1682 lines
72 KiB
HTML
1682 lines
72 KiB
HTML
<!DOCTYPE html>
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<html xmlns="http://www.w3.org/1999/xhtml" lang="en">
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<head>
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<meta charset="UTF-8"/>
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<meta http-equiv="X-UA-Compatible" content="IE=edge"/>
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<meta name="viewport" content="width=device-width, initial-scale=1.0"/>
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<meta name="generator" content="Asciidoctor 2.0.23"/>
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<title>My First Object Walk</title>
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<link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Open+Sans:300,300italic,400,400italic,600,600italic%7CNoto+Serif:400,400italic,700,700italic%7CDroid+Sans+Mono:400,700"/>
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<style>
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/*! Asciidoctor default stylesheet | MIT License | https://asciidoctor.org */
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/* Uncomment the following line when using as a custom stylesheet */
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</style>
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</head>
|
|
<body class="article">
|
|
<div id="header">
|
|
<h1>My First Object Walk</h1>
|
|
</div>
|
|
<div id="content">
|
|
<div class="sect1">
|
|
<h2 id="_whats_an_object_walk">What’s an Object Walk?</h2>
|
|
<div class="sectionbody">
|
|
<div class="paragraph">
|
|
<p>The object walk is a key concept in Git - this is the process that underpins
|
|
operations like object transfer and fsck. Beginning from a given commit, the
|
|
list of objects is found by walking parent relationships between commits (commit
|
|
X based on commit W) and containment relationships between objects (tree Y is
|
|
contained within commit X, and blob Z is located within tree Y, giving our
|
|
working tree for commit X something like <code>y/z.txt</code>).</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>A related concept is the revision walk, which is focused on commit objects and
|
|
their parent relationships and does not delve into other object types. The
|
|
revision walk is used for operations like <code>git</code> <code>log</code>.</p>
|
|
</div>
|
|
<div class="sect2">
|
|
<h3 id="_related_reading">Related Reading</h3>
|
|
<div class="ulist">
|
|
<ul>
|
|
<li>
|
|
<p><code>Documentation/user-manual.adoc</code> under "Hacking Git" contains some coverage of
|
|
the revision walker in its various incarnations.</p>
|
|
</li>
|
|
<li>
|
|
<p><code>revision.h</code></p>
|
|
</li>
|
|
<li>
|
|
<p><a href="https://eagain.net/articles/git-for-computer-scientists/">Git for Computer Scientists</a>
|
|
gives a good overview of the types of objects in Git and what your object
|
|
walk is really describing.</p>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="sect1">
|
|
<h2 id="_setting_up">Setting Up</h2>
|
|
<div class="sectionbody">
|
|
<div class="paragraph">
|
|
<p>Create a new branch from <code>master</code>.</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>git checkout -b revwalk origin/master</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>We’ll put our fiddling into a new command. For fun, let’s name it <code>git</code> <code>walken</code>.
|
|
Open up a new file <code>builtin/walken.c</code> and set up the command handler:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>/*
|
|
* "git walken"
|
|
*
|
|
* Part of the "My First Object Walk" tutorial.
|
|
*/
|
|
|
|
#include "builtin.h"
|
|
#include "trace.h"
|
|
|
|
int cmd_walken(int argc, const char **argv, const char *prefix)
|
|
{
|
|
trace_printf(_("cmd_walken incoming...\n"));
|
|
return 0;
|
|
}</pre>
|
|
</div>
|
|
</div>
|
|
<div class="admonitionblock note">
|
|
<table>
|
|
<tr>
|
|
<td class="icon">
|
|
<div class="title">Note</div>
|
|
</td>
|
|
<td class="content">
|
|
<code>trace_printf</code>(), defined in <code>trace.h</code>, differs from <code>printf</code>() in
|
|
that it can be turned on or off at runtime. For the purposes of this
|
|
tutorial, we will write <code>walken</code> as though it is intended for use as
|
|
a "plumbing" command: that is, a command which is used primarily in
|
|
scripts, rather than interactively by humans (a "porcelain" command).
|
|
So we will send our debug output to <code>trace_printf</code>() instead.
|
|
When running, enable trace output by setting the environment variable <code>GIT_TRACE</code>.
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Add usage text and <code>-h</code> handling, like all subcommands should consistently do
|
|
(our test suite will notice and complain if you fail to do so).
|
|
We’ll need to include the <code>parse-options.h</code> header.</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>#include "parse-options.h"
|
|
|
|
...
|
|
|
|
int cmd_walken(int argc, const char **argv, const char *prefix)
|
|
{
|
|
const char * const walken_usage[] = {
|
|
N_("git walken"),
|
|
NULL,
|
|
};
|
|
struct option options[] = {
|
|
OPT_END()
|
|
};
|
|
|
|
argc = parse_options(argc, argv, prefix, options, walken_usage, 0);
|
|
|
|
...
|
|
}</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Also add the relevant line in <code>builtin.h</code> near <code>cmd_whatchanged</code>():</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>int cmd_walken(int argc, const char **argv, const char *prefix);</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Include the command in <code>git.c</code> in <code>commands</code>[] near the entry for <code>whatchanged</code>,
|
|
maintaining alphabetical ordering:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>{ "walken", cmd_walken, RUN_SETUP },</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Add it to the <code>Makefile</code> near the line for <code>builtin/worktree.o</code>:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>BUILTIN_OBJS += builtin/walken.o</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Build and test out your command, without forgetting to ensure the <code>DEVELOPER</code>
|
|
flag is set, and with <code>GIT_TRACE</code> enabled so the debug output can be seen:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>$ echo DEVELOPER=1 >>config.mak
|
|
$ make
|
|
$ GIT_TRACE=1 ./bin-wrappers/git walken</pre>
|
|
</div>
|
|
</div>
|
|
<div class="admonitionblock note">
|
|
<table>
|
|
<tr>
|
|
<td class="icon">
|
|
<div class="title">Note</div>
|
|
</td>
|
|
<td class="content">
|
|
For a more exhaustive overview of the new command process, take a look at
|
|
<code>Documentation/MyFirstContribution.adoc</code>.
