jj/docs/tutorial.md

# Tutorial

This text assumes that the reader is familiar with Git.

## Preparation

If you haven't already, make sure you
[install and configure Jujutsu](../README.md#Installation).

## Cloning a Git repo

Let's start by cloning the Jujutsu Git repo using `jj`:
```shell script
# Note the "git" before "clone" (there is no support for cloning native jj
# repos yet)
$ jj git clone https://github.com/martinvonz/jj.git
Fetching into new repo in "<dir>/jj"
Working copy now at: 265ecf5cab2d (no description set)
Added 98 files, modified 0 files, removed 0 files
$ cd jj
```

Running `jj st` (short for`jj status`) now yields something like this:
```shell script
$ jj st
Parent commit: 723ebb380971 cleanup: restructure escaped newlines to make new rustc happy
Working copy : 265ecf5cab2d (no description set)
The working copy is clean
```

We can see from the output above that our working copy has a commit ID
(`265ecf5cab2d` in the example).

Let's check out a particular commit, so we get more predicable output:
```shell script
$ jj co 080a9b37ff7e
Working copy now at: 608c179a60df
Added 7 files, modified 65 files, removed 21 files
$ jj st
Parent commit: 080a9b37ff7e cli: make `jj st` show parent commit before working copy commit
Working copy : 608c179a60df (no description set)
The working copy is clean
```

You might have noticed that even though we asked to check out some commit
(`080a9b37ff7e`), our working-copy commit ended up being another commit
(`608c179a60df`). That is because `jj co` (short for `jj checkout`) creates a
new commit on top of the commit you asked it to check out. The new commit is for
the working-copy changes.

## Creating our first change

Now let's say we want to edit the `README.md` file in the repo to say that Jujutsu
is ready for use. Let's start by describing the change (adding a commit message)
so we don't forget what we're working on:
```shell script
# This will bring up $EDITOR (or `pico` by default). Enter something like
# "Jujutsu is ready!" in the editor and then close it.
$ jj describe
Working copy now at: b2985d68096d Jujutsu is ready!
```

Now make the change in the README:
```shell script
# Adjust as necessary for compatibility with your flavor of `sed`
$ sed -i 's/not ready/ready/' README.md
$ jj st
Parent commit: 080a9b37ff7e cli: make `jj st` show parent commit before working copy commit
Working copy : 5f80190c44b9 Jujutsu is ready!
Working copy changes:
M README.md
```
Note that you didn't have to tell Jujutsu to add the change like you would with
`git add`. You actually don't even need to tell it when you add new files or
remove existing files. To untrack a path, add it to your `.gitignore` and run
`jj untrack <path>`.

To see the diff, run `jj diff`:
```shell script
$ jj diff --git  # Feel free to skip the `--git` flag
diff --git a/README.md b/README.md
index aa9b9e31a8...c30897997c 100644
--- a/README.md
+++ b/README.md
@@ -4,7 +4,7 @@
 ## Disclaimer

 This is not a Google product. It is an experimental version-control system
-(VCS). It is not ready for use. It was written by me, Martin von Zweigbergk
+(VCS). It is ready for use. It was written by me, Martin von Zweigbergk
 (martinvonz@google.com). It is my personal hobby project. It does not indicate
 any commitment or direction from Google.

```
Jujutsu's diff format currently defaults to inline coloring of the diff (like
`git diff --color-words`), so we used `--git` above to make the diff visible in
this tutorial.

As you may have noticed, the working-copy commit's ID changed both when we
edited the description and when we edited the README. However, the parent commit
stayed the same. Each change to the working-copy commit amends the previous
version. So how do we tell Jujutsu that we are done amending the current change
and want to start working on a new one? That is what `jj new` is for. That will
create a new commit on top of your current working-copy commit. The new commit
is for the working-copy changes. That may remind you of what we said earlier
that `jj checkout` does; `jj checkout` is in fact practically a synonym for
`jj new` (you can specify a destination for `jj new` as well).

