unpack_strategy: allow unpacking .crate (as a gzipped tar)

[cho-m]

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Related to discussion in Homebrew/homebrew-core#166955 (comment)

Will need Homebrew/homebrew-core#167208 first to avoid breaking corresponding formula builds

[cho-m]

Need to think about this a bit more as Crate needs to be detected before Tar, but we don't want reverse also too for UnpackStrategy.from_magic(...).

Options:

• May need to add explicit check on extension inside Crate.can_extract?.
• Could just allow .crate extension inside Tar instead. Simplest change as it only adds extra string to unpack_strategy/tar.rb.

[Bo98]

• Could just allow .crate extension inside Tar instead. Simplest change as it only adds extra string to unpack_strategy/tar.rb.

If .crate is just a renamed .tar.gz then it makes sense to do this.

[cho-m]

If .crate is just a renamed .tar.gz then it makes sense to do this.

Currently it is though there is no documentation guaranteeing it. Assuming Rust doesn't switch to some obscure/specialized format, shouldn't be too difficult to maintain.

https://github.com/rust-lang/cargo/blob/0.78.0/src/cargo/ops/cargo_package.rs#L689-L694

[carlocab]

Currently it is though there is no documentation guaranteeing it.

I think we can assume it is for now and then deal with it if/when things break.

Perhaps leave a comment mentioning that we make an assumption based on undocumented behaviour of cargo.

[Bo98]

While it is an implementation detail, realistically a change to the format would likely break older cargo versions without branching off the API to download it.

And if it did break in-place, we would still have to adjust anyway if it was a separate strategy.

[MikeMcQuaid]

I think we can assume it is for now and then deal with it if/when things break.

Agreed 👍🏻

[MikeMcQuaid]

Makes sense to me, thanks again @cho-m!

[cho-m]

May still need Homebrew/homebrew-core#167208 beforehand for existing usage.

And then need to follow up to drop the nounzip and remove system "tar", ... during install.