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="admonitionblock note">
|
|
<table>
|
|
<tr>
|
|
<td class="icon">
|
|
<div class="title">Note</div>
|
|
</td>
|
|
<td class="content">
|
|
A reference implementation can be found at
|
|
<a href="https://github.com/nasamuffin/git/tree/revwalk" class="bare">https://github.com/nasamuffin/git/tree/revwalk</a>.
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="sect2">
|
|
<h3 id="_struct_rev_cmdline_info"><code>struct</code> <code>rev_cmdline_info</code></h3>
|
|
<div class="paragraph">
|
|
<p>The definition of <code>struct</code> <code>rev_cmdline_info</code> can be found in <code>revision.h</code>.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>This struct is contained within the <code>rev_info</code> struct and is used to reflect
|
|
parameters provided by the user over the CLI.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p><code>nr</code> represents the number of <code>rev_cmdline_entry</code> present in the array.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p><code>alloc</code> is used by the <code>ALLOC_GROW</code> macro. Check <code>alloc.h</code> - this variable is
|
|
used to track the allocated size of the list.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Per entry, we find:</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p><code>item</code> is the object provided upon which to base the object walk. Items in Git
|
|
can be blobs, trees, commits, or tags. (See <code>Documentation/gittutorial-2.adoc</code>.)</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p><code>name</code> is the object ID (OID) of the object - a hex string you may be familiar
|
|
with from using Git to organize your source in the past. Check the tutorial
|
|
mentioned above towards the top for a discussion of where the OID can come
|
|
from.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p><code>whence</code> indicates some information about what to do with the parents of the
|
|
specified object. We’ll explore this flag more later on; take a look at
|
|
<code>Documentation/revisions.adoc</code> to get an idea of what could set the <code>whence</code>
|
|
value.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p><code>flags</code> are used to hint the beginning of the revision walk and are the first
|
|
block under the #include`s <code>in</code> `revision.<code>h</code>. The most likely ones to be set in
|
|
the <code>rev_cmdline_info</code> are <code>UNINTERESTING</code> and <code>BOTTOM</code>, but these same flags
|
|
can be used during the walk, as well.</p>
|
|
</div>
|
|
</div>
|
|
<div class="sect2">
|
|
<h3 id="_struct_rev_info"><code>struct</code> <code>rev_info</code></h3>
|
|
<div class="paragraph">
|
|
<p>This one is quite a bit longer, and many fields are only used during the walk
|
|
by <code>revision.c</code> - not configuration options. Most of the configurable flags in
|
|
<code>struct</code> <code>rev_info</code> have a mirror in <code>Documentation/rev-list-options.adoc</code>. It’s a
|
|
good idea to take some time and read through that document.</p>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="sect1">
|
|
<h2 id="_basic_commit_walk">Basic Commit Walk</h2>
|
|
<div class="sectionbody">
|
|
<div class="paragraph">
|
|
<p>First, let’s see if we can replicate the output of <code>git</code> <code>log</code> <code>--oneline</code>. We’ll
|
|
refer back to the implementation frequently to discover norms when performing
|
|
an object walk of our own.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>To do so, we’ll first find all the commits, in order, which preceded the current
|
|
commit. We’ll extract the name and subject of the commit from each.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Ideally, we will also be able to find out which ones are currently at the tip of
|
|
various branches.</p>
|
|
</div>
|
|
<div class="sect2">
|
|
<h3 id="_setting_up_2">Setting Up</h3>
|
|
<div class="paragraph">
|
|
<p>Preparing for your object walk has some distinct stages.</p>
|
|
</div>
|
|
<div class="olist arabic">
|
|
<ol class="arabic">
|
|
<li>
|
|
<p>Perform default setup for this mode, and others which may be invoked.</p>
|
|
</li>
|
|
<li>
|
|
<p>Check configuration files for relevant settings.</p>
|
|
</li>
|
|
<li>
|
|
<p>Set up the <code>rev_info</code> struct.</p>
|
|
</li>
|
|
<li>
|
|
<p>Tweak the initialized <code>rev_info</code> to suit the current walk.</p>
|
|
</li>
|
|
<li>
|
|
<p>Prepare the <code>rev_info</code> for the walk.</p>
|
|
</li>
|
|
<li>
|
|
<p>Iterate over the objects, processing each one.</p>
|
|
</li>
|
|
</ol>
|
|
</div>
|
|
<div class="sect3">
|
|
<h4 id="_default_setups">Default Setups</h4>
|
|
<div class="paragraph">
|
|
<p>Before examining configuration files which may modify command behavior, set up
|
|
default state for switches or options your command may have. If your command
|
|
utilizes other Git components, ask them to set up their default states as well.
