fix(button): hidden button is added when form is set async (#27955)

Issue number: resolves #27952

---------

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issue. -->

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etc). Submit multiple pull requests if needed. -->

## What is the current behavior?
<!-- Please describe the current behavior that you are modifying. -->

The hidden button in `ion-button` that is responsible for submitting the
form does not get added when the `form` property is set async.

## What is the new behavior?
<!-- Please describe the behavior or changes that are being added by
this PR. -->

- `ion-button` now checks to see if it needs to render a hidden button
whenever it re-renders. This allows it to account for changes to the
`type` property, `form` property, etc.

Since this code can potentially run multiple times I added an extra
check so we don't add multiple buttons to the form.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

<!-- If this introduces a breaking change, please describe the impact
and migration path for existing applications below. -->


## Other information

<!-- Any other information that is important to this PR such as
screenshots of how the component looks before and after the change. -->

Dev build: `7.2.3-dev.11691523847.1760ab58`

core/src/components/button/button.tsx

@@ -153,19 +153,27 @@ export class Button implements ComponentInterface, AnchorInterface, ButtonInterf
    */
   @Event() ionBlur!: EventEmitter<void>;
 
-  connectedCallback(): void {
-    // Allow form to be submitted through `ion-button`
-    if (this.type !== 'button' && hasShadowDom(this.el)) {
-      this.formEl = this.findForm();
-      if (this.formEl) {
-        // Create a hidden native button inside of the form
-        this.formButtonEl = document.createElement('button');
-        this.formButtonEl.type = this.type;
-        this.formButtonEl.style.display = 'none';
-        // Only submit if the button is not disabled.
-        this.formButtonEl.disabled = this.disabled;
-        this.formEl.appendChild(this.formButtonEl);
+  private renderHiddenButton() {
+    const formEl = (this.formEl = this.findForm());
+    if (formEl) {
+      const { formButtonEl } = this;
+
+      /**
+       * If the form already has a rendered form button
+       * then do not append a new one again.
+       */
+      if (formButtonEl !== null && formEl.contains(formButtonEl)) {
+        return;
       }
+
+      // Create a hidden native button inside of the form
+      const newFormButtonEl = (this.formButtonEl = document.createElement('button'));
+      newFormButtonEl.type = this.type;
+      newFormButtonEl.style.display = 'none';
+      // Only submit if the button is not disabled.
+      newFormButtonEl.disabled = this.disabled;
+
+      formEl.appendChild(newFormButtonEl);
     }
   }
 
@@ -314,6 +322,11 @@ export class Button implements ComponentInterface, AnchorInterface, ButtonInterf
     if (fill == null) {
       fill = this.inToolbar || this.inListHeader ? 'clear' : 'solid';
     }
+
+    {
+      type !== 'button' && this.renderHiddenButton();
+    }
+
     return (
       <Host
         onClick={this.handleClick}

core/src/components/button/test/form-reference/button.e2e.ts

@@ -130,6 +130,29 @@ configs({ directions: ['ltr'], modes: ['ios'] }).forEach(({ title, config }) =>
 
       expect(submitEvent).not.toHaveReceivedEvent();
     });
+
+    test('should submit the form by id when form is set async', async ({ page }, testInfo) => {
+      testInfo.annotations.push({
+        type: 'issue',
+        description: 'https://github.com/ionic-team/ionic-framework/issues/27952',
+      });
+      await page.setContent(
+        `
+        <form id="myForm"></form>
+        <ion-button type="submit">Submit</ion-button>
+      `,
+        config
+      );
+
+      const submitEvent = await page.spyOnEvent('submit');
+      const button = page.locator('ion-button');
+
+      await button.evaluate((el: HTMLIonButtonElement) => (el.form = 'myForm'));
+
+      await page.click('ion-button');
+
+      expect(submitEvent).toHaveReceivedEvent();
+    });
   });
 
   test.describe(title('should throw a warning if the form cannot be found'), () => {

core/src/components/button/test/form-reference/button.spec.ts

@@ -0,0 +1,31 @@
+import { newSpecPage } from '@stencil/core/testing';
+import { Button } from '../../button';
+
+describe('Button: Hidden Form Button', () => {
+  it('should not add multiple buttons to the form', async () => {
+    const page = await newSpecPage({
+      components: [Button],
+      html: `
+        <form id="my-form"></form>
+        <ion-button form="my-form" type="submit">Submit</ion-button>
+      `,
+    });
+
+    const getButtons = () => {
+      return page.body.querySelectorAll('form button');
+    };
+
+    const form = page.body.querySelectorAll('form');
+    const button = page.body.querySelector('ion-button');
+
+    await page.waitForChanges();
+
+    expect(getButtons().length).toEqual(1);
+
+    // Re-render the component
+    button.color = 'danger';
+    await page.waitForChanges();
+
+    expect(getButtons().length).toEqual(1);
+  });
+});