state: Add xkb_state_key_get_consumed_mods

This retrieves the mask of consumed modifiers for a given key and state,
which is helpful for toolkits without having them to do it one modifier
at a time, or pass in 0xFFFFFFFF to xkb_state_remove_consumed_mods to
"reverse-engineer" the consumed mods.

src/state.c

@@ -1169,3 +1169,14 @@ xkb_state_mod_mask_remove_consumed(struct xkb_state *state, xkb_keycode_t kc,
 
     return mask & ~key_get_consumed(state, key);
 }
+
+XKB_EXPORT xkb_mod_mask_t
+xkb_state_key_get_consumed_mods(struct xkb_state *state, xkb_keycode_t kc)
+{
+    const struct xkb_key *key = XkbKey(state->keymap, kc);
+
+    if (!key)
+        return 0;
+
+    return key_get_consumed(state, key);
+}

test/state.c

@@ -333,6 +333,9 @@ test_consume(struct xkb_keymap *keymap)
                                               mask);
     assert(mask == (1U << alt));
 
+    mask = xkb_state_key_get_consumed_mods(state, KEY_EQUAL + EVDEV_OFFSET);
+    assert(mask == (1U << shift));
+
     xkb_state_unref(state);
 }
 

xkbcommon/xkbcommon.h

@@ -1483,6 +1483,7 @@ xkb_state_mod_indices_are_active(struct xkb_state *state,
  * index is not valid in the keymap, returns -1.
  *
  * @sa xkb_state_mod_mask_remove_consumed()
+ * @sa xkb_state_key_get_consumed_mods()
  * @memberof xkb_state
  */
 int
@@ -1502,6 +1503,17 @@ xkb_mod_mask_t
 xkb_state_mod_mask_remove_consumed(struct xkb_state *state, xkb_keycode_t key,
                                    xkb_mod_mask_t mask);
 
+/**
+ * Get the mask of modifiers consumed by translating a given key.
+ *
+ * @returns a mask of the consumed modifiers.
+ *
+ * @sa xkb_state_mod_index_is_consumed()
+ * @memberof xkb_state
+ */
+xkb_mod_mask_t
+xkb_state_key_get_consumed_mods(struct xkb_state *state, xkb_keycode_t key);
+
 /**
  * Test whether a layout is active in a given keyboard state by name.
  *