstdc++ version 20060524
Boost version       : 1_33_1
Changes since base revision:
format_version "1"

new_manifest [f95da638a0aa17f7c5979d17a059faf6a46e9670]

old_revision [f92dd754bf5c1e6eddc9c462b8d68691cfeb7f8b]

  Generated from data cached in the distribution;
  further changes may have been made.





--
Issue: https://code.monotone.ca/p/monotone/issues/65/