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|
<html>
<head>
<title>Basic Revision Control</title>
</head>
<body>
<a name="Basic_Revision_Control"></a>
<a href="http://www.regexps.com">The Hackerlab at <code>regexps.com</code></a>
<h2 align=center>Basic Revision Control</h2>
<small>
<b>up: </b><a href="arch.html#arch">arch</a></br>
<b>next: </b><a href="basic-branching-and-merging.html#Basic_Branching_and_Merging">Basic Branching and Merging</a></br>
<b>prev: </b><a href="development-paths.html#Development_Paths">Development Paths</a></br>
</small>
<br>
<p>This chapter introduces the fundamental operations for storing
revisions in archives, retrieving them, doing clever things with
patches, and managing project trees for archived projects.
</p><ul>
<li><a href="basic-rc.html#The_First_Revision">The First Revision</a></li>
<li><a href="basic-rc.html#Successive_Revisions">Successive Revisions</a></li>
<li><a href="basic-rc.html#Patch_Levels_and_Development_Phases">Patch Levels and Development Phases</a></li>
<li><a href="basic-rc.html#Getting_a_Revision">Getting a Revision</a></li>
<li><a href="basic-rc.html#Optimizing_Archives_for_get">Optimizing Archives for get</a></li>
<li><a href="basic-rc.html#Finding_Out_What_Changed">Finding Out What Changed</a></li>
<li><a href="basic-rc.html#The_whats-missing_Command">The whats-missing Command</a></li>
<li><a href="basic-rc.html#Update">Update</a></li>
<li><a href="basic-rc.html#Replay">Replay</a></li>
<li><a href="basic-rc.html#The_Next_Version">The Next Version</a></li>
</ul>
<hr>
<a name="The_First_Revision"></a>
<h3 align=center>The First Revision</h3>
<small>
<b>up: </b><a href="basic-rc.html#Basic_Revision_Control">Basic Revision Control</a></br>
<b>next: </b><a href="basic-rc.html#Successive_Revisions">Successive Revisions</a></br>
</small>
<br>
<p><a name="index-pt:0"></a>
</p><p>When beginning a new project, the first step is to check in the very
first revision of the tree.
</p><p><strong><u>Prepare the Archive</u></strong> We've already seen how to prepare the archive by
creating the category, branch, and version for the project (see
<a href="development-paths.html#Creating_a_Development_Path">Creating a Development Path</a>). You have to perform those
steps before checking in the first revision:
</p><pre>
% larch make-category CATEGORY
% larch make-branch BRANCH
% larch make-version VERSION
</pre>
<p><strong><u>Prepare the Project Tree</u></strong> We've also seen how to turn an ordinary
directory into a project tree using the <code>init-tree</code>
command (see
<a href="project-trees.html#Initializing_a_Project_Tree">Initializing a Project Tree</a>). And we've seen how to set the
default version of a project tree using <code>set-tree-version</code>
(see
<a href="project-names.html#Labelling_Project_Trees">Labelling Project Trees</a>). Both of these steps must be
completed before checking in the first revision:
</p><pre>
% larch init-tree
% larch set-tree-version VERSION-NAME
</pre>
<p>In addition, you must create for the project tree a "patch log" --
where log entries for revisions in the development path <code>VERSION-NAME</code>
will be stored:
</p><pre>
% larch add-log VERSION-NAME
</pre>
<p>Patch logs are explained in detail in the next chapter. For now, just
accept the necessity of that command on faith.
</p><p><strong><u>Prepare a Log Message</u></strong> In the root of the project tree, the command:
</p><pre>
% larch make-log
</pre>
<p>creates a template for a log file (look for file whose name begins
with <code>++log</code>
). The details of what should go in a log message are
project specific. In general, the format of a log message uses
<code>RFC822</code>
style headers followed by a free-form body. When <code>arch</code>
stores a log message, it will add some headers of its own.
