Update Gerrit instructions

As JJ now supports Gerrit out of the box there is no longer need to
configure aliases.
The depot_tool example was also quite specific and not necessarily
something every Gerrit user would know about.

Update Gerrit guide to leverage the new jj gerrit upload command and
simplify the whole Gerrit experience.

Author: DanieleSassoli

src/sharing-code/gerrit.md

@@ -2,106 +2,41 @@
 
 The Gerrit-based workflow prefers small commits that get reviewed individually,
 as "changelists" (CLs). `jj` is well suited for this workflow: each `jj` change
-can be a single CL which you can update over time.
+can be a single CL which you can update over time. Each new update to a change
+is tracked as a new patchset, this will allow you to see how a
+change evolved over time directly in the UI.
 
 ## Change IDs
 
 Similar to `jj`'s change IDs, Gerrit associates commits with a common "change"
-using a `Change-Id` header in the commits. Gerrit repositories typically use a
-Git commit hook to add change IDs to commits, you can configure `jj` to do the
-same with this configuration:
-
-```toml
-[templates]
-commit_trailers = '''
-if(self.author().email() == "YOUR_EMAIL_HERE" &&
-  !trailers.contains_key("Change-Id"),
-  format_gerrit_change_id_trailer(self)
-)
-```
-
+using a `Change-Id` footer in the commits. When using the `jj gerrit upload`
+command, the footer is added automatically to all commits in the revset that
+don't already have one.
 
 ## Push workflow
 
 In a traditional Gerrit workflow, you push commits to the review server using
 `git push origin <rev>:refs/for/main`.
 
-Repositories using `depot_tools` will likely teach you about the `git cl upload`
-workflow instead: which by default will only push from a named, checked-out
-branch, and will squash all commits into a single change upstream
-(overrideable with `--no-squash`).
-
-
-If working with `jj`, it is convenient for a single `jj` change to be a single
-Gerrit change. `jj` also likes to keep the repository in "detached HEAD" mode,
-so `git cl upload` needs a `git checkout <branchname>` first to work. As such,
-`git cl upload` is not the best way to interact with a `jj` repository.
-
-Regardless of whether or not you are using `depot_tools`, `jj` works best with
-Gerrit when you build on top of the `refs/for/main` primitive.
-
+JJ support this workflow natively thanks to the `jj gerrit upload` command.
+With this command you can upload revsets to Gerrit directly, if a JJ change is
+missing the change-id footer, the command will add it automatically. You can
+also modify the footer manually if you wish to associate a specific JJ change
+with an already existing Gerrit change.
 
-The following alias makes uploading to Gerrit with `jj` convenient:
+If you want to triple check which commits will be modified and pushed with this
+command you can run `jj gerrit upload -r <revset> --remote-branch <branch-name> --dry-run`
 
-```toml
-[aliases]
-cl-up = ["util", "exec", "--", "bash", "-c", """
-set -euo pipefail
-INPUT=${1:-"@-"}
-HASH=$(jj log -r "${INPUT}" -T commit_id --no-graph)
-HASHINFO=$(git log -n 1 ${HASH} --oneline --color=always)
-echo "Pushing from commit ${HASHINFO}"
-git push origin "${HASH}":refs/for/main
-""", ""]
-```
+### Remote branch selection
 
-`jj cl-up <rev>` will push `<rev>` (`@-` if not specified) and its ancestors to
-`origin`, creating new CLs if necessary, updating existing ones otherwise.
+When using `jj gerrit upload` you can either have a default remote branch
+selected or overwrite it with each upload.
 
-Its output will look something like this:
+To configure a default remote branch please run:
+`jj config set --user gerrit.default-remote-branch <branch name>`
 
-```console
-$ jj
-@  wtzvnrmz [email protected] 2025-06-18 18:29:08 f694f9f1
-│  (empty) (no description set)
-○  zqlxpsus [email protected] 2025-06-18 18:29:08 git_head() 556b213a
-│  [temporal] Add Add/Subtract to all Temporal types
-│ ○  rnnrzqpt [email protected] 2025-06-18 18:29:08 8d16e5e5
-├─╯  [temporal] Add remaining .with() methods
-○  slwvqnrr [email protected] 2025-06-18 18:28:52 e68229d4
-│  [temporal] Add `wrapped_rust()` helper for writing generic code
-│ ○  vtszmlsx [email protected] 2025-06-18 18:25:38 c14b9e56
-├─╯  [temporal] Add PlainTime.{compare, with}
-○  xrvwxply [email protected] 2025-06-18 18:24:28 f4ac4ff7
-│  [temporal] Add IsPartialTemporalObject
-│ ○  tlmqwnpn [email protected] 2025-06-18 17:02:40 df3c2fa5
-├─╯  Fix comment about enable_rust
-◆  ytnpqlum [email protected] 2025-06-18 16:38:37 main@origin 1f5d17d2
-│  [temporal] Add GetTemporalRelativeToOption, use it
-~
+while if you want to change it for a specific push you can do:
+`jj gerrit upload -r <revset> --remote-branch <branch-name>`
 
-$ jj cl-up
-Pushing from commit 556b213a122 [temporal] Add Add/Subtract to all Temporal types
-Enumerating objects: 16, done.
-Counting objects: 100% (16/16), done.
-Delta compression using up to 14 threads
-Compressing objects: 100% (11/11), done.
-Writing objects: 100% (11/11), 2.77 KiB | 61.00 KiB/s, done.
-Total 11 (delta 9), reused 0 (delta 0), pack-reused 0 (from 0)
-remote: Resolving deltas: 100% (9/9)
-remote: Waiting for private key checker: 3/3 objects left
-remote: Processing changes: refs: 1, new: 1, updated: 1, done    
-remote: 
-remote: SUCCESS
-remote: 
-remote:   https://chromium-review.googlesource.com/c/v8/v8/+/6654560 [temporal] Add `wrapped_rust()` helper for writing generic code [NEW]
-remote:   https://chromium-review.googlesource.com/c/v8/v8/+/6653151 [temporal] Add Add/Subtract to all Temporal types
-remote: 
-To sso://chromium/v8/v8.git
- * [new reference]           556b213a122d5a0dad5bdd5dd0a1485a303e9ea1 -> refs/for/main
-```
 
-Here, it pushed commits `zqlxpsus` and `slwvqnrr`, creating/updating changes for
-them. Change `xrvwxply` was also in the history but not pushed since it was
-already up to date upstream. Other changes were not pushed since they were not ancestors of `@`.