Rust plugin: rewrite the Rust plugin for core20

[liushuyu]

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This pull request migrates the Rust plugin to the new plugin system and also makes it more intelligent.

Three new options have been added:

• One option for enabling LTO (more optimized binary)
• One option for specifying Rust toolchain channel/version
• One option for disabling default features in the Rust crate

[liushuyu]

Ready for review.

[cmatsuoka]

It seems that this plugin can be added to https://github.com/canonical/craft-parts/ instead.

[codecov-commenter]

Codecov Report

Merging #4297 (20d2494) into main (dc58181) will decrease coverage by 0.07%.
The diff coverage is 64.70%.

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@@            Coverage Diff             @@
##             main    #4297      +/-   ##
==========================================
- Coverage   89.18%   89.11%   -0.07%     
==========================================
  Files         318      318              
  Lines       21125    21165      +40     
==========================================
+ Hits        18840    18862      +22     
- Misses       2285     2303      +18     

Files Changed	Coverage Δ
snapcraft_legacy/plugins/v2/rust.py	69.84% <64.70%> (-25.82%)	⬇️

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[cmatsuoka]

Closing this PR, we have canonical/craft-parts#530.

[liushuyu]

Rebased and re-targeted the pull request to do the core20 version of the plugin.

[liushuyu]

The tests should be fixed now.

[cmatsuoka]

@liushuyu We have some test errors

[liushuyu]

@liushuyu We have some test errors

I don't quite understand why the CI is testing the new plugin system in the legacy plugin tests.

[cmatsuoka]

I don't quite understand why the CI is testing the new plugin system in the legacy plugin tests.

V1 and V2 plugins are legacy, and the craft-parts plugins will be used for core22 only after updating to 1.25.1.

[liushuyu]

I don't quite understand why the CI is testing the new plugin system in the legacy plugin tests.

V1 and V2 plugins are legacy, and the craft-parts plugins will be used for core22 only after updating to 1.25.1.

I realized I had mocked the wrong function. I have fixed that now.

[cmatsuoka]

This follows the mechanics of the craft-parts plugin. It deviates a bit from the regular v2 plugin which generally have less sophisticated possibilities regarding checking existing compilers, but in doing so it also reduces the impact in migrating to core22 or newer bases using the craft-parts plugin. We also need a spread test exercising rust part building using both V2 and craft-parts plugin. @liushuyu could you add such testing upon upgrading craft-parts to 1.25.1? @mr-cal, @sergiusens, any thoughts?

[mr-cal]

Agreed, I think adding a spread test after craft-parts is upgraded is a good plan.

[liushuyu]

Rebased against the latest main branch.

[mr-cal]

Thanks!