tests/test-check-code-hg.t

branchmap: Save changectx creation during update

The newly introduced `branchmap` function allows us to skip the
creation of changectx objects. This speeds up the construction of
the branchmap.

On the mozilla repository (117293 changesets, 15490 mutable)

Before:
  ! impactable 19.9
  ! mutable 0.576
  ! unserved 3.16

After:
  ! impactable 7.03 (2.8x faster)
  ! mutable 0.352 (1.6x)
  ! unserved 1.15 (2.7x)

On the cpython repository (81418 changesets, 6418 mutable)

Before:
  ! impactable 15.9
  ! mutable 0.451
  ! unserved 0.861

After:
  ! impactable 6.55 (2.4x faster)
  ! mutable 0.170 (2.6x faster)
  ! unserved 0.289 (2.9x faster)

On the pypy repository (58852 changesets)

Before:
  ! impactable 13.6

After:
  ! impactable 6.17 (2.2x faster)

On my Mercurial repository (18295 changesets, 2210 mutable)

Before:
  ! impactable 23.9
  ! mutable 0.368
  ! unserved 0.057

After:
  ! impactable 1.31 (18x faster)
  ! mutable 0.042 (8.7x)
  ! unserved 0.025 (2.2x)

  $ check_code="$TESTDIR"/../contrib/check-code.py
  $ cd "$TESTDIR"/..
  $ if hg identify -q > /dev/null; then :
  > else
  >     echo "skipped: not a Mercurial working dir" >&2
  >     exit 80
  > fi

New errors are not allowed. Warnings are strongly discouraged.

  $ hg manifest | xargs "$check_code" --warnings --nolineno --per-file=0