feat(select): add start and end slots (#28563)

Issue number: Part of #26297

---------

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issue. -->

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

With the modern form control syntax, it is not possible to add icon
buttons or other decorators to the sides of `ion-select`, as you can
with `ion-item`.

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

`start` and `end` slots added. While making this change, I also tweaked
the CSS selectors responsible for translating the label above the input
with `"stacked"` and `"floating"` placements, merging this logic into a
single class managed by the TSX. I needed to add a new class for whether
slot content is present, so the selectors were getting unwieldy
otherwise.

Docs PR TBA; I plan on knocking out all three components at once when
the features are all complete, to make dev builds easier to manage.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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and migration path for existing applications below. -->


## Other information

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screenshots of how the component looks before and after the change. -->

---------

Co-authored-by: ionitron <[email protected]>

Author: averyjohnston

core/src/components/select/select.ios.scss

@@ -21,11 +21,11 @@
   color: #{$text-color-step-350};
 }
 
-// Select Native Wrapper
+// Select Inner Wrapper
 // ----------------------------------------------------------------
 
-:host(.select-label-placement-stacked) .native-wrapper,
-:host(.select-label-placement-floating) .native-wrapper {
+:host(.select-label-placement-stacked) .select-wrapper-inner,
+:host(.select-label-placement-floating) .select-wrapper-inner {
   width: calc(100% - $select-ios-icon-size - $select-icon-margin-start);
 }
 

core/src/components/select/select.md.outline.scss

@@ -102,10 +102,7 @@
 /**
  * This makes the label sit above the select.
  */
-:host(.select-expanded.select-fill-outline.select-label-placement-floating) .label-text-wrapper,
-:host(.ion-focused.select-fill-outline.select-label-placement-floating) .label-text-wrapper,
-:host(.has-value.select-fill-outline.select-label-placement-floating) .label-text-wrapper,
-:host(.select-fill-outline.select-label-placement-stacked) .label-text-wrapper {
+:host(.label-floating.select-fill-outline) .label-text-wrapper {
   @include transform(translateY(-32%), scale(#{$form-control-label-stacked-scale}));
   @include margin(0);
 
@@ -252,9 +249,6 @@
  * the floating/stacked label. We simulate this "cut out"
  * by removing the top border from the notch fragment.
  */
-:host(.select-expanded.select-fill-outline.select-label-placement-floating) .select-outline-notch,
-:host(.ion-focused.select-fill-outline.select-label-placement-floating) .select-outline-notch,
-:host(.has-value.select-fill-outline.select-label-placement-floating) .select-outline-notch,
-:host(.select-fill-outline.select-label-placement-stacked) .select-outline-notch {
+:host(.label-floating.select-fill-outline) .select-outline-notch {
   border-top: none;
 }

core/src/components/select/select.md.scss

@@ -138,11 +138,11 @@
   --border-radius: 16px;
 }
 
-// Select Native Wrapper
+// Select Inner Wrapper
 // ----------------------------------------------------------------
 
-:host(.select-label-placement-stacked) .native-wrapper,
-:host(.select-label-placement-floating) .native-wrapper {
+:host(.select-label-placement-stacked) .select-wrapper-inner,
+:host(.select-label-placement-floating) .select-wrapper-inner {
   width: calc(100% - $select-md-icon-size - $select-icon-margin-start);
 }
 

core/src/components/select/select.md.solid.scss

@@ -68,10 +68,7 @@
 // Select Label
 // ----------------------------------------------------------------
 
-:host(.select-fill-solid.select-label-placement-stacked) .label-text-wrapper,
-:host(.select-expanded.select-fill-solid.select-label-placement-floating) .label-text-wrapper,
-:host(.ion-focused.select-fill-solid.select-label-placement-floating) .label-text-wrapper,
-:host(.has-value.select-fill-solid.select-label-placement-floating) .label-text-wrapper {
+:host(.label-floating.select-fill-solid) .label-text-wrapper {
   /**
    * Label text should not extend
    * beyond the bounds of the select.

core/src/components/select/select.scss

@@ -157,6 +157,13 @@ button {
   @include margin(0, 0, 0, $select-icon-margin-start);
 
   position: relative;
+
+  /**
+   * Prevent the icon from shrinking when the label and/or
+   * selected item text is long enough to fill the rest of
+   * the container.
+   */
+  flex-shrink: 0;
 }
 
 /**
@@ -259,6 +266,25 @@ button {
   transition: opacity 150ms cubic-bezier(0.4, 0, 0.2, 1);
 }
 
