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Document josh subtrees and update subtree repository list #2182

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Document josh subtrees and update subtree repository list
Kobzol Dec 30, 2024
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Kobzol Dec 30, 2024
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30 changes: 21 additions & 9 deletions src/external-repos.md
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Expand Up @@ -3,24 +3,22 @@
The `rust-lang/rust` git repository depends on several other repos in the `rust-lang` organization.
There are three main ways we use dependencies:
1. As a Cargo dependency through crates.io (e.g. `rustc-rayon`)
2. As a git subtree (e.g. `clippy`)
2. As a git (e.g. `clippy`) or a [josh][josh] (e.g. `miri`) subtree
3. As a git submodule (e.g. `cargo`)

As a general rule, use crates.io for libraries that could be useful for others in the ecosystem; use
subtrees for tools that depend on compiler internals and need to be updated if there are breaking
changes; and use submodules for tools that are independent of the compiler.

## External Dependencies (subtree)
## External Dependencies (subtrees)

As a developer to this repository, you don't have to treat the following external projects
differently from other crates that are directly in this repo:
The following external projects are managed using some form of a `subtree`:

* [Clippy](https://github.com/rust-lang/rust-clippy)
* [Miri]
* [clippy](https://github.com/rust-lang/rust-clippy)
* [miri](https://github.com/rust-lang/miri)
* [rustfmt](https://github.com/rust-lang/rustfmt)
* [rust-analyzer](https://github.com/rust-lang/rust-analyzer)

[Miri]: https://github.com/rust-lang/miri
* [rustc_codegen_cranelift](https://github.com/rust-lang/rustc_codegen_cranelift)

In contrast to `submodule` dependencies
(see below for those), the `subtree` dependencies are just regular files and directories which can
Expand All @@ -29,6 +27,20 @@ to these tools should be filed against the tools directly in their respective
upstream repositories. The exception is that when rustc changes are required to
implement a new tool feature or test, that should happen in one collective rustc PR.

`subtree` dependencies are currently managed by two distinct approaches:

* Using `git subtree`
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portable-simd also uses this; it seems to be entirely missing from this list?

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The list was incomplete before, I added a few entries, but since there was no global list before that, I didn't notice portable-simd. Good catch! Added it in #2214.

* `clippy` ([sync guide](https://doc.rust-lang.org/nightly/clippy/development/infrastructure/sync.html#performing-the-sync-from-rust-langrust-to-clippy))
* `rustfmt`
* `rustc_codegen_cranelift` ([sync script](https://github.com/rust-lang/rustc_codegen_cranelift/blob/113af154d459e41b3dc2c5d7d878e3d3a8f33c69/scripts/rustup.sh#L7))
* Using the [josh][josh] tool
* `miri` ([sync guide](https://github.com/rust-lang/miri/blob/master/CONTRIBUTING.md#advanced-topic-syncing-with-the-rustc-repo))
* `rust-analyzer` ([sync script](https://github.com/rust-lang/rust-analyzer/blob/2e13684be123eca7181aa48e043e185d8044a84a/xtask/src/release.rs#L147))

The [josh][josh] tool is an alternative to git subtrees, which manages git history in a different way and scales better to larger repositories. Specific tooling is required to work with josh, you can check out the `miri` or `rust-analyzer` scripts linked above for inspiration. If you want to migrate a subtree from `git subtree` to josh, you can check out [this guide](https://hackmd.io/7pOuxnkdQDaL1Y1FQr65xg).

Below you can find a guide on how to perform push and pull synchronization with the main rustc repo using `git subtree`, although these instructions might differ repo from repo.

### Synchronizing a subtree

Periodically the changes made to subtree based dependencies need to be synchronized between this
Expand Down Expand Up @@ -84,7 +96,6 @@ Now you're done, the `src/tools/clippy` directory behaves as if Clippy were
part of the rustc monorepo, so no one but you (or others that synchronize
subtrees) actually needs to use `git subtree`.


## External Dependencies (submodules)

Building Rust will also use external git repositories tracked using [git
Expand All @@ -111,3 +122,4 @@ the week leading up to the beta cut.
[The Rust Reference]: https://github.com/rust-lang/reference/
[toolstate website]: https://rust-lang-nursery.github.io/rust-toolstate/
[Toolstate chapter]: https://forge.rust-lang.org/infra/toolstate.html
[josh]: https://josh-project.github.io/josh/intro.html
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