+_Note:_ The first time running `git subtree push` a cache has to be built. This
+involves going through the complete Clippy history once. For this you have to
+increase the stack limit though, which you can do with `ulimit -s 60000`.
+Make sure to run the `ulimit` command from the same session you call git subtree.
+
+_Note:_ If you are a Debian user, `dash` is the shell used by default for scripts instead of `sh`.
+This shell has a hardcoded recursion limit set to 1000. In order to make this process work,
+you need to force the script to run `bash` instead. You can do this by editing the first
+line of the `git-subtree` script and changing `sh` to `bash`.
+
+### Performing the sync from [`rust-lang/rust`] to Clippy
+
+Here is a TL;DR version of the sync process (all of the following commands have
+to be run inside the `rust` directory):
+
+1. Clone the [`rust-lang/rust`] repository or make sure it is up to date.
+2. Checkout the commit from the latest available nightly. You can get it using `rustup check`.
+3. Sync the changes to the rust-copy of Clippy to your Clippy fork:
+ ```bash
+ # Make sure to change `your-github-name` to your github name in the following command
+ git subtree push -P src/tools/clippy git@github.com:your-github-name/rust-clippy sync-from-rust
+ ```
+
+ _Note:_ This will directly push to the remote repository. You can also push
+ to your local copy by replacing the remote address with `/path/to/rust-clippy`
+ directory.
+
+ _Note:_ Most of the time you have to create a merge commit in the
+ `rust-clippy` repo (this has to be done in the Clippy repo, not in the
+ rust-copy of Clippy):
+ ```bash
+ git fetch origin && git fetch upstream
+ git checkout sync-from-rust
+ git merge upstream/master
+ ```
+4. Open a PR to `rust-lang/rust-clippy` and wait for it to get merged (to
+ accelerate the process ping the `@rust-lang/clippy` team in your PR and/or
+ ~~annoy~~ ask them in the [Zulip] stream.)
+
+### Performing the sync from Clippy to [`rust-lang/rust`]
+
+All of the following commands have to be run inside the `rust` directory.
+
+1. Make sure Clippy itself is up-to-date by following the steps outlined in the previous
+section if necessary.
+
+2. Sync the `rust-lang/rust-clippy` master to the rust-copy of Clippy:
+ ```bash
+ git checkout -b sync-from-clippy
+ git subtree pull -P src/tools/clippy https://github.com/rust-lang/rust-clippy master
+ ```
+3. Open a PR to [`rust-lang/rust`]
+
+### Defining remotes
+
+You may want to define remotes, so you don't have to type out the remote
+addresses on every sync. You can do this with the following commands (these
+commands still have to be run inside the `rust` directory):
+
+```bash
+# Set clippy-upstream remote for pulls
+$ git remote add clippy-upstream https://github.com/rust-lang/rust-clippy
+# Make sure to not push to the upstream repo
+$ git remote set-url --push clippy-upstream DISABLED
+# Set clippy-origin remote to your fork for pushes
+$ git remote add clippy-origin git@github.com:your-github-name/rust-clippy
+# Set a local remote
+$ git remote add clippy-local /path/to/rust-clippy
+```