diff mbox series

[v8,03/37] hook: add list command

Message ID 20210311021037.3001235-4-emilyshaffer@google.com (mailing list archive)
State New, archived
Headers show
Series config-based hooks | expand

Commit Message

Emily Shaffer March 11, 2021, 2:10 a.m. UTC
Teach 'git hook list <hookname>', which checks the known configs in
order to create an ordered list of hooks to run on a given hook event.

Multiple commands can be specified for a given hook by providing
multiple "hook.<hookname>.command = <path-to-hook>" lines. Hooks will be
run in config order. If more properties need to be set on a given hook
in the future, commands can also be specified by providing
"hook.<hookname>.command = <hookcmd-name>", as well as a "[hookcmd
<hookcmd-name>]" subsection; this subsection should contain a
"hookcmd.<hookcmd-name>.command = <path-to-hook>" line.

For example:

  $ git config --list | grep ^hook
  hook.pre-commit.command=baz
  hook.pre-commit.command=~/bar.sh
  hookcmd.baz.command=~/baz/from/hookcmd.sh

  $ git hook list pre-commit
  global: ~/baz/from/hookcmd.sh
  local: ~/bar.sh

Signed-off-by: Emily Shaffer <emilyshaffer@google.com>
---

Notes:
    Since v7, fixed some nits from Jonathan Tan, one of which revealed a bug in
    how I was adding hooks to the list.

 Documentation/config/hook.txt |   9 +++
 Documentation/git-hook.txt    |  59 ++++++++++++++++-
 Makefile                      |   1 +
 builtin/hook.c                |  56 ++++++++++++++--
 hook.c                        | 120 ++++++++++++++++++++++++++++++++++
 hook.h                        |  25 +++++++
 t/t1360-config-based-hooks.sh |  81 ++++++++++++++++++++++-
 7 files changed, 341 insertions(+), 10 deletions(-)
 create mode 100644 Documentation/config/hook.txt
 create mode 100644 hook.c
 create mode 100644 hook.h

Comments

Ævar Arnfjörð Bjarmason March 12, 2021, 8:20 a.m. UTC | #1
On Thu, Mar 11 2021, Emily Shaffer wrote:

> diff --git a/Documentation/config/hook.txt b/Documentation/config/hook.txt
> new file mode 100644
> index 0000000000..71449ecbc7
> --- /dev/null
> +++ b/Documentation/config/hook.txt
> @@ -0,0 +1,9 @@
> +hook.<command>.command::
> +	A command to execute during the <command> hook event. This can be an
> +	executable on your device, a oneliner for your shell, or the name of a
> +	hookcmd. See linkgit:git-hook[1].
> +
> +hookcmd.<name>.command::
> +	A command to execute during a hook for which <name> has been specified
> +	as a command. This can be an executable on your device or a oneliner for
> +	your shell. See linkgit:git-hook[1].
> diff --git a/Documentation/git-hook.txt b/Documentation/git-hook.txt
> index 9eeab0009d..f19875ed68 100644
> --- a/Documentation/git-hook.txt
> +++ b/Documentation/git-hook.txt
> @@ -8,12 +8,65 @@ git-hook - Manage configured hooks
>  SYNOPSIS
>  --------
>  [verse]
> -'git hook'
> +'git hook' list <hook-name>

Having just read this far (maybe this pattern is shared in the rest of
the series): Let's just squash this and the 2nd patch together.

Sometimes it's worth doing the scaffolding first, but adding a new
built-in is so trivial that I don't think it's worth it, and it just
results in back & forth churn like the above...

>  DESCRIPTION
>  -----------
> -A placeholder command. Later, you will be able to list, add, and modify hooks
> -with this command.

...and this...

