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git-commit-vandalism/t/t6600-test-reach.sh
Derrick Stolee cbfe360b14 commit-reach: add tips_reachable_from_bases() 
Both 'git for-each-ref --merged=<X>' and 'git branch --merged=<X>' use
the ref-filter machinery to select references or branches (respectively)
that are reachable from a set of commits presented by one or more
--merged arguments. This happens within reach_filter(), which uses the
revision-walk machinery to walk history in a standard way.

However, the commit-reach.c file is full of custom searches that are
more efficient, especially for reachability queries that can terminate
early when reachability is discovered. Add a new
tips_reachable_from_bases() method to commit-reach.c and call it from
within reach_filter() in ref-filter.c. This affects both 'git branch'
and 'git for-each-ref' as tested in p1500-graph-walks.sh.

For the Linux kernel repository, we take an already-fast algorithm and
make it even faster:

Test                                            HEAD~1  HEAD
-------------------------------------------------------------------
1500.5: contains: git for-each-ref --merged     0.13    0.02 -84.6%
1500.6: contains: git branch --merged           0.14    0.02 -85.7%
1500.7: contains: git tag --merged              0.15    0.03 -80.0%

(Note that we remove the iterative 'git rev-list' test from p1500
because it no longer makes sense as a comparison to 'git for-each-ref'
and would just waste time running it for these comparisons.)

The algorithm is implemented in commit-reach.c in the method
tips_reachable_from_base(). This method takes a string_list of tips and
assigns the 'util' for each item with the value 1 if the base commit can
reach those tips.

Like other reachability queries in commit-reach.c, the fastest way to
search for "can A reach B?" is to do a depth-first search up to the
generation number of B, preferring to explore first parents before later
parents. While we must walk all reachable commits up to that generation
number when the answer is "no", the depth-first search can answer "yes"
much faster than other approaches in most cases.

This search becomes trickier when there are multiple targets for the
depth-first search. The commits with lower generation number are more
likely to be within the history of the start commit, but we don't want
to waste time searching commits of low generation number if the commit
target with lowest generation number has already been found.

The trick here is to take the input commits and sort them by generation
number in ascending order. Track the index within this order as
min_generation_index. When we find a commit, if its index in the list is
equal to min_generation_index, then we can increase the generation
number boundary of our search to the next-lowest value in the list.

With this mechanism, the number of commits to search is minimized with
respect to the depth-first search heuristic. We will walk all commits up
to the minimum generation number of a commit that is _not_ reachable
from the start, but we will walk only the necessary portion of the
depth-first search for the reachable commits of lower generation.

Add extra tests for this behavior in t6600-test-reach.sh as the
interesting data shape of that repository can sometimes demonstrate
corner case bugs.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-03-20 12:17:33 -07:00

