refactor: define Grouper.comparator and create a dummy default one

Author: ilandikov

src/Query/Filter/Field.ts

@@ -3,6 +3,7 @@ import type { Comparator } from '../Sorter';
 import * as RegExpTools from '../../lib/RegExpTools';
 import { Grouper } from '../Grouper';
 import type { GrouperFunction } from '../Grouper';
+import type { Task } from './../../Task';
 import type { FilterOrErrorMessage } from './Filter';
 
 /**
@@ -287,7 +288,7 @@ export abstract class Field {
      * @param reverse - false for normal group order, true for reverse group order.
      */
     public createGrouper(reverse: boolean): Grouper {
-        return new Grouper(this.fieldNameSingular(), this.grouper(), reverse);
+        return new Grouper(this.fieldNameSingular(), this.grouper(), reverse, this.defaultComparator);
     }
 
     /**
@@ -309,4 +310,8 @@ export abstract class Field {
     public createReverseGrouper(): Grouper {
         return this.createGrouper(true);
     }
+
+    protected defaultComparator: Comparator = (_a: Task, _b: Task) => {
+        return 0;
+    };
 }

src/Query/Filter/MultiTextField.ts

@@ -64,7 +64,7 @@ export abstract class MultiTextField extends TextField {
      * This overloads {@link Field.createGrouper} to put a plural field name in the {@link Grouper.property}.
      */
     public createGrouper(reverse: boolean): Grouper {
-        return new Grouper(this.fieldNamePlural(), this.grouper(), reverse);
+        return new Grouper(this.fieldNamePlural(), this.grouper(), reverse, this.defaultComparator);
     }
 
     protected grouperRegExp(): RegExp {

src/Query/Grouper.ts

@@ -1,4 +1,5 @@
 import type { Task } from '../Task';
+import type { Comparator } from './Sorter';
 
 /**
  * A group-naming function, that takes a Task object and returns zero or more
@@ -39,9 +40,12 @@ export class Grouper {
      */
     public readonly reverse: boolean;
 
-    constructor(property: string, grouper: GrouperFunction, reverse: boolean) {
+    public readonly comparator: Comparator;
+
+    constructor(property: string, grouper: GrouperFunction, reverse: boolean, comparator: Comparator) {
         this.property = property;
         this.grouper = grouper;
         this.reverse = reverse;
+        this.comparator = comparator;
     }
 }