So, let's say we're now done with this change, so we create a new change:
```shell script
$ jj new
Working copy now at: 192b456b024b (no description set)
$ jj st
Parent commit: fb563a4c6d26 Jujutsu is ready!
Working copy : 192b456b024b (no description set)
The working copy is clean
```

If we later realize that we want to make further changes, we can make them
in the working copy and then run `jj squash`. That command squashes the changes
from a given commit into its parent commit. Like most commands, it acts on the
working-copy commit by default. Alternatively, we can use `jj edit <commit>` to
resume editing a commit in the working copy. Any further changes in the working
copy will then amend the commit. Whether you choose to checkout-and-squash or to
edit typically depends on how done you are with the change; if the change is
almost done, it makes sense to use `jj checkout` so you can easily review your
adjustments with `jj diff` before running `jj squash`. 

## The log command, "revsets", and aliases

You're probably familiar with `git log`. Jujutsu has very similar functionality
in its `jj log` command:
```shell script
$ jj log
@ f39aeb1a0200 martinvonz@google.com 2021-05-23 23:10:27.000 -07:00 192b456b024b
| (no description set)
o f63e76f175b9 martinvonz@google.com 2021-05-23 22:13:45.000 -07:00 fb563a4c6d26
| Jujutsu is ready!
o 6a91b4ba16c7 martinvonz@google.com 2021-05-23 22:08:37.000 -07:00 main 080a9b37ff7e
~ cli: make `jj st` show parent commit before working copy commit
```

The `@` indicates the working-copy commit. The first hash on a line is the
"change ID", which is an ID that follows the commit as it's rewritten (similar
to Gerrit's Change-Id). The second hash is the commit ID, which changes when you
rewrite the commit. You can give either hash to commands that take revisions as
arguments. We will generally prefer change IDs because they stay the same when
the commit is rewritten.

By default, `jj log` lists your local commits, with some remote commits added
for context.  The `~` indicates that the commit has parents that are not
included in the graph. We can use the `-r` flag to select a different set of
revisions to list. The flag accepts a ["revset"](revsets.md), which is an
expression in a simple language for specifying revisions. For example, `@`
refers to the working-copy commit, `root` refers to the root commit,
`branches()` refers to all commits pointed to by branches. We can combine
expressions with `|` for union, `&` for intersection and `~` for difference. For
example:
```shell script
$ jj log -r '@ | root | branches()'
@ f39aeb1a0200 martinvonz@google.com 2021-05-23 23:10:27.000 -07:00 192b456b024b
: (no description set)
o 6a91b4ba16c7 martinvonz@google.com 2021-05-23 22:08:37.000 -07:00 main 080a9b37ff7e
: cli: make `jj st` show parent commit before working copy commit
o 000000000000  1970-01-01 00:00:00.000 +00:00 000000000000
  (no description set)
```

The `000000000000` commit is a virtual commit that's called the "root commit".
It's the root commit of every repo. The `root` symbol in the revset matches it.

There are also operators for getting the parents (`foo-`), children (`foo+`),
ancestors (`:foo`), descendants (`foo:`), DAG range (`foo:bar`, like
`git log --ancestry-path`), range (`foo..bar`, same as Git's). There are also a
few more functions, such as `heads(<set>)`, which filters out revisions in the
input set if they're ancestors of other revisions in the set.

## Conflicts

Now let's see how Jujutsu deals with merge conflicts. We'll start by making some
commits:
```shell script
# Start creating a chain of commits off of the grandparent of the working copy
$ jj new @-- -m A; echo a > file1
Working copy now at: 9164f1d6a011 A
Added 0 files, modified 1 files, removed 0 files
$ jj new -m B1; echo b1 > file1
Working copy now at: 5be91b2b5b69 B1
$ jj new -m B2; echo b2 > file1
Working copy now at: fd571967346e B2
$ jj new -m C; echo c > file2
Working copy now at: 4ae1e0587eef C
$ jj log
@ 8e6178b84ffb martinvonz@google.com 2021-05-26 12:39:35.000 -07:00 1769bdaa8d6d
| C
o 5548374c0794 martinvonz@google.com 2021-05-26 12:39:30.000 -07:00 de5690380f40
| B2
o ce619d39bd96 martinvonz@google.com 2021-05-26 12:39:20.000 -07:00 47e336632333
| B1
o cf49e6bec410 martinvonz@google.com 2021-05-26 12:39:12.000 -07:00 661432c51c08
~ A
```

