tests/test-mq-qimport-fail-cleanup.t

copies: filter out copies from non-existent source later in _chain()

_changesetforwardcopies() repeatedly calls _chain(). That is very
expensive because _chain() does lookups in the manifest. I hope to
split up the function in two parts: 1) simple chaining, not
considering end points, and 2) filter out files that don't exist in
the end points (and ping-pong copies/renames).

This patches gets us closer to that by moving the check for
non-existent source later in the function. Now there are no more
checks for "src" and "dst" in the first loop; all the filtering of
invalid copies is done in the second loop. The code also looks much
more consistent now.

No measureable impact on `hg debugpathcopies 4.0 4.8`. That shouldn't
be surprising since the only case we're doing more checks now is in
case of chained copies/renames, which are quire rare in practice.

Differential Revision: https://phab.mercurial-scm.org/D6277

Failed qimport of patches from files should cleanup by recording successfully
imported patches in series file.

  $ echo "[extensions]" >> $HGRCPATH
  $ echo "mq=" >> $HGRCPATH
  $ hg init repo
  $ cd repo
  $ echo a > a
  $ hg ci -Am'add a'
  adding a
  $ cat >b.patch<<EOF
  > diff --git a/a b/a
  > --- a/a
  > +++ b/a
  > @@ -1,1 +1,2 @@
  >  a
  > +b
  > EOF

empty series

  $ hg qseries

qimport valid patch followed by invalid patch

  $ hg qimport b.patch fakepatch
  adding b.patch to series file
  abort: unable to read file fakepatch
  [255]

valid patches before fail added to series

  $ hg qseries
  b.patch

  $ hg pull -q -r 0 . # update phase
  $ hg qimport -r 0
  abort: revision 0 is not mutable
  (see 'hg help phases' for details)
  [255]

  $ cd ..