> +You can list configured hooks with this command. Later, you will be able to run,
> +add, and modify hooks with this command.
> +
> +This command parses the default configuration files for sections `hook` and
> +`hookcmd`. `hook` is used to describe the commands which will be run during a
> +particular hook event; commands are run in the order Git encounters them during
> +the configuration parse (see linkgit:git-config[1]). `hookcmd` is used to
> +describe attributes of a specific command. If additional attributes don't need
> +to be specified, a command to run can be specified directly in the `hook`
> +section; if a `hookcmd` by that name isn't found, Git will attempt to run the
> +provided value directly. For example:
> +
> +Global config
> +----
> +  [hook "post-commit"]
> +    command = "linter"
> +    command = "~/typocheck.sh"
> +
> +  [hookcmd "linter"]
> +    command = "/bin/linter --c"
> +----
> +
> +Local config
> +----
> +  [hook "prepare-commit-msg"]
> +    command = "linter"
> +  [hook "post-commit"]
> +    command = "python ~/run-test-suite.py"
> +----
> +
> +With these configs, you'd then see:
> +
> +----
> +$ git hook list "post-commit"
> +global: /bin/linter --c
> +global: ~/typocheck.sh
> +local: python ~/run-test-suite.py
> +
> +$ git hook list "prepare-commit-msg"
> +local: /bin/linter --c
> +----
> +
> +COMMANDS
> +--------
> +
> +list `<hook-name>`::
> +
> +List the hooks which have been configured for `<hook-name>`. Hooks appear
> +in the order they should be run, and print the config scope where the relevant
> +`hook.<hook-name>.command` was specified, not the `hookcmd` (if applicable).
> +This output is human-readable and the format is subject to change over time.
> +
> +CONFIGURATION
> +-------------
> +include::config/hook.txt[]
>  
>  GIT
>  ---
> diff --git a/Makefile b/Makefile
> index 8e904a1ab5..3fa51597d8 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -891,6 +891,7 @@ LIB_OBJS += hash-lookup.o
>  LIB_OBJS += hashmap.o
>  LIB_OBJS += help.o
>  LIB_OBJS += hex.o
> +LIB_OBJS += hook.o
>  LIB_OBJS += ident.o
>  LIB_OBJS += json-writer.o
>  LIB_OBJS += kwset.o
> diff --git a/builtin/hook.c b/builtin/hook.c
> index b2bbc84d4d..bb64cd77ca 100644
> --- a/builtin/hook.c
> +++ b/builtin/hook.c
> @@ -1,21 +1,67 @@
>  #include "cache.h"
> -

Stray back & forth whitespace churn?

>  #include "builtin.h"
> +#include "config.h"
> +#include "hook.h"
>  #include "parse-options.h"
> +#include "strbuf.h"
>  
>  static const char * const builtin_hook_usage[] = {
> -	N_("git hook"),
> +	N_("git hook list <hookname>"),
>  	NULL
>  };
>  
> -int cmd_hook(int argc, const char **argv, const char *prefix)
> +static int list(int argc, const char **argv, const char *prefix)

...and here the cmd_hook() function being replaced (not really, just
moved below, but you get my drift...)

>  {
> -	struct option builtin_hook_options[] = {
> +	struct list_head *head, *pos;
> +	struct strbuf hookname = STRBUF_INIT;
> +
> +	struct option list_options[] = {
>  		OPT_END(),
>  	};
>  
> -	argc = parse_options(argc, argv, prefix, builtin_hook_options,
> +	argc = parse_options(argc, argv, prefix, list_options,
>  			     builtin_hook_usage, 0);
>  
> +	if (argc < 1) {
> +		usage_msg_opt(_("You must specify a hook event name to list."),
> +			      builtin_hook_usage, list_options);
> +	}
> +
> +	strbuf_addstr(&hookname, argv[0]);
> +
> +	head = hook_list(&hookname);
> +

More on strbuf usage later in another soon-to-be-sent E-Mail.

> +	if (list_empty(head)) {
> +		printf(_("no commands configured for hook '%s'\n"),
> +		       hookname.buf);
> +		strbuf_release(&hookname);
> +		return 0;
> +	}
> +
> +	list_for_each(pos, head) {
> +		struct hook *item = list_entry(pos, struct hook, list);
> +		if (item)
> +			printf("%s: %s\n",
> +			       config_scope_name(item->origin),
> +			       item->command.buf);
> +	}
> +
> +	clear_hook_list(head);
> +	strbuf_release(&hookname);
> +
>  	return 0;
>  }
> +
> +int cmd_hook(int argc, const char **argv, const char *prefix)
> +{
> +	struct option builtin_hook_options[] = {
> +		OPT_END(),
> +	};
> +	if (argc < 2)
> +		usage_with_options(builtin_hook_usage, builtin_hook_options);
> +
> +	if (!strcmp(argv[1], "list"))
> +		return list(argc - 1, argv + 1, prefix);
> +
> +	usage_with_options(builtin_hook_usage, builtin_hook_options);
> +}
> diff --git a/hook.c b/hook.c
> new file mode 100644
> index 0000000000..fede40e925
> --- /dev/null
> +++ b/hook.c
> @@ -0,0 +1,120 @@
> +#include "cache.h"
> +
> +#include "hook.h"
> +#include "config.h"
> +
> +void free_hook(struct hook *ptr)
> +{
> +	if (ptr) {
> +		strbuf_release(&ptr->command);
> +		free(ptr);
> +	}
> +}

Neither strbuf_release() nor free() need or should have a "if (ptr)" guard.

