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git-commit-vandalism/t/t6600-test-reach.sh
Abhishek Kumar e8b63005c4 commit-graph: implement generation data chunk 
As discovered by Ævar, we cannot increment graph version to
distinguish between generation numbers v1 and v2 [1]. Thus, one of
pre-requistes before implementing generation number v2 was to
distinguish between graph versions in a backwards compatible manner.

We are going to introduce a new chunk called Generation DATa chunk (or
GDAT). GDAT will store corrected committer date offsets whereas CDAT
will still store topological level.

Old Git does not understand GDAT chunk and would ignore it, reading
topological levels from CDAT. New Git can parse GDAT and take advantage
of newer generation numbers, falling back to topological levels when
GDAT chunk is missing (as it would happen with a commit-graph written
by old Git).

We introduce a test environment variable 'GIT_TEST_COMMIT_GRAPH_NO_GDAT'
which forces commit-graph file to be written without generation data
chunk to emulate a commit-graph file written by old Git.

To minimize the space required to store corrrected commit date, Git
stores corrected commit date offsets into the commit-graph file, instea
of corrected commit dates. This saves us 4 bytes per commit, decreasing
the GDAT chunk size by half, but it's possible for the offset to
overflow the 4-bytes allocated for storage. As such overflows are and
should be exceedingly rare, we use the following overflow management
scheme:

We introduce a new commit-graph chunk, Generation Data OVerflow ('GDOV')
to store corrected commit dates for commits with offsets greater than
GENERATION_NUMBER_V2_OFFSET_MAX.

If the offset is greater than GENERATION_NUMBER_V2_OFFSET_MAX, we set
the MSB of the offset and the other bits store the position of corrected
commit date in GDOV chunk, similar to how Extra Edge List is maintained.

We test the overflow-related code with the following repo history:

           F - N - U
          /         \
U - N - U            N
         \          /
	  N - F - N

Where the commits denoted by U have committer date of zero seconds
since Unix epoch, the commits denoted by N have committer date of
1112354055 (default committer date for the test suite) seconds since
Unix epoch and the commits denoted by F have committer date of
(2 ^ 31 - 2) seconds since Unix epoch.

The largest offset observed is 2 ^ 31, just large enough to overflow.

[1]: https://lore.kernel.org/git/87a7gdspo4.fsf@evledraar.gmail.com/

Signed-off-by: Abhishek Kumar <abhishekkumar8222@gmail.com>
Reviewed-by: Taylor Blau <me@ttaylorr.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2021-01-18 16:21:18 -08:00

