Re: [PATCH 11/30] directory rename detection: testcases exploring possibly suboptimal merges
- From
Stefan Beller <sbeller@google.com>
- Date
- Nov 14, 2017, 20:33 UTC
- Message-ID
- <CAGZ79kYCDBFwMhW4Qgwhomiv4kKRWS53cjMLuRG1NxrzULYwgg@mail.gmail.com>
- In-Reply-To
- <20171110190550.27059-12-newren@gmail.com>
On Fri, Nov 10, 2017 at 11:05 AM, Elijah Newren <newren@gmail.com> wrote:
Show 37 quoted lines
> Signed-off-by: Elijah Newren <newren@gmail.com>
> ---
> t/t6043-merge-rename-directories.sh | 371 ++++++++++++++++++++++++++++++++++++
> 1 file changed, 371 insertions(+)
>
> diff --git a/t/t6043-merge-rename-directories.sh b/t/t6043-merge-rename-directories.sh
> index 115d0d2622..bdfd943c88 100755
> --- a/t/t6043-merge-rename-directories.sh
> +++ b/t/t6043-merge-rename-directories.sh
> @@ -1683,4 +1683,375 @@ test_expect_failure '7e-check: transitive rename in rename/delete AND dirs in th
> test $(git hash-object y/d~C^0) = $(git rev-parse A:x/d)
> '
>
> +
> +###########################################################################
> +# SECTION 8: Suboptimal merges
> +#
> +# As alluded to in the last section, the ruleset we have built up for
> +# detecting directory renames unfortunately has some special cases where it
> +# results in slightly suboptimal or non-intuitive behavior. This section
> +# explores these cases.
> +#
> +# To be fair, we already had non-intuitive or suboptimal behavior for most
> +# of these cases in git before introducing implicit directory rename
> +# detection, but it'd be nice if there was a modified ruleset out there
> +# that handled these cases a bit better.
> +###########################################################################
> +
> +# Testcase 8a, Dual-directory rename, one into the others' way
> +# Commit A. x/{a,b}, y/{c,d}
> +# Commit B. x/{a,b,e}, y/{c,d,f}
> +# Commit C. y/{a,b}, z/{c,d}
> +#
> +# Possible Resolutions:
> +# Previous git: y/{a,b,f}, z/{c,d}, x/e
> +# Expected: y/{a,b,e,f}, z/{c,d}
> +# Preferred: y/{a,b,e}, z/{c,d,f}it might be tricky in the future to know what "previous git" is; "Previous git" means without directory renames enabled;
"expected" means we expect the algorithm presented in this series to produce this output, preferred is what we actually expect.
Show 5 quoted lines
> +# > +# Note: Both x and y got renamed and it'd be nice to detect both, and we do > +# better with directory rename detection than git did previously, but the > +# simple rule from section 5 prevents me from handling this as optimally as > +# we potentially could.
which were:
If a subset of to-be-renamed files have a file or directory in the way, "turn off" the directory rename for those specific sub-paths, falling back to old handling. But, sadly, see testcases 8a and 8b.
The tricky part is y in this example as x,y "swapped" its content in C, and moved 'old y content' to the new z/.
Makes sense, but I agree it might be painful to debug such a case from a users point of view.
Show 10 quoted lines
> +
> +# Testcase 8b, Dual-directory rename, one into the others' way, with conflicting filenames
> +# Commit A. x/{a_1,b_1}, y/{a_2,b_2}
> +# Commit B. x/{a_1,b_1,e_1}, y/{a_2,b_2,e_2}
> +# Commit C. y/{a_1,b_1}, z/{a_2,b_2}
> +#
> +# Possible Resolutions:
> +# Previous git: y/{a_1,b_1,e_2}, z/{a_2,b_2}, x/e_1
> +# Scary: y/{a_1,b_1}, z/{a_2,b_2}, CONFLICT(add/add, e_1 vs. e_2)
> +# Preferred: y/{a_1,b_1,e_1}, z/{a_2,b_2,e_2}It may be common to have sub directories with the same path having different blobs, e.g. when having say multiple hardware configurations in different sub directories configured. Then renaming becomes a pain when they overlap.