</p><p><strong><u>Archive the Tree</u></strong> Again, in the root of the project tree, use
the <code>import</code>
command to archive the tree:
</p><pre>
% larch import
</pre>
<p><code>import</code>
will print the headers of the log message (including headers
added by <code>arch</code>
), store the tree in the archive (as a compressed tar
file), and update the patch log of the working directory to reflect
the commit.
</p><p>After commiting a revision to, say, <code>hello--devo--1.0</code>
, you can use
the command <code>revisions</code>
to see a list of archived revisions:
</p><pre>
% larch revisions hello--devo--1.0
base-0
</pre>
<p><code>base-0</code>
is the "patch level name" for the first revision. Patch
levels are described in greater detail below.
</p>
<hr>
<a name="Successive_Revisions"></a>
<h3 align=center>Successive Revisions</h3>
<small>
<b>up: </b><a href="basic-rc.html#Basic_Revision_Control">Basic Revision Control</a></br>
<b>next: </b><a href="basic-rc.html#Patch_Levels_and_Development_Phases">Patch Levels and Development Phases</a></br>
<b>prev: </b><a href="basic-rc.html#The_First_Revision">The First Revision</a></br>
</small>
<br>
<p><a name="index-pt:1"></a>
</p><p>Suppose that you have continued to edit your working directory after
checking in the initial revision. Successive revisions can be checked
in with the command <code>commit</code>
, issued at the root of the working
directory. As with <code>import</code>
, you must first use <code>make-log</code>
to
prepare a log message for each commit:
</p><pre>
% larch make-log
</pre>
<pre>
[...edit log message...]
</pre>
<pre>
% larch commit
[output omitted]
</pre>
<p>After several commits, you'll have a number of patch levels:
</p><pre>
% larch revisions hello--devo--1.0
base-0
patch-1
patch-2
patch-3
...
</pre>
<p>As a point of interest, the base revision is stored as a compressed
tar file of the entire tree. Each <code>patch-N</code>
is stored as a compressed
tar file of just a patch set that describes how to derive that
revision from the previous revision.
</p>
<hr>
<a name="Patch_Levels_and_Development_Phases"></a>
<h3 align=center>Patch Levels and Development Phases</h3>
<small>
<b>up: </b><a href="basic-rc.html#Basic_Revision_Control">Basic Revision Control</a></br>
<b>next: </b><a href="basic-rc.html#Getting_a_Revision">Getting a Revision</a></br>
<b>prev: </b><a href="basic-rc.html#Successive_Revisions">Successive Revisions</a></br>
</small>
<br>
<p>Within a version, there is a sequence of revisions, each of which is a
different <em>
<a name="index-pt:2"></a>
patch level
</em>
. Every patch level has a <em>
<a name="index-pt:3"></a>
patch level name
</em>
,
derived from the version name by adding a suffix:
</p><pre>
hello--devo--1.0--base-0
hello--devo--1.0--patch-1
hello--devo--1.0--patch-2
hello--devo--1.0--patch-3
...
</pre>
<p>Just as with version names, there is also such a thing as a <em>
<a name="index-pt:4"></a>
fully
qualified patch level name
</em>
:
</p><pre>
joe.hacker@gnu.org--test-archive/hello--devo--1.0--patch-3
</pre>
<p>Development within a version may be optionally divided into four
phases: <em>
<a name="index-pt:5"></a>
base revision
</em>
, <em>
<a name="index-pt:6"></a>
pre-patches
</em>
, <em>
<a name="index-pt:7"></a>
version revision
</em>
, and
<em>
<a name="index-pt:8"></a>
post-patches
</em>
. Conceptually, "pre-patches" are revisions made
before the version is "done". "Post-patches" are revisions made
after the version is done (e.g. "bug fix patches").
</p><p>At the beginning of a development path is the <em>
<a name="index-pt:9"></a>
base revision
</em>
(called <code>base-0</code>
). Between the pre-patch and post-patch phases is the
<em>
<a name="index-pt:10"></a>
version revision
</em>
(called <code>version-0</code>
). Post-patches have names like
<code>versionfix-1</code>
, <code>versionfix-2</code>
, etc.
