feat(select): add helperText and errorText properties

core/src/components.d.ts

@@ -2755,6 +2755,10 @@ export namespace Components {
           * If `true`, the user cannot interact with the select.
          */
         "disabled": boolean;
+        /**
+          * Text that is placed under the select and displayed when an error is detected.
+         */
+        "errorText"?: string;
         /**
           * The toggle icon to show when the select is open. If defined, the icon rotation behavior in `md` mode will be disabled. If undefined, `toggleIcon` will be used for when the select is both open and closed.
          */
@@ -2763,6 +2767,10 @@ export namespace Components {
           * The fill for the item. If `"solid"` the item will have a background. If `"outline"` the item will be transparent with a border. Only available in `md` mode.
          */
         "fill"?: 'outline' | 'solid';
+        /**
+          * Text that is placed under the select and displayed when no error is detected.
+         */
+        "helperText"?: string;
         /**
           * The interface the select should use: `action-sheet`, `popover`, `alert`, or `modal`.
          */
@@ -7568,6 +7576,10 @@ declare namespace LocalJSX {
           * If `true`, the user cannot interact with the select.
          */
         "disabled"?: boolean;
+        /**
+          * Text that is placed under the select and displayed when an error is detected.
+         */
+        "errorText"?: string;
         /**
           * The toggle icon to show when the select is open. If defined, the icon rotation behavior in `md` mode will be disabled. If undefined, `toggleIcon` will be used for when the select is both open and closed.
          */
@@ -7576,6 +7588,10 @@ declare namespace LocalJSX {
           * The fill for the item. If `"solid"` the item will have a background. If `"outline"` the item will be transparent with a border. Only available in `md` mode.
          */
         "fill"?: 'outline' | 'solid';
+        /**
+          * Text that is placed under the select and displayed when no error is detected.
+         */
+        "helperText"?: string;
         /**
           * The interface the select should use: `action-sheet`, `popover`, `alert`, or `modal`.
          */

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

@@ -5,6 +5,8 @@
 // --------------------------------------------------
 
 :host {
+  --border-width: #{$hairlines-width};
+  --border-color: #{$item-ios-border-color};
   --highlight-height: 0px;
 }
 

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

@@ -32,6 +32,10 @@
   --border-color: var(--highlight-color);
 }
 
+/**
+ * The bottom content should never have
+ * a border with the solid style.
+ */
 :host(.select-fill-solid) .select-bottom {
   border-top: none;
 }

core/src/components/select/select.scss

@@ -25,6 +25,8 @@
    * @prop --border-width: Width of the select border
    *
    * @prop --ripple-color: The color of the ripple effect on MD mode.
+   *
+   * TODO: add supporting text css vars
    */
   --padding-top: 0px;
   --padding-end: 0px;
@@ -275,6 +277,71 @@ button {
   --highlight-color: var(--highlight-color-valid);
 }
 
+// Select Bottom Content
+// ----------------------------------------------------------------
+
+.select-bottom {
+  /**
+   * The bottom content should take on the start and end
+   * padding so it is always aligned with either the label
+   * or the start of the text select.
+   */
+  @include padding(5px, var(--padding-end), 0, var(--padding-start));
+
+  display: flex;
+
+  justify-content: space-between;
+
+  border-top: var(--border-width) var(--border-style) var(--border-color);
+
+  font-size: dynamic-font(12px);
+
+  white-space: normal;
+}
+
+/**
+ * If the select has a validity state, the
+ * border and label should reflect that as a color.
+ * The invalid state should show if the select is
+ * invalid and has already been touched.
+ * The valid state should show if the select
+ * is valid, has already been touched, and
+ * is currently focused. Do not show the valid
+ * highlight when the select is blurred.
+ */
+:host(.has-focus.ion-valid),
+:host(.ion-touched.ion-invalid) {
+  --border-color: var(--highlight-color);
+}
+
+// Select Hint Text
+// ----------------------------------------------------------------
+
+/**
+ * Error text should only be shown when .ion-invalid is
+ * present on the select. Otherwise the helper text should
+ * be shown.
+ */
+ .select-bottom .error-text {
+  display: none;
+
+  color: var(--highlight-color-invalid);
+}
+
+.select-bottom .helper-text {
+  display: block;
+
+  color: $text-color-step-300;
+}
+
+:host(.ion-touched.ion-invalid) .select-bottom .error-text {
+  display: block;
+}
+
+:host(.ion-touched.ion-invalid) .select-bottom .helper-text {
+  display: none;
+}
+
 // Select Label
 // ----------------------------------------------------------------
 