> +# Note: Very similar to 8a, except instead of 'e' and 'f' in directories x and > +# y, both are named 'e'. Without directory rename detection, neither file > +# moves directories. Implment directory rename detection suboptimally, and
Implement
Show 7 quoted lines
> +# you get an add/add conflict, but both files were added in commit B, so this > +# is an add/add conflict where one side of history added both files -- > +# something we can't represent in the index. Obviously, we'd prefer the last > +# resolution, but our previous rules are too coarse to allow it. Using both > +# the rules from section 4 and section 5 save us from the Scary resolution, > +# making us fall back to pre-directory-rename-detection behavior for both > +# e_1 and e_2.
ok, so add "Expected" as well? (repeating "Previous git", or so?)
Show 11 quoted lines
> +
> +# Testcase 8c, rename+modify/delete
> +# (Related to testcases 5b and 8d)
> +# Commit A: z/{b,c,d}
> +# Commit B: y/{b,c}
> +# Commit C: z/{b,c,d_modified,e}
> +# Expected: y/{b,c,e}, CONFLICT(rename+modify/delete: x/d -> y/d or deleted)
> +#
> +# Note: This testcase doesn't present any concerns for me...until you
> +# compare it with testcases 5b and 8d. See notes in 8d for more
> +# details.Makes sense.
> +# Testcase 8d, rename/delete...or not? > +# (Related to testcase 5b; these may appear slightly inconsistent to users; > +# Also related to testcases 7d and 7e)
> +# Commit A: z/{b,c,d}
> +# Commit B: y/{b,c}
> +# Commit C: z/{b,c,d,e}
> +# Expected: y/{b,c,e}Why this? * d is deleted in B and not found in the result * the rename detection also worked well in z->y for adding e
I do not see the confusion, yet.
Show 18 quoted lines
> +# Note: It would also be somewhat reasonable to resolve this as
> +# y/{b,c,e}, CONFLICT(rename/delete: x/d -> y/d or deleted)
> +# The logic being that the only difference between this testcase and 8c
> +# is that there is no modification to d. That suggests that instead of a
> +# rename/modify vs. delete conflict, we should just have a rename/delete
> +# conflict, otherwise we are being inconsistent.
> +#
> +# However...as far as consistency goes, we didn't report a conflict for
> +# path d_1 in testcase 5b due to a different file being in the way. So,
> +# we seem to be forced to have cases where users can change things
> +# slightly and get what they may perceive as inconsistent results. It
> +# would be nice to avoid that, but I'm not sure I see how.
> +#
> +# In this case, I'm leaning towards: commit B was the one that deleted z/d
> +# and it did the rename of z to y, so the two "conflicts" (rename vs.
> +# delete) are both coming from commit B, which is non-sensical. Conflicts
> +# during merging are supposed to be about opposite sides doing things
> +# differently."Sensical has not yet become an "official" word in the English language, which would be why you can't use it. Nonsense is a word, therefore nonsensical can used to describe something of nonsense. However, sense has different meanings and doesn't have an adjective for something of sense"
from https://english.stackexchange.com/questions/38582/antonym-of-nonsensical I don't mind it, the spell checker just made me go on a detour. Maybe illogical?
Show 22 quoted lines
> +# Testcase 8e, Both sides rename, one side adds to original directory
> +# Commit A: z/{b,c}
> +# Commit B: y/{b,c}
> +# Commit C: w/{b,c}, z/d
> +#
> +# Possible Resolutions:
> +# Previous git: z/d, CONFLICT(z/b -> y/b vs. w/b), CONFLICT(z/c -> y/c vs. w/c)
> +# Expected: y/d, CONFLICT(z/b -> y/b vs. w/b), CONFLICT(z/c -> y/c vs. w/c)
> +# Preferred: ??
> +#
> +# Notes: In commit B, directory z got renamed to y. In commit C, directory z
> +# did NOT get renamed; the directory is still present; instead it is
> +# considered to have just renamed a subset of paths in directory z
> +# elsewhere. Therefore, the directory rename done in commit B to z/
> +# applies to z/d and maps it to y/d.
> +#
> +# It's possible that users would get confused about this, but what
> +# should we do instead? Silently leaving at z/d seems just as bad or
> +# maybe even worse. Perhaps we could print a big warning about z/d
> +# and how we're moving to y/d in this case, but when I started thinking
> +# abouty the ramifications of doing that, I didn't know how to rule out
> +# that opening other weird edge and corner cases so I just punted.s/about/abouty
It sort of makes sense from a users POV.