We now have a few commits, where A, B1, and B2 modify the same file, while C
modifies a different file. Let's now rebase B2 directly onto A:
```shell script
$ jj rebase -s 5548374c0794 -d cf49e6bec410
Rebased 2 commits
Working copy now at: 9195b6d2e8dc C
Added 0 files, modified 1 files, removed 0 files
$ jj log
@ 8e6178b84ffb martinvonz@google.com 2021-05-26 12:39:35.000 -07:00 66274d5a7d2d conflict
| C
o 5548374c0794 martinvonz@google.com 2021-05-26 12:39:30.000 -07:00 0c305a9e6b27 conflict
| B2
| o ce619d39bd96 martinvonz@google.com 2021-05-26 12:39:20.000 -07:00 47e336632333
|/  B1
o cf49e6bec410 martinvonz@google.com 2021-05-26 12:39:12.000 -07:00 661432c51c08
~ A
```

There are several things worth noting here. First, the `jj rebase` command said
"Rebased 2 commits". That's because we asked it to rebase commit B2 with the
`-s` option, which also rebases descendants (commit C in this case). Second,
because B2 modified the same file (and word) as B1, rebasing
it resulted in conflicts, as the `jj log` output indicates. Third, the conflicts
did not prevent the rebase from completing successfully, nor did it prevent C
from getting rebased on top.

Now let's resolve the conflict in B2. We'll do that by creating a new commit on
top of B2. Once we've resolved the conflict, we'll squash the conflict
resolution into the conflicted B2. That might look like this:
```shell script
$ jj new 5548374c0794  # Replace the hash by what you have for B2
Working copy now at: 619f58d8a988 (no description set)
Added 0 files, modified 1 files, removed 0 files
$ jj st
Parent commit: 5548374c0794 B2
Working copy : 619f58d8a988 (no description set)
The working copy is clean
There are unresolved conflicts at these paths:
file1
$ cat file1
<<<<<<<
%%%%%%%
-b1
+a
+++++++
b2
>>>>>>>
$ echo resolved > file1
$ jj squash
Rebased 1 descendant commits
Working copy now at: e659edc4a9fc (no description set)
$ jj log
@ 461f38324592 martinvonz@google.com 2021-05-26 12:53:08.000 -07:00 e659edc4a9fc
| (no description set)
| o 8e6178b84ffb martinvonz@google.com 2021-05-26 12:39:35.000 -07:00 69dbcf76642a
|/  C
o 5548374c0794 martinvonz@google.com 2021-05-26 12:39:30.000 -07:00 576d647acf36
| B2
| o ce619d39bd96 martinvonz@google.com 2021-05-26 12:39:20.000 -07:00 47e336632333
|/  B1
o cf49e6bec410 martinvonz@google.com 2021-05-26 12:39:12.000 -07:00 661432c51c08
~ A
```

Note that commit C automatically got rebased on top of the resolved B2, and that
C is also resolved (since it modified only a different file).

By the way, if we want to get rid of B1 now, we can run `jj abandon
47e336632333`. That will hide the commit from the log output and will rebase any
descendants to its parent.

## The operation log

Jujutsu keeps a record of all changes you've made to the repo in what's called
the "operation log". Use the `jj op` (short for `jj operation`) family of
commands to interact with it. To list the operations, use `jj op log`:
```shell script
$ jj op log
@ 5bd384507342 martinvonz@<hostname> 2021-05-26 12:53:08.339 -07:00 - 2021-05-26 12:53:08.350 -07:00
| squash commit 41f0d2289b568bfcdcf35f73d4f70f3ab6696398
| args: jj squash
o 2fd266a8a2e0 martinvonz@<hostname> 2021-05-26 12:53:08.335 -07:00 - 2021-05-26 12:53:08.338 -07:00
| commit working copy
o 1e6dd15305a3 martinvonz@<hostname> 2021-05-26 12:52:39.374 -07:00 - 2021-05-26 12:52:39.382 -07:00
| check out commit 0c305a9e6b274bc09b2bca85635299dcfdc6811c
| args: jj co 0c305a9e6b27
o 401652a2f61e martinvonz@<hostname> 2021-05-26 12:44:51.872 -07:00 - 2021-05-26 12:44:51.882 -07:00
| rebase commit de5690380f40f3f7fc6b7d66d43a4f68ee606228 and descendants
| args: jj rebase -s de5690380f40 -d 661432c51c08
[many more lines]
```

