cargo build doesn't always pick up changes in components/ crates

[fabricedesre]

STR:

• Do a full build with cargo build
• Introduce obvious syntax error in components/dnschallenge/mains.rs
• Run cargo build again.

Expected:

• We rebuild dnschallenge and foxbox.

Observed:

• We don't rebuild anything, so we have to run cargo clean first, and clobber the main foxbox crate.

I'm not sure if we can do everything we need in something driven by cargo or if we need to go the mach route like servo (that would make me a bit sad).

ping @JohanLorenzo @samgiles

[JohanLorenzo]

I think this is caused by build.rs not being called because cargo didn't notice a file has changed. It doesn't occur with a library stored under components/.

I think we can solve it by either a Makefile/mach or making dns_challenge both a library and a binary. This library would be declared in the root Cargo.toml so it can detect any of its changes. What do you think @samgiles ?

[fabricedesre]

Or we could maybe fix cargo to understand this kind of setup.

[julienw]

should be fixed by ecc92fa