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

+###########################################################################
+# SECTION 9: Other testcases
+#
+# I came up with the testcases in the first eight sections before coding up
+# the implementation.  The testcases in this section were mostly ones I
+# thought of while coding/debugging, and which I was too lazy to insert
+# into the previous sections because I didn't want to re-label with all the
+# testcase references.  :-)

This might also be commit message material, as it describes the workflow,
not the 'misc' aspect of these test cases.

+###########################################################################
+
+# Testcase 9a, Inner renamed directory within outer renamed directory
+#   (Related to testcase 1f)
+#   Commit A: z/{b,c,d/{e,f,g}}
+#   Commit B: y/{b,c}, x/w/{e,f,g}
+#   Commit C: z/{b,c,d/{e,f,g,h},i}
+#   Expected: y/{b,c,i}, x/w/{e,f,g,h}
+#   NOTE: The only reason this one is interesting is because when a directory
+#         is split into multiple other directories, we determine by the weight
+#         of which one had the most paths going to it.  A naive implementation
+#         of that could take the new file in commit C at z/i to x/w/i or x/i.

Makes sense.

+# Testcase 9b, Transitive rename with content merge
+#   (Related to testcase 1c)
+#   Commit A: z/{b,c},   x/d_1
+#   Commit B: y/{b,c},   x/d_2
+#   Commit C: z/{b,c,d_3}
+#   Expected: y/{b,c,d_merged}

Makes sense.

+# Testcase 9c, Doubly transitive rename?
+#   (Related to testcase 1c, 7e, and 9d)
+#   Commit A: z/{b,c},     x/{d,e},    w/f
+#   Commit B: y/{b,c},     x/{d,e,f,g}
+#   Commit C: z/{b,c,d,e},             w/f
+#   Expected: y/{b,c,d,e}, x/{f,g}
+#
+#   NOTE: x/f and x/g may be slightly confusing here.  The rename from w/f to
+#         x/f is clear.  Let's look beyond that.  Here's the logic:
+#            Commit C renamed x/ -> z/
+#            Commit B renamed z/ -> y/
+#         So, we could possibly further rename x/f to z/f to y/f, a doubly
+#         transient rename.  However, where does it end?  We can chain these
+#         indefinitely (see testcase 9d).  What if there is a D/F conflict
+#         at z/f/ or y/f/?  Or just another file conflict at one of those
+#         paths?  In the case of an N-long chain of transient renamings,
+#         where do we "abort" the rename at?  Can the user make sense of
+#         the resulting conflict and resolve it?
+#
+#         To avoid this confusion I use the simple rule that if the other side
+#         of history did a directory rename to a path that your side renamed
+#         away, then ignore that particular rename from the other side of
+#         history for any implicit directory renames.

This is repeated in the rule of section 9 below.
Makes sense.

+# 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?
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.

+# 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!

+# 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

+# 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.

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}

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.

+# Rules suggested by section 9:
+#
+#   If the other side of history did a directory rename to a path that your
+#   side renamed away, then ignore that particular rename from the other
+#   side of history for any implicit directory renames.