"spin up" should build when needed

[tshepang]

I forgot to first spin build, so I had this...

❯ spin up
Error: Cannot create module for component foo from file /home/tshepang/spin/foo/target/wasm32-wasi/release/foo.wasm

Caused by:
    0: failed to read input file
    1: No such file or directory (os error 2)
Error: exit status: 1

Not opening issue, for there could be a reason this does not happen automatically.

[radu-matei]

The main reason we don't currently have this implemented is because reliably understanding "when needed" is a bit difficult.

If the module source is not present, this would be straightforward, and we could run spin build.
But what should happen if the module is present? We could hash the entire directory and if anything changed, we would rebuild (we are exploring something similar for spin deploy, cc @michelleN)

Is that what you had in mind?

Thanks!

[tshepang]

One special case would be automatically building if .wasm is found to not exist.

Regarding hashing things, I was thinking that spin up could behave like cargo watch, and just rebuild when changes are detected (probably using something inotify). It could also have an option to disable that watcher behavior, in case some do not desire the magic.