PHD: allow patched Crucible dependencies

[hawkw]

phd-runner uses the dependency on Crucible specified in the workspace's Cargo.toml to determine which downstairs artifact to download from Buildomat. This only works when the Crucible dependency is a Git dep on the oxidecomputer/crucible GitHub repo. In some cases, developers may patch Crucible to a local checkout or a different repository, such as for testing changes that haven't been merged to oxidecomputer/crucible. Unfortunately, the phd-runner build script fails in this case, which makes running any PHD tests impossible.

This is unfortunate. PHD tests can still be run when the Crucible dependency is patched, either by disabling the Crucible-based tests, or by manually providing a Crucible downstairs binary path. However, because the build script fails in this case, it's impossible to build phd-runner, which sucks. Instead, we should allow the build to succeed and just disable the --crucible-downstairs-commit auto CLI option when the dependency isn't pointed at the Crucible GitHub repo.

This commit does that. Now, we just log a warning and set the env var to a sentinel value that means we couldn't determine the SHA for auto mode. The phd-runner binary will then exit with an error if --crucible-downstairs-commit auto is selected when compiled without a known Git SHA.

To test this, I patched Crucible with a local checkout:

[patch."https://github.com/oxidecomputer/crucible"]
crucible = { path = "../crucible/upstairs" }
crucible-client-types = { path = "../crucible/crucible-client-types" }

Running cargo build -p phd-runner now succeeds:

eliza@theseus ~/Code/oxide/propolis $ cargo build -p phd-runner
     Locking 4 packages to latest compatible versions
      Adding crucible v0.0.1 (/home/eliza/Code/oxide/crucible/upstairs)
      Adding crucible-client-types v0.1.0 (/home/eliza/Code/oxide/crucible/crucible-client-types)
      Adding crucible-common v0.0.1 (/home/eliza/Code/oxide/crucible/common)
      Adding crucible-protocol v0.0.0 (/home/eliza/Code/oxide/crucible/protocol)
   Compiling propolis-client v0.1.0 (/home/eliza/Code/oxide/propolis/lib/propolis-client)
   Compiling phd-runner v0.1.0 (/home/eliza/Code/oxide/propolis/phd-tests/runner)
warning: phd-runner@0.1.0: Crucible dependency is patched with a local checkout, so the `--crucible-downstairs-commit auto` flag will be disabled in this PHD build
   Compiling phd-framework v0.1.0 (/home/eliza/Code/oxide/propolis/phd-tests/framework)
   Compiling phd-testcase v0.1.0 (/home/eliza/Code/oxide/propolis/phd-tests/testcase)
   Compiling phd-tests v0.1.0 (/home/eliza/Code/oxide/propolis/phd-tests/tests)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 11.63s

Fixes #770

[gjcolombo]

Off-the-wall idea here, but: is it possible to get cargo xtask phd to notice that the Crucible path has been patched and to build a downstairs binary from that path? We could then try to pipe it into a (separate) environment var and have --crucible-downstairs-commit auto try to pick that up: the git rev isn't valid, but I have a proposed path to a Crucible downstairs on the local machine, so let me try that instead.

If that's intractable for some reason (and I could totally believe it is, because e.g. we don't really know if the Crucible dep is local or we don't want to build other projects like that while building this one), then this LGTM as-is.

[gjcolombo]

If we can't or don't want to go the "try to infer where the binary should be based on the path to the checkout" route, perhaps this message (and/or the one in build.rs) should advertise the --crucible-downstairs-cmd option so that folks building a local Crucible know they can run PHD with it?

[hawkw]

Yeah, that's a good idea.

[hawkw]

It now says:

Error: Because Crucible dependency is patched with a local checkout, phd-runner's build script could not determine the Crucible Git SHA, so the `--crucible-downstairs-commit auto` option has been disabled. You can provide a local Crucible binary using `--crucible-downstairs-command`.

[hawkw]

Off-the-wall idea here, but: is it possible to get cargo xtask phd to notice that the Crucible path has been patched and to build a downstairs binary from that path? We could then try to pipe it into a (separate) environment var and have --crucible-downstairs-commit auto try to pick that up: the git rev isn't valid, but I have a proposed path to a Crucible downstairs on the local machine, so let me try that instead.

Hmm, that's a good idea, and I'm sure it's possible, although it might be a bit annoying. I have a slight preference for merging this change and then going and doing that, though, because the current state of the world is totally broken if you've patched Crucible, and I'd like cargo build to work sooner rather than later.

[gjcolombo]

The new message looks great--thanks for tweaking it!

[hawkw]

@gjcolombo I've opened #779 to track having cargo xtask phd build a downstairs if needed, that was a good idea!