feat(fill): allow filling based on the label selector (#4342)

This enables filling the input based on the connected label:

```html
<label for=target>Name</label><input id=target>
```

```js
await page.fill('text=Name', 'Alice');
```

docs/input.md

@@ -2,7 +2,7 @@
 
 <!-- GEN:toc-top-level -->
 - [Text input](#text-input)
-- [Checkboxes](#checkboxes)
+- [Checkboxes and radio buttons](#checkboxes-and-radio-buttons)
 - [Select options](#select-options)
 - [Mouse click](#mouse-click)
 - [Type characters](#type-characters)
@@ -15,7 +15,7 @@
 
 ## Text input
 
-This is the easiest way to fill out the form fields. It focuses the element and triggers an `input` event with the entered text. It works for `<input>`, `<textarea>` and `[contenteditable]` elements.
+This is the easiest way to fill out the form fields. It focuses the element and triggers an `input` event with the entered text. It works for `<input>`, `<textarea>`, `[contenteditable]` and `<label>` associated with an input or textarea.
 
 ```js
 // Text input
@@ -29,6 +29,9 @@ await page.fill('#time', '13-15');
 
 // Local datetime input
 await page.fill('#local', '2020-03-02T05:15');
+
+// Input through label
+await page.fill('text=First Name', 'Peter');
 ```
 
 #### API reference
@@ -39,9 +42,9 @@ await page.fill('#local', '2020-03-02T05:15');
 
 <br/>
 
-## Checkboxes
+## Checkboxes and radio buttons
 
-This is the easiest way to check and uncheck a checkbox. This method can be used on the `input[type=checkbox]` and on the `label` associated with that input.
+This is the easiest way to check and uncheck a checkbox or a radio button. This method can be used with `input[type=checkbox]`, `input[type=radio]`, `[role=checkbox]` or `label` associated with checkbox or radio button.
 
 ```js
 // Check the checkbox
@@ -49,6 +52,9 @@ await page.check('#agree');
 
 // Uncheck by input <label>.
 await page.uncheck('#subscribe-label');
+
+// Select the radio button
+await page.check('text=XL');
 ```
 
 #### API reference

src/server/injected/injectedScript.ts

@@ -261,10 +261,10 @@ export class InjectedScript {
     return this.pollRaf((progress, continuePolling) => {
       if (node.nodeType !== Node.ELEMENT_NODE)
         return 'error:notelement';
-      const element = node as Element;
-      if (!element.isConnected)
+      const element = this.findLabelTarget(node as Element);
+      if (element && !element.isConnected)
         return 'error:notconnected';
-      if (!this.isVisible(element)) {
+      if (!element || !this.isVisible(element)) {
         progress.logRepeating('    element is not visible - waiting...');
         return continuePolling;
       }
@@ -438,27 +438,22 @@ export class InjectedScript {
     return 'done';
   }
 
+  findLabelTarget(element: Element): Element | undefined {
+    return element.nodeName === 'LABEL' ? (element as HTMLLabelElement).control || undefined : element;
+  }
+
   isCheckboxChecked(node: Node) {
     if (node.nodeType !== Node.ELEMENT_NODE)
       throw new Error('Not a checkbox or radio button');
-
-    let element: Element | undefined = node as Element;
+    const element = node as Element;
     if (element.getAttribute('role') === 'checkbox')
       return element.getAttribute('aria-checked') === 'true';
-
-    if (element.nodeName === 'LABEL') {
-      const forId = element.getAttribute('for');
-      if (forId && element.ownerDocument)
-        element = element.ownerDocument.querySelector(`input[id="${forId}"]`) || undefined;
-      else
-        element = element.querySelector('input[type=checkbox],input[type=radio]') || undefined;
-    }
-    if (element && element.nodeName === 'INPUT') {
-      const type = element.getAttribute('type');
-      if (type && (type.toLowerCase() === 'checkbox' || type.toLowerCase() === 'radio'))
-        return (element as HTMLInputElement).checked;
-    }
-    throw new Error('Not a checkbox');
+    const input = this.findLabelTarget(element);
+    if (!input || input.nodeName !== 'INPUT')
+      throw new Error('Not a checkbox or radio button');
+    if (!['radio', 'checkbox'].includes((input as HTMLInputElement).type.toLowerCase()))
+      throw new Error('Not a checkbox or radio button');
+    return (input as HTMLInputElement).checked;
   }
 
   setInputFiles(node: Node, payloads: { name: string, mimeType: string, buffer: string }[]) {

test/check.spec.ts

@@ -58,6 +58,23 @@ it('should check the box inside label w/o id', async ({page}) => {
   expect(await page.evaluate(() => window['checkbox'].checked)).toBe(true);
 });
 
+it('should check the box outside shadow dom label', async ({page}) => {
+  await page.setContent('<div></div>');
+  await page.$eval('div', div => {
+    const root = div.attachShadow({ mode: 'open' });
+    const label = document.createElement('label');
+    label.setAttribute('for', 'target');
+    label.textContent = 'Click me';
+    root.appendChild(label);
+    const input = document.createElement('input');
+    input.setAttribute('type', 'checkbox');
+    input.setAttribute('id', 'target');
+    root.appendChild(input);
+  });
+  await page.check('label');
+  expect(await page.$eval('input', input => input.checked)).toBe(true);
+});
+
 it('should check radio', async ({page}) => {
   await page.setContent(`
     <input type='radio'>one</input>

test/page-fill.spec.ts

@@ -34,6 +34,24 @@ it('should fill input', async ({page, server}) => {
   expect(await page.evaluate(() => window['result'])).toBe('some value');
 });
 
+it('should fill input with label', async ({page}) => {
+  await page.setContent(`<label for=target>Fill me</label><input id=target>`);
+  await page.fill('text=Fill me', 'some value');
+  expect(await page.$eval('input', input => input.value)).toBe('some value');
+});
+
+it('should fill input with label 2', async ({page}) => {
+  await page.setContent(`<label>Fill me<input id=target></label>`);
+  await page.fill('text=Fill me', 'some value');
+  expect(await page.$eval('input', input => input.value)).toBe('some value');
+});
+
+it('should fill textarea with label', async ({page}) => {
+  await page.setContent(`<label for=target>Fill me</label><textarea id=target>hey</textarea>`);
+  await page.fill('text=Fill me', 'some value');
+  expect(await page.$eval('textarea', textarea => textarea.value)).toBe('some value');
+});
+
 it('should throw on unsupported inputs', async ({page, server}) => {
   await page.goto(server.PREFIX + '/input/textarea.html');
   for (const type of ['color', 'file']) {