The most useful command is `jj undo` (alias for `jj op undo`), which will undo
an operation. By default, it will undo the most recent operation. Let's try it:
```shell script
$ jj undo
Working copy now at: 41f0d2289b56
$ jj log
@ b1e3a4afde5e martinvonz@google.com 2021-05-26 12:52:39.000 -07:00 41f0d2289b56
| (no description set)
| o 8e6178b84ffb martinvonz@google.com 2021-05-26 12:39:35.000 -07:00 66274d5a7d2d conflict
|/  C
o 5548374c0794 martinvonz@google.com 2021-05-26 12:39:30.000 -07:00 0c305a9e6b27 conflict
| B2
| o ce619d39bd96 martinvonz@google.com 2021-05-26 12:39:20.000 -07:00 47e336632333
|/  B1
o cf49e6bec410 martinvonz@google.com 2021-05-26 12:39:12.000 -07:00 661432c51c08
~ A
```
As you can perhaps see, that undid the `jj squash` invocation we used for
squashing the conflict resolution into commit B2 earlier. Notice that it also
updated the working copy.

You can also view the repo the way it looked after some earlier operation. For
example, if you want to see `jj log` output right after the `jj rebase` operation,
try `jj log --at-op=401652a2f61e` but use the hash from your own `jj op log`.

## Moving content changes between commits

You have already seen how `jj squash` can combine the changes from two commits
into one. There are several other commands for changing the contents of existing
commits. These commands assume that you have `meld` installed. If you prefer
`vimdiff`, add this to your `~/.jjconfig.toml` file:
```
[ui]
diff-editor = "vimdiff"
```

We'll need some more complex content to test these commands, so let's create a
few more commits:
```shell script
$ jj new origin/main -m abc; printf 'a\nb\nc\n' > file
Working copy now at: 61b0efa09dbe abc
Added 0 files, modified 0 files, removed 1 files
$ jj new -m ABC; printf 'A\nB\nc\n' > file
Working copy now at: 9d97c5018b23 ABC
$ jj new -m ABCD; printf 'A\nB\nC\nD\n' > file
Working copy now at: c5a985bc3f41 ABCD
$ jj log
@ 874f2d307594 martinvonz@google.com 2021-05-26 14:36:38.000 -07:00 687009839bae 
| ABCD
o 2bbc0c1eb382 martinvonz@google.com 2021-05-26 14:36:26.000 -07:00 ad9b1ce3b5d0 
| ABC
o 3680117711f5 martinvonz@google.com 2021-05-26 14:36:05.000 -07:00 a355fb177b21 
~ abc
```

We "forgot" to capitalize "c" in the second commit when we capitalized the other
letters. We then fixed that in the third commit when we also added "D". It would
be cleaner to move the capitalization of "c" into the second commit. We can do
that by running `jj squash -i` (short for `jj squash --interactive`) on the
third commit. Remember that `jj squash` moves all the changes from one commit
into its parent. `jj squash -i` moves only part of the changes into its parent.
Now try that:
```shell script
$ jj squash -i
Working copy now at: 4b4c714b36aa ABCD
```
That will bring up Meld with a diff of the changes in the "ABCD" commit. Modify
the right side of the diff to have the desired end state in "ABC" by removing
the "D" line. Then close Meld. If we look at the diff of the second commit, we
now see that all three lines got capitalized:
```shell script
$ jj diff -r @-
Modified regular file file:
   1    1: aA
   2    2: bB
   3    3: cC
```

The child change ("ABCD" in our case) will have the same content *state* after
the `jj squash` command. That means that you can move any changes you want into
the parent change, even if they touch the same word, and it won't cause any
conflicts.

Let's try one final command for changing the contents of an exiting commit. That
command is `jj diffedit`, which lets you edit the contents of a commit without
checking it out.
```shell script
$ jj diffedit -r @-
Created 2423c134ea70 ABC
Rebased 1 descendant commits
Working copy now at: d31c52e8ca41 ABCD
Added 0 files, modified 1 files, removed 0 files
```
When Meld starts, edit the right side by e.g. adding something to the first
line. Then close Meld. You can now inspect the rewritten commit with
`jj diff -r @-` again and you should see your addition to the first line.
Unlike `jj squash -i`, which left the content state of the commit unchanged,
`jj diffedit` (typically) results in a different state, which means that
descendant commits may have conflicts.

Other commands for rewriting contents of existing commits are `jj restore -i`,
`jj split`, `jj unsquash -i`. Now that you've seen how `jj squash -i` and
`jj diffedit` work, you can hopefully figure out how those work (with the help of
the instructions in the diff).