Warn for unused panels and pages

Fixes #1 (closed)

src/language-server/dashboarder-validator.ts

-import { ValidationAcceptor, ValidationCheck, ValidationRegistry } from 'langium';
+import { AstNode, Reference, ValidationAcceptor, ValidationCheck, ValidationRegistry } from 'langium';
 import { DashboarderAstType, Page, Panel } from './generated/ast';
 import { DashboarderServices } from './dashboarder-module';
 import _ from 'lodash';
@@ -13,8 +13,8 @@ export class DashboarderValidationRegistry extends ValidationRegistry {
         super(services);
         const validator = services.validation.DashboarderValidator;
         const checks: DashboarderChecks = {
-            Panel: [validator.checkPanelStartsWithCapital],
-            Page: [validator.checkPositionInGrid, validator.checkPanelOverlap],
+            Panel: [validator.checkPanelStartsWithCapital, validator.checkUnusedPanel],
+            Page: [validator.checkPositionInGrid, validator.checkPanelOverlap, validator.checkUnusedPage],
         };
         this.register(checks, validator);
     }
@@ -71,6 +71,20 @@ export class DashboarderValidator {
             accept('warning', `Panel overlaps with ${value.map(panel => panel.name).join(', ')}`, { node: page, property: 'positions', index });
         });
     }
+
+    checkUnusedPanel(node: Panel, accept: ValidationAcceptor) {
+        const pages = node.$container.pages;
+        for (let page of pages) {
+            if (page.panels.find(isReferenced(node))) return;
+        }
+        accept('warning', 'Panel is unused', { node, property: 'name' });
+    }
+
+    checkUnusedPage(node: Page, accept: ValidationAcceptor) {
+        const sidebar = node.$container.sidebar;
+        if(sidebar.pages.find(isReferenced(node))) return;
+        accept('warning', 'Page is unused', { node, property: 'name' });
+    }
 }
 
 interface Position {
@@ -97,3 +111,6 @@ const convertToPosition = (position: string): Position => {
 
     return { rowStart: _.min(rowElements)!, rowEnd: _.max(rowElements)!, columnStart: _.min(columnElements)!, columnEnd: _.max(columnElements)! };
 }
+
+
+export const isReferenced = <T extends AstNode>(node: T) => (ref: Reference<T>): boolean => (ref.ref === node);