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Using 'test_must_be_empty' is shorter and more idiomatic than
>empty &&
test_cmp empty out
as it saves the creation of an empty file. Furthermore, sometimes the
expected empty file doesn't have such a descriptive name like 'empty',
and its creation is far away from the place where it's finally used
for comparison (e.g. in 't7600-merge.sh', where two expected empty
files are created in the 'setup' test, but are used only about 500
lines later).
These cases were found by instrumenting 'test_cmp' to error out the
test script when it's used to compare empty files, and then converted
manually.
Note that even after this patch there still remain a lot of cases
where we use 'test_cmp' to check empty files:
- Sometimes the expected output is not hard-coded in the test, but
'test_cmp' is used to ensure that two similar git commands produce
the same output, and that output happens to be empty, e.g. the
test 'submodule update --merge - ignores --merge for new
submodules' in 't7406-submodule-update.sh'.
- Repetitive common tasks, including preparing the expected results
and running 'test_cmp', are often extracted into a helper
function, and some of this helper's callsites expect no output.
- For the same reason as above, the whole 'test_expect_success'
block is within a helper function, e.g. in 't3070-wildmatch.sh'.
- Or 'test_cmp' is invoked in a loop, e.g. the test 'cvs update
(-p)' in 't9400-git-cvsserver-server.sh'.
Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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We do not allow cycles in the delta graph of a pack (i.e., A
is a delta of B which is a delta of A) for the obvious
reason that you cannot actually access any of the objects in
such a case.
There's a last-ditch attempt to notice cycles during the
write phase, during which we issue a warning to the user and
write one of the objects out in full. However, this is
"last-ditch" for two reasons:
1. By this time, it's too late to find another delta for
the object, so the resulting pack is larger than it
otherwise could be.
2. The warning is there because this is something that
_shouldn't_ ever happen. If it does, then either:
a. a pack we are reusing deltas from had its own
cycle
b. we are reusing deltas from multiple packs, and
we found a cycle among them (i.e., A is a delta of
B in one pack, but B is a delta of A in another,
and we choose to use both deltas).
c. there is a bug in the delta-search code
So this code serves as a final check that none of these
things has happened, warns the user, and prevents us
from writing a bogus pack.
Right now, (2b) should never happen because of the static
ordering of packs in want_object_in_pack(). If two objects
have a delta relationship, then they must be in the same
pack, and therefore we will find them from that same pack.
However, a future patch would like to change that static
ordering, which will make (2b) a common occurrence. In
preparation, we should be able to handle those kinds of
cycles better. This patch does by introducing a
cycle-breaking step during the get_object_details() phase,
when we are deciding which deltas can be reused. That gives
us the chance to feed the objects into the delta search as
if the cycle did not exist.
We'll leave the detection and warning in the write_object()
phase in place, as it still serves as a check for case (2c).
This does mean we will stop warning for (2a). That case is
caused by bogus input packs, and we ideally would warn the
user about it. However, since those cycles show up after
picking reusable deltas, they look the same as (2b) to us;
our new code will break the cycles early and the last-ditch
check will never see them.
We could do analysis on any cycles that we find to
distinguish the two cases (i.e., it is a bogus pack if and
only if every delta in the cycle is in the same pack), but
we don't need to. If there is a cycle inside a pack, we'll
run into problems not only reusing the delta, but accessing
the object data at all. So when we try to dig up the actual
size of the object, we'll hit that same cycle and kick in
our usual complain-and-try-another-source code.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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