|
|
For instance, <code>git</code> <code>log</code> takes advantage of <code>grep</code> and <code>diff</code> functionality, so
|
|
its <code>init_log_defaults</code>() sets its own state (<code>decoration_style</code>) and asks
|
|
<code>grep</code> and <code>diff</code> to initialize themselves by calling each of their
|
|
initialization functions.</p>
|
|
</div>
|
|
</div>
|
|
<div class="sect3">
|
|
<h4 id="_configuring_from_gitconfig">Configuring From .<code>gitconfig</code></h4>
|
|
<div class="paragraph">
|
|
<p>Next, we should have a look at any relevant configuration settings (i.e.,
|
|
settings readable and settable from <code>git</code> <code>config</code>). This is done by providing a
|
|
callback to <code>git_config</code>(); within that callback, you can also invoke methods
|
|
from other components you may need that need to intercept these options. Your
|
|
callback will be invoked once per each configuration value which Git knows about
|
|
(global, local, worktree, etc.).</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Similarly to the default values, we don’t have anything to do here yet
|
|
ourselves; however, we should call <code>git_default_config</code>() if we aren’t calling
|
|
any other existing config callbacks.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Add a new function to <code>builtin/walken.c</code>.
|
|
We’ll also need to include the <code>config.h</code> header:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>#include "config.h"
|
|
|
|
...
|
|
|
|
static int git_walken_config(const char *var, const char *value,
|
|
const struct config_context *ctx, void *cb)
|
|
{
|
|
/*
|
|
* For now, we don't have any custom configuration, so fall back to
|
|
* the default config.
|
|
*/
|
|
return git_default_config(var, value, ctx, cb);
|
|
}</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Make sure to invoke <code>git_config</code>() with it in your <code>cmd_walken</code>():</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>int cmd_walken(int argc, const char **argv, const char *prefix)
|
|
{
|
|
...
|
|
|
|
git_config(git_walken_config, NULL);
|
|
|
|
...
|
|
}</pre>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="sect3">
|
|
<h4 id="_setting_up_rev_info">Setting Up <code>rev_info</code></h4>
|
|
<div class="paragraph">
|
|
<p>Now that we’ve gathered external configuration and options, it’s time to
|
|
initialize the <code>rev_info</code> object which we will use to perform the walk. This is
|
|
typically done by calling <code>repo_init_revisions</code>() with the repository you intend
|
|
to target, as well as the <code>prefix</code> argument of <code>cmd_walken</code> and your <code>rev_info</code>
|
|
struct.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Add the <code>struct</code> <code>rev_info</code> and the <code>repo_init_revisions</code>() call.
|
|
We’ll also need to include the <code>revision.h</code> header:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>#include "revision.h"
|
|
|
|
...
|
|
|
|
int cmd_walken(int argc, const char **argv, const char *prefix)
|
|
{
|
|
/* This can go wherever you like in your declarations.*/
|
|
struct rev_info rev;
|
|
...
|
|
|
|
/* This should go after the git_config() call. */
|
|
repo_init_revisions(the_repository, &rev, prefix);
|
|
|
|
...
|
|
}</pre>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="sect3">
|
|
<h4 id="_tweaking_rev_info_for_the_walk">Tweaking <code>rev_info</code> For the Walk</h4>
|
|
<div class="paragraph">
|
|
<p>We’re getting close, but we’re still not quite ready to go. Now that <code>rev</code> is
|
|
initialized, we can modify it to fit our needs. This is usually done within a
|
|
helper for clarity, so let’s add one:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>static void final_rev_info_setup(struct rev_info *rev)
|
|
{
|
|
/*
|
|
* We want to mimic the appearance of `git log --oneline`, so let's
|
|
* force oneline format.
|
|
*/
|
|
get_commit_format("oneline", rev);
|
|
|
|
/* Start our object walk at HEAD. */
|
|
add_head_to_pending(rev);
|
|
}</pre>
|
|
</div>
|
|
</div>
|
|
<div class="admonitionblock note">
|
|
<table>
|
|
<tr>
|
|
<td class="icon">
|
|
<div class="title">Note</div>
|
|
</td>
|
|
<td class="content">
|
|
<div class="paragraph">
|
|
<p>Instead of using the shorthand <code>add_head_to_pending</code>(), you could do
|
|
something like this:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre> struct setup_revision_opt opt;
|
|
|
|
memset(&opt, 0, sizeof(opt));
|
|
opt.def = "HEAD";
|
|
opt.revarg_opt = REVARG_COMMITTISH;
|
|
setup_revisions(argc, argv, rev, &opt);</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Using a <code>setup_revision_opt</code> gives you finer control over your walk’s starting
|
|
point.</p>
|
|
</div>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Then let’s invoke <code>final_rev_info_setup</code>() after the call to
|
|
<code>repo_init_revisions</code>():</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>int cmd_walken(int argc, const char **argv, const char *prefix)
|
|
{
|
|
...
|
|
|
|
final_rev_info_setup(&rev);
|
|
|
|
...
|
|
}</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Later, we may wish to add more arguments to <code>final_rev_info_setup</code>(). But for
|
|
now, this is all we need.</p>
|
|
</div>
|
|
</div>
|
|
<div class="sect3">
|
|
<h4 id="_preparing_rev_info_for_the_walk">Preparing <code>rev_info</code> For the Walk</h4>
|
|
<div class="paragraph">
|
|
<p>Now that <code>rev</code> is all initialized and configured, we’ve got one more setup step
|
|
before we get rolling. We can do this in a helper, which will both prepare the
|
|
<code>rev_info</code> for the walk, and perform the walk itself. Let’s start the helper
|
|
with the call to <code>prepare_revision_walk</code>(), which can return an error without
|
|
dying on its own:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>static void walken_commit_walk(struct rev_info *rev)
|
|
{
|
|
if (prepare_revision_walk(rev))
|
|
die(_("revision walk setup failed"));
|
|
}</pre>
|
|
</div>
|
|
</div>
|
|
<div class="admonitionblock note">
|
|
<table>
|
|
<tr>
|
|
<td class="icon">
|
|
<div class="title">Note</div>
|
|
</td>
|
|
<td class="content">
|
|
<code>die</code>() prints to <code>stderr</code> and exits the program. Since it will print to
|
|
<code>stderr</code> it’s likely to be seen by a human, so we will localize it.
