Verify fastly crate version during compute build.

[phamann]

TL;DR

Verifies that the fastly crate exists as a dependency and is up-to-date during fastly compute build. This allows us to ensure that the package program is compatible with the edge runtime environment at compilation time.

[acfoltzer]

This looks really nice! Unfortunately cargo update is not gonna be sufficient for our needs here 😞

[acfoltzer]

Looks good! I can't really comment on the Go style but the semantics look right to me 😂

[phamann]

@acfoltzer and I discussed this PR on slack, we realised that prompting a user to add fastly = "^0.3.2" to their Cargo.toml wasn't a sufficient fix as the lock file also need updating before the verification runs again. Therefore, we've now added a dual step remediation message in these cases. However if their current version is within the semver minor range of the latest, then only a cargo update -p fastly is needed, the logic now caters for these edge cases and serves the appropriate message. I've also added a more robust test suit to ensure this new logic is covered.

@peterbourgon When/If you have some spare time, I'd appreciate a quick review on this. Danke!

[peterbourgon]

Some nits but I grok it 👍

[peterbourgon]

Not a request for change, but I'm surprised this level of semantic version "parsing" is required by Verify...

[phamann]

Haha me too 😆