Add hb_language_matches()

New API:
+ hb_language_matches()

docs/harfbuzz-sections.txt

@@ -135,6 +135,7 @@ hb_script_get_horizontal_direction
 hb_language_from_string
 hb_language_to_string
 hb_language_get_default
+hb_language_matches
 hb_feature_from_string
 hb_feature_to_string
 hb_variation_from_string

src/hb-aat-layout-morx-table.hh

@@ -983,7 +983,7 @@ struct Chain
 #ifndef HB_NO_AAT
 	else if (type == HB_AAT_LAYOUT_FEATURE_TYPE_LANGUAGE_TAG_TYPE && setting &&
 		 /* TODO: Rudimentary language matching. */
-		 map->face->table.ltag->get_language (setting - 1) == map->props.language)
+		 hb_language_matches (map->face->table.ltag->get_language (setting - 1), map->props.language))
 	{
 	  flags &= feature.disableFlags;
 	  flags |= feature.enableFlags;

src/hb-common.cc

@@ -441,6 +441,38 @@ hb_language_get_default ()
   return language;
 }
 
+/**
+ * hb_language_matches:
+ * @language: The #hb_language_t to work on
+ * @specific: Another #hb_language_t
+ *
+ * Check whether a second language tag is the same or a more
+ * specific version of the provided language tag.  For example,
+ * "fa_IR.utf8" is a more specific tag for "fa" or for "fa_IR".
+ *
+ * Return value: `true` if languages match, `false` otherwise.
+ *
+ * Since: REPLACEME
+ **/
+hb_bool_t
+hb_language_matches (hb_language_t language,
+		     hb_language_t specific)
+{
+  if (language == specific) return true;
+  if (!language || !specific) return false;
+
+  const char *l = language->s;
+  const char *s = specific->s;
+  unsigned ll = strlen (l);
+  unsigned sl = strlen (s);
+
+  if (ll > sl)
+    return false;
+
+  return strncmp (l, s, ll) == 0 &&
+	 (s[ll] == '\0' || s[ll] == '-');
+}
+
 
 /* hb_script_t */
 

src/hb-common.h

@@ -326,6 +326,9 @@ hb_language_to_string (hb_language_t language);
 HB_EXTERN hb_language_t
 hb_language_get_default (void);
 
+HB_EXTERN hb_bool_t
+hb_language_matches (hb_language_t language,
+		     hb_language_t specific);
 
 /**
  * hb_script_t:

src/hb-ot-name-table.hh

@@ -175,15 +175,11 @@ _hb_ot_name_entry_cmp_key (const void *pa, const void *pb, bool exact)
 
   signed c = strcmp (astr, bstr);
 
-  if (!exact && c)
-  {
-    unsigned la = strlen (astr);
-    unsigned lb = strlen (bstr);
-    // 'a' is the user request, and 'b' is string in the font.
-    // If eg. user asks for "en-us" and font has "en", approve.
-    if (la > lb && astr[lb] == '-' && !strncmp (astr, bstr, lb))
-      return 0;
-  }
+  // 'a' is the user request, and 'b' is string in the font.
+  // If eg. user asks for "en-us" and font has "en", approve.
+  if (!exact && c &&
+      hb_language_matches (b->language, a->language))
+    return 0;
 
   return c;
 }

src/hb-ot-tag.cc

@@ -214,6 +214,8 @@ lang_matches (const char *lang_str,
 	      const char *spec,
 	      unsigned    spec_len)
 {
+  /* Same as hb_language_matches(); duplicated. */
+
   if (likely ((unsigned) (limit - lang_str) < spec_len))
     return false;