</p><p>So the total sequence of revisions within a development path has the
form:
</p><pre>
The Initial Revision:
</pre>
<pre>
base-0
</pre>
<pre>
Pre-Patches:
</pre>
<pre>
patch-1
patch-2
patch-3
...
patch-N
</pre>
<pre>
The Version Revision:
</pre>
<pre>
version-0
</pre>
<pre>
Post-Patches:
</pre>
<pre>
versionfix-1
versionfix-2
versionfix-3
...
</pre>
<p>Typically, the <code>version-0</code>
revision is what would be released under
the version number and the post-patch revisions are fixes made after
the release.
</p><p>The ordinary <code>commit</code>
command creates pre-patches (<code>patch-N</code>
revisions).
</p><p>To create the version revision, use <code>commit --seal</code>
:
</p><pre>
% larch commit --seal
</pre>
<p>After the version revision exists, ordinary commit will no longer
work. To create a post-patch revision, use <code>commit --fix</code>
:
</p><pre>
% larch commit --fix
</pre>
<p>It is perhaps worth mentioning that patch level names can be sorted
easily using:
</p><pre>
sort -t - -k 1,1 -k 2,2n
</pre>
<p>or in reverse:
</p><pre>
sort -t - -k 1,1r -k 2,2rn
</pre>
<p>If you are familiar with other revision control systems, a four-phased
development process may at first seem somewhat arbitrary and
needlessly complicated. Two points are worth mentioning:
</p><p>First, phased development is entirely optional. Nothing requires you
to ever <code>--seal</code>
a version, and if you never seal a version,
you never need to use <code>--fix</code>
. Instead, every revision (after
<code>base-0</code>
) will be a <code>patch-N</code>
revision.
</p><p>Second, phased development is a handy way to prevent accidents when
organizing more complex projects. Sealing a version is a
way to set a flag that says, in effect, "ordinary development in this
version has stopped -- you might not really want to make a new
revision here." You can make a new revision if you insist (by
specifying <code>--fix</code>
), but the requirement that you insist helps alert
you to the fact that your new revision might need to be merged with
later versions of the same project; or that that version you are
revising has already been released. Phased development is a
bookkeeping convenience: for the most part, <code>arch</code>
treats all
revisions equally, regardless of their phase.
</p>
<hr>
<a name="Getting_a_Revision"></a>
<h3 align=center>Getting a Revision</h3>
<small>
<b>up: </b><a href="basic-rc.html#Basic_Revision_Control">Basic Revision Control</a></br>
<b>next: </b><a href="basic-rc.html#Optimizing_Archives_for_get">Optimizing Archives for get</a></br>
<b>prev: </b><a href="basic-rc.html#Patch_Levels_and_Development_Phases">Patch Levels and Development Phases</a></br>
</small>
<br>
<p>To retrieve a revision from an archive, use <code>larch get</code>
:
</p><pre>
% larch get REVISION DIR
</pre>
<p>as in:
</p><pre>
% larch get hello--devo--1.0--patch-4 hello
</pre>
<p>to retrieve the revision <code>patch-4</code>
and store it in the new directory
<code>hello</code>
.
</p><p>An abbreviation can be used to obtain the most recent revision of a
version:
</p><pre>
% larch get hello--devo--1.0 hello
</pre>
<p>or to obtain the most recent revsion of the highest-numbered version:
</p><pre>
% larch get hello--devo hello
</pre>
<p>A fully-qualified name can be used to obtain a revision from someplace
other than the default archive:
</p><pre>
% larch get joe.hacker@gnu.org--test-archive/hello--devo
</pre>
<hr>
<a name="Optimizing_Archives_for_get"></a>
<h3 align=center>Optimizing Archives for get</h3>
<small>
<b>up: </b><a href="basic-rc.html#Basic_Revision_Control">Basic Revision Control</a></br>
<b>next: </b><a href="basic-rc.html#Finding_Out_What_Changed">Finding Out What Changed</a></br>
<b>prev: </b><a href="basic-rc.html#Getting_a_Revision">Getting a Revision</a></br>
</small>
<br>
<p>The way that <code>get</code>
ordinarilly works is that it searches backwards
from the desired revision to find the nearest full-source base
revision. It gets the compressed tar file for that base revision and
creates a source tree. Then, for each intermediate patch level, it
gets a compressed tar file of the patch set, uncompresses and un-tars
the patch-set, and applies the patch-set to the source tree.
