D724: templater: extract shortest() logic from template function

[yuja (Yuya Nishihara)]

yuja added a comment.


  > \What I originally thought was `shortest` may have alternative implementation if the changelog is not backed by revlog (in the far far future).
  
  Okay, got it. Even if it's backed by revlog, shortest can be implemented as a one-pass
  lookup of prefix tree.

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D724

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