Add support for sccache

[idealseal]

This depends on projg2/shadowman#4 and a patched sccache ebuild.

It works exactly as the ccache implementation.

Docs are still missing. Maybe this can be combined with the ccache instructions?

[eli-schwartz]

Specifically, it depends on projg2/shadowman#4

[idealseal]

I'm thinking about how rust could be integrated: should we export RUSTC_WRAPPER and where would this happen? Should this happen in the eclasses?

[thesamesam]

Can you explain what this is useful for, given the build cache issue (it keys on the full path)? Are you really using it with live ebuilds enough for it to pay off?

[idealseal]

given the build cache issue (it keys on the full path)?

I've not thought about this at all. However I have flang live installed, so yes I could benefit from that.

Also I'd be interested to support rust packages, where I also have a couple of live packages installed. Not that it would matter a lot.

But I can see why this might not be worth the hassle.

[eli-schwartz]

I would personally be less concerned about "how often is it even used, and is it worth the hassle" and be more concerned about the exact opposite problem:

People will use it.

And it will be a bad thing that they use it. They will enable it because they think it sounds like a good thing and then they will suffer a pure loss due to the cache fullpath issue.

I'm strongly against merging sccache support in any form, unless it at least answers the question of how to make sure users have a fighting chance of understanding when it's a good idea vs when it's a bad idea. Mostly indifferent as long as that is handled.

One possibility of the top of my head is to make the FEATURES=sccache be ignored unless PROPERTIES=live is also set?

[mgorny]

Isn't the path issue specific to Rust?

[idealseal]

No that happens for all supported compilers

[idealseal]

One possibility of the top of my head is to make the FEATURES=sccache be ignored unless PROPERTIES=live is also set?

Might be worth the rename the feature flag as well to avoid confusion from the start