tests/test-flags.t

simplemerge: stop merging file flags

As 384df4db6520 (merge: merge file flags together with file content,
2013-01-09) explains, we shouldn't do a 3-way merge of the
symlink. However, since 84614212ae39 (flags: actually merge flags in
simplemerge, 2020-05-16), we do that in
`simplemerge.simplemerge()`. What's more, the merging of the
executable flag there isn't actually necessary; it was made a no-op by
the very next commit, i.e. 4234c9af515d (flags: read flag from
dirstate/disk for workingcopyctx (issue5743), 2020-05-16).

I found the overall flag-merging code (not the bit in
`simplemerge.py`) very hard to follow, but I think I now finally
understand how it works. `mergestate.resolve()` calculates the merged
file flags and sets them on the local side of the merge (confusingly
by calling `_restore_backup()`). Then it calls
`filemerge.filemerge()`, which in turn calls
`simplemerge.simplemerge()` (if premerge is enabled). That means that
the flags on the local side `fcs.flags()` are already correct when the
flag-merging code in `simplemerge.simplemerge()` runs. Interestingly,
that code still works when the local side already has the merged
value, it just doesn't change the value. Here's a truth table to
explain why:

```
BLOMCAR
0000000
0011111
0101011
0111111
1000000
1010000
1100000
1111101
```

B: Base
L: Local
O: Other
M: Merged flags from `mergestate.resolve()`, i.e. what's called "local"
   when we get to `simplemerge.simplemerge()`
C: `commonflags` in `simplemerge.simplemerge()`, i.e. `M & O`
A: `addedflags` in `simplemerge.simplemerge()`, i.e. `(M ^ O) - B`
R: Re-merged flags `simplemerge.simplemerge()`, i.e. `C | A`

As you can see, the re-merged flags are always unchanged compared to
the initial merged flags (R equals M).

Therefore, this patch effectively backs out 84614212ae39. (I might
later refactor this code to have the flags explicitly passed in.)

`simplemerge.simplemerge()` is also called from
`contrib/simplemerge.py`, but that code never passes any flags.

Differential Revision: https://phab.mercurial-scm.org/D11879

#require execbit

  $ umask 027

  $ hg init test1
  $ cd test1
  $ touch a b
  $ hg add a b
  $ hg ci -m "added a b"

  $ cd ..
  $ hg clone test1 test3
  updating to branch default
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ hg init test2
  $ cd test2
  $ hg pull ../test1
  pulling from ../test1
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 2 changes to 2 files
  new changesets 22a449e20da5
  (run 'hg update' to get a working copy)
  $ hg co
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ chmod +x a
  $ hg ci -m "chmod +x a"

the changelog should mention file a:

  $ hg tip --template '{files}\n'
  a

  $ cd ../test1
  $ echo 123 >>a
  $ hg ci -m "a updated"

  $ hg pull ../test2
  pulling from ../test2
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 0 changes to 0 files (+1 heads)
  new changesets 7f4313b42a34
  1 local changesets published
  (run 'hg heads' to see heads, 'hg merge' to merge)
  $ hg heads
  changeset:   2:7f4313b42a34
  tag:         tip
  parent:      0:22a449e20da5
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     chmod +x a
  
  changeset:   1:c6ecefc45368
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     a updated
  
  $ hg history
  changeset:   2:7f4313b42a34
  tag:         tip
  parent:      0:22a449e20da5
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     chmod +x a
  
  changeset:   1:c6ecefc45368
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     a updated
  
  changeset:   0:22a449e20da5
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     added a b
  

  $ hg -v merge
  resolving manifests
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ cat a
  123
  $ [ -x a ]

  $ cd ../test3
  $ echo 123 >>b
  $ hg ci -m "b updated"

  $ hg pull ../test2
  pulling from ../test2
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 0 changes to 0 files (+1 heads)
  new changesets 7f4313b42a34
  (run 'hg heads' to see heads, 'hg merge' to merge)
  $ hg heads
  changeset:   2:7f4313b42a34
  tag:         tip
  parent:      0:22a449e20da5
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     chmod +x a
  
  changeset:   1:dc57ead75f79
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     b updated
  
  $ hg history
  changeset:   2:7f4313b42a34
  tag:         tip
  parent:      0:22a449e20da5
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     chmod +x a
  
  changeset:   1:dc57ead75f79
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     b updated
  
  changeset:   0:22a449e20da5
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     added a b
  

  $ hg -v merge
  resolving manifests
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ ls -l ../test[123]/a > foo
  $ cut -b 1-10 < foo
  -rwxr-x---
  -rwxr-x---
  -rwxr-x---

  $ hg debugindex a
     rev linkrev nodeid       p1           p2
       0       0 b80de5d13875 000000000000 000000000000
  $ hg debugindex -R ../test2 a
     rev linkrev nodeid       p1           p2
       0       0 b80de5d13875 000000000000 000000000000
  $ hg debugindex -R ../test1 a
     rev linkrev nodeid       p1           p2
       0       0 b80de5d13875 000000000000 000000000000
       1       1 7fe919cc0336 b80de5d13875 000000000000

  $ cd ..