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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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27 changes: 20 additions & 7 deletions src/external-repos.md
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Expand Up @@ -3,24 +3,23 @@
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:
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That's not quite true, tools generally prefer PRs to their own repos when changes don't have to be done in lockstep with Rust compiler changes.

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This was pre-existing, but I agree it was confusing, I reworded it.


* [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 +28,20 @@ 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` directly
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Suggested change
* Using `git subtree` directly
* Using `git subtree`

There's no "indirect" usage so I find the additional qualifier confusing

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I wanted to distinguish "using subtrees via josh" and "using subtrees via git subtree", but the word was extraneous, I suppose. Removed it.

* `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. The differences between `git subtree` and josh are described [here](https://hackmd.io/7pOuxnkdQDaL1Y1FQr65xg). It requires specific tooling to work with josh, you can check out the `miri` or `rust-analyzer` scripts linked above for inspiration.

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 +97,6 @@ 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 +123,4 @@ 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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