+.select-wrapper-inner {
+  display: flex;
+
+  align-items: center;
+
+  overflow: hidden;
+}
+
+:host(.select-label-placement-stacked) .select-wrapper-inner,
+:host(.select-label-placement-floating) .select-wrapper-inner {
+  /**
+   * When using a stacked/floating label, the inner wrapper is
+   * stacked vertically under the label container. This line
+   * ensures that the inner wrapper fills all the remaining height
+   * of the component.
+   */
+  flex-grow: 1;
+}
+
 // Select Highlight
 // ----------------------------------------------------------------
 
@@ -519,11 +545,23 @@ button {
  * The placeholder should be hidden when the label
  * is on top of the select. This prevents the label
  * from overlapping any placeholder value.
+ *
+ * TODO(FW-5592): Remove :not(.label-floating) piece
  */
-:host(.select-label-placement-floating) .native-wrapper .select-placeholder {
+:host(.select-label-placement-floating:not(.label-floating)) .native-wrapper .select-placeholder {
   opacity: 0;
 }
 
+/**
+ * We don't use .label-floating here because that would
+ * also include the case where the label is floating due
+ * to content in the start/end slot. We want the opacity
+ * to remain at the default in this case, since the select
+ * isn't being actively interacted with.
+ *
+ * TODO(FW-5592): Change entire selector to:
+ * :host(.label-floating.select-label-placement-floating) .native-wrapper .select-placeholder
+ */
 :host(.select-expanded.select-label-placement-floating) .native-wrapper .select-placeholder,
 :host(.ion-focused.select-label-placement-floating) .native-wrapper .select-placeholder,
 :host(.has-value.select-label-placement-floating) .native-wrapper .select-placeholder {
@@ -533,10 +571,7 @@ button {
 /**
  * This makes the label sit above the input.
  */
-:host(.select-label-placement-stacked) .label-text-wrapper,
-:host(.select-expanded.select-label-placement-floating) .label-text-wrapper,
-:host(.ion-focused.select-label-placement-floating) .label-text-wrapper,
-:host(.has-value.select-label-placement-floating) .label-text-wrapper {
+:host(.label-floating) .label-text-wrapper {
   @include transform(translateY(50%), scale(#{$form-control-label-stacked-scale}));
 
   /**
@@ -545,3 +580,23 @@ button {
    */
   max-width: calc(100% / #{$form-control-label-stacked-scale});
 }
+
+// Start/End Slots
+// ----------------------------------------------------------------
+
+::slotted([slot="start"]), ::slotted([slot="end"]) {
+  /**
+   * Prevent the slots from shrinking when the label and/or
+   * selected item text is long enough to fill the rest of
+   * the container.
+   */
+  flex-shrink: 0;
+}
+
+::slotted([slot="start"]) {
+  margin-inline-end: $form-control-label-margin;
+}
+
+::slotted([slot="end"]) {
+  margin-inline-start: $form-control-label-margin;
+}

core/src/components/select/select.tsx

@@ -33,6 +33,8 @@ import type { SelectChangeEventDetail, SelectInterface, SelectCompareFn } from '
  * @virtualProp {"ios" | "md"} mode - The mode determines which platform styles to use.
  *
  * @slot label - The label text to associate with the select. Use the `labelPlacement` property to control where the label is placed relative to the select. Use this if you need to render a label with custom HTML.
+ * @slot start - Content to display at the leading edge of the select.
+ * @slot end - Content to display at the trailing edge of the select.
  *
  * @part placeholder - The text displayed in the select when there is no value.
  * @part text - The displayed value of the select.
@@ -762,8 +764,22 @@ export class Select implements ComponentInterface {
   }
 
   private onClick = (ev: UIEvent) => {
-    this.setFocus();
-    this.open(ev);
+    const target = ev.target as HTMLElement;
+    const closestSlot = target.closest('[slot="start"], [slot="end"]');
+
+    if (target === this.el || closestSlot === null) {
+      this.setFocus();
+      this.open(ev);
+    } else {
+      /**
+       * Prevent clicks to the start/end slots from opening the select.
+       * We ensure the target isn't this element in case the select is slotted
+       * in, for example, an item. This would prevent the select from ever
+       * being opened since the element itself has slot="start"/"end".
+       */
+      ev.stopPropagation();
+      ev.preventDefault();
+    }
   };
 
   private onFocus = () => {
@@ -864,8 +880,31 @@ export class Select implements ComponentInterface {
     const inItem = hostContext('ion-item', this.el);
     const shouldRenderHighlight = mode === 'md' && fill !== 'outline' && !inItem;
 