</p><p>If there are many intermediate patch-sets, that process can be slow.
In such cases, you can ask <code>arch</code>
to cache a full-source copy of an
arbitrary revision, with the command:
</p><pre>
% larch archive-cache-revision [ARCHIVE/]REVISION
</pre>
<p>That command first builds the requested revision, then it builds a
compressed tar file of the revision, then it stores the tar file back
in the archive. Subsequent attempts to <code>get</code>
the same revision (or
any later revision) will use the cached tree.
</p><p>To remove a previously cached tree, use:
</p><pre>
% larch archive-uncache-revision [ARCHIVE/]REVISION
</pre>
<p>For each user, <code>arch</code>
also maintains a "client side" cache of
revisions that can speed up <code>get</code>
(and other operations). The details
of client side caching are documented in a later chapter (xref!!!).
</p>
<hr>
<a name="Finding_Out_What_Changed"></a>
<h3 align=center>Finding Out What Changed</h3>
<small>
<b>up: </b><a href="basic-rc.html#Basic_Revision_Control">Basic Revision Control</a></br>
<b>next: </b><a href="basic-rc.html#The_whats-missing_Command">The whats-missing Command</a></br>
<b>prev: </b><a href="basic-rc.html#Optimizing_Archives_for_get">Optimizing Archives for get</a></br>
</small>
<br>
<p><a name="index-pt:11"></a>
</p><p>Before performing a <code>commit</code>
, you might want to check to see what
has actually changed -- that is, find out exactly what patch set your
<code>commit</code>
will create.
</p><p>You can do that with the command <code>what-changed</code>
:
</p><pre>
% larch what-changed
[...patch set report...]
</pre>
<p><code>what-changed</code>
computes a patch set between your modified project tree
and the latest patch level for which your project tree is up-to-date.
In other words, it tells you what changes have been made to your tree
compared to the tree in the archive.
</p><p><code>what-changed</code>
leaves behind a directory containing the patch set and
patch report, which you can usefully browse by hand.
</p><pre>
% ls
,,what-changed.arch--devo--0.5--patch-14--lord@regexps.com--arch-1
[...]
</pre>
<p>The default output of <code>what-changed</code>
is formatted for use with the
<code>outline</code>
mode of <strong>GNU Emacs</strong>.
</p><p>You can ask <code>what-changed</code>
to also generate an HTML-formatted report
with:
</p><pre>
% larch what-changed --url
URL of patch report
</pre>
<p>The HTML report has links to each context diff, added, and removed
file. The output of the command is a <code>file:</code>
method URL. For
example, a useful command for <code>netscape</code>
users is:
</p><pre>
% netscape --remote "openURL(`larch what-changed --url`)"
</pre>
<hr>
<a name="The_whats-missing_Command"></a>
<h3 align=center>The whats-missing Command</h3>
<small>
<b>up: </b><a href="basic-rc.html#Basic_Revision_Control">Basic Revision Control</a></br>
<b>next: </b><a href="basic-rc.html#Update">Update</a></br>
<b>prev: </b><a href="basic-rc.html#Finding_Out_What_Changed">Finding Out What Changed</a></br>
</small>
<br>
<p><a name="index-pt:12"></a>
</p><p>Suppose that more than one programmer is checking revisions into a
version, Alice and Bob for example.
</p><p>Alice and Bob both start with working directories and both make some
changes. Alice commits several changes. Now Bob's working directory
has fallen behind archived development path.
</p><p>The command <code>whats-missing</code>
can be used to tell Bob which patches he
is missing:
</p><pre>
% larch whats-missing --summary
patch-N
summary of patch N
patch-N+1
summary of patch N+1
...