> +
> +static void append_or_move_hook(struct list_head *head, const char *command)
> +{
> +	struct list_head *pos = NULL, *tmp = NULL;
> +	struct hook *to_add = NULL;
> +
> +	/*
> +	 * remove the prior entry with this command; we'll replace it at the
> +	 * end.
> +	 */
> +	list_for_each_safe(pos, tmp, head) {
> +		struct hook *it = list_entry(pos, struct hook, list);
> +		if (!strcmp(it->command.buf, command)) {
> +		    list_del(pos);
> +		    /* we'll simply move the hook to the end */
> +		    to_add = it;
> +		    break;
> +		}
> +	}
> +
> +	if (!to_add) {
> +		/* adding a new hook, not moving an old one */
> +		to_add = xmalloc(sizeof(*to_add));
> +		strbuf_init(&to_add->command, 0);
> +		strbuf_addstr(&to_add->command, command);
> +	}
> +
> +	/* re-set the scope so we show where an override was specified */
> +	to_add->origin = current_config_scope();
> +
> +	list_add_tail(&to_add->list, head);
> +}
> +
> +static void remove_hook(struct list_head *to_remove)
> +{
> +	struct hook *hook_to_remove = list_entry(to_remove, struct hook, list);
> +	list_del(to_remove);
> +	free_hook(hook_to_remove);
> +}
> +
> +void clear_hook_list(struct list_head *head)
> +{
> +	struct list_head *pos, *tmp;
> +	list_for_each_safe(pos, tmp, head)
> +		remove_hook(pos);
> +}
> +
> +struct hook_config_cb
> +{
> +	struct strbuf *hookname;
> +	struct list_head *list;
> +};
> +
> +static int hook_config_lookup(const char *key, const char *value, void *cb_data)
> +{
> +	struct hook_config_cb *data = cb_data;
> +	const char *hook_key = data->hookname->buf;
> +	struct list_head *head = data->list;
> +
> +	if (!strcmp(key, hook_key)) {
> +		const char *command = value;
> +		struct strbuf hookcmd_name = STRBUF_INIT;
> +
> +		/*
> +		 * Check if a hookcmd with that name exists. If it doesn't,
> +		 * 'git_config_get_value()' is documented not to touch &command,
> +		 * so we don't need to do anything.
> +		 */
> +		strbuf_addf(&hookcmd_name, "hookcmd.%s.command", command);
> +		git_config_get_value(hookcmd_name.buf, &command);
> +
> +		if (!command) {
> +			strbuf_release(&hookcmd_name);
> +			BUG("git_config_get_value overwrote a string it shouldn't have");
> +		}
> +
> +		/*
> +		 * TODO: implement an option-getting callback, e.g.
> +		 *   get configs by pattern hookcmd.$value.*
> +		 *   for each key+value, do_callback(key, value, cb_data)
> +		 */
> +
> +		append_or_move_hook(head, command);
> +
> +		strbuf_release(&hookcmd_name);
> +	}
> +
> +	return 0;
> +}
> +
> +struct list_head* hook_list(const struct strbuf* hookname)
> +{
> +	struct strbuf hook_key = STRBUF_INIT;
> +	struct list_head *hook_head = xmalloc(sizeof(struct list_head));
> +	struct hook_config_cb cb_data = { &hook_key, hook_head };
> +
> +	INIT_LIST_HEAD(hook_head);
> +
> +	if (!hookname)
> +		return NULL;

...if a strbuf being passed in is NULL?

> [...]
> +ROOT=
> +if test_have_prereq MINGW
> +then
> +	# In Git for Windows, Unix-like paths work only in shell scripts;
> +	# `git.exe`, however, will prefix them with the pseudo root directory
> +	# (of the Unix shell). Let's accommodate for that.
> +	ROOT="$(cd / && pwd)"
> +fi

I didn't read up on previous rounds, but if we're squashing this into 02
having a seperate commit summarizing this little hack would be most
welcome, or have it in this commit message.

