Merge branch 'cc/merge-base-many'
* cc/merge-base-many: git-merge-octopus: use (merge-base A (merge B C D E...)) for stepwise merge merge-base-many: add trivial tests based on the documentation documentation: merge-base: explain "git merge-base" with more than 2 args merge-base: teach "git merge-base" to drive underlying merge_bases_many()
This commit is contained in:
Junio C Hamano
commit
0569d7566e
@ -8,26 +8,81 @@ git-merge-base - Find as good common ancestors as possible for a merge
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SYNOPSIS
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--------
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'git merge-base' [--all] <commit> <commit>
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'git merge-base' [--all] <commit> <commit>...
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DESCRIPTION
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-----------
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'git-merge-base' finds as good a common ancestor as possible between
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the two commits. That is, given two commits A and B, `git merge-base A
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B` will output a commit which is reachable from both A and B through
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the parent relationship.
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'git-merge-base' finds best common ancestor(s) between two commits to use
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in a three-way merge. One common ancestor is 'better' than another common
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ancestor if the latter is an ancestor of the former. A common ancestor
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that does not have any better common ancestor than it is a 'best common
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ancestor', i.e. a 'merge base'. Note that there can be more than one
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merge bases between two commits.
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Given a selection of equally good common ancestors it should not be
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relied on to decide in any particular way.
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The 'git-merge-base' algorithm is still in flux - use the source...
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Among the two commits to compute their merge bases, one is specified by
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the first commit argument on the command line; the other commit is a
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(possibly hypothetical) commit that is a merge across all the remaining
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commits on the command line. As the most common special case, giving only
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two commits from the command line means computing the merge base between
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the given two commits.
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OPTIONS
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-------
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--all::
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Output all common ancestors for the two commits instead of
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just one.
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Output all merge bases for the commits, instead of just one.
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DISCUSSION
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----------
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Given two commits 'A' and 'B', `git merge-base A B` will output a commit
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which is reachable from both 'A' and 'B' through the parent relationship.
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For example, with this topology:
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o---o---o---B
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/
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---o---1---o---o---o---A
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the merge base between 'A' and 'B' is '1'.
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Given three commits 'A', 'B' and 'C', `git merge-base A B C` will compute the
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merge base between 'A' and an hypothetical commit 'M', which is a merge
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between 'B' and 'C'. For example, with this topology:
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o---o---o---o---C
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/
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/ o---o---o---B
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/ /
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---2---1---o---o---o---A
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the result of `git merge-base A B C` is '1'. This is because the
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equivalent topology with a merge commit 'M' between 'B' and 'C' is:
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o---o---o---o---o
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/ \
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/ o---o---o---o---M
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/ /
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---2---1---o---o---o---A
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and the result of `git merge-base A M` is '1'. Commit '2' is also a
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common ancestor between 'A' and 'M', but '1' is a better common ancestor,
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because '2' is an ancestor of '1'. Hence, '2' is not a merge base.
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When the history involves criss-cross merges, there can be more than one
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'best' common ancestors between two commits. For example, with this
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topology:
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---1---o---A
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\ /
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X
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/ \
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---2---o---o---B
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both '1' and '2' are merge-base of A and B. Neither one is better than
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the other (both are 'best' merge base). When `--all` option is not given,
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it is unspecified which best one is output.
