Merge branch 'jc/merge-refuse-new-root'

"git pull" has been taught to pass --allow-unrelated-histories
option to underlying "git merge".

* jc/merge-refuse-new-root:
  pull: pass --allow-unrelated-histories to "git merge"
  t3033: avoid 'ambiguous refs' warning

Documentation/git-merge.txt

@@ -11,6 +11,7 @@ SYNOPSIS
 [verse]
 'git merge' [-n] [--stat] [--no-commit] [--squash] [--[no-]edit]
 	[-s <strategy>] [-X <strategy-option>] [-S[<keyid>]]
+	[--[no-]allow-unrelated-histories]
 	[--[no-]rerere-autoupdate] [-m <msg>] [<commit>...]
 'git merge' <msg> HEAD <commit>...
 'git merge' --abort
@@ -98,19 +99,6 @@ commit or stash your changes before running 'git merge'.
 'git merge --abort' is equivalent to 'git reset --merge' when
 `MERGE_HEAD` is present.
 
---allow-unrelated-histories::
-	By default, `git merge` command refuses to merge histories
-	that do not share a common ancestor.  This option can be
-	used to override this safety when merging histories of two
-	projects that started their lives independently.  As that is
-	a very rare occasion, no configuration variable to enable
-	this by default exists and will not be added, and the list
-	of options at the top of this documentation does not mention
-	this option.  Also `git pull` does not pass this option down
-	to `git merge` (instead, you `git fetch` first, examine what
-	you will be merging and then `git merge` locally with this
-	option).
-
 <commit>...::
 	Commits, usually other branch heads, to merge into our branch.
 	Specifying more than one commit will create a merge with

Documentation/merge-options.txt

@@ -114,3 +114,11 @@ ifndef::git-pull[]
 	reporting.
 
 endif::git-pull[]
+
+--allow-unrelated-histories::
+	By default, `git merge` command refuses to merge histories
+	that do not share a common ancestor.  This option can be
+	used to override this safety when merging histories of two
+	projects that started their lives independently. As that is
+	a very rare occasion, no configuration variable to enable
+	this by default exists and will not be added.

builtin/pull.c

@@ -91,6 +91,7 @@ static int config_autostash;
 static struct argv_array opt_strategies = ARGV_ARRAY_INIT;
 static struct argv_array opt_strategy_opts = ARGV_ARRAY_INIT;
 static char *opt_gpg_sign;
+static int opt_allow_unrelated_histories;
 
 /* Options passed to git-fetch */
 static char *opt_all;
@@ -163,6 +164,9 @@ static struct option pull_options[] = {
 	OPT_PASSTHRU('S', "gpg-sign", &opt_gpg_sign, N_("key-id"),
 		N_("GPG sign commit"),
 		PARSE_OPT_OPTARG),
+	OPT_SET_INT(0, "allow-unrelated-histories",
+		    &opt_allow_unrelated_histories,
+		    N_("allow merging unrelated histories"), 1),
 
 	/* Options passed to git-fetch */
 	OPT_GROUP(N_("Options related to fetching")),
@@ -628,6 +632,8 @@ static int run_merge(void)
 	argv_array_pushv(&args, opt_strategy_opts.argv);
 	if (opt_gpg_sign)
 		argv_array_push(&args, opt_gpg_sign);
+	if (opt_allow_unrelated_histories > 0)
+		argv_array_push(&args, "--allow-unrelated-histories");
 
 	argv_array_push(&args, "FETCH_HEAD");
 	ret = run_command_v_opt(args.argv, RUN_GIT_CMD);

t/t3033-merge-toplevel.sh

@@ -19,7 +19,7 @@ test_expect_success setup '
 	test_commit three &&
 	git checkout right &&
 	test_commit four &&
-	git checkout --orphan five &&
+	git checkout --orphan newroot &&
 	test_commit five &&
 	git checkout master
 '

t/t5521-pull-options.sh

@@ -144,4 +144,25 @@ test_expect_success 'git pull --all --dry-run' '
 	)
 '
 
+test_expect_success 'git pull --allow-unrelated-histories' '
+	test_when_finished "rm -fr src dst" &&
+	git init src &&
+	(
+		cd src &&
+		test_commit one &&
+		test_commit two
+	) &&
+	git clone src dst &&
+	(
+		cd src &&
+		git checkout --orphan side HEAD^ &&
+		test_commit three
+	) &&
+	(
+		cd dst &&
+		test_must_fail git pull ../src side &&
+		git pull --allow-unrelated-histories ../src side
+	)
+'
+
 test_done