D4314: setdiscovery: use a revset instead of dagutil.descendantset()

[yuja (Yuya Nishihara)]

yuja added a comment.


  >   @yuja: I thought I'd draw your attention to the potential revset parser bug detailed in the commit message
  
  `x :: - y ::` is ambiguous because `::` can be infix/postfix op, and `-` can
  be prefix/infix op. The infix `::` just wins as the parser only looks for the
  next token (1 look-ahead), and the expression is parsed as `(x :: (- y)) ::`,
  which is unfortunately valid.

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D4314

To: indygreg, #hg-reviewers
Cc: yuja, mercurial-devel