Re: [PATCH v7 03/17] hook: add list command

On Sat, Jan 30, 2021 at 07:10:11PM -0800, Jonathan Tan wrote:

quoted

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; at minimum, this subsection must contain a
"hookcmd.<hookcmd-name>.command = <path-to-hook>" line.

I learned later that this isn't true - in patch 6, the commit message
and one of the tests therein describe being able to skip a previously
inline command by making a hookcmd section of the same name and just
specifying "skip = true" there (without any command).

Maybe just delete the "at minimum" part.

Thanks, nice catch. I dropped "at minimum" and s/must/should/. Since I
received feedback during the dogfood internally that there's no
documentation on "hookcmd.<thing>.skip" whatsoever, I'll try to make
a more detailed overview of hookcmd acting as an alias in the
user-facing docs in that commit.

quoted

+static int list(int argc, const char **argv, const char *prefix)
 {
-	struct option builtin_hook_options[] = {
+	struct list_head *head, *pos;
+	struct hook *item;

You asked for review on nits too so here's one: "item" should be
declared in the list_for_each block. (That also makes it easier to see
that we don't need to free it.)

Ok, done.

quoted

diff --git a/hook.c b/hook.c
new file mode 100644
index 0000000000..937dc768c8
--- /dev/null
+++ b/hook.c

@@ -0,0 +1,115 @@
+#include "cache.h"
+
+#include "hook.h"
+#include "config.h"

Usually we put all the includes together without any intervening blank
lines.

Done.

quoted

+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" here?

I think it's safe to do so, but I think I left it out in case duplicates
do make it into the list somehow. But if they're always being inserted
via "append_or_move_hook()" that should not be an issue, so I'll add the
break.

In fact, fixing this exposed a bug. Later, I add using 'pos' instead of
'head':
  list_add_tail(&to_add->list, pos);
When I'm guaranteed to iterate to the end of the list, that works fine,
because in this implementation the last element of the list has "->next"
set back to "head". But when 'pos' isn't sure to be at the end of the
list, it breaks the list. Whoops.. :)

quoted

+		}
+	}
+
+	if (!to_add) {
+		/* adding a new hook, not moving an old one */
+		to_add = xmalloc(sizeof(struct hook));

Style is to write sizeof(*to_add), I think.

Sure.

[snip]

quoted

+struct hook_config_cb
+{
+	struct strbuf *hookname;

struct declarations have "{" not on a line on its own.

Sure, I can change it. Although, 'git grep -E "struct \w+$"' tells me
there are a few other offenders :) But the count (60ish minus
doc/relnotes references) is much lower than 'git grep -E "struct \w+
\{$"' (800+ matches) so I'm definitely doing it wrong :D

Also, "hookname" could just be a char *?

Hrmph. I think my C++ background is showing - to me, calling ".buf"
(which is cheap) a few times is a small price to pay to get length
info and so on for free. "hookname" can come from the user - "git
hook (list|run) repo-special-magic-hook" - so I worry about leaving it as a raw
char* with no size info associated. Am I being too paranoid?

quoted

+	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. */
+		strbuf_addf(&hookcmd_name, "hookcmd.%s.command", command);
+		git_config_get_value(hookcmd_name.buf, &command);

So we don't really care whether git_config_get_value returns 0 or 1 as
long as it doesn't touch "command" if there is no such hookcmd. That
fits with how git_config_get_value() is documented, so that's great.
Perhaps better to document as:

  If a hookcmd.%s.command config exists, replace the command with the
  value of that config. (If not, do nothing - git_config_get_value() is
  documented to not overwrite the value argument in this case.)

OK. Thanks, done.

quoted

+
+		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)

"const char *hookname" should suffice?

Also, search for "* " and replace with " *" where applicable (also in
the .h file).

See above.

quoted

+{
+	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, (void*)&cb_data);

Do we need this void* cast?

Nope. Dropped, thanks.

quoted

+
+	strbuf_release(&hook_key);
+	return hook_head;
+}

diff --git a/hook.h b/hook.h
new file mode 100644
index 0000000000..8ffc4f14b6
--- /dev/null
+++ b/hook.h

@@ -0,0 +1,26 @@
+#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;

"char *" would suffice?

Since 'command' comes directly from user input and is executed, I'm
nervous about using a char* instead of a strbuf even more so than for
the hookname.

The tests look fine.

Thanks for the nitpicky review, it was great! :)

 - Emily