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
</div>
|
|
<div class="sect3">
|
|
<h4 id="_performing_the_walk">Performing the Walk!</h4>
|
|
<div class="paragraph">
|
|
<p>Finally! We are ready to begin the walk itself. Now we can see that <code>rev_info</code>
|
|
can also be used as an iterator; we move to the next item in the walk by using
|
|
<code>get_revision</code>() repeatedly. Add the listed variable declarations at the top and
|
|
the walk loop below the <code>prepare_revision_walk</code>() call within your
|
|
<code>walken_commit_walk</code>():</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>#include "pretty.h"
|
|
|
|
...
|
|
|
|
static void walken_commit_walk(struct rev_info *rev)
|
|
{
|
|
struct commit *commit;
|
|
struct strbuf prettybuf = STRBUF_INIT;
|
|
|
|
...
|
|
|
|
while ((commit = get_revision(rev))) {
|
|
strbuf_reset(&prettybuf);
|
|
pp_commit_easy(CMIT_FMT_ONELINE, commit, &prettybuf);
|
|
puts(prettybuf.buf);
|
|
}
|
|
strbuf_release(&prettybuf);
|
|
}</pre>
|
|
</div>
|
|
</div>
|
|
<div class="admonitionblock note">
|
|
<table>
|
|
<tr>
|
|
<td class="icon">
|
|
<div class="title">Note</div>
|
|
</td>
|
|
<td class="content">
|
|
<code>puts</code>() prints a <code>char</code>* to <code>stdout</code>. Since this is the part of the
|
|
command we expect to be machine-parsed, we’re sending it directly to stdout.
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Give it a shot.</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>$ make
|
|
$ ./bin-wrappers/git walken</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>You should see all of the subject lines of all the commits in
|
|
your tree’s history, in order, ending with the initial commit, "Initial revision
|
|
of "git", the information manager from hell". Congratulations! You’ve written
|
|
your first revision walk. You can play with printing some additional fields
|
|
from each commit if you’re curious; have a look at the functions available in
|
|
<code>commit.h</code>.</p>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="sect2">
|
|
<h3 id="_adding_a_filter">Adding a Filter</h3>
|
|
<div class="paragraph">
|
|
<p>Next, let’s try to filter the commits we see based on their author. This is
|
|
equivalent to running <code>git</code> <code>log</code> <code>--author=</code><em><pattern></em>. We can add a filter by
|
|
modifying <code>rev_info.grep_filter</code>, which is a <code>struct</code> <code>grep_opt</code>.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>First some setup. Add <code>grep_config</code>() to <code>git_walken_config</code>():</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>static int git_walken_config(const char *var, const char *value,
|
|
const struct config_context *ctx, void *cb)
|
|
{
|
|
grep_config(var, value, ctx, cb);
|
|
return git_default_config(var, value, ctx, cb);
|
|
}</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Next, we can modify the <code>grep_filter</code>. This is done with convenience functions
|
|
found in <code>grep.h</code>. For fun, we’re filtering to only commits from folks using a
|
|
<code>gmail.com</code> email address - a not-very-precise guess at who may be working on
|
|
Git as a hobby. Since we’re checking the author, which is a specific line in the
|
|
header, we’ll use the <code>append_header_grep_pattern</code>() helper. We can use
|
|
the <code>enum</code> <code>grep_header_field</code> to indicate which part of the commit header we want
|
|
to search.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>In <code>final_rev_info_setup</code>(), add your filter line:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>static void final_rev_info_setup(int argc, const char **argv,
|
|
const char *prefix, struct rev_info *rev)
|
|
{
|
|
...
|
|
|
|
append_header_grep_pattern(&rev->grep_filter, GREP_HEADER_AUTHOR,
|
|
"gmail");
|
|
compile_grep_patterns(&rev->grep_filter);
|
|
|
|
...
|
|
}</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p><code>append_header_grep_pattern</code>() adds your new "gmail" pattern to <code>rev_info</code>, but
|
|
it won’t work unless we compile it with <code>compile_grep_patterns</code>().</p>
|
|
</div>
|
|
<div class="admonitionblock note">
|
|
<table>
|
|
<tr>
|
|
<td class="icon">
|
|
<div class="title">Note</div>
|
|
</td>
|
|
<td class="content">
|
|
If you are using <code>setup_revisions</code>() (for example, if you are passing a
|
|
<code>setup_revision_opt</code> instead of using <code>add_head_to_pending</code>()), you don’t need
|
|
to call <code>compile_grep_patterns</code>() because <code>setup_revisions</code>() calls it for you.
