Idle Time

Every good version-control system has this as a built-in feature.

In the below, $TMP is a staging directory, such as “build”, “/tmp”, or “/Volumes/RAM Disk”. It’s also where the final archive will end up.

• svn: Sort of. svn export $TMP/MyProject && cd $TMP && tar cjf MyProject.tbz MyProject
• darcs: darcs dist (outputs a .tar.gz file in the current working directory)
• bzr: bzr export --format=tbz2 $TMP/MyProject.tbz
• git: git archive --format=tar master | bzip2 > $TMP/MyProject.tbz
• hg: hg archive -p MyProject -t tbz2 $TMP/MyProject.tbz

Darcs lets you choose which changes you want to include in a patch (commit). For example:

darcs rec                                                   %~/ASL test apps/aslsearch(0)
move ./aslsearch.m ./aslsearch.c
Shall I record this change? (1/?)  [ynWsfqadjkc], or ? for help: y
hunk ./aslsearch.c 1
-#import <Foundation/Foundation.h>
-
-#include <stdlib.h>
-#include <stdbool.h>
-#include <stdio.h>
-#include <unistd.h>
-#include <string.h>
-#include <vis.h>
-#include <asl.h>
-
Shall I record this change? (2/?)  [ynWsfqadjkc], or ? for help: n
hunk ./aslsearch.c 29
-       NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
-
Shall I record this change? (3/?)  [ynWsfqadjkc], or ? for help: y
hunk ./aslsearch.c 75
-       [pool release];
Shall I record this change? (4/?)  [ynWsfqadjkc], or ? for help: y
hunk ./aslsearch.c 194
+       fprintf(stderr, "key: \e2\80\9c%s\e2\80\9d\noperator: 0x%x\nvalue: \e2\80\9c%s\e2\80\9d\n", key, operator, value);
Shall I record this change? (5/?)  [ynWsfqadjkc], or ? for help: n
hunk ./aslsearch.xcodeproj/project.pbxproj 10
-               8DD76F9A0486AA7600D96B5E /* aslsearch.m in Sources */ = {isa = PBXBuildFile; fileRef = 08FB7796FE84155DC02AAC07 /* aslsearch.m */; settings = {ATTRIBUTES = (); }; };
+               8DD76F9A0486AA7600D96B5E /* aslsearch.c in Sources */ = {isa = PBXBuildFile; fileRef = 08FB7796FE84155DC02AAC07 /* aslsearch.c */; settings = {ATTRIBUTES = (); }; };
Shall I record this change? (6/?)  [ynWsfqadjkc], or ? for help: ?
How to use record...
y: record this patch
n: don't record it
w: wait and decide later, defaulting to no

s: don't record the rest of the changes to this file
f: record the rest of the changes to this file

d: record selected patches, skipping all the remaining patches
a: record all the remaining patches
q: cancel record

j: skip to next patch
k: back up to previous patch
c: calculate number of patches
h or ?: show this help

<Space>: accept the current default (which is capitalized)
hunk ./aslsearch.xcodeproj/project.pbxproj 10
-               8DD76F9A0486AA7600D96B5E /* aslsearch.m in Sources */ = {isa = PBXBuildFile; fileRef = 08FB7796FE84155DC02AAC07 /* aslsearch.m */; settings = {ATTRIBUTES = (); }; };
+               8DD76F9A0486AA7600D96B5E /* aslsearch.c in Sources */ = {isa = PBXBuildFile; fileRef = 08FB7796FE84155DC02AAC07 /* aslsearch.c */; settings = {ATTRIBUTES = (); }; };
Shall I record this change? (6/?)  [ynWsfqadjkc], or ? for help: f
hunk ./aslsearch_Prefix.pch 5
-#ifdef __OBJC__
-#      import <Foundation/Foundation.h>
-#endif
-
Shall I record this change? (10/?)  [ynWsfqadjkc], or ? for help: y
hunk ./aslsearch_Prefix.pch 8
+#include <unistd.h>
Shall I record this change? (11/?)  [ynWsfqadjkc], or ? for help: n
What is the patch name? Switched source file from Obj-C to pure C
Do you want to add a long comment? [yn]n
Finished recording patch 'Switched source file from Obj-C to pure C'

(Before you mention the UTF-8 sequences that Darcs called out as invalid ASCII: Yes, I know.)

If you’re an svn user looking at darcs, you may wonder how to find unknown files—that is, files that you’ve created in your working directory, but haven’t yet told your VCS about (with svn add or darcs add). In svn, the command is svn st, but in darcs, the procedure is not obvious.

The darcs command that most seems like what you need is darcs whatsnew, or, as I type it, simply darcs what. Like svn st, this shows you all files that have been added, removed, or modified; it also includes a diff, so not only is it your substitute for svn st, it’s also your substitute for svn diff. But it doesn’t show you unknown files.

Until you use the -l (that’s a lowercase L) option.

darcs what -l changes the output greatly, as it’s in a completely different format: one similar to that of svn st. The format is actually that of darcs what -s (summary mode); the difference is that -l also lists unknown files.

There are some differences between darcs what -l and svn st. Some of these differences are:

• darcs uses fewer columns than svn: It has one status column, whereas svn has six.
• darcs uses ‘a’ to indicate an unknown file, whereas svn uses ‘?’.
• darcs uses ‘R’ to indicate a file that you’ve removed, whereas svn uses ‘D’ to indicate a file that you’ve deleted. (svn supports remove and rm as synonyms for its delete command, but darcs does not support delete nor rm as synonyms for its remove command.)

Here’s a real-world situation that tells you why I’m falling in love with darcs.

I’m working on a plug-in that logs all notifications posted by Apple Mail to a couple of files. The idea of this plug-in is to enable Mail-bundle developers to develop more reliable plug-ins by listening for notifications rather than posing as Mail’s classes or swizzling its methods.

(As you know, I don’t ordinarily announce what I’m working on before it’s ready; for this post, it’s important to provide context.)

The first revision of the plug-in used NSLog, but I found that this spammed console.log rather heavily. So I changed it to use two separate log files, which I write to using NSFileHandles.

Then I started work on a new feature: datestamps. While working on that, however, I noticed that I had forgotten to close and release my two file handles in -dealloc. Oops.

Now, remember that I had local changes. If this code were versioned in svn, I would have to:

1. bzip2 the source file (which renames it as a side-effect).
2. svn up the file in order to restore the pristine copy.
3. Open it in a separate editor (so as not to lose undo history) and add the closeFile and release messages that I’d forgotten.
4. Save and exit.
5. Commit.
6. Delete the committed file and bunzip2 my original one.
7. Go through an svn diff and redo the fix in my modified file so I don’t clobber the changes in my next commit.

What a hassle. But darcs has first-class support for just this situation.

All I had to do was darcs amend-record. darcs asked me whether the most recent commit was the one I wanted to amend, then it offered me the choice of which hunks of local changes I wanted to include in the amendment. I said yes to the one with the closeFile and release messages and no to all the others. That’s all I had to do.

Let me summarize that for you: I was able to retroactively fix my previous commit while I had other local changes in the same file, without sweeping up those other changes into the commit.

That’s awesome.