tests/test-server-view.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

  $ hg init test
  $ cd test
  $ hg debugbuilddag '+2'
  $ hg phase --public 0

  $ hg serve -p $HGPORT -d --pid-file=hg.pid -E errors.log
  $ cat hg.pid >> $DAEMON_PIDS
  $ cd ..
  $ hg init test2
  $ cd test2
  $ hg incoming http://foo:xyzzy@localhost:$HGPORT/
  comparing with http://foo:***@localhost:$HGPORT/
  changeset:   0:1ea73414a91b
  user:        debugbuilddag
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     r0
  
  changeset:   1:66f7d451a68b
  tag:         tip
  user:        debugbuilddag
  date:        Thu Jan 01 00:00:01 1970 +0000
  summary:     r1
  
  $ killdaemons.py

  $ cd ..
  $ hg -R test --config server.view=immutable serve -p $HGPORT -d --pid-file=hg.pid -E errors.log
  $ cat hg.pid >> $DAEMON_PIDS
  $ hg -R test2 incoming http://foo:xyzzy@localhost:$HGPORT/
  comparing with http://foo:***@localhost:$HGPORT/
  changeset:   0:1ea73414a91b
  tag:         tip
  user:        debugbuilddag
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     r0
  
  $ cat errors.log
  $ killdaemons.py