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="admonitionblock note">
|
|
<table>
|
|
<tr>
|
|
<td class="icon">
|
|
<div class="title">Note</div>
|
|
</td>
|
|
<td class="content">
|
|
We could add the same filter via the <code>append_grep_pattern</code>() helper if we
|
|
wanted to, but <code>append_header_grep_pattern</code>() adds the <code>enum</code> <code>grep_context</code> and
|
|
<code>enum</code> <code>grep_pat_token</code> for us.
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
</div>
|
|
<div class="sect2">
|
|
<h3 id="_changing_the_order">Changing the Order</h3>
|
|
<div class="paragraph">
|
|
<p>There are a few ways that we can change the order of the commits during a
|
|
revision walk. Firstly, we can use the <code>enum</code> <code>rev_sort_order</code> to choose from some
|
|
typical orderings.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p><code>topo_order</code> is the same as <code>git</code> <code>log</code> <code>--topo-order</code>: we avoid showing a parent
|
|
before all of its children have been shown, and we avoid mixing commits which
|
|
are in different lines of history. (<code>git</code> <code>help</code> <code>log</code>'s section on <code>--topo-order</code>
|
|
has a very nice diagram to illustrate this.)</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Let’s see what happens when we run with <code>REV_SORT_BY_COMMIT_DATE</code> as opposed to
|
|
<code>REV_SORT_BY_AUTHOR_DATE</code>. Add the following:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>static void final_rev_info_setup(int argc, const char **argv,
|
|
const char *prefix, struct rev_info *rev)
|
|
{
|
|
...
|
|
|
|
rev->topo_order = 1;
|
|
rev->sort_order = REV_SORT_BY_COMMIT_DATE;
|
|
|
|
...
|
|
}</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Let’s output this into a file so we can easily diff it with the walk sorted by
|
|
author date.</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>$ make
|
|
$ ./bin-wrappers/git walken > commit-date.txt</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Then, let’s sort by author date and run it again.</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>static void final_rev_info_setup(int argc, const char **argv,
|
|
const char *prefix, struct rev_info *rev)
|
|
{
|
|
...
|
|
|
|
rev->topo_order = 1;
|
|
rev->sort_order = REV_SORT_BY_AUTHOR_DATE;
|
|
|
|
...
|
|
}</pre>
|
|
</div>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>$ make
|
|
$ ./bin-wrappers/git walken > author-date.txt</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Finally, compare the two. This is a little less helpful without object names or
|
|
dates, but hopefully we get the idea.</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>$ diff -u commit-date.txt author-date.txt</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>This display indicates that commits can be reordered after they’re written, for
|
|
example with <code>git</code> <code>rebase</code>.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Let’s try one more reordering of commits. <code>rev_info</code> exposes a <code>reverse</code> flag.
|
|
Set that flag somewhere inside of <code>final_rev_info_setup</code>():</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>static void final_rev_info_setup(int argc, const char **argv, const char *prefix,
|
|
struct rev_info *rev)
|
|
{
|
|
...
|
|
|
|
rev->reverse = 1;
|
|
|
|
...
|
|
}</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Run your walk again and note the difference in order. (If you remove the grep
|
|
pattern, you should see the last commit this call gives you as your current
|
|
HEAD.)</p>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="sect1">
|
|
<h2 id="_basic_object_walk">Basic Object Walk</h2>
|
|
<div class="sectionbody">
|
|
<div class="paragraph">
|
|
<p>So far we’ve been walking only commits. But Git has more types of objects than
|
|
that! Let’s see if we can walk <em>all</em> objects, and find out some information
|
|
about each one.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>We can base our work on an example. <code>git</code> <code>pack-objects</code> prepares all kinds of
|
|
objects for packing into a bitmap or packfile. The work we are interested in
|
|
resides in <code>builtin/pack-objects.c:get_object_list</code>(); examination of that
|
|
function shows that the all-object walk is being performed by
|
|
<code>traverse_commit_list</code>() or <code>traverse_commit_list_filtered</code>(). Those two
|
|
functions reside in <code>list-objects.c</code>; examining the source shows that, despite
|
|
the name, these functions traverse all kinds of objects. Let’s have a look at
|
|
the arguments to <code>traverse_commit_list</code>().</p>
|
|
</div>
|
|
<div class="ulist">
|
|
<ul>
|
|
<li>
|
|
<p><code>struct</code> <code>rev_info</code> *revs: This is the <code>rev_info</code> used for the walk. If
|
|
its <code>filter</code> member is not <code>NULL</code>, then <code>filter</code> contains information for
|
|
how to filter the object list.</p>
|
|
</li>
|
|
<li>
|
|
<p><code>show_commit_fn</code> <code>show_commit</code>: A callback which will be used to handle each
|
|
individual commit object.</p>
|
|
</li>
|
|
<li>
|
|
<p><code>show_object_fn</code> <code>show_object</code>: A callback which will be used to handle each
|
|
non-commit object (so each blob, tree, or tag).</p>
|
|
</li>
|
|
<li>
|
|
<p><code>void</code> *show_data: A context buffer which is passed in turn to <code>show_commit</code>
|
|
and <code>show_object</code>.</p>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>In addition, <code>traverse_commit_list_filtered</code>() has an additional parameter:</p>
|
|
</div>
|
|
<div class="ulist">
|
|
<ul>
|
|
<li>
|
|
<p><code>struct</code> <code>oidset</code> *omitted: A linked-list of object IDs which the provided
|
|
