On Wed, Nov 15, 2017 at 12:03 PM, Stefan Beller [off-list ref] wrote:

On Fri, Nov 10, 2017 at 11:05 AM, Elijah Newren [off-list ref] wrote:

quoted

+# Testcase 9d, N-fold transitive rename?
+#   (Related to testcase 9c...and 1c and 7e)
+#   Commit A: z/a, y/b, x/c, w/d, v/e, u/f
+#   Commit B:  y/{a,b},  w/{c,d},  u/{e,f}
+#   Commit C: z/{a,t}, x/{b,c}, v/{d,e}, u/f
+#   Expected: <see NOTE first>
+#
+#   NOTE: z/ -> y/ (in commit B)
+#         y/ -> x/ (in commit C)
+#         x/ -> w/ (in commit B)
+#         w/ -> v/ (in commit C)
+#         v/ -> u/ (in commit B)
+#         So, if we add a file to z, say z/t, where should it end up?  In u?
+#         What if there's another file or directory named 't' in one of the
+#         intervening directories and/or in u itself?  Also, shouldn't the
+#         same logic that places 't' in u/ also move ALL other files to u/?
+#         What if there are file or directory conflicts in any of them?  If
+#         we attempted to do N-way (N-fold? N-ary? N-uple?) transitive renames
+#         like this, would the user have any hope of understanding any
+#         conflicts or how their working tree ended up?  I think not, so I'm
+#         ruling out N-ary transitive renames for N>1.
+#
+#   Therefore our expected result is:
+#     z/t, y/a, x/b, w/c, u/d, u/e, u/f
+#   The reason that v/d DOES get transitively renamed to u/d is that u/ isn't
+#   renamed somewhere.  A slightly sub-optimal result, but it uses fairly
+#   simple rules that are consistent with what we need for all the other
+#   testcases and simplifies things for the user.

Does the merge order matter here?

No.

If B and C were swapped, applying the same logic presented in the NOTE,
one could argue that we expect:

    z/t y/a x/b w/c v/d v/e u/f

I can make a strong point for y/a here, but the v/{d,e} also seem to deviate.

I don't understand; I thought my argument as presented was agnostic of
direction.  Perhaps I have an unstated assumption I'm not realizing or
something; could you explain how my logic above could lead to this
conclusion?

Also, let me try a different tack to see if it's clearer than the
above argument I made.  Looking at each path:

* z/t from commit C does not get renamed to y/t despite B's rename of
z/ -> y/ because C renamed y/ elsewhere.
* z/a from commit A was renamed to y/a in commit B.  We do not
transitively rename further from y/a to x/a (despite C's rename of y/
to x/) because B renamed x/ elsewhere.
* y/b from commit A was renamed to x/b in commit C.  We do not
transitively rename further from x/b to w/b (despite B's rename of x/
to w/) because C renamed w/ elsewhere.
* x/c from commit A was renamed to w/c in commit B.  We do not
transitively rename further from w/c to v/c (despite C's rename from
w/ to v/) because B renamed v/ elsewhere.
* w/d from commit A was renamed to v/d in commit C.  We DO
transitively rename from v/d to u/d because of B's rename of v/ to u/
and because C did not rename u/ to somewhere else.

(And, to complete the list, e and f are simple: v/e is renamed to u/e
in commit B, and there's no directory name on u on either side, so
there's no special logic needed at all.  u/f is even simpler; there's
no renames or directory renames or anything affecting it.)

quoted

+# Testcase 9e, N-to-1 whammo
+#   (Related to testcase 9c...and 1c and 7e)
+#   Commit A: dir1/{a,b}, dir2/{d,e}, dir3/{g,h}, dirN/{j,k}
+#   Commit B: dir1/{a,b,c,yo}, dir2/{d,e,f,yo}, dir3/{g,h,i,yo}, dirN/{j,k,l,yo}
+#   Commit C: combined/{a,b,d,e,g,h,j,k}
+#   Expected: combined/{a,b,c,d,e,f,g,h,i,j,k,l}, CONFLICT(Nto1) warnings,
+#             dir1/yo, dir2/yo, dir3/yo, dirN/yo

Very neat!

:-)

quoted

+# Testcase 9f, Renamed directory that only contained immediate subdirs
+#   (Related to testcases 1e & 9g)
+#   Commit A: goal/{a,b}/$more_files
+#   Commit B: priority/{a,b}/$more_files
+#   Commit C: goal/{a,b}/$more_files, goal/c
+#   Expected: priority/{a,b}/$more_files, priority/c

quoted

+# Testcase 9g, Renamed directory that only contained immediate subdirs, immediate subdirs renamed
+#   (Related to testcases 1e & 9f)
+#   Commit A: goal/{a,b}/$more_files
+#   Commit B: priority/{alpha,bravo}/$more_files
+#   Commit C: goal/{a,b}/$more_files, goal/c
+#   Expected: priority/{alpha,bravo}/$more_files, priority/c

and if C also added goal/a/another_file, we'd expect it to
become priority/alpha/another_file.

Yep!  I thought that was covered enough by other tests, but do you
feel I should add that to this testcase?

What happens in moving dir hierarchies?

A: root/node1/{leaf1, leaf2}, root/node2/{leaf3, leaf4}
B: "Move node2 one layer down into node1"
    root/node1/{leaf1, leaf2, node2/{leaf3, leaf4}}
C: "Add more leaves"
    root/node1/{leaf1, leaf2, leaf5}, root/node2/{leaf3, leaf4, leaf6}

Works just fine; similar to testcase 9a.  Do you feel this one is
different enough to add to the testsuite?  I'm happy to do so.

Or chaining putting things in one another:
(Same A)
B: "Move node2 one layer down into node1"
    root/node1/{leaf1, leaf2, node2/{leaf3, leaf4}}
C: "Move node1 one layer down into node2"
    root/node2/{leaf3, leaf4, node1/{leaf1, leaf2}}

Just food for thought.

That's evil.  I mean, it's a brilliant testcase designed to really
mess things up.  I'm not entirely sure what the right answer should
be, but I am confident saying my current implementation handles it
wrong.  I'm digging into why.