Isn't this sort of thing generally usable, maybe we can add it under a
longer variable name to test-lib.sh?
Emily Shaffer March 24, 2021, 5:31 p.m. UTC | #2
On Fri, Mar 12, 2021 at 09:20:05AM +0100, Ævar Arnfjörð Bjarmason wrote:
> 
> 
> On Thu, Mar 11 2021, Emily Shaffer wrote:
> 
> > diff --git a/Documentation/config/hook.txt b/Documentation/config/hook.txt
> > new file mode 100644
> > index 0000000000..71449ecbc7
> > --- /dev/null
> > +++ b/Documentation/config/hook.txt
> > @@ -0,0 +1,9 @@
> > +hook.<command>.command::
> > +	A command to execute during the <command> hook event. This can be an
> > +	executable on your device, a oneliner for your shell, or the name of a
> > +	hookcmd. See linkgit:git-hook[1].
> > +
> > +hookcmd.<name>.command::
> > +	A command to execute during a hook for which <name> has been specified
> > +	as a command. This can be an executable on your device or a oneliner for
> > +	your shell. See linkgit:git-hook[1].
> > diff --git a/Documentation/git-hook.txt b/Documentation/git-hook.txt
> > index 9eeab0009d..f19875ed68 100644
> > --- a/Documentation/git-hook.txt
> > +++ b/Documentation/git-hook.txt
> > @@ -8,12 +8,65 @@ git-hook - Manage configured hooks
> >  SYNOPSIS
> >  --------
> >  [verse]
> > -'git hook'
> > +'git hook' list <hook-name>
> 
> Having just read this far (maybe this pattern is shared in the rest of
> the series): Let's just squash this and the 2nd patch together.
> 
> Sometimes it's worth doing the scaffolding first, but adding a new
> built-in is so trivial that I don't think it's worth it, and it just
> results in back & forth churn like the above...

Yeah, I think you are right here :)

> > +void free_hook(struct hook *ptr)
> > +{
> > +	if (ptr) {
> > +		strbuf_release(&ptr->command);
> > +		free(ptr);
> > +	}
> > +}
> 
> Neither strbuf_release() nor free() need or should have a "if (ptr)" guard.

I'll take free() out of the if guard, but I think
'strbuf_release(&<null>->command)' will go poorly - dereferencing the
NULL to even invoke strbuf_release will not be a happy time, and
strbuf_release internally is not NULL-resistant.

> > +struct list_head* hook_list(const struct strbuf* hookname)
> > +{
> > +	struct strbuf hook_key = STRBUF_INIT;
> > +	struct list_head *hook_head = xmalloc(sizeof(struct list_head));
> > +	struct hook_config_cb cb_data = { &hook_key, hook_head };
> > +
> > +	INIT_LIST_HEAD(hook_head);
> > +
> > +	if (!hookname)
> > +		return NULL;
> 
> ...if a strbuf being passed in is NULL?

Yeah, I think this is misplaced. But since it sounds like generally
folks don't like having the strbuf at the input here, I will address the
error checking then also.

> 
> > [...]
> > +ROOT=
> > +if test_have_prereq MINGW
> > +then
> > +	# In Git for Windows, Unix-like paths work only in shell scripts;
> > +	# `git.exe`, however, will prefix them with the pseudo root directory
> > +	# (of the Unix shell). Let's accommodate for that.
> > +	ROOT="$(cd / && pwd)"
> > +fi
> 
> I didn't read up on previous rounds, but if we're squashing this into 02
> having a seperate commit summarizing this little hack would be most
> welcome, or have it in this commit message.

Sure. I squashed it in from a commit dscho sent, so I can preserve that
commit in tree instead.

> 
> Isn't this sort of thing generally usable, maybe we can add it under a
> longer variable name to test-lib.sh?

I wonder. `git grep cd \/ &&` shows me that this hack also happens in
t1509-root-work-tree.sh. I think most tests must use relative paths, so
this must not be in broad use? But since it's not used elsewhere I feel
ambivalent about adding a helper to test-lib.sh. I can if you feel
strongly :)

 - Emily
Ævar Arnfjörð Bjarmason March 25, 2021, 12:36 p.m. UTC | #3
On Wed, Mar 24 2021, Emily Shaffer wrote:

