[PATCH 0/3] git-merge-base -a vs. git-show-branch --merge-base

@@ -8,12 +8,12 @@ git-merge-base - Find as good common ancestors as possible for a merge
 
 SYNOPSIS
 --------
-'git merge-base' [--all] <commit> <commit>...
+'git merge-base' [-a|--all] <commit> <commit>...
 
 DESCRIPTION
 -----------
 
-'git-merge-base' finds best common ancestor(s) between two commits to use
+'git merge-base' finds best common ancestor(s) between two commits to use
 in a three-way merge.  One common ancestor is 'better' than another common
 ancestor if the latter is an ancestor of the former.  A common ancestor
 that does not have any better common ancestor is a 'best common

@@ -29,6 +29,7 @@ the given two commits.
 
 OPTIONS
 -------
+-a::
 --all::
 	Output all merge bases for the commits, instead of just one.
 

@@ -8,11 +8,12 @@ git-show-branch - Show branches and their commits
 SYNOPSIS
 --------
 [verse]
-'git show-branch' [--all] [--remotes] [--topo-order | --date-order]
-		[--current] [--color | --no-color]
+'git show-branch' [-a|--all] [-r|--remotes] [--topo-order | --date-order]
+		[--current] [--color | --no-color] [--sparse]
 		[--more=<n> | --list | --independent | --merge-base]
 		[--no-name | --sha1-name] [--topics]
 		[<rev> | <glob>]...
+
 'git show-branch' (-g|--reflog)[=<n>[,<base>]] [--list] [<ref>]
 
 DESCRIPTION

@@ -23,7 +23,7 @@ static int show_merge_base(struct commit **rev, int rev_nr, int show_all)
 }
 
 static const char * const merge_base_usage[] = {
-	"git merge-base [--all] <commit-id> <commit-id>...",
+	"git merge-base [-a|--all] <commit> <commit>...",
 	NULL
 };
 

@@ -6,8 +6,8 @@
 #include "parse-options.h"
 
 static const char* show_branch_usage[] = {
-    "git show-branch [--sparse] [--current] [--all] [--remotes] [--topo-order] [--more=count | --list | --independent | --merge-base] [--topics] [--color] [<refs>...]",
-    "--reflog[=n[,b]] [--list] [--color] <branch>",
+    "git show-branch [-a|--all] [-r|--remotes] [--topo-order | --date-order] [--current] [--color | --no-color] [--sparse] [--more=<n> | --list | --independent | --merge-base] [--no-name | --sha1-name] [--topics] [<rev> | <glob>]...",
+    "git show-branch (-g|--reflog)[=<n>[,<base>]] [--list] [<ref>]",
     NULL
 };
 

@@ -110,6 +110,18 @@ test_expect_success 'compute merge-base (all)' \
 
 # Another set to demonstrate base between one commit and a merge
 # in the documentation.
+#
+# * C (MMC) * B (MMB) * A  (MMA)
+# * o       * o       * o
+# * o       * o       * o
+# * o       * o       * o
+# * o       | _______/
+# |         |/
+# |         * 1 (MM1)
+# | _______/
+# |/
+# * root (MMR)
+
 
 test_expect_success 'merge-base for octopus-step (setup)' '
 	test_tick && git commit --allow-empty -m root && git tag MMR &&

@@ -27,6 +27,10 @@ commits on the command line.  As the most common special case, specifying only
 two commits on the command line means computing the merge base between
 the given two commits.
 
+As a consequence, the 'merge base' is not necessarily contained in each of the
+commit arguments if more than two commits are specified. This is different
+from linkgit:git-show-branch[1] when used with the `--merge-base` option.
+
 OPTIONS
 -------
 -a::

@@ -82,9 +82,11 @@ OPTIONS
 	Synonym to `--more=-1`
 
 --merge-base::
-	Instead of showing the commit list, just act like the
-	'git-merge-base -a' command, except that it can accept
-	more than two heads.
+	Instead of showing the commit list, determine possible
+	merge bases for the specified commits. All merge bases
+	will be contained in all specified commits. This is
+	different from how linkgit:git-merge-base[1] handles
+	the case of three or more commits.
 
 --independent::
 	Among the <reference>s given, display only the ones that

@@ -665,7 +665,7 @@ int cmd_show_branch(int ac, const char **av, const char *prefix)
 		OPT_BOOLEAN(0, "sha1-name", &sha1_name,
 			    "name commits with their object names"),
 		OPT_BOOLEAN(0, "merge-base", &merge_base,
-			    "act like git merge-base -a"),
+			    "show possible merge bases"),
 		OPT_BOOLEAN(0, "independent", &independent,
 			    "show refs unreachable from any other ref"),
 		OPT_BOOLEAN(0, "topo-order", &lifo,

@@ -149,6 +149,12 @@ test_expect_success 'merge-base A B C' '
 	test "$MM1" = "$MB"
 '
 
+test_expect_success 'merge-base A B C using show-branch' '
+	MB=$(git show-branch --merge-base MMA MMB MMC) &&
+	MMR=$(git rev-parse --verify MMR) &&
+	test "$MMR" = "$MB"
+'
+
 test_expect_success 'criss-cross merge-base for octopus-step (setup)' '
 	git reset --hard MMR &&
 	test_tick && git commit --allow-empty -m 1 && git tag CC1 &&