Support EnforcedStyleForEmptyBraces for SpaceBeforeBlockBraces cop

[palkan]

I've started to integrate Rubocop into Puma development (puma/puma#1325) and found out that SpaceBeforeBlockBraces cannot handle empty braces differently (like, for example, SpaceInsideBlockBraces does).

There is a lot of code like this:

# I don't want this one to be an offense
conf = Rack::Handler::Puma.config(->{}, @options)

Although for non-empty blocks there is always a space before the block.

This PR adds EnforcedStyleForEmptyBraces configuration parameter for Layout/SpaceBeforeBlockBracescop to allow handle empty braces differently.

[rrosenblum]

It looks like you are missing setting a default value for EnforcedStyleForEmptyBraces. Based on the other usages, it looks like it should be set to no_space.

[palkan]

That was made intentionally to avoid breaking changes. I'd prefer to fallback to EnforcedStyle if EnforcedStyleForEmptyBraces is missing.

[bbatsov]

Shouldn't some of the existing tests go under this context?

[palkan]

We can put this context inside the 'EnforcedStyle' => 'space' one, for example.

We can event extract these example into a shared examples group and include it into 'EnforcedStyle' => 'space' (without explicit 'EnforcedStyleForEmptyBraces') and this context (with explicit 'EnforcedStyleForEmptyBraces').

[bbatsov]

Sounds reasonable.

[bbatsov]

Btw, it seems to me that this cop is not solving the problem it wants to. Doesn't the LambdaLiteral cop have support for this behavior? I don't see anything except lambda literals that would benefit from something like this...

[bbatsov]

Or not https://github.com/bbatsov/rubocop/blob/master/manual/cops_style.md#stylestabbylambdaparentheses

[palkan]

it seems to me that this cop is not solving the problem it wants to.

Sorry, don't understand what do you mean.

The problem I want to solve is to accept these two examples:

# no need of space before empty braces
fn = ->{}

# but always use space if lambda is not no-op
fn = -> { do_something }

Currently, I cannot achieve this with the SpaceBeforeBlockBraces cop, so I have to disable it (although I don't want to).

[bbatsov]

Yeah, I made a mistake I think.

Anyways, this has to be rebase on master - I see the changelog entry is in some weird place.

[palkan]

@bbatsov

this has to be rebase on master

Done. And green)