Introduce a format flag for subcommands

[caspervonb]

Coverage, test, lint etc have different output formats, adding flags for each isn't scalable.
We should collapse these into a single enum selector, something along the lines of --format=<name> for 2.0.

Usage:

deno test --format=pretty # (default)
deno test --format=terse
deno test --format=json
deno coverage --format=pretty # (default)
deno coverage --format=lcov
deno coverage --format=json
deno lint --format=pretty # default
deno lint --format=json

[jaydenseric]

Presumably you're just referring to the formatting of the CLI stdout/stderr, and not the formatting of any files created in the filesystem by the command? The naming of this new flag must to be clear about which of these it applies to as there might need to also be a CLI flag for the latter, see:

denoland/deno_emit#53

[wojpawlik]

deno test --format=terse should look similarly to https://github.com/substack/faucet IMO.
deno test --format=tap would be nice to have.

[bartlomieju]

Discussed internally and decided on the following:

1. we add --format flag that accepts a value
2. for deno test we keep existing --reporter flag working (which is an alias for --format) in this particular case we want to keep showing the "reporter" flag, and hide the format flag
3. All existing "standalone flags" (eg. deno lint --compat) should still be supported and kept in the help output.

[EliphazBouye]

@bartlomieju this issue is still relevant ?