1469248 - Add a mach command to edit a vendored rust crate

Status: NEW

(Firefox Build System :: General, enhancement)

Description

[(not currently active) Ted Mielczarek]

bug 1323557 ensured that editing a vendored Rust crate in third_party/rust worked (with the right incantation in .cargo/config). We should add a mach command to make this simple.

bug 1323557 comment 30 explains what's necessary, which I will repeat here:
1) Ensure you have the latest version of cargo-vendor installed.
2) Add a section to .cargo/config like:
```
[patch.crates-io]
zip = { path = "third_party/rust/zip" }
```

We generate .cargo/config from a source file, so the mach command should edit the source file in-place so that pushing the change to try works:
https://dxr.mozilla.org/mozilla-central/source/.cargo/config.in

3) Run `mach vendor rust` to update Cargo.lock.

Comment 1

[Myk Melez [:myk] [@mykmelez]]

(In reply to Ted Mielczarek [:ted] [:ted.mielczarek] from comment #0)
> 2) Add a section to .cargo/config like:
> ```
> [patch.crates-io]
> zip = { path = "third_party/rust/zip" }
> ```

In bug 1323557 comment 30, I added this section to Cargo.toml (or rather added the patched crate's entry to the existing [patch.crates-io] section).  I don't  think Cargo observes [patch] sections in .cargo/config files (at least I don't see any documentation to that effect, nor was my attempt to add one successful).


> 3) Run `mach vendor rust` to update Cargo.lock.

This'll need to be `mach vendor rust --ignore-modified` (or you can commit the Cargo.toml change before vendoring, but then the first commit will leave the repo in an inconsistent state; better to commit the Cargo.toml and Cargo.lock changes together).

Comment 2

[Mike Hommey [:glandium]]

[patch.crates-io] can be added to top-level workspace Cargo.toml