> On Fri, Mar 12, 2021 at 09:20:05AM +0100, �var Arnfj�r� Bjarmason wrote:
>> 
>> 
>> On Thu, Mar 11 2021, Emily Shaffer wrote:
>> 
>> > diff --git a/Documentation/config/hook.txt b/Documentation/config/hook.txt
>> > new file mode 100644
>> > index 0000000000..71449ecbc7
>> > --- /dev/null
>> > +++ b/Documentation/config/hook.txt
>> > @@ -0,0 +1,9 @@
>> > +hook.<command>.command::
>> > +	A command to execute during the <command> hook event. This can be an
>> > +	executable on your device, a oneliner for your shell, or the name of a
>> > +	hookcmd. See linkgit:git-hook[1].
>> > +
>> > +hookcmd.<name>.command::
>> > +	A command to execute during a hook for which <name> has been specified
>> > +	as a command. This can be an executable on your device or a oneliner for
>> > +	your shell. See linkgit:git-hook[1].
>> > diff --git a/Documentation/git-hook.txt b/Documentation/git-hook.txt
>> > index 9eeab0009d..f19875ed68 100644
>> > --- a/Documentation/git-hook.txt
>> > +++ b/Documentation/git-hook.txt
>> > @@ -8,12 +8,65 @@ git-hook - Manage configured hooks
>> >  SYNOPSIS
>> >  --------
>> >  [verse]
>> > -'git hook'
>> > +'git hook' list <hook-name>
>> 
>> Having just read this far (maybe this pattern is shared in the rest of
>> the series): Let's just squash this and the 2nd patch together.
>> 
>> Sometimes it's worth doing the scaffolding first, but adding a new
>> built-in is so trivial that I don't think it's worth it, and it just
>> results in back & forth churn like the above...
>
> Yeah, I think you are right here :)
>
>> > +void free_hook(struct hook *ptr)
>> > +{
>> > +	if (ptr) {
>> > +		strbuf_release(&ptr->command);
>> > +		free(ptr);
>> > +	}
>> > +}
>> 
>> Neither strbuf_release() nor free() need or should have a "if (ptr)" guard.
>
> I'll take free() out of the if guard, but I think
> 'strbuf_release(&<null>->command)' will go poorly - dereferencing the
> NULL to even invoke strbuf_release will not be a happy time, and
> strbuf_release internally is not NULL-resistant.

Sorry I meant something like:

    if (ptr) strbuf_release(&ptr->command);
    free(ptr);

But maybe even more idiomatic would be:

    if (!ptr)
	return;
    strbuf_release(&ptr->command);
    free(ptr);

Or some other variant of checking teh container struct early. Anyway,
this doesn't really matter, per a below comment I had more meaningful
feedback in [1]. Most of my other traffic on this topic (including this)
was some stream-of-consciousness notes as I went along.

>> > +struct list_head* hook_list(const struct strbuf* hookname)
>> > +{
>> > +	struct strbuf hook_key = STRBUF_INIT;
>> > +	struct list_head *hook_head = xmalloc(sizeof(struct list_head));
>> > +	struct hook_config_cb cb_data = { &hook_key, hook_head };
>> > +
>> > +	INIT_LIST_HEAD(hook_head);
>> > +
>> > +	if (!hookname)
>> > +		return NULL;
>> 
>> ...if a strbuf being passed in is NULL?
>
> Yeah, I think this is misplaced. But since it sounds like generally
> folks don't like having the strbuf at the input here, I will address the
> error checking then also.
>
>> 
>> > [...]
>> > +ROOT=
>> > +if test_have_prereq MINGW
>> > +then
>> > +	# In Git for Windows, Unix-like paths work only in shell scripts;
>> > +	# `git.exe`, however, will prefix them with the pseudo root directory
>> > +	# (of the Unix shell). Let's accommodate for that.
>> > +	ROOT="$(cd / && pwd)"
>> > +fi
>> 
>> I didn't read up on previous rounds, but if we're squashing this into 02
>> having a seperate commit summarizing this little hack would be most
>> welcome, or have it in this commit message.
>
> Sure. I squashed it in from a commit dscho sent, so I can preserve that
> commit in tree instead.
>
>> 
>> Isn't this sort of thing generally usable, maybe we can add it under a
>> longer variable name to test-lib.sh?
>
> I wonder. `git grep cd \/ &&` shows me that this hack also happens in
> t1509-root-work-tree.sh. I think most tests must use relative paths, so
> this must not be in broad use? But since it's not used elsewhere I feel
> ambivalent about adding a helper to test-lib.sh. I can if you feel
> strongly :)

After I sent this I saw that pretty much the same thing is happening in
t1300-config.sh for the --show-origin option.

