tests/test-parseindex.t

scmutil: consistently return subrepos relative to ctx1 from itersubrepos()

Previously, if a subrepo was added in ctx2 and then compared to another without
it (ctx1), the subrepo for ctx2 was returned amongst all of the ctx1 based
subrepos, since no subrepo exists in ctx1 to replace it in the 'subpaths' dict.
The two callers of this, basectx.status() and cmdutil.diffordiffstat(), both
compare the yielded subrepo against ctx2, and thus saw no changes when ctx2's
subrepo was returned.  The tests here previously didn't mention 's/a' for the
'p1()' case.

This appears to have been a known issue, because some diffordiffstat() comments
mention that the subpath disappeared, and "the best we can do is ignore it".  I
originally ran into the issue with some custom convert code to flatten a tree of
subrepos causing hg.putcommit() to abort, but this new behavior seems like the
correct status and diff behavior regardless.  (The abort in convert isn't
something users will see, because convert doesn't currently support subrepos in
the official repo.)

revlog.parseindex must be able to parse the index file even if
an index entry is split between two 64k blocks.  The ideal test
would be to create an index file with inline data where
64k < size < 64k + 64 (64k is the size of the read buffer, 64 is
the size of an index entry) and with an index entry starting right
before the 64k block boundary, and try to read it.
We approximate that by reducing the read buffer to 1 byte.

  $ hg init a
  $ cd a
  $ echo abc > foo
  $ hg add foo
  $ hg commit -m 'add foo'
  $ echo >> foo
  $ hg commit -m 'change foo'
  $ hg log -r 0:
  changeset:   0:7c31755bf9b5
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     add foo
  
  changeset:   1:26333235a41c
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     change foo
  
  $ cat >> test.py << EOF
  > from mercurial import changelog, scmutil
  > from mercurial.node import *
  > 
  > class singlebyteread(object):
  >     def __init__(self, real):
  >         self.real = real
  > 
  >     def read(self, size=-1):
  >         if size == 65536:
  >             size = 1
  >         return self.real.read(size)
  > 
  >     def __getattr__(self, key):
  >         return getattr(self.real, key)
  > 
  > def opener(*args):
  >     o = scmutil.opener(*args)
  >     def wrapper(*a):
  >         f = o(*a)
  >         return singlebyteread(f)
  >     return wrapper
  > 
  > cl = changelog.changelog(opener('.hg/store'))
  > print len(cl), 'revisions:'
  > for r in cl:
  >     print short(cl.node(r))
  > EOF
  $ python test.py
  2 revisions:
  7c31755bf9b5
  26333235a41c

  $ cd ..