[Gnu-arch-users] Fai update: Native merge, submit trees and more

[Aaron Bentley]

Here's the latest on Fai development
(to install get started with Fai, see 
"http://www.sourcecontrol.net/~abentley/fai/";)

Current dist revision:
address@hidden/fai--dist--0.2--patch-78

Current devel revision:
address@hidden/fai--devel--0--patch-205

I'm happy with Fai's current state-- it's very usable for what I do. 
There are still some niggly things; I want a native replay command, for 
example; I want to specify patchlevels for single-revision mode, and I 
want to specify "--micro" or "--non-dependencies --reverse" for multiple 
-revision mode.

I'd like hear from anyone who's using it, and especially anyone who's 
tried it and chosen not to use it, what you think of it.

Various minor tweaks and bugfixes aren't mentioned, but there's a fine 
changelog to read.
http://www.sourcecontrol.net/~abentley/fai/changelog.php

Looking at new names
====================
Fai needs a new name, since "fai" is already "Fully Automated 
Installation", which is provided by at least Debian.  I'm considering 
"afa" for "Accessible Front-end for Arch".

Changeset Munger
================
Broke the ChangesetMunger into a changeset representation and a set of 
munging options.

Documentation Fixups
====================
Some tweakage from David Allouche

Revert
======
Revert gained the ability to revert only logs or all control files, and 
to revert files based on pattern matches.  ("revert --logs", "revert 
--control-files", "revert --pattern-files")

Revisions
=========
Added --micro: revisions in the partner version with a "Microbranch:" 
header for this revision.
Added --skip-present
Added --present: missing revisions that have patchlogs in the tree

Changes
=======
Changes now allows users to specify the diff options for viewing diffs.
("changes --diffopts -c").  Standard diff output is native, too.
The generated changesets are unaffected.

Commit and elog
===============
Better handling of situations where the user doesn't provide a suitable log

Terminal codes
==============
David Allouche: detection of whether to use terminal control codes for 
colour and title bars

Alias
=====
The alias command went native, and now allows you to list all aliases, 
list one alias, set an alias or delete an alias.  Per-tree aliases are 
supported.

Submit Trees
============
Fai now supports submit trees, which means the following:
If you have a {arch}/+submit-version file, Fai uses its contents as the 
tree's "submit version".  Every time you merge from the tree's submit 
version, Fai will perform "revert", "changes" and "commit" relative to 
the newest submit revision.  Once you have committed, their behaviour 
returns to normal.  I use this functionality for preparing tla merge 
requests against James' latest revision.

This functionality requires commit --base, which I expect to submit soon.

Native merge
============
Fai takes more control than ever over merging, with its own 
ancestor-picker.  This algorithm is heavily based on the star-merge 
ancestor-picker, but has a few nice tweaks:
- it follows ancestry across continuations
- it halts when it encounters parallel merges, instead of doing the 
wrong thing.

Since it follows continuations, the native merge never needs a 
--reference.  This, in turn, simplifies the algorithm.  It also handles 
mixed versions properly.

The Canonical crew and I independently discovered that star-merge can't 
handle parallel merges.  (See the "Star-merge Fatally Wounded" thread.) 
 Fai's merge also requires an unambiguous last-merge, so it suffers 
from the same weakness.  But unlike star-merge, it can detect situations 
in which there is no unambiguous last merge, and exit with an error 
explaining the situation.

You may be wondering why I didn't simply fix star-merge; there are a few 
reasons:

1. Tom is very conservative about star-merge.  Hopefully, the Fai 
implementation can serve to show that the ideas are sound, and 
eventually lead to improving star-merge

2. It was easy.  The ancestor picker is less than 40 lines of code.

3. It allows Fai to support graphical merging.

Graphical three-way merging has been described by Linus Torvalds as a 
must-have feature for any RCS hoping to replace BitKeeper.  While Fai 
can perform the merge using the apply-delta strategy, it can also simply 
return the name of the selected revision.  Fai's get command can 
retrieve the desired trees.  Fai's revert --renames command can rename 
all files to match their names in the working tree's revision.  You can 
then invoke any three-way merge tool you like, and remove the extra 
trees afterward.

It should be easy to add Arch support to Meld, since Meld is also 
Python-based.

Aaron