[set] Add hb_set_is_inverted()

diff --git a/docs/harfbuzz-sections.txt b/docs/harfbuzz-sections.txt
index 7a6848b..78158df 100644
--- a/docs/harfbuzz-sections.txt
+++ b/docs/harfbuzz-sections.txt

@@ -750,6 +750,7 @@
 hb_set_union
 hb_set_symmetric_difference
 hb_set_invert
+hb_set_is_inverted
 hb_set_is_equal
 hb_set_is_subset
 hb_set_next

diff --git a/src/hb-bit-set-invertible.hh b/src/hb-bit-set-invertible.hh
index ff8aecc..1eb1b1c 100644
--- a/src/hb-bit-set-invertible.hh
+++ b/src/hb-bit-set-invertible.hh

@@ -74,6 +74,11 @@
       inverted = !inverted;
   }
 
+  bool is_inverted () const
+  {
+    return inverted;
+  }
+
   bool is_empty () const
   {
     hb_codepoint_t v = INVALID;

diff --git a/src/hb-set.cc b/src/hb-set.cc
index 0270b21..4496120 100644
--- a/src/hb-set.cc
+++ b/src/hb-set.cc

@@ -492,6 +492,22 @@
 }
 
 /**
+ * hb_set_is_inverted:
+ * @set: A set
+ *
+ * Returns whether the set is inverted.
+ *
+ * Return value: `true` if the set is inverted, `false` otherwise
+ *
+ * Since: REPLACEME
+ **/
+hb_bool_t
+hb_set_is_inverted (const hb_set_t *set)
+{
+  return set->is_inverted ();
+}
+
+/**
  * hb_set_get_population:
  * @set: A set
  *

diff --git a/src/hb-set.h b/src/hb-set.h
index 93636ab..de53231 100644
--- a/src/hb-set.h
+++ b/src/hb-set.h

@@ -98,6 +98,9 @@
 hb_set_invert (hb_set_t *set);
 
 HB_EXTERN hb_bool_t
+hb_set_is_inverted (const hb_set_t *set);
+
+HB_EXTERN hb_bool_t
 hb_set_has (const hb_set_t *set,
 	    hb_codepoint_t  codepoint);
 

diff --git a/src/hb-set.hh b/src/hb-set.hh
index b13d537..6048023 100644
--- a/src/hb-set.hh
+++ b/src/hb-set.hh

@@ -79,6 +79,7 @@
   void reset () { s.reset (); }
   void clear () { s.clear (); }
   void invert () { s.invert (); }
+  bool is_inverted () const { return s.is_inverted (); }
   bool is_empty () const { return s.is_empty (); }
   uint32_t hash () const { return s.hash (); }
 

diff --git a/src/test-set.cc b/src/test-set.cc
index a0b7ac9..9fe319d 100644
--- a/src/test-set.cc
+++ b/src/test-set.cc

@@ -132,7 +132,8 @@
     assert (last == 4);
     assert (!s.previous_range (&start, &last));
 
-    /* Inverted set returns true for invalid value. */
+    assert (s.is_inverted ());
+    /* Inverted set returns true for invalid value; oh well. */
     assert (s.has (HB_SET_VALUE_INVALID));
   }