feat: A few enhancements to our RPC messages.

* More fine grained status reporting when saving changes. Needed to we
  can notify the client if we've got errors saving settings due to
  running out of space, etc.
* Return the max layer name lenght in the keymap payload, for the UI to
  leverage.

app/src/keymap.c

@@ -432,7 +432,7 @@ int zmk_keymap_check_unsaved_changes(void) {
 #define LAYER_NAME_SETTINGS_KEY "keymap/l_n/%d"
 #define LAYER_BINDING_SETTINGS_KEY "keymap/l/%d/%d"
 
-static void save_bindings(void) {
+static int save_bindings(void) {
     for (int l = 0; l < ZMK_KEYMAP_LAYERS_LEN; l++) {
         uint8_t *pending = zmk_keymap_layer_pending_changes[l];
 
@@ -461,45 +461,64 @@ static void save_bindings(void) {
                 char setting_name[20];
                 sprintf(setting_name, LAYER_BINDING_SETTINGS_KEY, l, kp);
 
-                settings_save_one(setting_name, &binding_setting, len);
+                int ret = settings_save_one(setting_name, &binding_setting, len);
+                if (ret < 0) {
+                    LOG_ERR("Failed to save keymap binding at %d on layer %d (%d)", l, kp, ret);
+                    return ret;
+                }
             }
         }
 
         *pending = 0;
     }
+
+    return 0;
 }
 
 #if IS_ENABLED(CONFIG_ZMK_KEYMAP_LAYER_REORDERING)
-static void save_layer_orders(void) {
-    settings_save_one(LAYER_ORDER_SETTINGS_KEY, keymap_layer_orders,
-                      ARRAY_SIZE(keymap_layer_orders));
+static int save_layer_orders(void) {
+    int ret = settings_save_one(LAYER_ORDER_SETTINGS_KEY, keymap_layer_orders,
+                                ARRAY_SIZE(keymap_layer_orders));
+    if (ret < 0) {
+        return ret;
+    }
+
     memcpy(settings_layer_orders, keymap_layer_orders, ARRAY_SIZE(keymap_layer_orders));
+    return 0;
 }
 #endif // IS_ENABLED(CONFIG_ZMK_KEYMAP_LAYER_REORDERING)
 
-static void save_layer_names(void) {
+static int save_layer_names(void) {
     for (int id = 0; id < ZMK_KEYMAP_LAYERS_LEN; id++) {
         if (changed_layer_names & BIT(id)) {
             char setting_name[14];
             sprintf(setting_name, LAYER_NAME_SETTINGS_KEY, id);
-            settings_save_one(setting_name, zmk_keymap_layer_names[id],
-                              strlen(zmk_keymap_layer_names[id]));
+            int ret = settings_save_one(setting_name, zmk_keymap_layer_names[id],
+                                        strlen(zmk_keymap_layer_names[id]));
+            if (ret < 0) {
+                return ret;
+            }
         }
     }
 
     changed_layer_names = 0;
+    return 0;
 }
 
 int zmk_keymap_save_changes(void) {
-    save_bindings();
+    int ret = save_bindings();
+    if (ret < 0) {
+        return ret;
+    }
 
 #if IS_ENABLED(CONFIG_ZMK_KEYMAP_LAYER_REORDERING)
-    save_layer_orders();
+    ret = save_layer_orders();
+    if (ret < 0) {
+        return ret;
+    }
 #endif // IS_ENABLED(CONFIG_ZMK_KEYMAP_LAYER_REORDERING)
 
-    save_layer_names();
-
-    return 0;
+    return save_layer_names();
 }
 
 #if IS_ENABLED(CONFIG_ZMK_KEYMAP_LAYER_REORDERING)

app/src/studio/keymap_subsystem.c

@@ -103,6 +103,7 @@ zmk_studio_Response get_keymap(const zmk_studio_Request *req) {
 
     resp.layers.funcs.encode = encode_keymap_layers;
 
+    resp.max_layer_name_length = CONFIG_ZMK_KEYMAP_LAYER_NAME_MAX_LEN;
     resp.available_layers = 0;
 
     for (zmk_keymap_layer_index_t index = 0; index < ZMK_KEYMAP_LAYERS_LEN; index++) {
@@ -174,25 +175,47 @@ zmk_studio_Response check_unsaved_changes(const zmk_studio_Request *req) {
     return KEYMAP_RESPONSE(check_unsaved_changes, layout_changes > 0 || keymap_changes > 0);
 }
 
+static void map_errno_to_save_resp(int err, zmk_keymap_SaveChangesResponse *resp) {
+    resp->which_result = zmk_keymap_SaveChangesResponse_err_tag;
+
+    switch (err) {
+    case -ENOTSUP:
+        resp->result.err = zmk_keymap_SaveChangesErrorCode_SAVE_CHANGES_ERR_NOT_SUPPORTED;
+        break;
+    case -ENOSPC:
+        resp->result.err = zmk_keymap_SaveChangesErrorCode_SAVE_CHANGES_ERR_NO_SPACE;
+        break;
+    default:
+        resp->result.err = zmk_keymap_SaveChangesErrorCode_SAVE_CHANGES_ERR_GENERIC;
+        break;
+    }
+}
+
 zmk_studio_Response save_changes(const zmk_studio_Request *req) {
+    zmk_keymap_SaveChangesResponse resp = zmk_keymap_SaveChangesResponse_init_zero;
+    resp.which_result = zmk_keymap_SaveChangesResponse_ok_tag;
+    resp.result.ok = true;
+
     LOG_DBG("");
     int ret = zmk_physical_layouts_save_selected();
 
     if (ret < 0) {
         LOG_WRN("Failed to save selected physical layout (%d)", ret);
-        return ZMK_RPC_SIMPLE_ERR(GENERIC);
+        map_errno_to_save_resp(ret, &resp);
+        return KEYMAP_RESPONSE(save_changes, resp);
     }
 
     ret = zmk_keymap_save_changes();
     if (ret < 0) {
         LOG_WRN("Failed to save keymap changes (%d)", ret);
-        return ZMK_RPC_SIMPLE_ERR(GENERIC);
+        map_errno_to_save_resp(ret, &resp);
+        return KEYMAP_RESPONSE(save_changes, resp);
     }
 
     raise_zmk_studio_rpc_notification((struct zmk_studio_rpc_notification){
         .notification = KEYMAP_NOTIFICATION(unsaved_changes_status_changed, false)});
 
-    return KEYMAP_RESPONSE(save_changes, true);
+    return KEYMAP_RESPONSE(save_changes, resp);
 }
 
 zmk_studio_Response discard_changes(const zmk_studio_Request *req) {

app/west.yml

@@ -34,7 +34,7 @@ manifest:
       path: modules/lib/nanopb
       remote: zephyrproject-rtos
     - name: zmk-studio-messages
-      revision: a79267a9661241a6603b6da3d2b3f71e8023a9d9
+      revision: 6cb4c283e76209d59c45fbcb218800cd19e9339d
       path: modules/msgs/zmk-studio-messages
       remote: zmkfirmware
   self: