Translate conditionals in in statements

[st0012]

Motivation

Closes #204

When investigating #204 I found that Parser's IfGuard and UnlessGuard are associated with these comments:

And I found that they're not handled by the current pattern translation yet. For example:

# pattern matching with if guards
case bar
in x if x == 1
  "in with if"
in a, b if b == 2
  "in with 2 args and if"
in c, d; c if c == 3
  "in with 2 args, semicolon, and if"
end

# pattern matching with unless guards
case baz
in x unless x == 1
  "in with unless"
in a, b unless b == 2
  "in with 2 args and unless"
in c, d; c unless c == 3
  "in with 2 args, semicolon, and unless"
end

So this PR adds support for those cases.

Test plan

See included automated tests.

[amomchilov]

Suggested change

	if (prismStatements->body.size != 1) {
	unreachable("In pattern-matching's `in` clause, a guard must have a single statement.");
	}
	ENFORCE(prismStatements->body.size == 1,
	"In pattern-matching's `in` clause, a guard must have a single statement.");

[amomchilov]

Enforcing this is good for now, but we'll eventually want to tolerate this error and report it as a syntax error.

This is the current Sorbet's parser behaviour:

  case quux
# ^^^^ error: unexpected token "case"
  in x if 1, 2
  end

Interestingly, the , 2 makes the case invalid, not the in or if. Removing that makes it parse correctly.

[st0012]

in x if 1, 2 in this case doesn't enter this check though because the conditional still only has one statement (x)?

[amomchilov]

Are you sure it's not the 1, 2? Maybe I'm misunderstanding.

[st0012]

Yes I'm sure because the prismStatements is referring to the statements under the IfNode, not the InNode:

case bar
in x if 1, 2
end

I will rename the variable to make that clearer.

[amomchilov]

LGTM, thanks for rebasing on my big changes!

Can you please open an issue for use to follow up and diagnose this correctly?

  case quux
# ^^^^ error: unexpected token "case"
  in x if 1, 2
  end

[amomchilov]

Are you sure it's not the 1, 2? Maybe I'm misunderstanding.

[st0012]

Added the issue here: #303

[amomchilov]

Forgot to approve, myb