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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 || return 1
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-$i || return 1
done
done &&
git commit-graph write --reachable &&
mv .git/objects/info/commit-graph commit-graph-full &&
chmod u+w commit-graph-full &&
git show-ref -s commit-5-5 | git commit-graph write --stdin-commits &&
mv .git/objects/info/commit-graph commit-graph-half &&
chmod u+w commit-graph-half &&
git -c commitGraph.generationVersion=1 commit-graph write --reachable &&
mv .git/objects/info/commit-graph commit-graph-no-gdat &&
chmod u+w commit-graph-no-gdat &&
git config core.commitGraph true
'
run_all_modes () {
test_when_finished rm -rf .git/objects/info/commit-graph &&
"$@" <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_expect_success 'for-each-ref ahead-behind:linear' '
cat >input <<-\EOF &&
refs/heads/commit-1-1
refs/heads/commit-1-3
refs/heads/commit-1-5
refs/heads/commit-1-8
EOF
cat >expect <<-\EOF &&
refs/heads/commit-1-1 0 8
refs/heads/commit-1-3 0 6
refs/heads/commit-1-5 0 4
refs/heads/commit-1-8 0 1
EOF
run_all_modes git for-each-ref \
--format="%(refname) %(ahead-behind:commit-1-9)" --stdin
'
test_expect_success 'for-each-ref ahead-behind:all' '
cat >input <<-\EOF &&
refs/heads/commit-1-1
refs/heads/commit-2-4
refs/heads/commit-4-2
refs/heads/commit-4-4
EOF
cat >expect <<-\EOF &&
refs/heads/commit-1-1 0 24
refs/heads/commit-2-4 0 17
refs/heads/commit-4-2 0 17
refs/heads/commit-4-4 0 9
EOF
run_all_modes git for-each-ref \
--format="%(refname) %(ahead-behind:commit-5-5)" --stdin
'
test_expect_success 'for-each-ref ahead-behind:some' '
cat >input <<-\EOF &&
refs/heads/commit-1-1
refs/heads/commit-5-3
refs/heads/commit-4-8
refs/heads/commit-9-9
EOF
cat >expect <<-\EOF &&
refs/heads/commit-1-1 0 53
refs/heads/commit-4-8 8 30
refs/heads/commit-5-3 0 39
refs/heads/commit-9-9 27 0
EOF
run_all_modes git for-each-ref \
--format="%(refname) %(ahead-behind:commit-9-6)" --stdin
'
test_expect_success 'for-each-ref ahead-behind:some, multibase' '
cat >input <<-\EOF &&
refs/heads/commit-1-1
refs/heads/commit-5-3
refs/heads/commit-7-8
refs/heads/commit-4-8
refs/heads/commit-9-9
EOF
cat >expect <<-\EOF &&
refs/heads/commit-1-1 0 53 0 53
refs/heads/commit-4-8 8 30 0 22
refs/heads/commit-5-3 0 39 0 39
refs/heads/commit-7-8 14 12 8 6
refs/heads/commit-9-9 27 0 27 0
EOF
run_all_modes git for-each-ref \
--format="%(refname) %(ahead-behind:commit-9-6) %(ahead-behind:commit-6-9)" \
--stdin
'
test_expect_success 'for-each-ref ahead-behind:none' '
cat >input <<-\EOF &&
refs/heads/commit-7-5
refs/heads/commit-4-8
refs/heads/commit-9-9
EOF
cat >expect <<-\EOF &&
refs/heads/commit-4-8 16 16
refs/heads/commit-7-5 7 4
refs/heads/commit-9-9 49 0
EOF
run_all_modes git for-each-ref \
--format="%(refname) %(ahead-behind:commit-8-4)" --stdin
'
test_expect_success 'for-each-ref merged:linear' '
cat >input <<-\EOF &&
refs/heads/commit-1-1
refs/heads/commit-1-3
refs/heads/commit-1-5
refs/heads/commit-1-8
refs/heads/commit-2-1
refs/heads/commit-5-1
refs/heads/commit-9-1
EOF
cat >expect <<-\EOF &&
refs/heads/commit-1-1
refs/heads/commit-1-3
refs/heads/commit-1-5
refs/heads/commit-1-8
EOF
run_all_modes git for-each-ref --merged=commit-1-9 \
--format="%(refname)" --stdin
'
test_expect_success 'for-each-ref merged:all' '
cat >input <<-\EOF &&
refs/heads/commit-1-1
refs/heads/commit-2-4
refs/heads/commit-4-2
refs/heads/commit-4-4
EOF
cat >expect <<-\EOF &&
refs/heads/commit-1-1
refs/heads/commit-2-4
refs/heads/commit-4-2
refs/heads/commit-4-4
EOF
run_all_modes git for-each-ref --merged=commit-5-5 \
--format="%(refname)" --stdin
'
test_expect_success 'for-each-ref ahead-behind:some' '
cat >input <<-\EOF &&
refs/heads/commit-1-1
refs/heads/commit-5-3
refs/heads/commit-4-8
refs/heads/commit-9-9
EOF
cat >expect <<-\EOF &&
refs/heads/commit-1-1
refs/heads/commit-5-3
EOF
run_all_modes git for-each-ref --merged=commit-9-6 \
--format="%(refname)" --stdin
'
test_expect_success 'for-each-ref merged:some, multibase' '
cat >input <<-\EOF &&
refs/heads/commit-1-1
refs/heads/commit-5-3
refs/heads/commit-7-8
refs/heads/commit-4-8
refs/heads/commit-9-9
EOF
cat >expect <<-\EOF &&
refs/heads/commit-1-1
refs/heads/commit-4-8
refs/heads/commit-5-3
EOF
run_all_modes git for-each-ref \
--merged=commit-5-8 \
--merged=commit-8-5 \
--format="%(refname)" \
--stdin
'
test_expect_success 'for-each-ref merged:none' '
cat >input <<-\EOF &&
refs/heads/commit-7-5
refs/heads/commit-4-8
refs/heads/commit-9-9
EOF
>expect &&
run_all_modes git for-each-ref --merged=commit-8-4 \
--format="%(refname)" --stdin
'
test_done
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