tests: add criss cross merging tests whose behavior need to be fixed

Merging two changesets can mark a file as removed post merge. However, in some
cases, a user might not want to remove that file and they revert the removal
back and commit the merge. All this works perfectly well.

However, when we do criss-cross merges with such merge where user explicitly
choose to revert the removal with one where another user choose the removal,
we does not get any conflict.

The intent here is conflicting and merge should result in conflicts. One user
merged and want to keep the file while other user merged and want to remove the
file. Merging those merges should result in conflicts.

This patch adds test cases for these cases.

Differential Revision: https://phab.mercurial-scm.org/D8939

tests/test-merge-criss-cross.t

@@ -469,3 +469,225 b' Verify that the old context ancestor wor'
   getting d2/b
   1 files updated, 0 files merged, 2 files removed, 0 files unresolved
   (branch merge, don't forget to commit)
+
+
+Check that removal reversion does not go unotified
+==================================================
+
+On a merge, a file can be removed and user can revert that removal. This means
+user has made an explicit choice of keeping the file or reverting the removal
+even though the merge algo wanted to remove it.
+Based on this, when we do criss cross merges, merge algorithm should not again
+choose to remove the file as in one of the merges, user made an explicit choice
+to revert the removal.
+Following test cases demonstrate how merge algo does not take in account
+explicit choices made by users to revert the removal and on criss-cross merging
+removes the file again.
+
+"Simple" case where the filenode changes
+----------------------------------------
+
+  $ cd ..
+  $ hg init criss-cross-merge-reversal-with-update
+  $ cd criss-cross-merge-reversal-with-update
+  $ echo the-file > the-file
+  $ echo other-file > other-file
+  $ hg add the-file other-file
+  $ hg ci -m 'root-commit'
+  $ echo foo >> the-file
+  $ echo bar >> other-file
+  $ hg ci -m 'updating-both-file'
+  $ hg up 'desc("root-commit")'
+  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg rm the-file
+  $ hg ci -m 'delete-the-file'
+  created new head
+  $ hg log -G -T '{node|short} {desc}\n'
+  @  7801bc9b9899 delete-the-file
+  |
+  | o  9b610631ab29 updating-both-file
+  |/
+  o  955800955977 root-commit
+  
+
+Do all the merge combination (from the deleted or the update side × keeping and deleting the file
+
+  $ hg update 'desc("delete-the-file")'
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg merge 'desc("updating-both-file")' -t :local
+  1 files updated, 1 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  $ hg ci -m "merge-deleting-the-file-from-deleted"
+  $ hg manifest
+  other-file
+
+  $ hg update 'desc("updating-both-file")'
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg merge 'desc("delete-the-file")' -t :other
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  $ hg ci -m "merge-deleting-the-file-from-updated"
+  created new head
+  $ hg manifest
+  other-file
+
+  $ hg update 'desc("delete-the-file")'
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg merge 'desc("updating-both-file")' -t :other
+  1 files updated, 1 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  $ hg ci -m "merge-keeping-the-file-from-deleted"
+  created new head
+  $ hg manifest
+  other-file
+  the-file
+
+  $ hg update 'desc("updating-both-file")'
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg merge 'desc("delete-the-file")' -t :local
+  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  $ hg ci -m "merge-keeping-the-file-from-updated"
+  created new head
+  $ hg manifest
+  other-file
+  the-file
+
+There the resulting merge together (leading to criss cross situation). Check
+the conflict is properly detected.
+
+(merging two deletion together → no conflict)
+
+  $ hg update --clean 'desc("merge-deleting-the-file-from-deleted")'
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  $ hg merge          'desc("merge-deleting-the-file-from-updated")'
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  $ ls -1
+  other-file
+
+(merging a deletion with keeping → conflict)
+BROKEN: this should result in conflict
+
+  $ hg update --clean 'desc("merge-deleting-the-file-from-deleted")'
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg merge          'desc("merge-keeping-the-file-from-deleted")'
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  $ ls -1
+  other-file
+  the-file
+
+(merging a deletion with keeping → conflict)
+BROKEN: this should result in conflict
+
+  $ hg update --clean 'desc("merge-deleting-the-file-from-deleted")'
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  $ hg merge          'desc("merge-keeping-the-file-from-updated")'
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  $ ls -1
+  other-file
+  the-file
+
+(merging two deletion together → no conflict)
+
+  $ hg update --clean 'desc("merge-deleting-the-file-from-updated")'
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  $ hg merge          'desc("merge-deleting-the-file-from-deleted")'
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  $ ls -1
+  other-file
+
+(merging a deletion with keeping → conflict)
+BROKEN: this should result in conflict
+
+  $ hg update --clean 'desc("merge-deleting-the-file-from-updated")'
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg merge          'desc("merge-keeping-the-file-from-deleted")'
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  $ ls -1
+  other-file
+  the-file
+
+(merging a deletion with keeping → conflict)
+BROKEN: this should result in conflict
+
+  $ hg update --clean 'desc("merge-deleting-the-file-from-updated")'
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  $ hg merge          'desc("merge-keeping-the-file-from-updated")'
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  $ ls -1
+  other-file
+  the-file
+
+(merging two "keeping" together → no conflict)
+
+  $ hg update --clean 'desc("merge-keeping-the-file-from-updated")'
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg merge          'desc("merge-keeping-the-file-from-deleted")'
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  $ ls -1
+  other-file
+  the-file
+
+(merging a deletion with keeping → conflict)
+BROKEN: this should result in conflict
+
+  $ hg update --clean 'desc("merge-keeping-the-file-from-updated")'
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg merge          'desc("merge-deleted-the-file-from-deleted")'
+  abort: empty revision set
+  [255]
+  $ ls -1
+  other-file
+  the-file
+
+(merging a deletion with keeping → conflict)
+BROKEN: this should result in conflict
+
+  $ hg update --clean 'desc("merge-keeping-the-file-from-updated")'
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg merge          'desc("merge-deleting-the-file-from-updated")'
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  $ ls -1
+  other-file
+
+(merging two "keeping" together → no conflict)
+
+  $ hg update --clean 'desc("merge-keeping-the-file-from-deleted")'
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg merge          'desc("merge-keeping-the-file-from-updated")'
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  $ ls -1
+  other-file
+  the-file
+
+(merging a deletion with keeping → conflict)
+BROKEN: this should result in conflict
+
+  $ hg update --clean 'desc("merge-keeping-the-file-from-deleted")'
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg merge          'desc("merge-deleted-the-file-from-deleted")'
+  abort: empty revision set
+  [255]
+  $ ls -1
+  other-file
+  the-file
+
+(merging a deletion with keeping → conflict)
+BROKEN: this should result in conflict
+
+  $ hg update --clean 'desc("merge-keeping-the-file-from-deleted")'
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg merge          'desc("merge-deleting-the-file-from-updated")'
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  $ ls -1
+  other-file