hook: introduce hook_config_cache_entry for per-hook data

Replace the bare `char *command` util pointer stored in each string_list
item with a heap-allocated `struct hook_config_cache_entry` that carries
that command string.

This is just a refactoring with no behavior changes, to give the cache
entry room to grow, so it can carry the additional hook metadata we'll
be adding in the following commits.

Signed-off-by: Adrian Ratiu <adrian.ratiu@collabora.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: 10ne1

hook.c

@@ -108,6 +108,15 @@ static void list_hooks_add_default(struct repository *r, const char *hookname,
 	string_list_append(hook_list, hook_path)->util = h;
 }
 
+/*
+ * Cache entry stored as the .util pointer of string_list items inside the
+ * hook config cache. For now carries only the command for the hook. Next
+ * commits will add more data.
+ */
+struct hook_config_cache_entry {
+	char *command;
+};
+
 /*
  * Callback struct to collect all hook.* keys in a single config pass.
  * commands: friendly-name to command map.
@@ -202,7 +211,12 @@ void hook_cache_clear(struct strmap *cache)
 
 	strmap_for_each_entry(cache, &iter, e) {
 		struct string_list *hooks = e->value;
-		string_list_clear(hooks, 1); /* free util (command) pointers */
+		for (size_t i = 0; i < hooks->nr; i++) {
+			struct hook_config_cache_entry *entry = hooks->items[i].util;
+			free(entry->command);
+			free(entry);
+		}
+		string_list_clear(hooks, 0);
 		free(hooks);
 	}
 	strmap_clear(cache, 0);
@@ -232,6 +246,7 @@ static void build_hook_config_map(struct repository *r, struct strmap *cache)
 
 		for (size_t i = 0; i < hook_names->nr; i++) {
 			const char *hname = hook_names->items[i].string;
+			struct hook_config_cache_entry *entry;
 			char *command;
 
 			/* filter out disabled hooks */
@@ -245,9 +260,10 @@ static void build_hook_config_map(struct repository *r, struct strmap *cache)
 				      "'hook.%s.event' must be removed;"
 				      " aborting."), hname, hname);
 
-			/* util stores the command; owned by the cache. */
-			string_list_append(hooks, hname)->util =
-				xstrdup(command);
+			/* util stores a cache entry; owned by the cache. */
+			CALLOC_ARRAY(entry, 1);
+			entry->command = xstrdup(command);
+			string_list_append(hooks, hname)->util = entry;
 		}
 
 		strmap_put(cache, e->key, hooks);
@@ -309,7 +325,7 @@ static void list_hooks_add_configured(struct repository *r,
 	/* Iterate through configured hooks and initialize internal states */
 	for (size_t i = 0; configured_hooks && i < configured_hooks->nr; i++) {
 		const char *friendly_name = configured_hooks->items[i].string;
-		const char *command = configured_hooks->items[i].util;
+		struct hook_config_cache_entry *entry = configured_hooks->items[i].util;
 		struct hook *hook;
 
 		CALLOC_ARRAY(hook, 1);
@@ -327,7 +343,7 @@ static void list_hooks_add_configured(struct repository *r,
 
 		hook->kind = HOOK_CONFIGURED;
 		hook->u.configured.friendly_name = xstrdup(friendly_name);
-		hook->u.configured.command = xstrdup(command);
+		hook->u.configured.command = xstrdup(entry->command);
 
 		string_list_append(list, friendly_name)->util = hook;
 	}