refactor(config): enable stencil's experimental slot fixes (#28995)

Issue number: N/A

---------

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

the stencil team has been working on fixing multiple issues with slots
elements in the stencil code base. to make these changes backwards
compatible and communicate that they were volatile, we added two
configuration flags for these fixes that were prefixed with the word
"experimental".

now that the effort to provide these fixes has largely solidified, the
features behind these flags are slightly less volatile. while the
"experimental" aspect still technically holds true, we've requested
the Framework team to enable these flags in a v8 beta. the stencil
team expects these flags to be set to `true` by default in stencil
v5, which ought to help prepare for future migrations the ionic
framework has to undergo.

Previously, Stencil would allow content to project through to a
component even when a slot was not present. However, with the changes in
`extras.experimentalScopedSlotChanges`, this behavior was changed to
hide elements without a destination slot - matching the behavior of a
shadow encapsulated component.

As such, elements projected through the `ion-label` or `ion-buttons`
components would no longer be visible in rendered output.

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

This commit adds an explicit `slot` tag to components in core leveraging
"scoped" encapsulation with no rendered content (i.e. elements with only
a `Host` tag and styles).

`subtree` was added to a mutation observer.
This fixes an issue with the `ion-input` component not re-rendering in
some cases when using the label slot functionality.

HTML element patches in Stencil that are enabled by the
`experimentalSlotFixes` flag result in DOM manipulations that won't
trigger the current mutation observer configuration and callback.

## Does this introduce a breaking change?

- [] Yes
- [x] No

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## Other information

Would you like us to update the commit message to include the `BREAKING
CHANGE:` comment? Unsure of the actual impact on end users here.

Similarly, would you like us to update the commit message here from
`chore()` to something else?
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screenshots of how the component looks before and after the change. -->

---------

Co-authored-by: Tanner Reits <[email protected]>
Co-authored-by: Liam DeBeasi <[email protected]>
Co-authored-by: Tanner Reits <[email protected]>
Co-authored-by: Maria Hutt <[email protected]>

Author: 5 people

core/src/components/buttons/buttons.tsx

@@ -34,7 +34,9 @@ export class Buttons implements ComponentInterface {
           [mode]: true,
           ['buttons-collapse']: this.collapse,
         }}
-      ></Host>
+      >
+        <slot></slot>
+      </Host>
     );
   }
 }

core/src/components/label/label.tsx

@@ -107,7 +107,9 @@ export class Label implements ComponentInterface {
           [`label-no-animate`]: this.noAnimate,
           'label-rtl': document.dir === 'rtl',
         })}
-      ></Host>
+      >
+        <slot></slot>
+      </Host>
     );
   }
 }

core/src/utils/slot-mutation-controller.ts

@@ -50,6 +50,18 @@ export const createSlotMutationController = (
 
     hostMutationObserver.observe(el, {
       childList: true,
+      /**
+       * This fixes an issue with the `ion-input` and
+       * `ion-textarea` not re-rendering in some cases
+       * when using the label slot functionality.
+       *
+       * HTML element patches in Stencil that are enabled
+       * by the `experimentalSlotFixes` flag in Stencil v4
+       * result in DOM manipulations that won't trigger
+       * the current mutation observer configuration and
+       * callback.
+       */
+      subtree: true,
     });
   }
 

core/stencil.config.ts

@@ -257,4 +257,18 @@ export const config: Config = {
   globalScript: 'src/global/ionic-global.ts',
   enableCache: true,
   transformAliasedImportPaths: true,
+  extras: {
+    /**
+     * `experimentalSlotFixes` is necessary in Stencil v4 until the fixes described in
+     * {@link https://stenciljs.com/docs/config-extras#experimentalslotfixes the Stencil docs for the flag} are the
+     * default behavior (slated for a future Stencil major version).
+     */
+    experimentalSlotFixes: true,
+    /**
+     * `experimentalScopedSlotChanges` is necessary in Stencil v4 until the fixes described in
+     * {@link https://stenciljs.com/docs/config-extras#experimentalscopedslotchanges the Stencil docs for the flag} are
+     * the default behavior (slated for a future Stencil major version).
+     */
+    experimentalScopedSlotChanges: true,
+  }
 };