FormatOps: in one-arg-per-line, handle lbrace case

[kitbellew]

The scalafmt error described in #1599 turns out to be mainly due to the rule which formats multiple method arguments one per line. Router would attempt to format , { combination as a newline followed by the entire block on a single line, or a space without additional rules instead.

Two problems with this approach:

• because of some aspect of BestFirstSearch algorithm that I don't yet fully understand, having these two possible splits led to the search reaching a dead end before it attempted the space split
  • the expectation was that having additional splits could only lead to a search state exploded error, not this)
  • removing the newline split (leaving the space split only) solved the problem
• also, in cases when the space split was chosen, the result wasn't guaranteed to have one argument per line

Instead:

• force a newline for regular or partial functions
• for all other blocks, modify the space rule to force breaks after { and before }.

Fixes #1599.

scala-repos diffs: kitbellew/scala-repos@e2042d0?w=1

[kitbellew]

@olafurpg would appreciate some insight on the behaviour of BestFirstSearch algorithm. why would it stop searching when there are two splits for a given token, but not when one of them is removed? i had been under impression that more splits might potentially lead to explosion of search state, not to pruning of the search tree.

[kitbellew]

@olafurpg @tanishiking @poslegm PTAL