merge-base: "--is-ancestor A B"
In many scripted Porcelain commands, we find this idiom: if test "$(git rev-parse --verify A)" = "$(git merge-base A B)" then ... A is an ancestor of B ... fi But you do not have to compute exact merge-base only to see if A is an ancestor of B. Give them a more direct way to use the underlying machinery. Signed-off-by: Junio C Hamano <gitster@pobox.com>
Junio C Hamano committed
Aug 30, 2012 at 14:52 UTC
5907cda1b2e0bd7dc5c26466f60b9cbb60288cc5
2 files changed
+50
Documentation/git-merge-base.txt
+28
@@ -11,6 +11,7 @@ SYNOPSIS
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[verse]
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'git merge-base' [-a|--all] <commit> <commit>...
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'git merge-base' [-a|--all] --octopus <commit>...
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+'git merge-base' --is-ancestor <commit> <commit>
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'git merge-base' --independent <commit>...
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DESCRIPTION
@@ -50,6 +51,12 @@ from linkgit:git-show-branch[1] when used with the `--merge-base` option.
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from any other. This mimics the behavior of 'git show-branch
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--independent'.
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+--is-ancestor::
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+ Check if the first <commit> is an ancestor of the second <commit>,
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+ and exit with status 0 if true, or with status 1 if not.
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+ Errors are signaled by a non-zero status that is not 1.
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+
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+
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OPTIONS
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-------
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-a::
@@ -110,6 +117,27 @@ both '1' and '2' are merge-bases of A and B. Neither one is better than
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the other (both are 'best' merge bases). When the `--all` option is not given,
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it is unspecified which best one is output.
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+A common idiom to check "fast-forward-ness" between two commits A
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+and B is (or at least used to be) to compute the merge base between
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+A and B, and check if it is the same as A, in which case, A is an
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+ancestor of B. You will see this idiom used often in older scripts.
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+
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+ A=$(git rev-parse --verify A)
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+ if test "$A" = "$(git merge-base A B)"
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+ then
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+ ... A is an ancestor of B ...
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+ fi
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+
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+In modern git, you can say this in a more direct way:
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+
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+ if git merge-base --is-ancestor A B
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+ then
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+ ... A is an ancestor of B ...
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+ fi
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+
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+instead.
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+
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+
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See also
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--------
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linkgit:git-rev-list[1],
builtin/merge-base.c
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@@ -26,6 +26,7 @@ static const char * const merge_base_usage[] = {
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"git merge-base [-a|--all] <commit> <commit>...",
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"git merge-base [-a|--all] --octopus <commit>...",
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"git merge-base --independent <commit>...",
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+ "git merge-base --is-ancestor <commit> <commit>",
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NULL
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};
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@@ -70,6 +71,20 @@ static int handle_octopus(int count, const char **args, int reduce, int show_all
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return 0;
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}
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+static int handle_is_ancestor(int argc, const char **argv)
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+{
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+ struct commit *one, *two;
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+
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+ if (argc != 2)
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+ die("--is-ancestor takes exactly two commits");
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+ one = get_commit_reference(argv[0]);
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+ two = get_commit_reference(argv[1]);
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+ if (in_merge_bases(one, two))
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+ return 0;
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+ else
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+ return 1;
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+}
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+
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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 **rev;
@@ -77,11 +92,14 @@ int cmd_merge_base(int argc, const char **argv, const char *prefix)
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int show_all = 0;
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int octopus = 0;
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int reduce = 0;
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+ int is_ancestor = 0;
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struct option options[] = {
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OPT_BOOLEAN('a', "all", &show_all, "output all common ancestors"),
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OPT_BOOLEAN(0, "octopus", &octopus, "find ancestors for a single n-way merge"),
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OPT_BOOLEAN(0, "independent", &reduce, "list revs not reachable from others"),
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+ OPT_BOOLEAN(0, "is-ancestor", &is_ancestor,
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+ "is the first one ancestor of the other?"),
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OPT_END()
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};
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@@ -89,6 +107,10 @@ int cmd_merge_base(int argc, const char **argv, const char *prefix)
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argc = parse_options(argc, argv, prefix, options, merge_base_usage, 0);
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if (!octopus && !reduce && argc < 2)
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usage_with_options(merge_base_usage, options);
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+ if (is_ancestor && (show_all | octopus | reduce))
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+ die("--is-ancestor cannot be used with other options");
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+ if (is_ancestor)
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+ return handle_is_ancestor(argc, argv);
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if (reduce && (show_all || octopus))
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die("--independent cannot be used with other options");
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