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Author
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------
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@ -2,9 +2,11 @@
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#include "cache.h"
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#include "commit.h"
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static int show_merge_base(struct commit *rev1, struct commit *rev2, int show_all)
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static int show_merge_base(struct commit **rev, int rev_nr, int show_all)
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{
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struct commit_list *result = get_merge_bases(rev1, rev2, 0);
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struct commit_list *result;
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result = get_merge_bases_many(rev[0], rev_nr - 1, rev + 1, 0);
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if (!result)
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return 1;
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@ -20,7 +22,7 @@ static int show_merge_base(struct commit *rev1, struct commit *rev2, int show_al
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}
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static const char merge_base_usage[] =
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"git merge-base [--all] <commit-id> <commit-id>";
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"git merge-base [--all] <commit-id> <commit-id>...";
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static struct commit *get_commit_reference(const char *arg)
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{
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@ -38,7 +40,8 @@ static struct commit *get_commit_reference(const char *arg)
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int cmd_merge_base(int argc, const char **argv, const char *prefix)
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{
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struct commit *rev1, *rev2;
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struct commit **rev;
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int rev_nr = 0;
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int show_all = 0;
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git_config(git_default_config, NULL);
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@ -51,10 +54,15 @@ int cmd_merge_base(int argc, const char **argv, const char *prefix)
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usage(merge_base_usage);
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argc--; argv++;
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}
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if (argc != 3)
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if (argc < 3)
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usage(merge_base_usage);
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rev1 = get_commit_reference(argv[1]);
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rev2 = get_commit_reference(argv[2]);
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return show_merge_base(rev1, rev2, show_all);
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rev = xmalloc((argc - 1) * sizeof(*rev));
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do {
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rev[rev_nr++] = get_commit_reference(argv[1]);
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argc--; argv++;
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} while (argc > 1);
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return show_merge_base(rev, rev_nr, show_all);
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}
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1
commit.h
1
commit.h
@ -121,6 +121,7 @@ int read_graft_file(const char *graft_file);
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struct commit_graft *lookup_commit_graft(const unsigned char *sha1);
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extern struct commit_list *get_merge_bases(struct commit *rev1, struct commit *rev2, int cleanup);
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extern struct commit_list *get_merge_bases_many(struct commit *one, int n, struct commit **twos, int cleanup);
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extern struct commit_list *get_octopus_merge_bases(struct commit_list *in);
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extern int register_shallow(const unsigned char *sha1);
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@ -61,7 +61,7 @@ do
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exit 2
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esac
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common=$(git merge-base --all $MRC $SHA1) ||
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common=$(git merge-base --all $SHA1 $MRC) ||
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die "Unable to find common commit with $SHA1"
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case "$LF$common$LF" in
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@ -100,14 +100,7 @@ do
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next=$(git write-tree 2>/dev/null)
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fi
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# We have merged the other branch successfully. Ideally
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# we could implement OR'ed heads in merge-base, and keep
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# a list of commits we have merged so far in MRC to feed
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# them to merge-base, but we approximate it by keep using
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# the current MRC. We used to update it to $common, which
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# was incorrectly doing AND'ed merge-base here, which was
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# unneeded.
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MRC="$MRC $SHA1"
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MRT=$next
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done
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@ -108,4 +108,52 @@ test_expect_success 'compute merge-base (all)' \
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'MB=$(git merge-base --all PL PR) &&
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expr "$(git name-rev "$MB")" : "[0-9a-f]* tags/C2"'
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# Another set to demonstrate base between one commit and a merge
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# in the documentation.
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test_expect_success 'merge-base for octopus-step (setup)' '
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test_tick && git commit --allow-empty -m root && git tag MMR &&
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test_tick && git commit --allow-empty -m 1 && git tag MM1 &&
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test_tick && git commit --allow-empty -m o &&
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test_tick && git commit --allow-empty -m o &&
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test_tick && git commit --allow-empty -m o &&
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test_tick && git commit --allow-empty -m A && git tag MMA &&
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git checkout MM1 &&
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test_tick && git commit --allow-empty -m o &&
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test_tick && git commit --allow-empty -m o &&
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test_tick && git commit --allow-empty -m o &&
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test_tick && git commit --allow-empty -m B && git tag MMB &&
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git checkout MMR &&
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test_tick && git commit --allow-empty -m o &&
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test_tick && git commit --allow-empty -m o &&
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test_tick && git commit --allow-empty -m o &&
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test_tick && git commit --allow-empty -m o &&
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test_tick && git commit --allow-empty -m C && git tag MMC
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'
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test_expect_success 'merge-base A B C' '
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MB=$(git merge-base --all MMA MMB MMC) &&
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MM1=$(git rev-parse --verify MM1) &&
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test "$MM1" = "$MB"
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'
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test_expect_success 'criss-cross merge-base for octopus-step (setup)' '
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git reset --hard MMR &&
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test_tick && git commit --allow-empty -m 1 && git tag CC1 &&
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git reset --hard E &&
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test_tick && git commit --allow-empty -m 2 && git tag CC2 &&
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test_tick && git merge -s ours CC1 &&
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test_tick && git commit --allow-empty -m o &&
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test_tick && git commit --allow-empty -m B && git tag CCB &&
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git reset --hard CC1 &&
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test_tick && git merge -s ours CC2 &&
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test_tick && git commit --allow-empty -m A && git tag CCA
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'
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test_expect_success 'merge-base B A^^ A^^2' '
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MB0=$(git merge-base --all CCB CCA^^ CCA^^2 | sort) &&
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MB1=$(git rev-parse CC1 CC2 | sort) &&
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test "$MB0" = "$MB1"
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'
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test_done
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