feat: Implement basic general folder support (#2051)

- Related: #1748

tests/cache/equality-map.test.ts

@@ -0,0 +1,91 @@
+import { describe, expect, it } from 'vitest';
+import { EqualityMap } from '../../src/cache/equality-map';
+
+describe('EqualityMap', () => {
+  it('should set and get values with primitive keys', () => {
+    const map = new EqualityMap<string, number>();
+    map.set('a', 1);
+    expect(map.get('a')).toBe(1);
+    expect(map.has('a')).toBe(true);
+    expect(map.get('b')).toBeUndefined();
+    expect(map.has('b')).toBe(false);
+  });
+
+  it('should set and get values with object keys using deep equality', () => {
+    const map = new EqualityMap<{ x: number }, string>();
+    map.set({ x: 1 }, 'foo');
+    expect(map.get({ x: 1 })).toBe('foo');
+    expect(map.has({ x: 1 })).toBe(true);
+    expect(map.get({ x: 2 })).toBeUndefined();
+  });
+
+  it('should overwrite value if key is deeply equal', () => {
+    const map = new EqualityMap<{ y: number }, string>();
+    map.set({ y: 2 }, 'bar');
+    map.set({ y: 2 }, 'baz');
+    expect(map.get({ y: 2 })).toBe('baz');
+    expect(map.size).toBe(1);
+  });
+
+  it('should delete values by deep equality', () => {
+    const map = new EqualityMap<{ z: number }, string>();
+    map.set({ z: 3 }, 'val');
+    expect(map.delete({ z: 3 })).toBe(true);
+    expect(map.get({ z: 3 })).toBeUndefined();
+    expect(map.size).toBe(0);
+  });
+
+  it('should clear all values', () => {
+    const map = new EqualityMap<number, string>();
+    map.set(1, 'a');
+    map.set(2, 'b');
+    map.clear();
+    expect(map.size).toBe(0);
+    expect(map.get(1)).toBeUndefined();
+    expect(map.get(2)).toBeUndefined();
+  });
+
+  it('should iterate entries', () => {
+    const map = new EqualityMap<string, number>();
+    map.set('a', 1);
+    map.set('b', 2);
+    const entries = Array.from(map);
+    expect(entries).toContainEqual(['a', 1]);
+    expect(entries).toContainEqual(['b', 2]);
+  });
+
+  it('should iterate keys', () => {
+    const map = new EqualityMap<string, number>();
+    map.set('x', 10);
+    map.set('y', 20);
+    const keys = Array.from(map.keys());
+    expect(keys).toContain('x');
+    expect(keys).toContain('y');
+  });
+
+  it('should iterate values', () => {
+    const map = new EqualityMap<string, number>();
+    map.set('foo', 100);
+    map.set('bar', 200);
+    const values = Array.from(map.values());
+    expect(values).toContain(100);
+    expect(values).toContain(200);
+  });
+
+  it('should call forEach with correct arguments', () => {
+    const map = new EqualityMap<string, number>();
+    map.set('a', 1);
+    map.set('b', 2);
+    const calls: [number, string][] = [];
+    map.forEach((value, key) => {
+      calls.push([value, key]);
+    });
+    expect(calls).toContainEqual([1, 'a']);
+    expect(calls).toContainEqual([2, 'b']);
+  });
+
+  it('should have correct Symbol.toStringTag', () => {
+    const map = new EqualityMap<number, number>();
+    expect(Object.prototype.toString.call(map)).toBe('[object EqualityMap]');
+  });
+});