fix(cdk/collections): Do not deselect comparable already selected value with setSelection (#28267)

(cherry picked from commit 58d4958)

Author: stijnvn

src/cdk/collections/selection-model.ts

@@ -94,7 +94,7 @@ export class SelectionModel<T> {
     const newSelectedSet = new Set(values);
     values.forEach(value => this._markSelected(value));
     oldValues
-      .filter(value => !newSelectedSet.has(value))
+      .filter(value => !newSelectedSet.has(this._getConcreteValue(value, newSelectedSet)))
       .forEach(value => this._unmarkSelected(value));
     const changed = this._hasQueuedChanges();
     this._emitChangeEvent();
@@ -234,11 +234,12 @@ export class SelectionModel<T> {
   }
 
   /** Returns a value that is comparable to inputValue by applying compareWith function, returns the same inputValue otherwise. */
-  private _getConcreteValue(inputValue: T): T {
+  private _getConcreteValue(inputValue: T, selection?: Set<T>): T {
     if (!this.compareWith) {
       return inputValue;
     } else {
-      for (let selectedValue of this._selection) {
+      selection = selection ?? this._selection;
+      for (let selectedValue of selection) {
         if (this.compareWith!(inputValue, selectedValue)) {
           return selectedValue;
         }

src/cdk/collections/selection.spec.ts

@@ -299,4 +299,19 @@ describe('SelectionModel', () => {
     model.deselect(v2);
     expect(model.selected.length).toBe(1);
   });
+
+  describe('setSelection', () => {
+    it('should not deselect an already selected value', () => {
+      type Item = {key: number; value: string};
+      const v1: Item = {key: 1, value: 'blue'};
+      const v2: Item = {key: 1, value: 'apple'};
+      const compareFun = (x: Item, y: Item) => x.key === y.key;
+      const model = new SelectionModel<Item>(false, [v1], false, compareFun);
+
+      model.setSelection(v2);
+
+      expect(model.selected.length).toBe(1);
+      expect(compareFun(model.selected[0], v2)).toBeTruthy();
+    });
+  });
 });