    ! test_have_prereq MINGW ||
    HOME="$(pwd)" # convert to Windows path

I don't feel strongly about this at all, but per the outstanding
feedback I had in[1] I wondered whether this whole thing wouln't be
better as some variant of "git config --show-origin",

1. https://lore.kernel.org/git/87mtv8fww3.fsf@evledraar.gmail.com/#t
diff mbox series

Patch

diff --git a/Documentation/config/hook.txt b/Documentation/config/hook.txt
new file mode 100644
index 0000000000..71449ecbc7
--- /dev/null
+++ b/Documentation/config/hook.txt
@@ -0,0 +1,9 @@ 
+hook.<command>.command::
+	A command to execute during the <command> hook event. This can be an
+	executable on your device, a oneliner for your shell, or the name of a
+	hookcmd. See linkgit:git-hook[1].
+
+hookcmd.<name>.command::
+	A command to execute during a hook for which <name> has been specified
+	as a command. This can be an executable on your device or a oneliner for
+	your shell. See linkgit:git-hook[1].
diff --git a/Documentation/git-hook.txt b/Documentation/git-hook.txt
index 9eeab0009d..f19875ed68 100644
--- a/Documentation/git-hook.txt
+++ b/Documentation/git-hook.txt
@@ -8,12 +8,65 @@  git-hook - Manage configured hooks
 SYNOPSIS
 --------
 [verse]
-'git hook'
+'git hook' list <hook-name>
 
 DESCRIPTION
 -----------
-A placeholder command. Later, you will be able to list, add, and modify hooks
-with this command.
+You can list configured hooks with this command. Later, you will be able to run,
+add, and modify hooks with this command.
+
+This command parses the default configuration files for sections `hook` and
+`hookcmd`. `hook` is used to describe the commands which will be run during a
+particular hook event; commands are run in the order Git encounters them during
+the configuration parse (see linkgit:git-config[1]). `hookcmd` is used to
+describe attributes of a specific command. If additional attributes don't need
+to be specified, a command to run can be specified directly in the `hook`
+section; if a `hookcmd` by that name isn't found, Git will attempt to run the
+provided value directly. For example:
+
+Global config
+----
+  [hook "post-commit"]
+    command = "linter"
+    command = "~/typocheck.sh"
+
+  [hookcmd "linter"]
+    command = "/bin/linter --c"
+----
+
+Local config
+----
+  [hook "prepare-commit-msg"]
+    command = "linter"
+  [hook "post-commit"]
+    command = "python ~/run-test-suite.py"
+----
+
+With these configs, you'd then see:
+
+----
+$ git hook list "post-commit"
+global: /bin/linter --c
+global: ~/typocheck.sh
+local: python ~/run-test-suite.py
+
+$ git hook list "prepare-commit-msg"
+local: /bin/linter --c
+----
+
+COMMANDS
+--------
+
+list `<hook-name>`::
+
+List the hooks which have been configured for `<hook-name>`. Hooks appear
+in the order they should be run, and print the config scope where the relevant
+`hook.<hook-name>.command` was specified, not the `hookcmd` (if applicable).
+This output is human-readable and the format is subject to change over time.
+
+CONFIGURATION
+-------------
+include::config/hook.txt[]
 
 GIT
 ---
diff --git a/Makefile b/Makefile
index 8e904a1ab5..3fa51597d8 100644
--- a/Makefile
+++ b/Makefile
@@ -891,6 +891,7 @@  LIB_OBJS += hash-lookup.o
 LIB_OBJS += hashmap.o
 LIB_OBJS += help.o
 LIB_OBJS += hex.o
+LIB_OBJS += hook.o
 LIB_OBJS += ident.o
 LIB_OBJS += json-writer.o
 LIB_OBJS += kwset.o
diff --git a/builtin/hook.c b/builtin/hook.c
index b2bbc84d4d..bb64cd77ca 100644
--- a/builtin/hook.c
+++ b/builtin/hook.c
@@ -1,21 +1,67 @@ 
 #include "cache.h"
-
 #include "builtin.h"
+#include "config.h"
+#include "hook.h"
 #include "parse-options.h"
+#include "strbuf.h"
 
 static const char * const builtin_hook_usage[] = {
-	N_("git hook"),
+	N_("git hook list <hookname>"),
 	NULL
 };
 
-int cmd_hook(int argc, const char **argv, const char *prefix)
+static int list(int argc, const char **argv, const char *prefix)
 {
-	struct option builtin_hook_options[] = {
+	struct list_head *head, *pos;
+	struct strbuf hookname = STRBUF_INIT;
+
+	struct option list_options[] = {
 		OPT_END(),
 	};
 