</pre>
<p>For each patch that Bob is missing, <code>whats-missing --summary</code>
prints
the name of the patch and the contents of the <code>Summary:</code>
header from
its log message.
</p><p>The <code>whats-missing</code>
command is explained in greater detail in a later
chapter (see <a href="patch-logs.html#Patch_Logs_and_ChangeLogs">Patch Logs and ChangeLogs</a>).
</p>
<hr>
<a name="Update"></a>
<h3 align=center>Update</h3>
<small>
<b>up: </b><a href="basic-rc.html#Basic_Revision_Control">Basic Revision Control</a></br>
<b>next: </b><a href="basic-rc.html#Replay">Replay</a></br>
<b>prev: </b><a href="basic-rc.html#The_whats-missing_Command">The whats-missing Command</a></br>
</small>
<br>
<p>So Bob is behind by a few patches, but also has his own modifications.
</p><p>Diagramatically, we have something like:
</p><pre>
Patch Levels Bob's Working
in the Directory
Archive:
------------------------------
</pre>
<pre>
base-0
</pre>
<pre>
patch-1
patch-2
patch-3
patch-4 --------> bob-0 (Bob's initial working directory)
patch-5 |
patch-6 |
patch-7 V
patch-8 bob-1 (Bob's working dir with changes)
</pre>
<p>Bob is missing patches five through eight.
</p><p>The command <code>update</code>
can be used to fix the situation:
</p><pre>
% larch update OLD-DIR NEW-DIR
</pre>
<p>as in:
</p><pre>
% larch update bob-1 bob-2
</pre>
<p><code>update</code>
works in several steps. First, it gets a copy of the latest
revision (<code>patch-8</code>
in this case). It also gets a copy of the
revision from which <code>OLD-DIR</code>
is dervied (<code>patch-4</code>
in this case).
Then it uses <code>mkpatch</code>
to compute the differences between <code>OLD-DIR</code>
and its source revision, and applies those differences (using
<code>dopatch</code>
) to the latest revision.
</p><p>In the example, update will create the directory <code>bob-2</code>
, with
the source:
</p><pre>
delta(patch-4, bob-1)[patch-8]
</pre>
<p>(For information about this notation, see <a href="theory-of-patches.html#The_Theory_of_Patches_and_Revisions">The Theory of Patches and Revisions</a>.)
</p><p>Applying that patch might cause conflicts. In that case, <code>update</code>
will print a message telling Bob to look for <code>.rej</code>
files.
</p><p>As a convenience, <code>update</code>
also copies all "precious" non-source
files from <code>OLD-DIR</code>
to <code>NEW-DIR</code>
(see <a href="inventory.html#arch_Project_Inventories">arch Project Inventories</a>).
</p><p>Of course, if Bob only wanted to "partly update", he could do that
with an extra parameter to <code>update</code>
, as in the example:
</p><pre>
# update, but only up to patch level 6:
#
</pre>
<pre>
% larch update bob-1 bob-2 hello--devo--1.1--patch-6
</pre>
<p>Finally, <code>update</code>
can replace <code>OLD-DIR</code>
with the updated directory if
given the <code>--in-place</code>
flag:
</p><pre>
% larch update --in-place OLD-DIR
</pre>
<hr>
<a name="Replay"></a>
<h3 align=center>Replay</h3>
<small>
<b>up: </b><a href="basic-rc.html#Basic_Revision_Control">Basic Revision Control</a></br>
<b>next: </b><a href="basic-rc.html#The_Next_Version">The Next Version</a></br>
<b>prev: </b><a href="basic-rc.html#Update">Update</a></br>
</small>
<br>
<p><code>update</code>
isn't the only way to catch-up with a development path.