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#!/bin/sh
test_description='basic commit reachability tests'
. ./test-lib.sh
# Construct a grid-like commit graph with points (x,y)
# with 1 <= x <= 10, 1 <= y <= 10, where (x,y) has
# parents (x-1, y) and (x, y-1), keeping in mind that
# we drop a parent if a coordinate is nonpositive.
#
# (10,10)
# / \
# (10,9) (9,10)
# / \ / \
# (10,8) (9,9) (8,10)
# / \ / \ / \
# ( continued...)
# \ / \ / \ /
# (3,1) (2,2) (1,3)
# \ / \ /
# (2,1) (2,1)
# \ /
# (1,1)
#
# We use branch 'commit-x-y' to refer to (x,y).
# This grid allows interesting reachability and
# non-reachability queries: (x,y) can reach (x',y')
# if and only if x' <= x and y' <= y.
test_expect_success 'setup' '
for i in $(test_seq 1 10)
do
test_commit "1-$i" &&
git branch -f commit-1-$i &&
git tag -a -m "1-$i" tag-1-$i commit-1-$i
done &&
for j in $(test_seq 1 9)
do
git reset --hard commit-$j-1 &&
x=$(($j + 1)) &&
test_commit "$x-1" &&
git branch -f commit-$x-1 &&
git tag -a -m "$x-1" tag-$x-1 commit-$x-1 &&
for i in $(test_seq 2 10)
do
git merge commit-$j-$i -m "$x-$i" &&
git branch -f commit-$x-$i &&
git tag -a -m "$x-$i" tag-$x-$i commit-$x-$i
done
done &&
git commit-graph write --reachable &&
mv .git/objects/info/commit-graph commit-graph-full &&
chmod u+w commit-graph-full &&
git show-ref -s commit-5-5 | git commit-graph write --stdin-commits &&
mv .git/objects/info/commit-graph commit-graph-half &&
chmod u+w commit-graph-half &&
GIT_TEST_COMMIT_GRAPH_NO_GDAT=1 git commit-graph write --reachable &&
mv .git/objects/info/commit-graph commit-graph-no-gdat &&
chmod u+w commit-graph-no-gdat &&
git config core.commitGraph true
'
run_all_modes () {
test_when_finished rm -rf .git/objects/info/commit-graph &&
"$@" <input >actual &&
test_cmp expect actual &&
cp commit-graph-full .git/objects/info/commit-graph &&
"$@" <input >actual &&
test_cmp expect actual &&
cp commit-graph-half .git/objects/info/commit-graph &&
"$@" <input >actual &&
test_cmp expect actual &&
cp commit-graph-no-gdat .git/objects/info/commit-graph &&
"$@" <input >actual &&
test_cmp expect actual
}
test_all_modes () {
run_all_modes test-tool reach "$@"
}
test_expect_success 'ref_newer:miss' '
cat >input <<-\EOF &&
A:commit-5-7
B:commit-4-9
EOF
echo "ref_newer(A,B):0" >expect &&
test_all_modes ref_newer
'
test_expect_success 'ref_newer:hit' '
cat >input <<-\EOF &&
A:commit-5-7
B:commit-2-3
EOF
echo "ref_newer(A,B):1" >expect &&
test_all_modes ref_newer
'
test_expect_success 'in_merge_bases:hit' '
cat >input <<-\EOF &&
A:commit-5-7
B:commit-8-8
EOF
echo "in_merge_bases(A,B):1" >expect &&
test_all_modes in_merge_bases
'
test_expect_success 'in_merge_bases:miss' '
cat >input <<-\EOF &&
A:commit-6-8
B:commit-5-9
EOF
echo "in_merge_bases(A,B):0" >expect &&
test_all_modes in_merge_bases
'
test_expect_success 'in_merge_bases_many:hit' '
cat >input <<-\EOF &&
A:commit-6-8
X:commit-6-9
X:commit-5-7
EOF
echo "in_merge_bases_many(A,X):1" >expect &&
test_all_modes in_merge_bases_many
'
test_expect_success 'in_merge_bases_many:miss' '
cat >input <<-\EOF &&
A:commit-6-8
X:commit-7-7
X:commit-8-6
EOF
echo "in_merge_bases_many(A,X):0" >expect &&
test_all_modes in_merge_bases_many
'
test_expect_success 'in_merge_bases_many:miss-heuristic' '
