proposal: cmd/go: generate add flag to fail fast

[tzachshabtay]

In our project we run go generate ./... on a big code-base, if there's an error go generate skips the package and carries on, only returning an error code at the end. This makes it hard to scroll through the mountain of logs to find the actual error.

It would be great if we had a fail fast flag, i.e something like go generate --fail-fast ./... that would stop on the first error it sees, to make it clear where the error is coming from (and also to save time).

[mvdan]

Worth noting that go test -failfast exists; see go help testflag. Though right now I can't remember if it works per-package, or across all packages being tested. The docs aren't clear.

[ianlancetaylor]

CC @bcmills @matloob