-	argc = parse_options(argc, argv, prefix, builtin_hook_options,
+	argc = parse_options(argc, argv, prefix, list_options,
 			     builtin_hook_usage, 0);
 
+	if (argc < 1) {
+		usage_msg_opt(_("You must specify a hook event name to list."),
+			      builtin_hook_usage, list_options);
+	}
+
+	strbuf_addstr(&hookname, argv[0]);
+
+	head = hook_list(&hookname);
+
+	if (list_empty(head)) {
+		printf(_("no commands configured for hook '%s'\n"),
+		       hookname.buf);
+		strbuf_release(&hookname);
+		return 0;
+	}
+
+	list_for_each(pos, head) {
+		struct hook *item = list_entry(pos, struct hook, list);
+		if (item)
+			printf("%s: %s\n",
+			       config_scope_name(item->origin),
+			       item->command.buf);
+	}
+
+	clear_hook_list(head);
+	strbuf_release(&hookname);
+
 	return 0;
 }
+
+int cmd_hook(int argc, const char **argv, const char *prefix)
+{
+	struct option builtin_hook_options[] = {
+		OPT_END(),
+	};
+	if (argc < 2)
+		usage_with_options(builtin_hook_usage, builtin_hook_options);
+
+	if (!strcmp(argv[1], "list"))
+		return list(argc - 1, argv + 1, prefix);
+
+	usage_with_options(builtin_hook_usage, builtin_hook_options);
+}
diff --git a/hook.c b/hook.c
new file mode 100644
index 0000000000..fede40e925
--- /dev/null
+++ b/hook.c
@@ -0,0 +1,120 @@ 
+#include "cache.h"
+
+#include "hook.h"
+#include "config.h"
+
+void free_hook(struct hook *ptr)
+{
+	if (ptr) {
+		strbuf_release(&ptr->command);
+		free(ptr);
+	}
+}
+
+static void append_or_move_hook(struct list_head *head, const char *command)
+{
+	struct list_head *pos = NULL, *tmp = NULL;
+	struct hook *to_add = NULL;
+
+	/*
+	 * remove the prior entry with this command; we'll replace it at the
+	 * end.
+	 */
+	list_for_each_safe(pos, tmp, head) {
+		struct hook *it = list_entry(pos, struct hook, list);
+		if (!strcmp(it->command.buf, command)) {
+		    list_del(pos);
+		    /* we'll simply move the hook to the end */
+		    to_add = it;
+		    break;
+		}
+	}
+
+	if (!to_add) {
+		/* adding a new hook, not moving an old one */
+		to_add = xmalloc(sizeof(*to_add));
+		strbuf_init(&to_add->command, 0);
+		strbuf_addstr(&to_add->command, command);
+	}
+
+	/* re-set the scope so we show where an override was specified */
+	to_add->origin = current_config_scope();
+
+	list_add_tail(&to_add->list, head);
+}
+
+static void remove_hook(struct list_head *to_remove)
+{
+	struct hook *hook_to_remove = list_entry(to_remove, struct hook, list);
+	list_del(to_remove);
+	free_hook(hook_to_remove);
+}
+
+void clear_hook_list(struct list_head *head)
+{
+	struct list_head *pos, *tmp;
+	list_for_each_safe(pos, tmp, head)
+		remove_hook(pos);
+}
+
+struct hook_config_cb
+{
+	struct strbuf *hookname;
+	struct list_head *list;
+};
+
+static int hook_config_lookup(const char *key, const char *value, void *cb_data)
+{
+	struct hook_config_cb *data = cb_data;
+	const char *hook_key = data->hookname->buf;
+	struct list_head *head = data->list;
+
+	if (!strcmp(key, hook_key)) {
+		const char *command = value;
+		struct strbuf hookcmd_name = STRBUF_INIT;
+
+		/*
+		 * Check if a hookcmd with that name exists. If it doesn't,
+		 * 'git_config_get_value()' is documented not to touch &command,
+		 * so we don't need to do anything.
+		 */
+		strbuf_addf(&hookcmd_name, "hookcmd.%s.command", command);
+		git_config_get_value(hookcmd_name.buf, &command);
+
+		if (!command) {
+			strbuf_release(&hookcmd_name);
+			BUG("git_config_get_value overwrote a string it shouldn't have");
+		}
+
+		/*
+		 * TODO: implement an option-getting callback, e.g.
+		 *   get configs by pattern hookcmd.$value.*
+		 *   for each key+value, do_callback(key, value, cb_data)
+		 */
+
+		append_or_move_hook(head, command);
+
+		strbuf_release(&hookcmd_name);
+	}
+
+	return 0;
+}
+
+struct list_head* hook_list(const struct strbuf* hookname)
+{
+	struct strbuf hook_key = STRBUF_INIT;
+	struct list_head *hook_head = xmalloc(sizeof(struct list_head));
+	struct hook_config_cb cb_data = { &hook_key, hook_head };
+
+	INIT_LIST_HEAD(hook_head);
+
+	if (!hookname)
+		return NULL;
+
+	strbuf_addf(&hook_key, "hook.%s.command", hookname->buf);
+
+	git_config(hook_config_lookup, &cb_data);
+
+	strbuf_release(&hook_key);
+	return hook_head;
+}
diff --git a/hook.h b/hook.h
new file mode 100644
index 0000000000..e48dfc6d27
--- /dev/null
+++ b/hook.h
@@ -0,0 +1,25 @@ 
+#include "config.h"
+#include "list.h"
+#include "strbuf.h"
+
+struct hook {
+	struct list_head list;
+	/*
+	 * Config file which holds the hook.*.command definition.
+	 * (This has nothing to do with the hookcmd.<name>.* configs.)
+	 */
+	enum config_scope origin;
+	/* The literal command to run. */
+	struct strbuf command;
+};
+
+/*
+ * Provides a linked list of 'struct hook' detailing commands which should run
+ * in response to the 'hookname' event, in execution order.
+ */
+struct list_head* hook_list(const struct strbuf *hookname);
+
+/* Free memory associated with a 'struct hook' */
+void free_hook(struct hook *ptr);
+/* Empties the list at 'head', calling 'free_hook()' on each entry */
+void clear_hook_list(struct list_head *head);
diff --git a/t/t1360-config-based-hooks.sh b/t/t1360-config-based-hooks.sh
index 34b0df5216..6e4a3e763f 100755
--- a/t/t1360-config-based-hooks.sh
+++ b/t/t1360-config-based-hooks.sh
@@ -4,8 +4,85 @@  test_description='config-managed multihooks, including git-hook command'
 