filter caused to be omitted.</p>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>It looks like these methods use callbacks we provide instead of needing us
|
|
to call it repeatedly ourselves. Cool! Let’s add the callbacks first.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>For the sake of this tutorial, we’ll simply keep track of how many of each kind
|
|
of object we find. At file scope in <code>builtin/walken.c</code> add the following
|
|
tracking variables:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>static int commit_count;
|
|
static int tag_count;
|
|
static int blob_count;
|
|
static int tree_count;</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Commits are handled by a different callback than other objects; let’s do that
|
|
one first:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>static void walken_show_commit(struct commit *cmt, void *buf)
|
|
{
|
|
commit_count++;
|
|
}</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>The <code>cmt</code> argument is fairly self-explanatory. But it’s worth mentioning that
|
|
the <code>buf</code> argument is actually the context buffer that we can provide to the
|
|
traversal calls - <code>show_data</code>, which we mentioned a moment ago.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Since we have the <code>struct</code> <code>commit</code> object, we can look at all the same parts that
|
|
we looked at in our earlier commit-only walk. For the sake of this tutorial,
|
|
though, we’ll just increment the commit counter and move on.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>The callback for non-commits is a little different, as we’ll need to check
|
|
which kind of object we’re dealing with:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>static void walken_show_object(struct object *obj, const char *str, void *buf)
|
|
{
|
|
switch (obj->type) {
|
|
case OBJ_TREE:
|
|
tree_count++;
|
|
break;
|
|
case OBJ_BLOB:
|
|
blob_count++;
|
|
break;
|
|
case OBJ_TAG:
|
|
tag_count++;
|
|
break;
|
|
case OBJ_COMMIT:
|
|
BUG("unexpected commit object in walken_show_object\n");
|
|
default:
|
|
BUG("unexpected object type %s in walken_show_object\n",
|
|
type_name(obj->type));
|
|
}
|
|
}</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Again, <code>obj</code> is fairly self-explanatory, and we can guess that <code>buf</code> is the same
|
|
context pointer that <code>walken_show_commit</code>() receives: the <code>show_data</code> argument
|
|
to <code>traverse_commit_list</code>() and <code>traverse_commit_list_filtered</code>(). Finally,
|
|
<code>str</code> contains the name of the object, which ends up being something like
|
|
<code>foo.txt</code> (blob), <code>bar/baz</code> (tree), or <code>v1.2.3</code> (tag).</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>To help assure us that we aren’t double-counting commits, we’ll include some
|
|
complaining if a commit object is routed through our non-commit callback; we’ll
|
|
also complain if we see an invalid object type. Since those two cases should be
|
|
unreachable, and would only change in the event of a semantic change to the Git
|
|
codebase, we complain by using <code>BUG</code>() - which is a signal to a developer that
|
|
the change they made caused unintended consequences, and the rest of the
|
|
codebase needs to be updated to understand that change. <code>BUG</code>() is not intended
|
|
to be seen by the public, so it is not localized.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Our main object walk implementation is substantially different from our commit
|
|
walk implementation, so let’s make a new function to perform the object walk. We
|
|
can perform setup which is applicable to all objects here, too, to keep separate
|
|
from setup which is applicable to commit-only walks.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>We’ll start by enabling all types of objects in the <code>struct</code> <code>rev_info</code>. We’ll
|
|
also turn on <code>tree_blobs_in_commit_order</code>, which means that we will walk a
|
|
commit’s tree and everything it points to immediately after we find each commit,
|
|
as opposed to waiting for the end and walking through all trees after the commit
|
|
history has been discovered. With the appropriate settings configured, we are
|
|
ready to call <code>prepare_revision_walk</code>().</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>static void walken_object_walk(struct rev_info *rev)
|
|
{
|
|
rev->tree_objects = 1;
|
|
rev->blob_objects = 1;
|
|
rev->tag_objects = 1;
|
|
rev->tree_blobs_in_commit_order = 1;
|
|
|
|
if (prepare_revision_walk(rev))
|
|
die(_("revision walk setup failed"));
|
|
|
|
commit_count = 0;
|
|
tag_count = 0;
|
|
blob_count = 0;
|
|
tree_count = 0;</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Let’s start by calling just the unfiltered walk and reporting our counts.
|
|
Complete your implementation of <code>walken_object_walk</code>().
|
|
We’ll also need to include the <code>list-objects.h</code> header.</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>#include "list-objects.h"
|
|
|
|
...
|
|
|
|
traverse_commit_list(rev, walken_show_commit, walken_show_object, NULL);
|
|
|
|
printf("commits %d\nblobs %d\ntags %d\ntrees %d\n", commit_count,
|
|
blob_count, tag_count, tree_count);
|
|
}</pre>
|
|
</div>
|
|
</div>
|
|
<div class="admonitionblock note">
|
|
<table>
|
|
<tr>
|
|
<td class="icon">
|
|
<div class="title">Note</div>
|
|
</td>
|
|
<td class="content">
|
|
This output is intended to be machine-parsed. Therefore, we are not
|
|
sending it to <code>trace_printf</code>(), and we are not localizing it - we need scripts
|
|
to be able to count on the formatting to be exactly the way it is shown here.
|
|
If we were intending this output to be read by humans, we would need to localize
|
|
it with <code>_</code>().
