[PATCH 2/2] format-patch: introduce format.defaultTo

[Ramkumar Ramachandra <artagnon@gmail.com>]

A very common workflow for preparing patches involves working off a
topic branch and generating patches against 'master' to send off to the
maintainer. However, a plain

  $ git format-patch -o outgoing

is a no-op on a topic branch, and the user has to remember to specify
'master' explicitly everytime. Save the user the extra keystrokes by
introducing format.defaultTo which can contain the name of a branch
against which to base patches.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
---
 Documentation/config.txt               |  4 ++++
 builtin/log.c                          |  7 +++++++
 contrib/completion/git-completion.bash |  1 +
 t/t4014-format-patch.sh                | 10 ++++++++++
 4 files changed, 22 insertions(+)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index a405806..b90abd1 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -1135,6 +1135,10 @@ format.coverLetter::
 	format-patch is invoked, but in addition can be set to "auto", to
 	generate a cover-letter only when there's more than one patch.
 
+format.defaultTo::
+	The name of a branch against which to generate patches by
+	default. You'd usually want this to be 'master'.
+
 filter.<driver>.clean::
 	The command which is used to convert the content of a worktree
 	file to a blob upon checkin.  See linkgit:gitattributes[5] for
diff --git a/builtin/log.c b/builtin/log.c
index b97373d..ebc419e 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -674,6 +674,7 @@ static int thread;
 static int do_signoff;
 static const char *signature = git_version_string;
 static int config_cover_letter;
+static const char *config_defaultto;
 
 enum {
 	COVER_UNSET,
@@ -750,6 +751,8 @@ static int git_format_config(const char *var, const char *value, void *cb)
 		config_cover_letter = git_config_bool(var, value) ? COVER_ON : COVER_OFF;
 		return 0;
 	}
+	if (!strcmp(var, "format.defaultto"))
+		return git_config_string(&config_defaultto, var, value);
 
 	return git_log_config(var, value, cb);
 }
@@ -1324,6 +1327,10 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 		die (_("--subject-prefix and -k are mutually exclusive."));
 	rev.preserve_subject = keep_subject;
 
+	if (argc < 2 && config_defaultto) {
+		argv[1] = config_defaultto;
+		argc++;
+	}
 	argc = setup_revisions(argc, argv, &rev, &s_r_opt);
 	if (argc > 1)
 		die (_("unrecognized argument: %s"), argv[1]);
diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index 39b81f7..75699d4 100644
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -1992,6 +1992,7 @@ _git_config ()
 		format.attach
 		format.cc
 		format.coverLetter
+		format.defaultTo
 		format.headers
 		format.numbered
 		format.pretty
diff --git a/t/t4014-format-patch.sh b/t/t4014-format-patch.sh
index 73194b2..46c0337 100755
--- a/t/t4014-format-patch.sh
+++ b/t/t4014-format-patch.sh
@@ -1370,4 +1370,14 @@ test_expect_success 'cover letter auto user override' '
 	test_line_count = 2 list
 '
 
+test_expect_success 'defaultTo side' '
+	mkdir -p tmp &&
+	test_when_finished "rm -rf tmp;
+		git config --unset format.defaultTo" &&
+
+	git config format.defaultTo side &&
+	git format-patch -o tmp >list &&
+	test_line_count = 3 list
+'
+
 test_done
-- 
1.8.5.2.229.g4448466.dirty