[name] Implement approximate language matching

Very rudimentary.

Fixes https://github.com/harfbuzz/harfbuzz/issues/3354

src/hb-ot-name-table.hh

@@ -156,7 +156,7 @@ struct NameRecord
 };
 
 static int
-_hb_ot_name_entry_cmp_key (const void *pa, const void *pb)
+_hb_ot_name_entry_cmp_key (const void *pa, const void *pb, bool exact)
 {
   const hb_ot_name_entry_t *a = (const hb_ot_name_entry_t *) pa;
   const hb_ot_name_entry_t *b = (const hb_ot_name_entry_t *) pb;
@@ -169,8 +169,23 @@ _hb_ot_name_entry_cmp_key (const void *pa, const void *pb)
   if (a->language == b->language) return 0;
   if (!a->language) return -1;
   if (!b->language) return +1;
-  return strcmp (hb_language_to_string (a->language),
+
-		 hb_language_to_string (b->language));
+  const char *astr = hb_language_to_string (a->language);
+  const char *bstr = hb_language_to_string (b->language);
+
+  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;
+  }
+
+  return c;
 }
 
 static int
@@ -178,7 +193,7 @@ _hb_ot_name_entry_cmp (const void *pa, const void *pb)
 {
   /* Compare by name_id, then language, then score, then index. */
 
-  int v = _hb_ot_name_entry_cmp_key (pa, pb);
+  int v = _hb_ot_name_entry_cmp_key (pa, pb, true);
   if (v)
     return v;
 
@@ -330,7 +345,18 @@ struct name
       const hb_ot_name_entry_t *entry = hb_bsearch (key, (const hb_ot_name_entry_t *) this->names,
 						    this->names.length,
 						    sizeof (hb_ot_name_entry_t),
-						    _hb_ot_name_entry_cmp_key);
+						    _hb_ot_name_entry_cmp_key,
+						    true);
+
+      if (!entry)
+      {
+	entry = hb_bsearch (key, (const hb_ot_name_entry_t *) this->names,
+			    this->names.length,
+			    sizeof (hb_ot_name_entry_t),
+			    _hb_ot_name_entry_cmp_key,
+			    false);
+      }
+
       if (!entry)
 	return -1;
 

test/api/test-ot-name.c

@@ -93,10 +93,17 @@ test_ot_name (void)
   name_id = entries[3].name_id;
   g_assert_cmpuint (3, ==, name_id);
   lang = entries[3].language;
+
   g_assert_cmpstr (hb_language_to_string (lang), ==, "en");
   g_assert_cmpuint (27, ==, hb_ot_name_get_utf8 (face, name_id, lang, &text_size, text));
   g_assert_cmpuint (9, ==, text_size);
   g_assert_cmpstr (text, ==, "FontForge");
+
+  g_assert_cmpuint (27, ==, hb_ot_name_get_utf8 (face, name_id, hb_language_from_string ("en_US", -1), &text_size, text));
+  g_assert_cmpuint (8, ==, text_size);
+  g_assert_cmpstr (text, ==, "FontForg");
+
+  g_assert_cmpuint (0, ==, hb_ot_name_get_utf8 (face, name_id, hb_language_from_string ("fa_IR", -1), &text_size, text));
 }
 
 int