fix(VDataTable): page resets when server-items-length is zero (#8594)

we should not limit page to the current max page when using server-items-length
since all items are not loaded.

closes #8359

packages/vuetify/src/components/VData/VData.ts

@@ -339,7 +339,9 @@ export default Vue.extend({
       this.internalOptions = {
         ...this.internalOptions,
         ...options,
-        page: Math.max(1, Math.min(options.page || this.internalOptions.page, this.pageCount)),
+        page: this.serverItemsLength < 0
+          ? Math.max(1, Math.min(options.page || this.internalOptions.page, this.pageCount))
+          : options.page || this.internalOptions.page,
       }
     },
     sortItems (items: any[]) {

packages/vuetify/src/components/VDataTable/__tests__/VDataTable.spec.ts

@@ -399,6 +399,42 @@ describe('VDataTable.ts', () => {
     expect(wrapper.html()).toMatchSnapshot()
   })
 
+  // https://github.com/vuetifyjs/vuetify/issues/8359
+  it('should not limit page to current item count when using server-items-length', async () => {
+    const wrapper = mountFunction({
+      propsData: {
+        headers: testHeaders,
+        items: [],
+        page: 2,
+        itemsPerPage: 5,
+        serverItemsLength: 0,
+      },
+    })
+
+    expect(wrapper.html()).toMatchSnapshot()
+
+    wrapper.setProps({
+      items: testItems.slice(5),
+      serverItemsLength: 20,
+    })
+    await wrapper.vm.$nextTick()
+
+    expect(wrapper.html()).toMatchSnapshot()
+  })
+
+  // https://github.com/vuetifyjs/vuetify/issues/8359
+  it('should limit page to current page count if not using server-items-length', async () => {
+    const wrapper = mountFunction({
+      propsData: {
+        headers: testHeaders,
+        items: testItems,
+        page: 3,
+        itemsPerPage: 5,
+      },
+    })
+
+    expect(wrapper.html()).toMatchSnapshot()
+  })
   // https://github.com/vuetifyjs/vuetify/issues/8184
   it('should default to first option in itemsPerPageOptions if it does not include itemsPerPage', async () => {
     const itemsPerPage = jest.fn()