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Auto merge of #5562 - flip1995:clippyup_up, r=phansch

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Update contributing section about syncing Clippy

[Rendered](https://github.com/flip1995/rust-clippy/blob/clippyup_up/CONTRIBUTING.md#fixing-build-failures-caused-by-rust)

r? @oli-obk Did I get the sync process right?

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bors 2020-05-26 11:42:15 +00:00
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CONTRIBUTING.md
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@ -155,47 +155,77 @@ That's why the `else_if_without_else` example uses the `register_early_pass` fun
## Fixing build failures caused by Rust
Clippy will sometimes fail to build from source because building it depends on unstable internal Rust features. Most of
the times we have to adapt to the changes and only very rarely there's an actual bug in Rust. Fixing build failures
caused by Rust updates, can be a good way to learn about Rust internals.
Clippy currently gets built with `rustc` of the `rust-lang/rust` `master`
branch. Most of the times we have to adapt to the changes and only very rarely
there's an actual bug in Rust.
In order to find out why Clippy does not work properly with a new Rust commit, you can use the [rust-toolstate commit
history][toolstate_commit_history]. You will then have to look for the last commit that contains
`test-pass -> build-fail` or `test-pass -> test-fail` for the `clippy-driver` component.
[Here][toolstate_commit] is an example.
If you decide to make Clippy work again with a Rust commit that breaks it, you
have to sync the `rust-lang/rust-clippy` repository with the `subtree` copy of
Clippy in the `rust-lang/rust` repository.
The commit message contains a link to the PR. The PRs are usually small enough to discover the breaking API change and
if they are bigger, they likely include some discussion that may help you to fix Clippy.
For general information about `subtree`s in the Rust repository see [Rust's
`CONTRIBUTING.md`][subtree].
To check if Clippy is available for a specific target platform, you can check
the [rustup component history][rustup_component_history].
Here is a TL;DR version of the sync process (all of the following commands have
to be run inside the `rust` directory):
If you decide to make Clippy work again with a Rust commit that breaks it,
you probably want to install the latest Rust from master locally and run Clippy
using that version of Rust.
1. Clone the [`rust-lang/rust`] repository
2. 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.
You can set up the master toolchain by running `./setup-toolchain.sh`. That script will install
[rustup-toolchain-install-master][rtim] and master toolchain, then run `rustup override set master`.
_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
```
3. 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 [Discord] channel.)
4. 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
```
5. Open a PR to [`rust-lang/rust`]
After fixing the build failure on this repository, we can submit a pull request
to [`rust-lang/rust`] to fix the toolstate.
To submit a pull request, you should follow these steps:
Also, 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
# Assuming you already cloned the rust-lang/rust repo and you're in the correct directory
git submodule update --remote src/tools/clippy
cargo update -p clippy
git add -u
git commit -m "Update Clippy"
./x.py test -i --stage 1 src/tools/clippy # This is optional and should succeed anyway
# Open a PR in rust-lang/rust
# 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
```
[rustup_component_history]: https://rust-lang.github.io/rustup-components-history
[toolstate_commit_history]: https://github.com/rust-lang-nursery/rust-toolstate/commits/master
[toolstate_commit]: https://github.com/rust-lang-nursery/rust-toolstate/commit/aad74d8294e198a7cf8ac81a91aebb7f3bbcf727
[rtim]: https://github.com/kennytm/rustup-toolchain-install-master
You can then sync with the remote names from above, e.g.:
```bash
$ git subtree push -P src/tools/clippy clippy-local sync-from-rust
```
_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`. For
this to work, you will need the fix of `git subtree` available
[here][gitgitgadget-pr].
[gitgitgadget-pr]: https://github.com/gitgitgadget/git/pull/493
[subtree]: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#external-dependencies-subtree
[`rust-lang/rust`]: https://github.com/rust-lang/rust
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