Another option is <code>replay</code>
:
</p><pre>
% larch replay old-dir new-dir
</pre>
<p>Using the same example:
</p><pre>
Patch Levels Bob's Working
in the Directory
Archive:
------------------------------
</pre>
<pre>
base-0
</pre>
<pre>
patch-1
patch-2
patch-3
patch-4 --------> bob-0 (Bob's initial working directory)
patch-5 |
patch-6 |
patch-7 V
patch-8 bob-1 (Bob's working dir with changes)
</pre>
<p>and the command:
</p><pre>
% larch replay bob-1 bob-2
</pre>
<p><code>replay</code>
will first copy <code>bob-1</code>
to create <code>bob-2</code>
. Then it will
apply each missing patch in succession until <code>bob-2</code>
is up-to-date, or
until a merge conflict occurs.
</p><p>Thus, if no conflict occurs, <code>replay</code>
computes:
</p><pre>
patch-8 [ patch-7 [ patch-6 [ patch-5 [ bob-1 ]]]]
</pre>
<p>If a conflict occured in, say, <code>patch-6</code>
, then <code>replay</code>
would compute:
</p><pre>
patch-6 [ patch-5 [ bob-1 ]]
</pre>
<p>and after fixing the conflict, Bob could use a second <code>replay</code>
command
to apply patches seven and eight.
</p><p>As with <code>update</code>
, <code>replay</code>
also copies all "precious" non-source
files from <code>OLD-DIR</code>
to <code>NEW-DIR</code>
(see <a href="inventory.html#arch_Project_Inventories">arch Project Inventories</a>).
</p><p>Of course, if Bob only wanted to "partly replay", he could do that
with an extra parameter to <code>replay</code>
, as in the example:
</p><pre>
# replay, but only up to patch level 6:
#
</pre>
<pre>
% larch replay bob-1 bob-2 hello--devo--1.1--patch-6
</pre>
<p>You can use <code>replay</code>
to modify an existing directory rather than
creating a new directory:
</p><pre>
% larch replay --in-place DIR [REVISION]
</pre>
<p>but be careful: if <code>DIR</code>
contains precious local changes, and
conflicts occur, or if you simply decide the <code>replay</code>
wasn't a good
idea, you'll have to do some work to revert the <code>replay</code>
.
</p>
<hr>
<a name="The_Next_Version"></a>
<h3 align=center>The Next Version</h3>
<small>
<b>up: </b><a href="basic-rc.html#Basic_Revision_Control">Basic Revision Control</a></br>
<b>prev: </b><a href="basic-rc.html#Replay">Replay</a></br>
</small>
<br>
<p>In simple situations, a version like <code>hello--devo--1.0</code>
will be
followed by the <em>
<a name="index-pt:13"></a>
next version
</em>
: <code>hello--devo--1.1</code>
or
<code>hello--devo--2.0</code>
, for example.
</p><p>Such a version is called a <em>
<a name="index-pt:14"></a>
continuation
</em>
of the previous version and
it is created with this sequence of commands (in the root of a working
directory):
</p><pre>
% larch make-version NEXT-VERSION
% larch add-log NEXT-VERSION
% larch set-tree-version NEXT-VERSION
% larch make-log
[...edit log message...]
% larch commit --continuation PREVIOUS-VERSION
</pre>
<p>as in:
</p><pre>
% larch make-version hello--devo--1.1
% larch add-log hello--devo--1.1
% larch set-tree-version hello--devo--1.1
% larch make-log
[...edit log message...]
% larch commit --continuation hello--devo--1.0
</pre>
<p>Those commands create the <code>base-0</code>
revision of the new version but
instead of storing complete source for the base revision, they store a
pointer to the older revision which the base revision is equal to.
</p><p>On the other hand, if you wanted the next version to start completely
from scratch (perhaps because a program is being replaced by an
entirely new implementation), the <code>import</code>
command can create the next
version as documented earlier in this chapter.
</p><p>Finally, there is another command (besides <code>commit --continuation</code>
)
for creating the next version, <code>larch tag</code>
, described in the next
chapter.
</p>
<small><i>arch: The arch Revision Control System
</i></small><br>
<a href="http://www.regexps.com">The Hackerlab at <code>regexps.com</code></a>
</body>
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