cat >input <<-\EOF &&
A:commit-6-8
X:commit-7-5
X:commit-6-6
EOF
echo "in_merge_bases_many(A,X):0" >expect &&
test_all_modes in_merge_bases_many
'
test_expect_success 'is_descendant_of:hit' '
cat >input <<-\EOF &&
A:commit-5-7
X:commit-4-8
X:commit-6-6
X:commit-1-1
EOF
echo "is_descendant_of(A,X):1" >expect &&
test_all_modes is_descendant_of
'
test_expect_success 'is_descendant_of:miss' '
cat >input <<-\EOF &&
A:commit-6-8
X:commit-5-9
X:commit-4-10
X:commit-7-6
EOF
echo "is_descendant_of(A,X):0" >expect &&
test_all_modes is_descendant_of
'
test_expect_success 'get_merge_bases_many' '
cat >input <<-\EOF &&
A:commit-5-7
X:commit-4-8
X:commit-6-6
X:commit-8-3
EOF
{
echo "get_merge_bases_many(A,X):" &&
git rev-parse commit-5-6 \
commit-4-7 | sort
} >expect &&
test_all_modes get_merge_bases_many
'
test_expect_success 'reduce_heads' '
cat >input <<-\EOF &&
X:commit-1-10
X:commit-2-8
X:commit-3-6
X:commit-4-4
X:commit-1-7
X:commit-2-5
X:commit-3-3
X:commit-5-1
EOF
{
echo "reduce_heads(X):" &&
git rev-parse commit-5-1 \
commit-4-4 \
commit-3-6 \
commit-2-8 \
commit-1-10 | sort
} >expect &&
test_all_modes reduce_heads
'
test_expect_success 'can_all_from_reach:hit' '
cat >input <<-\EOF &&
X:commit-2-10
X:commit-3-9
X:commit-4-8
X:commit-5-7
X:commit-6-6
X:commit-7-5
X:commit-8-4
X:commit-9-3
Y:commit-1-9
Y:commit-2-8
Y:commit-3-7
Y:commit-4-6
Y:commit-5-5
Y:commit-6-4
Y:commit-7-3
Y:commit-8-1
EOF
echo "can_all_from_reach(X,Y):1" >expect &&
test_all_modes can_all_from_reach
'
test_expect_success 'can_all_from_reach:miss' '
cat >input <<-\EOF &&
X:commit-2-10
X:commit-3-9
X:commit-4-8
X:commit-5-7
X:commit-6-6
X:commit-7-5
X:commit-8-4
X:commit-9-3
Y:commit-1-9
Y:commit-2-8
Y:commit-3-7
Y:commit-4-6
Y:commit-5-5
Y:commit-6-4
Y:commit-8-5
EOF
echo "can_all_from_reach(X,Y):0" >expect &&
test_all_modes can_all_from_reach
'
test_expect_success 'can_all_from_reach_with_flag: tags case' '
cat >input <<-\EOF &&
X:tag-2-10
X:tag-3-9
X:tag-4-8
X:commit-5-7
X:commit-6-6
X:commit-7-5
X:commit-8-4
X:commit-9-3
Y:tag-1-9
Y:tag-2-8
Y:tag-3-7
Y:commit-4-6
Y:commit-5-5
Y:commit-6-4
Y:commit-7-3
Y:commit-8-1
EOF
echo "can_all_from_reach_with_flag(X,_,_,0,0):1" >expect &&
test_all_modes can_all_from_reach_with_flag
'
test_expect_success 'commit_contains:hit' '
cat >input <<-\EOF &&
A:commit-7-7
X:commit-2-10
X:commit-3-9
X:commit-4-8
X:commit-5-7
X:commit-6-6
X:commit-7-5
X:commit-8-4
X:commit-9-3
EOF
echo "commit_contains(_,A,X,_):1" >expect &&
test_all_modes commit_contains &&
test_all_modes commit_contains --tag
'
test_expect_success 'commit_contains:miss' '
cat >input <<-\EOF &&
A:commit-6-5
X:commit-2-10
X:commit-3-9
X:commit-4-8
X:commit-5-7
X:commit-6-6
X:commit-7-5
X:commit-8-4
X:commit-9-3
EOF
echo "commit_contains(_,A,X,_):0" >expect &&
test_all_modes commit_contains &&
test_all_modes commit_contains --tag
'
test_expect_success 'rev-list: basic topo-order' '
git rev-parse \
commit-6-6 commit-5-6 commit-4-6 commit-3-6 commit-2-6 commit-1-6 \
commit-6-5 commit-5-5 commit-4-5 commit-3-5 commit-2-5 commit-1-5 \
commit-6-4 commit-5-4 commit-4-4 commit-3-4 commit-2-4 commit-1-4 \
commit-6-3 commit-5-3 commit-4-3 commit-3-3 commit-2-3 commit-1-3 \
commit-6-2 commit-5-2 commit-4-2 commit-3-2 commit-2-2 commit-1-2 \