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Finally, we’ll ask <code>cmd_walken</code>() to use the object walk instead. Discussing
|
|
command line options is out of scope for this tutorial, so we’ll just hardcode
|
|
a branch we can change at compile time. Where you call <code>final_rev_info_setup</code>()
|
|
and <code>walken_commit_walk</code>(), instead branch like so:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre> if (1) {
|
|
add_head_to_pending(&rev);
|
|
walken_object_walk(&rev);
|
|
} else {
|
|
final_rev_info_setup(argc, argv, prefix, &rev);
|
|
walken_commit_walk(&rev);
|
|
}</pre>
|
|
</div>
|
|
</div>
|
|
<div class="admonitionblock note">
|
|
<table>
|
|
<tr>
|
|
<td class="icon">
|
|
<div class="title">Note</div>
|
|
</td>
|
|
<td class="content">
|
|
For simplicity, we’ve avoided all the filters and sorts we applied in
|
|
<code>final_rev_info_setup</code>() and simply added <code>HEAD</code> to our pending queue. If you
|
|
want, you can certainly use the filters we added before by moving
|
|
<code>final_rev_info_setup</code>() out of the conditional and removing the call to
|
|
<code>add_head_to_pending</code>().
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Now we can try to run our command! It should take noticeably longer than the
|
|
commit walk, but an examination of the output will give you an idea why. Your
|
|
output should look similar to this example, but with different counts:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>Object walk completed. Found 55733 commits, 100274 blobs, 0 tags, and 104210 trees.</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>This makes sense. We have more trees than commits because the Git project has
|
|
lots of subdirectories which can change, plus at least one tree per commit. We
|
|
have no tags because we started on a commit (<code>HEAD</code>) and while tags can point to
|
|
commits, commits can’t point to tags.</p>
|
|
</div>
|
|
<div class="admonitionblock note">
|
|
<table>
|
|
<tr>
|
|
<td class="icon">
|
|
<div class="title">Note</div>
|
|
</td>
|
|
<td class="content">
|
|
You will have different counts when you run this yourself! The number of
|
|
objects grows along with the Git project.
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="sect2">
|
|
<h3 id="_adding_a_filter_2">Adding a Filter</h3>
|
|
<div class="paragraph">
|
|
<p>There are a handful of filters that we can apply to the object walk laid out in
|
|
<code>Documentation/rev-list-options.adoc</code>. These filters are typically useful for
|
|
operations such as creating packfiles or performing a partial clone. They are
|
|
defined in <code>list-objects-filter-options.h</code>. For the purposes of this tutorial we
|
|
will use the "tree:1" filter, which causes the walk to omit all trees and blobs
|
|
which are not directly referenced by commits reachable from the commit in
|
|
<code>pending</code> when the walk begins. (<code>pending</code> is the list of objects which need to
|
|
be traversed during a walk; you can imagine a breadth-first tree traversal to
|
|
help understand. In our case, that means we omit trees and blobs not directly
|
|
referenced by <code>HEAD</code> or <code>HEAD</code>'s history, because we begin the walk with only
|
|
<code>HEAD</code> in the <code>pending</code> list.)</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>For now, we are not going to track the omitted objects, so we’ll replace those
|
|
parameters with <code>NULL</code>. For the sake of simplicity, we’ll add a simple
|
|
build-time branch to use our filter or not. Preface the line calling
|
|
<code>traverse_commit_list</code>() with the following, which will remind us which kind of
|
|
walk we’ve just performed:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre> if (0) {
|
|
/* Unfiltered: */
|
|
trace_printf(_("Unfiltered object walk.\n"));
|
|
} else {
|
|
trace_printf(
|
|
_("Filtered object walk with filterspec 'tree:1'.\n"));
|
|
|
|
parse_list_objects_filter(&rev->filter, "tree:1");
|
|
}
|
|
traverse_commit_list(rev, walken_show_commit,
|
|
walken_show_object, NULL);</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>The <code>rev-</code>><code>filter</code> member is usually built directly from a command
|
|
line argument, so the module provides an easy way to build one from a string.
|
|
Even though we aren’t taking user input right now, we can still build one with
|
|
a hardcoded string using <code>parse_list_objects_filter</code>().</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>With the filter spec "tree:1", we are expecting to see <em>only</em> the root tree for
|
|
each commit; therefore, the tree object count should be less than or equal to
|
|
the number of commits. (For an example of why that’s true: <code>git</code> <code>commit</code> <code>--revert</code>
|
|
points to the same tree object as its grandparent.)</p>
|
|
</div>
|
|
</div>
|
|
<div class="sect2">
|
|
<h3 id="_counting_omitted_objects">Counting Omitted Objects</h3>
|
|
<div class="paragraph">
|
|
<p>We also have the capability to enumerate all objects which were omitted by a
|
|
filter, like with <code>git</code> <code>log</code> <code>--filter=</code><em><spec></em> <code>--filter-print-omitted</code>. To do this,
|
|
change <code>traverse_commit_list</code>() to <code>traverse_commit_list_filtered</code>(), which is
|
|
able to populate an <code>omitted</code> list. Asking for this list of filtered objects
|
|
may cause performance degradations, however, because in this case, despite
|
|
filtering objects, the possibly much larger set of all reachable objects must
|
|
be processed in order to populate that list.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>First, add the <code>struct</code> <code>oidset</code> and related items we will use to iterate it:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>#include "oidset.h"
|
|
|
|
...
|
|
|
|
static void walken_object_walk(
|
|
...
|
|
|
|
struct oidset omitted;
|
|
struct oidset_iter oit;
|
|
struct object_id *oid = NULL;
|
|
int omitted_count = 0;
|
|
oidset_init(&omitted, 0);
|
|
|
|
...</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Replace the call to <code>traverse_commit_list</code>() with
|
|
<code>traverse_commit_list_filtered</code>() and pass a pointer to the <code>omitted</code> oidset
|
|
defined and initialized above:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre> ...
