[PATCH 5/6] hook: remove prior hook with '---'

[Emily Shaffer <emilyshaffer@google.com>]

It's possible a user may want to run a hook for nearly every repo,
except for one. Rather than requiring the user to specify the hook
locally in all but one repo, teach 'git hook' how to interpret config
lines intended to remove hooks specified earlier during the config
parse. This means a user can specify such a hook at the system or global
level and override it at the local level.

For example:

$ grep -A2 "\[hook\]" ~/.gitconfig
[hook]
        pre-commit = 001:~/test.sh
        pre-commit = 999:~/baz.sh
$ grep -A2 "\[hook\]" ~/git/.git/config
[hook]
        pre-commit = 900:~/bar.sh
        pre-commit = ---:~/baz.sh
$ ./bin-wrappers/git hook --list pre-commit
001     global  ~/test.sh
900     repo    ~/bar.sh

Signed-off-by: Emily Shaffer <emilyshaffer@google.com>
---
 Documentation/git-hook.txt    |  8 ++++++++
 hook.c                        | 15 ++++++++++-----
 t/t1360-config-based-hooks.sh | 13 +++++++++++++
 3 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/Documentation/git-hook.txt b/Documentation/git-hook.txt
index 0f7115f826..b4a992d43f 100644
--- a/Documentation/git-hook.txt
+++ b/Documentation/git-hook.txt
@@ -28,6 +28,14 @@ The order number of a hook can be changed at a more local scope, e.g.:
 When the order number is respecified this way, the previously specified hook
 configuration is overridden.
 
+A hook specified at a more global scope can be removed by specifying "---"
+instead of an order number, e.g.:
+
+  git config --add --global hook.pre-commit "001:/foo.sh"
+  git config --add --local hook.pre-commit "---:/foo.sh"
+
+When the hook is removed in this way, `/foo.sh` will not be run at all.
+
 OPTIONS
 -------
 
diff --git a/hook.c b/hook.c
index a7dcd18a2e..e7afa140c8 100644
--- a/hook.c
+++ b/hook.c
@@ -49,9 +49,14 @@ static int check_config_for_hooks(const char *var, const char *value, void *hook
 		// TODO this is bad - open to overflows
 		char command[256];
 		int added = 0;
-		if (!sscanf(value, "%d:%s", &order, command))
-			die(_("hook config '%s' doesn't match expected format"),
-			    value);
+		int remove = 0;
+		if (!sscanf(value, "%d:%s", &order, command)) {
+			if (sscanf(value, "---:%s", command))
+				remove = 1;
+			else
+				die(_("hook config '%s' doesn't match expected format"),
+				    value);
+		}
 
 		list_for_each_safe(pos, p, &hook_head) {
 			item = list_entry(pos, struct hook, list);
@@ -60,7 +65,7 @@ static int check_config_for_hooks(const char *var, const char *value, void *hook
 			 * the new entry should go just before the first entry
 			 * which has a higher order number than it.
 			 */
-			if (item->order > order && !added) {
+			if (item->order > order && !added && !remove) {
 				emplace_hook(pos, order, command);
 				added = 1;
 			}
@@ -73,7 +78,7 @@ static int check_config_for_hooks(const char *var, const char *value, void *hook
 				remove_hook(pos);
 		}
 
-		if (!added)
+		if (!added && !remove)
 			emplace_hook(pos, order, command);
 	}
 
diff --git a/t/t1360-config-based-hooks.sh b/t/t1360-config-based-hooks.sh
index 1af43ef18d..66e70ae222 100755
--- a/t/t1360-config-based-hooks.sh
+++ b/t/t1360-config-based-hooks.sh
@@ -61,4 +61,17 @@ test_expect_success 'adding a command with a different number reorders list' '
 	test_cmp expected actual
 '
 
+test_expect_success 'remove a command with "---:/path/to/cmd"' '
+	cat >expected <<-\EOF &&
+	010	repo	/path/abc
+	050	repo	/path/def
+	100	repo	/path/ghi
+	990	repo	/path/rst
+	EOF
+
+	git config --add --local hook.pre-commit "---:/path/uvw" &&
+	git hook --list pre-commit >actual &&
+	test_cmp expected actual
+'
+
 test_done
-- 
2.24.0.393.g34dc348eaf-goog