Make rustfmt optional

[jyn514]

I got this error building console-api just now:

error: failed to run custom build command for `console-api v0.1.0`

Caused by:
  process didn't exit successfully: `/home/jnelson/work/redacted/target/debug/build/console-api-fe07466b9cc39039/build-script-build` (exit status: 1)
  --- stderr
  error: 'rustfmt' is not installed for the toolchain '1.58-x86_64-unknown-linux-gnu'
  To install, run `rustup component add rustfmt --toolchain 1.58-x86_64-unknown-linux-gnu`

Rustfmt shouldn't be strictly necessary for console to build - could you make the build script handle the error gracefully instead of raising a hard error?

[hawkw]

I believe we can do this by disabling the rustfmt feature flag on the tonic-build dependency.

[hawkw]

...huh, that's weird, it looks like the rustfmt feature is disabled, since we depend on tonic-build with default-features = false:

console/console-api/Cargo.toml

Lines 40 to 43 in 80d7f42

	[build-dependencies]
	tonic-build = { version = "0.6", default-features = false, features = [
	"prost",
	] }

[hawkw]

FWIW, it looks like tonic-build will completely drop the runtime rustfmt dependency in the next release: hyperium/tonic#904

[jyn514]

Ah, this is my fault, sorry - I had another dependency that depended on tonic-build and didn't disable the default features. Cargo unified the feature between the other dependency and console.