commit-6-1 commit-5-1 commit-4-1 commit-3-1 commit-2-1 commit-1-1 \
>expect &&
run_all_modes git rev-list --topo-order commit-6-6
'
test_expect_success 'rev-list: first-parent topo-order' '
git rev-parse \
commit-6-6 \
commit-6-5 \
commit-6-4 \
commit-6-3 \
commit-6-2 \
commit-6-1 commit-5-1 commit-4-1 commit-3-1 commit-2-1 commit-1-1 \
>expect &&
run_all_modes git rev-list --first-parent --topo-order commit-6-6
'
test_expect_success 'rev-list: range topo-order' '
git rev-parse \
commit-6-6 commit-5-6 commit-4-6 commit-3-6 commit-2-6 commit-1-6 \
commit-6-5 commit-5-5 commit-4-5 commit-3-5 commit-2-5 commit-1-5 \
commit-6-4 commit-5-4 commit-4-4 commit-3-4 commit-2-4 commit-1-4 \
commit-6-3 commit-5-3 commit-4-3 \
commit-6-2 commit-5-2 commit-4-2 \
commit-6-1 commit-5-1 commit-4-1 \
>expect &&
run_all_modes git rev-list --topo-order commit-3-3..commit-6-6
'
test_expect_success 'rev-list: range topo-order' '
git rev-parse \
commit-6-6 commit-5-6 commit-4-6 \
commit-6-5 commit-5-5 commit-4-5 \
commit-6-4 commit-5-4 commit-4-4 \
commit-6-3 commit-5-3 commit-4-3 \
commit-6-2 commit-5-2 commit-4-2 \
commit-6-1 commit-5-1 commit-4-1 \
>expect &&
run_all_modes git rev-list --topo-order commit-3-8..commit-6-6
'
test_expect_success 'rev-list: first-parent range topo-order' '
git rev-parse \
commit-6-6 \
commit-6-5 \
commit-6-4 \
commit-6-3 \
commit-6-2 \
commit-6-1 commit-5-1 commit-4-1 \
>expect &&
run_all_modes git rev-list --first-parent --topo-order commit-3-8..commit-6-6
'
test_expect_success 'rev-list: ancestry-path topo-order' '
git rev-parse \
commit-6-6 commit-5-6 commit-4-6 commit-3-6 \
commit-6-5 commit-5-5 commit-4-5 commit-3-5 \
commit-6-4 commit-5-4 commit-4-4 commit-3-4 \
commit-6-3 commit-5-3 commit-4-3 \
>expect &&
run_all_modes git rev-list --topo-order --ancestry-path commit-3-3..commit-6-6
'
test_expect_success 'rev-list: symmetric difference topo-order' '
git rev-parse \
commit-6-6 commit-5-6 commit-4-6 \
commit-6-5 commit-5-5 commit-4-5 \
commit-6-4 commit-5-4 commit-4-4 \
commit-6-3 commit-5-3 commit-4-3 \
commit-6-2 commit-5-2 commit-4-2 \
commit-6-1 commit-5-1 commit-4-1 \
commit-3-8 commit-2-8 commit-1-8 \
commit-3-7 commit-2-7 commit-1-7 \
>expect &&
run_all_modes git rev-list --topo-order commit-3-8...commit-6-6
'
test_expect_success 'get_reachable_subset:all' '
cat >input <<-\EOF &&
X:commit-9-1
X:commit-8-3
X:commit-7-5
X:commit-6-6
X:commit-1-7
Y:commit-3-3
Y:commit-1-7
Y:commit-5-6
EOF
(
echo "get_reachable_subset(X,Y)" &&
git rev-parse commit-3-3 \
commit-1-7 \
commit-5-6 | sort
) >expect &&
test_all_modes get_reachable_subset
'
test_expect_success 'get_reachable_subset:some' '
cat >input <<-\EOF &&
X:commit-9-1
X:commit-8-3
X:commit-7-5
X:commit-1-7
Y:commit-3-3
Y:commit-1-7
Y:commit-5-6
EOF
(
echo "get_reachable_subset(X,Y)" &&
git rev-parse commit-3-3 \
commit-1-7 | sort
) >expect &&
test_all_modes get_reachable_subset
'
test_expect_success 'get_reachable_subset:none' '
cat >input <<-\EOF &&
X:commit-9-1
X:commit-8-3
X:commit-7-5
X:commit-1-7
Y:commit-9-3
Y:commit-7-6
Y:commit-2-8
EOF
echo "get_reachable_subset(X,Y)" >expect &&
test_all_modes get_reachable_subset
'
test_done
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