+    const hasValue = this.hasValue();
+    const hasStartEndSlots = el.querySelector('[slot="start"], [slot="end"]') !== null;
+
     renderHiddenInput(true, el, name, parseValue(value), disabled);
 
+    /**
+     * If the label is stacked, it should always sit above the select.
+     * For floating labels, the label should move above the select if
+     * the select has a value, is open, or has anything in either
+     * the start or end slot.
+     *
+     * If there is content in the start slot, the label would overlap
+     * it if not forced to float. This is also applied to the end slot
+     * because with the default or solid fills, the select is not
+     * vertically centered in the container, but the label is. This
+     * causes the slots and label to appear vertically offset from each
+     * other when the label isn't floating above the input. This doesn't
+     * apply to the outline fill, but this was not accounted for to keep
+     * things consistent.
+     *
+     * TODO(FW-5592): Remove hasStartEndSlots condition
+     */
+    const labelShouldFloat =
+      labelPlacement === 'stacked' || (labelPlacement === 'floating' && (hasValue || isExpanded || hasStartEndSlots));
+
     return (
       <Host
         onClick={this.onClick}
@@ -876,7 +915,8 @@ export class Select implements ComponentInterface {
           'select-disabled': disabled,
           'select-expanded': isExpanded,
           'has-expanded-icon': expandedIcon !== undefined,
-          'has-value': this.hasValue(),
+          'has-value': hasValue,
+          'label-floating': labelShouldFloat,
           'has-placeholder': placeholder !== undefined,
           'ion-focusable': true,
           [`select-${rtl}`]: true,
@@ -888,17 +928,23 @@ export class Select implements ComponentInterface {
       >
         <label class="select-wrapper" id="select-label">
           {this.renderLabelContainer()}
-          <div class="native-wrapper" ref={(el) => (this.nativeWrapperEl = el)} part="container">
-            {this.renderSelectText()}
+          <div class="select-wrapper-inner">
+            <slot name="start"></slot>
+            <div class="native-wrapper" ref={(el) => (this.nativeWrapperEl = el)} part="container">
+              {this.renderSelectText()}
+              {this.renderListbox()}
+            </div>
+            <slot name="end"></slot>
             {!hasFloatingOrStackedLabel && this.renderSelectIcon()}
-            {this.renderListbox()}
           </div>
           {/**
            * The icon in a floating/stacked select
            * must be centered with the entire select,
-           * not just the native control. As a result,
-           * we need to render the icon outside of
-           * the native wrapper.
+           * while the start/end slots and native control
+           * are vertically offset in the default or
+           * solid fills. As a result, we render the
+           * icon outside the inner wrapper, which holds
+           * those components.
            */}
           {hasFloatingOrStackedLabel && this.renderSelectIcon()}
           {shouldRenderHighlight && <div class="select-highlight"></div>}

core/src/components/select/test/a11y/index.html

@@ -41,6 +41,16 @@ <h1>Select - a11y</h1>
         <ion-select-option value="oranges">Oranges</ion-select-option>
       </ion-select>
 
+      <ion-select label="My Label" label-placement="floating">
+        <ion-icon slot="start" name="pizza" aria-hidden="true"></ion-icon>
+        <ion-select-option value="apples">Apples</ion-select-option>
+        <ion-select-option value="bananas">Bananas</ion-select-option>
+        <ion-select-option value="oranges">Oranges</ion-select-option>
+        <ion-button slot="end" aria-label="button">
+          <ion-icon slot="icon-only" name="lock-closed" aria-hidden="true"></ion-icon>
+        </ion-button>
+      </ion-select>
+
       <ion-item>
         <ion-select label="My Label" value="apples">
           <ion-select-option value="apples">Apples</ion-select-option>

core/src/components/select/test/label/select.e2e.ts

@@ -171,7 +171,7 @@ configs().forEach(({ title, screenshot, config }) => {
       test('label should appear on top of the select when the select is expanded', async ({ page }) => {
         await page.setContent(
           `
-           <ion-select class="select-expanded" label="Label" label-placement="floating" placeholder="Select a Fruit">
+           <ion-select class="select-expanded label-floating" label="Label" label-placement="floating" placeholder="Select a Fruit">
              <ion-select-option value="apples">Apples</ion-select-option>
            </ion-select>
          `,