tests/test-merge-changedelete.t

filectx: add isabsent method

This will indicate whether this filectx represents a file that is *not* in a
changectx. This will be used by merge and filemerge code to know about when a
conflict is a change/delete conflict.

While this is kind of hacky, it is the least bad of all the alternatives. Other
options considered but rejected include:
- isinstance(fctx, ...) -- not very Pythonic, doesn't support duck typing
- fctx.size() is None -- the 'size()' call on workingfilectxes causes a disk stat
- fctx.filenode() == nullid -- the semantics around filenode are incredibly
  confusing. In particular, for workingfilectxes, filenode() is always None no
  matter whether the file is present on disk or in either parent. Having different
  behavior for None versus nullid in the merge code is just asking for pain.

Thanks to Pierre-Yves David for early review feedback here.

Test for
b5605d88dc27: Make ui.prompt repeat on "unrecognized response" again
 (issue897)

840e2b315c1f: Fix misleading error and prompts during update/merge
 (issue556)

Make sure HGMERGE doesn't interfere with the test
  $ unset HGMERGE

  $ status() {
  >     echo "--- status ---"
  >     hg st -A file1 file2
  >     for file in file1 file2; do
  >         if [ -f $file ]; then
  >             echo "--- $file ---"
  >             cat $file
  >         else
  >             echo "*** $file does not exist"
  >         fi
  >     done
  > }

  $ hg init

  $ echo 1 > file1
  $ echo 2 > file2
  $ hg ci -Am 'added file1 and file2'
  adding file1
  adding file2

  $ hg rm file1
  $ echo changed >> file2
  $ hg ci -m 'removed file1, changed file2'

  $ hg co 0
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ echo changed >> file1
  $ hg rm file2
  $ hg ci -m 'changed file1, removed file2'
  created new head


Non-interactive merge:

  $ hg merge -y
  local changed file1 which remote deleted
  use (c)hanged version or (d)elete? c
  remote changed file2 which local deleted
  use (c)hanged version or leave (d)eleted? c
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ status
  --- status ---
  M file2
  C file1
  --- file1 ---
  1
  changed
  --- file2 ---
  2
  changed


Interactive merge:

  $ hg co -C
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ hg merge --config ui.interactive=true <<EOF
  > c
  > d
  > EOF
  local changed file1 which remote deleted
  use (c)hanged version or (d)elete? c
  remote changed file2 which local deleted
  use (c)hanged version or leave (d)eleted? d
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ status
  --- status ---
  file2: * (glob)
  C file1
  --- file1 ---
  1
  changed
  *** file2 does not exist


Interactive merge with bad input:

  $ hg co -C
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ hg merge --config ui.interactive=true <<EOF
  > foo
  > bar
  > d
  > baz
  > c
  > EOF
  local changed file1 which remote deleted
  use (c)hanged version or (d)elete? foo
  unrecognized response
  local changed file1 which remote deleted
  use (c)hanged version or (d)elete? bar
  unrecognized response
  local changed file1 which remote deleted
  use (c)hanged version or (d)elete? d
  remote changed file2 which local deleted
  use (c)hanged version or leave (d)eleted? baz
  unrecognized response
  remote changed file2 which local deleted
  use (c)hanged version or leave (d)eleted? c
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ status
  --- status ---
  M file2
  R file1
  *** file1 does not exist
  --- file2 ---
  2
  changed


Interactive merge with not enough input:

  $ hg co -C
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ hg merge --config ui.interactive=true <<EOF
  > d
  > EOF
  local changed file1 which remote deleted
  use (c)hanged version or (d)elete? d
  remote changed file2 which local deleted
  use (c)hanged version or leave (d)eleted? abort: response expected
  [255]

  $ status
  --- status ---
  file2: * (glob)
  C file1
  --- file1 ---
  1
  changed
  *** file2 does not exist

Non-interactive linear update

  $ hg co -C 0
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo changed >> file1
  $ hg rm file2
  $ hg update 1 -y
  local changed file1 which remote deleted
  use (c)hanged version or (d)elete? c
  remote changed file2 which local deleted
  use (c)hanged version or leave (d)eleted? c
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ status
  --- status ---
  A file1
  C file2
  --- file1 ---
  1
  changed
  --- file2 ---
  2
  changed