Build failure with Cargo workspaces

[gfx]

Version

$ fastly version
Fastly CLI version 0.19.0 (98cb4ff)
Built with go version unknown

What happened

Build failure with a project using Cargo workspaces.

A minimum project to reproduce this problem: https://github.com/fastly/ecp-workspace-example

You can see the following error messages by make build.

(cd app && fastly compute build)
✓ Initializing...
✓ Verifying package manifest...
✓ Verifying local rust toolchain...
✗ Building package using rust toolchain...

ERROR: copying wasm binary: cannot read source file: /Users/goro-fuji/ghq/github.com/fastly/ecp-workspace-example/app/target/wasm32-wasi/release/fastly-template-rust-default.wasm.

If you believe this error is the result of a bug, please file an issue: https://github.com/fastly/cli/issues/new?labels=bug&template=bug_report.md

I'm using Cargo workspaces to test the core logic in my local machine, but it seems that fastly compute build cannot recognize the workspace project.

Good news: cargo test -p core works! 🎉

[Integralist]

Thanks @gfx

We'll take a look into this and report back once we've identified the cause of the problem.

[pchickey]

The cli is currently looking for a target/ inside the package directory, and using cargo's workspaces feature breaks this assumption. Per @alexcrichton there are two ways to go about fixing this:

1. use cargo metadata --format-version 1 and parse out the target_directory field (e.g. | jq .target_directory). The downside is this can sometimes take ~100ms or so.
2. build with cargo build --message-format=json and parse the file paths out of the output.