[PATCH v2] Give git-pull a --reset option

[Alex Henrie <alexhenrie24@gmail.com>]

A common workflow is to make a commit on a local branch, push the branch
to the remote, check out the remote branch on a second computer, amend
the commit on the second computer, force-push back to the remote branch,
and finally submit a pull request. However, if the user switches back to
the first computer, they must then run the cumbersome command
`git fetch && git reset --hard origin`. (Actually, at this point Git
novices often try running `git pull --force`, but it doesn't do what
they expect.) This patch adds the shortcut `git pull --reset` to serve
as a complement to `git push --force`.

Signed-off-by: Alex Henrie <alexhenrie24@gmail.com>
---
 Documentation/git-pull.txt |  8 ++++++++
 builtin/pull.c             | 23 +++++++++++++++++++++++
 t/t5520-pull.sh            | 24 ++++++++++++++++++++++++
 3 files changed, 55 insertions(+)

diff --git a/Documentation/git-pull.txt b/Documentation/git-pull.txt
index 118d9d86f7..032a5c2e34 100644
--- a/Documentation/git-pull.txt
+++ b/Documentation/git-pull.txt
@@ -23,6 +23,7 @@ More precisely, 'git pull' runs 'git fetch' with the given
 parameters and calls 'git merge' to merge the retrieved branch
 heads into the current branch.
 With `--rebase`, it runs 'git rebase' instead of 'git merge'.
+With `--reset`, it runs `git reset --hard` instead of 'git merge'.
 
 <repository> should be the name of a remote repository as
 passed to linkgit:git-fetch[1].  <refspec> can name an
@@ -141,6 +142,13 @@ unless you have read linkgit:git-rebase[1] carefully.
 +
 This option is only valid when "--rebase" is used.
 
+--reset::
+	Reset the local branch to be identical to the remote branch, discarding
+	any local commits or other changes.
+
+--no-reset::
+	Override earlier --reset.
+
 Options related to fetching
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/builtin/pull.c b/builtin/pull.c
index 33db889955..b32134c1f1 100644
--- a/builtin/pull.c
+++ b/builtin/pull.c
@@ -95,6 +95,7 @@ static int recurse_submodules = RECURSE_SUBMODULES_DEFAULT;
 
 /* Options passed to git-merge or git-rebase */
 static enum rebase_type opt_rebase = -1;
+static char *opt_reset;
 static char *opt_diffstat;
 static char *opt_log;
 static char *opt_signoff;
@@ -144,6 +145,9 @@ static struct option pull_options[] = {
 	  "(false|true|merges|preserve|interactive)",
 	  N_("incorporate changes by rebasing rather than merging"),
 	  PARSE_OPT_OPTARG, parse_opt_rebase },
+	OPT_PASSTHRU(0, "reset", &opt_reset, NULL,
+		N_("discard all local changes rather than merging"),
+		PARSE_OPT_NOARG | PARSE_OPT_NONEG),
 	OPT_PASSTHRU('n', NULL, &opt_diffstat, NULL,
 		N_("do not show a diffstat at the end of the merge"),
 		PARSE_OPT_NOARG | PARSE_OPT_NONEG),
@@ -860,6 +864,16 @@ static int run_rebase(const struct object_id *curr_head,
 	return ret;
 }
 
+/**
+ * Runs git-reset, returning its exit status.
+ */
+static int run_reset(void)
+{
+	static const char *argv[] = { "reset", "--hard", "FETCH_HEAD", NULL };
+
+	return run_command_v_opt(argv, RUN_GIT_CMD);
+}
+
 int cmd_pull(int argc, const char **argv, const char *prefix)
 {
 	const char *repo, **refspecs;
@@ -892,6 +906,9 @@ int cmd_pull(int argc, const char **argv, const char *prefix)
 	if (get_oid("HEAD", &orig_head))
 		oidclr(&orig_head);
 
+	if (opt_rebase && opt_reset)
+		die(_("--rebase and --reset are mutually exclusive"));
+
 	if (!opt_rebase && opt_autostash != -1)
 		die(_("--[no-]autostash option is only valid with --rebase."));
 
@@ -986,6 +1003,12 @@ int cmd_pull(int argc, const char **argv, const char *prefix)
 			ret = rebase_submodules();
 
 		return ret;
+	} else if (opt_reset) {
+		int ret = run_reset();
+		if (!ret && (recurse_submodules == RECURSE_SUBMODULES_ON ||
+			     recurse_submodules == RECURSE_SUBMODULES_ON_DEMAND))
+			ret = update_submodules();
+		return ret;
 	} else {
 		int ret = run_merge();
 		if (!ret && (recurse_submodules == RECURSE_SUBMODULES_ON ||
diff --git a/t/t5520-pull.sh b/t/t5520-pull.sh
index cf4cc32fd0..597f2429d5 100755
--- a/t/t5520-pull.sh
+++ b/t/t5520-pull.sh
@@ -708,4 +708,28 @@ test_expect_success 'git pull --rebase against local branch' '
 	test file = "$(cat file2)"
 '
 
+test_expect_success 'git pull --rebase --reset is an invalid combination' '
+	test_must_fail git pull --rebase --reset .
+'
+
+test_expect_success 'git pull --reset overwrites or deletes all tracked files' '
+	git init cloned &&
+	(
+		cd cloned &&
+		echo committed > committed &&
+		echo staged > staged &&
+		echo untracked > file &&
+		echo untracked > untracked &&
+		git add committed &&
+		git commit -m original &&
+		git add staged &&
+		git pull --reset .. &&
+		test ! -f committed &&
+		test ! -f staged &&
+		test "$(cat untracked)" = "untracked" &&
+		test "$(git status --porcelain)" = "?? untracked"
+	) &&
+	test_cmp file cloned/file
+'
+
 test_done
-- 
2.21.0