[API] Add HB_LANGUAGE_INVALID

src/hb-common.cc

@@ -169,16 +169,17 @@ hb_language_t
 hb_language_from_string (const char *str)
 {
   if (!str || !*str)
-    return NULL;
+    return HB_LANGUAGE_INVALID;
 
   hb_language_item_t *item = langs.find_or_insert (str, langs_lock);
 
-  return likely (item) ? item->lang : NULL;
+  return likely (item) ? item->lang : HB_LANGUAGE_INVALID;
 }
 
 const char *
 hb_language_to_string (hb_language_t language)
 {
+  /* This is actually NULL-safe! */
   return language->s;
 }
 

src/hb-common.h

@@ -114,6 +114,8 @@ hb_language_from_string (const char *str);
 const char *
 hb_language_to_string (hb_language_t language);
 
+#define HB_LANGUAGE_INVALID ((hb_language_t) NULL)
+
 hb_language_t
 hb_language_get_default (void);
 

src/hb-ot-tag.cc

@@ -610,7 +610,7 @@ hb_ot_tag_from_language (hb_language_t language)
   const char *lang_str, *s;
   const LangTag *lang_tag;
 
-  if (language == NULL)
+  if (language == HB_LANGUAGE_INVALID)
     return HB_OT_TAG_DEFAULT_LANGUAGE;
 
   lang_str = hb_language_to_string (language);

src/hb-shape.cc

@@ -79,7 +79,7 @@ hb_shape (hb_font_t          *font,
   }
 
   /* If language is not set, use default language from locale */
-  if (buffer->props.language == NULL) {
+  if (buffer->props.language == HB_LANGUAGE_INVALID) {
     /* TODO get_default_for_script? using $LANGUAGE */
     buffer->props.language = hb_language_get_default ();
   }

test/test-common.c

@@ -156,6 +156,8 @@ test_types_language (void)
   hb_language_t fa_ir = hb_language_from_string ("fa-ir");
   hb_language_t en = hb_language_from_string ("en");
 
+  g_assert (HB_LANGUAGE_INVALID == NULL);
+
   g_assert (fa != NULL);
   g_assert (fa_IR != NULL);
   g_assert (fa_IR == fa_ir);
@@ -167,13 +169,14 @@ test_types_language (void)
   g_assert (en == hb_language_from_string ("en"));
   g_assert (en == hb_language_from_string ("eN"));
 
-  g_assert (NULL == hb_language_from_string (NULL));
-  g_assert (NULL == hb_language_from_string (""));
+  g_assert (HB_LANGUAGE_INVALID == hb_language_from_string (NULL));
+  g_assert (HB_LANGUAGE_INVALID == hb_language_from_string (""));
+  g_assert (NULL == hb_language_to_string (HB_LANGUAGE_INVALID));
 
   /* Not sure how to test this better.  Setting env vars
    * here doesn't sound like the right approach, and I'm
    * not sure that it even works. */
-  g_assert (NULL != hb_language_get_default ());
+  g_assert (HB_LANGUAGE_INVALID != hb_language_get_default ());
 }
 
 int