[PATCH 03/20] userdiff: add and use for_each_userdiff_driver()

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

Refactor the userdiff_find_by_namelen() function so that a new
for_each_userdiff_driver() API function does most of the work.

This will be useful for the same reason we've got other for_each_*()
API functions as part of various APIs, and will be used in a follow-up
commit.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 userdiff.c | 61 +++++++++++++++++++++++++++++++++++++++++++-----------
 userdiff.h | 15 ++++++++++++++
 2 files changed, 64 insertions(+), 12 deletions(-)

diff --git a/userdiff.c b/userdiff.c
index c92cbcc054..92b5a97e12 100644
--- a/userdiff.c
+++ b/userdiff.c
@@ -250,20 +250,32 @@ static struct userdiff_driver driver_false = {
 	{ NULL, 0 }
 };
 
-static struct userdiff_driver *userdiff_find_by_namelen(const char *k, size_t len)
+struct for_each_userdiff_driver_cb {
+	const char *k;
+	size_t len;
+	struct userdiff_driver *driver;
+};
+
+static int userdiff_find_by_namelen_cb(struct userdiff_driver *driver,
+				       enum userdiff_driver_type type, void *priv)
 {
-	int i;
-	for (i = 0; i < ndrivers; i++) {
-		struct userdiff_driver *drv = drivers + i;
-		if (!strncmp(drv->name, k, len) && !drv->name[len])
-			return drv;
-	}
-	for (i = 0; i < ARRAY_SIZE(builtin_drivers); i++) {
-		struct userdiff_driver *drv = builtin_drivers + i;
-		if (!strncmp(drv->name, k, len) && !drv->name[len])
-			return drv;
+	struct for_each_userdiff_driver_cb *cb_data = priv;
+
+	if (!strncmp(driver->name, cb_data->k, cb_data->len) &&
+	    !driver->name[cb_data->len]) {
+		cb_data->driver = driver;
+		return -1; /* found it! */
 	}
-	return NULL;
+	return 0;
+}
+
+static struct userdiff_driver *userdiff_find_by_namelen(const char *k, size_t len)
+{
+	struct for_each_userdiff_driver_cb udcbdata = { .k = k, .len = len, .driver = NULL };
+
+	for_each_userdiff_driver(userdiff_find_by_namelen_cb,
+				 USERDIFF_DRIVER_TYPE_UNSPECIFIED, &udcbdata);
+	return udcbdata.driver;
 }
 
 static int parse_funcname(struct userdiff_funcname *f, const char *k,
@@ -364,3 +376,28 @@ struct userdiff_driver *userdiff_get_textconv(struct repository *r,
 
 	return driver;
 }
+
+int for_each_userdiff_driver(each_userdiff_driver_fn fn,
+			     enum userdiff_driver_type type, void *cb_data)
+{
+	int i, ret;
+	if (type & (USERDIFF_DRIVER_TYPE_UNSPECIFIED | USERDIFF_DRIVER_TYPE_CUSTOM)) {
+
+		for (i = 0; i < ndrivers; i++) {
+			struct userdiff_driver *drv = drivers + i;
+			ret = fn(drv, USERDIFF_DRIVER_TYPE_CUSTOM, cb_data);
+			if (ret)
+				return ret;
+		}
+	}
+	if (type & (USERDIFF_DRIVER_TYPE_UNSPECIFIED | USERDIFF_DRIVER_TYPE_BUILTIN)) {
+
+		for (i = 0; i < ARRAY_SIZE(builtin_drivers); i++) {
+			struct userdiff_driver *drv = builtin_drivers + i;
+			ret = fn(drv, USERDIFF_DRIVER_TYPE_BUILTIN, cb_data);
+			if (ret)
+				return ret;
+		}
+	}
+	return 0;
+}
diff --git a/userdiff.h b/userdiff.h
index 203057e13e..fe14014a77 100644
--- a/userdiff.h
+++ b/userdiff.h
@@ -21,6 +21,13 @@ struct userdiff_driver {
 	struct notes_cache *textconv_cache;
 	int textconv_want_cache;
 };
+enum userdiff_driver_type {
+	USERDIFF_DRIVER_TYPE_UNSPECIFIED = 1<<0,
+	USERDIFF_DRIVER_TYPE_BUILTIN = 1<<1,
+	USERDIFF_DRIVER_TYPE_CUSTOM = 1<<2,
+};
+typedef int (*each_userdiff_driver_fn)(struct userdiff_driver *,
+				       enum userdiff_driver_type, void *);
 
 int userdiff_config(const char *k, const char *v);
 struct userdiff_driver *userdiff_find_by_name(const char *name);
@@ -34,4 +41,12 @@ struct userdiff_driver *userdiff_find_by_path(struct index_state *istate,
 struct userdiff_driver *userdiff_get_textconv(struct repository *r,
 					      struct userdiff_driver *driver);
 
+/*
+ * Iterate over each driver of type userdiff_driver_type, or
+ * USERDIFF_DRIVER_TYPE_UNSPECIFIED for all of them. Return non-zero
+ * to exit from the loop.
+ */
+int for_each_userdiff_driver(each_userdiff_driver_fn,
+			     enum userdiff_driver_type, void *);
+
 #endif /* USERDIFF */
-- 
2.30.0.284.gd98b1dd5eaa7