 . ./test-lib.sh
 
-test_expect_success 'git hook command does not crash' '
-	git hook
+ROOT=
+if test_have_prereq MINGW
+then
+	# In Git for Windows, Unix-like paths work only in shell scripts;
+	# `git.exe`, however, will prefix them with the pseudo root directory
+	# (of the Unix shell). Let's accommodate for that.
+	ROOT="$(cd / && pwd)"
+fi
+
+setup_hooks () {
+	test_config hook.pre-commit.command "/path/ghi" --add
+	test_config_global hook.pre-commit.command "/path/def" --add
+}
+
+setup_hookcmd () {
+	test_config hook.pre-commit.command "abc" --add
+	test_config_global hookcmd.abc.command "/path/abc" --add
+}
+
+test_expect_success 'git hook rejects commands without a mode' '
+	test_must_fail git hook pre-commit
+'
+
+
+test_expect_success 'git hook rejects commands without a hookname' '
+	test_must_fail git hook list
+'
+
+test_expect_success 'git hook runs outside of a repo' '
+	setup_hooks &&
+
+	cat >expected <<-EOF &&
+	global: $ROOT/path/def
+	EOF
+
+	nongit git config --list --global &&
+
+	nongit git hook list pre-commit >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'git hook list orders by config order' '
+	setup_hooks &&
+
+	cat >expected <<-EOF &&
+	global: $ROOT/path/def
+	local: $ROOT/path/ghi
+	EOF
+
+	git hook list pre-commit >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'git hook list dereferences a hookcmd' '
+	setup_hooks &&
+	setup_hookcmd &&
+
+	cat >expected <<-EOF &&
+	global: $ROOT/path/def
+	local: $ROOT/path/ghi
+	local: $ROOT/path/abc
+	EOF
+
+	git hook list pre-commit >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'git hook list reorders on duplicate commands' '
+	setup_hooks &&
+
+	test_config hook.pre-commit.command "/path/def" --add &&
+
+	cat >expected <<-EOF &&
+	local: $ROOT/path/ghi
+	local: $ROOT/path/def
+	EOF
+
+	git hook list pre-commit >actual &&
+	test_cmp expected actual
 '
 
 test_done