|
|
|
|
traverse_commit_list_filtered(rev,
|
|
walken_show_commit, walken_show_object, NULL, &omitted);
|
|
|
|
...</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Then, after your traversal, the <code>oidset</code> traversal is pretty straightforward.
|
|
Count all the objects within and modify the print statement:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre> /* Count the omitted objects. */
|
|
oidset_iter_init(&omitted, &oit);
|
|
|
|
while ((oid = oidset_iter_next(&oit)))
|
|
omitted_count++;
|
|
|
|
printf("commits %d\nblobs %d\ntags %d\ntrees %d\nomitted %d\n",
|
|
commit_count, blob_count, tag_count, tree_count, omitted_count);</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>By running your walk with and without the filter, you should find that the total
|
|
object count in each case is identical. You can also time each invocation of
|
|
the <code>walken</code> subcommand, with and without <code>omitted</code> being passed in, to confirm
|
|
to yourself the runtime impact of tracking all omitted objects.</p>
|
|
</div>
|
|
</div>
|
|
<div class="sect2">
|
|
<h3 id="_changing_the_order_2">Changing the Order</h3>
|
|
<div class="paragraph">
|
|
<p>Finally, let’s demonstrate that you can also reorder walks of all objects, not
|
|
just walks of commits. First, we’ll make our handlers chattier - modify
|
|
<code>walken_show_commit</code>() and <code>walken_show_object</code>() to print the object as they
|
|
go:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>#include "hex.h"
|
|
|
|
...
|
|
|
|
static void walken_show_commit(struct commit *cmt, void *buf)
|
|
{
|
|
trace_printf("commit: %s\n", oid_to_hex(&cmt->object.oid));
|
|
commit_count++;
|
|
}
|
|
|
|
static void walken_show_object(struct object *obj, const char *str, void *buf)
|
|
{
|
|
trace_printf("%s: %s\n", type_name(obj->type), oid_to_hex(&obj->oid));
|
|
|
|
...
|
|
}</pre>
|
|
</div>
|
|
</div>
|
|
<div class="admonitionblock note">
|
|
<table>
|
|
<tr>
|
|
<td class="icon">
|
|
<div class="title">Note</div>
|
|
</td>
|
|
<td class="content">
|
|
Since we will be examining this output directly as humans, we’ll use
|
|
<code>trace_printf</code>() here. Additionally, since this change introduces a significant
|
|
number of printed lines, using <code>trace_printf</code>() will allow us to easily silence
|
|
those lines without having to recompile.
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>(Leave the counter increment logic in place.)</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>With only that change, run again (but save yourself some scrollback):</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>$ GIT_TRACE=1 ./bin-wrappers/git walken 2>&1 | head -n 10</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Take a look at the top commit with <code>git</code> <code>show</code> and the object ID you printed; it
|
|
should be the same as the output of <code>git</code> <code>show</code> <code>HEAD</code>.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Next, let’s change a setting on our <code>struct</code> <code>rev_info</code> within
|
|
<code>walken_object_walk</code>(). Find where you’re changing the other settings on <code>rev</code>,
|
|
such as <code>rev-</code>><code>tree_objects</code> and <code>rev-</code>><code>tree_blobs_in_commit_order</code>, and add the
|
|
<code>reverse</code> setting at the bottom:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre> ...
|
|
|
|
rev->tree_objects = 1;
|
|
rev->blob_objects = 1;
|
|
rev->tag_objects = 1;
|
|
rev->tree_blobs_in_commit_order = 1;
|
|
rev->reverse = 1;
|
|
|
|
...</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Now, run again, but this time, let’s grab the last handful of objects instead
|
|
of the first handful:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre>$ make
|
|
$ GIT_TRACE=1 ./bin-wrappers/git walken 2>&1 | tail -n 10</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>The last commit object given should have the same OID as the one we saw at the
|
|
top before, and running <code>git</code> <code>show</code> <em><oid></em> with that OID should give you again
|
|
the same results as <code>git</code> <code>show</code> <code>HEAD</code>. Furthermore, if you run and examine the
|
|
first ten lines again (with <code>head</code> instead of <code>tail</code> like we did before applying
|
|
the <code>reverse</code> setting), you should see that now the first commit printed is the
|
|
initial commit, <code>e83c5163</code>.</p>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="sect1">
|
|
<h2 id="_wrapping_up">Wrapping Up</h2>
|
|
<div class="sectionbody">
|
|
<div class="paragraph">
|
|
<p>Let’s review. In this tutorial, we:</p>
|
|
</div>
|
|
<div class="ulist">
|
|
<ul>
|
|
<li>
|
|
<p>Built a commit walk from the ground up</p>
|
|
</li>
|
|
<li>
|
|
<p>Enabled a grep filter for that commit walk</p>
|
|
</li>
|
|
<li>
|
|
<p>Changed the sort order of that filtered commit walk</p>
|
|
</li>
|
|
<li>
|
|
<p>Built an object walk (tags, commits, trees, and blobs) from the ground up</p>
|
|
</li>
|
|
<li>
|
|
<p>Learned how to add a filter-spec to an object walk</p>
|
|
</li>
|
|
<li>
|
|
<p>Changed the display order of the filtered object walk</p>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div id="footer">
|
|
<div id="footer-text">
|
|
Last updated 2025-03-17 07:09:38 UTC
|
|
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|
|
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|
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|
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