WASM support

[Byron]

The ability to compile to --target wasm32-unknown-unknown and wasm32-wasi. Here we track what's needed to make this happen as well as the progress thus far.

Note that this doesn't necessarily mean everything will work there - that's an entirely separate task

Tasks

• CI setup for compiling crates to WASM, to avoid regressions (--target wasm32-unknown-unknown seems like a good baseline)
• preliminary wasm32 support for git-pack #735
• Analysis - know what works and what doesn't

Crates that need the wasm feature toggle to compile

• git-diff
• git-pack

Crates to be fixed

Fixing them might move them up to the list of crates with the wasm feature toggle. Major crates to fix are git-sec and git-tempfile - with these more would probably run right away.

• git-config
• git-config-value
• git-credentials
• git-discover
• git-index
• git-lock
• git-prompt
• git-protocol (due to git-sec)
• git-ref
• git-sec
• git-tempfile
• git-transport (due to `git-sec
• git-url - home crate should be optional - it doesn't compile
• gix

Features of git-features that won't compile

And that's OK as wasm32 doesn't need the fastest implementation just yet.

• zlib-ng
• zlib-ng-compat
• zlib-stock

What to target

• look at this insightful comment which provides an idea on how WASM support could look like.

[dzmitry-lahoda]

you may consider support of no_std(it is the proper way to do wasm rather than just compile to target). afaik embedded and blockchain targets are no_std and these (wasm stems from being no_std

[dzmitry-lahoda]

on top of allowing in-browser ide to work better, this feature will allow more secure software release and dependency verifications. (there is usefull stuff to git in blockchain to verify gpg signatures. code oracle later when nix will be on chain, can verify whole build, for now just ci oracle would be good. ) just couple of words about future application.

[dzmitry-lahoda]

after no_std is done for core libs, can support wasi (os/fs interface of some no_std hosts). that is separate task.