Re: [Gnu-arch-users] Re: Binary Diff System in Arch

[Martin Pool]

On  5 Feb 2004, Tom Lord <address@hidden> wrote:

> Leaving those files is a fine idea and easy to do -- but xdiff3
> shouldn't do that itself.  As a stand-alone tool, it would be silly
> for xdiff3 to leave those files: the user has provided the three files
> as input in the first place.

Right.

> arch should be the one to store those three files in project trees
> (which is a pretty trivial change).   In this case, it's arch, not the
> user, that has the files on-hand.
> 
> I think there are four distinct behaviors that would be useful from
> tla (when doing 3-way merges):
> 
>    ~ default
> 
>      Text files: arch just leaves conflict markers (if any) in the
>      merged-into file and creates a ".rej" file that says "Hey, there
>      are conflict markers in that file.
> 
>      Binary files: arch can, indeed, leave the three files and create
>      a ".rej" file that says "binary merge conflicts occurred".
> 
> 
>    ~ --no-markers
> 
>      All files: do the merges that are conflictless.  If a merge would
>      have conflicts, leave the merged-into unmodified and store all
>      three files.   Store a ".rej" that says: "merge would have
>      conflicts".
> 
> 
>    ~ --no-inexact
> 
>      All files: if the merged-to file matches the ancestor precisely,
>      replace it with merged-from.   Otherwise, leave the three files 
>      and a .rej that says "merge needed".
> 
> 
>    ~ --merge-data-only
> 
>      All files: leave the three files.  Leave merged-to unmodified.
>      Make .rej that says "merge needed".

Perhaps there should be a separate tool that transforms a file plus
rejects into a file with conflict sections, and vice versa.  (In fact,
that would be pretty useful just for working with patches in general.
I wonder if it exists?)

There seem to be a few orthogonal variables here:

 - allow fuzzy merges?

 - insert conflict markers in text files?

I think it is harmless to always try the merge: if the user or GUI
doesn't like the result they can always discard it and redo it from
the three basis files.  Perhaps the easily-parsed output from the
attempted merge should make it clear whether the patch was exact,
approximate, or (partially) failed.

So the big question is, would you rather have cvs-style conflict
markers, or leftover chunks in a .rej file?  I think the user-visible
option ought to address this question directly: perhaps
--conflicts=markers or --conflicts=reject.

> (It's more obvious that xpatch should store the xdelta-diff in the
> .rej file.   I agree it will not _often_ be useful but sometimes it
> will be.   For example, I might have an editor-backup file to which it
> applies cleanly.)

Good point.

-- 
Martin

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