core/src/components/select/select.tsx

@@ -41,6 +41,9 @@ import type { SelectChangeEventDetail, SelectInterface, SelectCompareFn } from '
  * @part icon - The select icon container.
  * @part container - The container for the selected text or placeholder.
  * @part label - The label text describing the select.
+ * @part supporting-text - Supporting text displayed beneath the select.
+ * @part helper-text - Supporting text displayed beneath the select when the select is valid.
+ * @part error-text - Supporting text displayed beneath the select when the select is invalid and touched.
  */
 @Component({
   tag: 'ion-select',
@@ -52,6 +55,8 @@ import type { SelectChangeEventDetail, SelectInterface, SelectCompareFn } from '
 })
 export class Select implements ComponentInterface {
   private inputId = `ion-sel-${selectIds++}`;
+  private helperTextId = `${this.inputId}-helper-text`;
+  private errorTextId = `${this.inputId}-error-text`;
   private overlay?: OverlaySelect;
   private focusEl?: HTMLButtonElement;
   private mutationO?: MutationObserver;
@@ -98,6 +103,16 @@ export class Select implements ComponentInterface {
    */
   @Prop() fill?: 'outline' | 'solid';
 
+  /**
+   * Text that is placed under the select and displayed when an error is detected.
+   */
+  @Prop() errorText?: string;
+
+  /**
+   * Text that is placed under the select and displayed when no error is detected.
+   */
+  @Prop() helperText?: string;
+
   /**
    * The interface the select should use: `action-sheet`, `popover`, `alert`, or `modal`.
    */
@@ -983,13 +998,64 @@ export class Select implements ComponentInterface {
         aria-label={this.ariaLabel}
         aria-haspopup="dialog"
         aria-expanded={`${isExpanded}`}
+        aria-describedby={this.getHintTextID()}
+        aria-invalid={this.getHintTextID() === this.errorTextId}
         onFocus={this.onFocus}
         onBlur={this.onBlur}
         ref={(focusEl) => (this.focusEl = focusEl)}
       ></button>
     );
   }
 
+  private getHintTextID(): string | undefined {
+    const { el, helperText, errorText, helperTextId, errorTextId } = this;
+
+    if (el.classList.contains('ion-touched') && el.classList.contains('ion-invalid') && errorText) {
+      return errorTextId;
+    }
+
+    if (helperText) {
+      return helperTextId;
+    }
+
+    return undefined;
+  }
+
+  /**
+   * Renders the helper text or error text values
+   */
+  private renderHintText() {
+    const { helperText, errorText, helperTextId, errorTextId } = this;
+
+    return [
+      <div id={helperTextId} class="helper-text" part="supporting-text helper-text">
+        {helperText}
+      </div>,
+      <div id={errorTextId} class="error-text" part="supporting-text error-text">
+        {errorText}
+      </div>,
+    ];
+  }
+
+  /**
+   * Responsible for rendering helper text, and error text. This element
+   * should only be rendered if hint text is set.
+   */
+  private renderBottomContent() {
+    const { helperText, errorText } = this;
+
+    /**
+     * undefined and empty string values should
+     * be treated as not having helper/error text.
+     */
+    const hasHintText = !!helperText || !!errorText;
+    if (!hasHintText) {
+      return;
+    }
+
+    return <div class="select-bottom">{this.renderHintText()}</div>;
+  }
+
   render() {
     const { disabled, el, isExpanded, expandedIcon, labelPlacement, justify, placeholder, fill, shape, name, value } =
       this;
@@ -1069,6 +1135,7 @@ export class Select implements ComponentInterface {
           {hasFloatingOrStackedLabel && this.renderSelectIcon()}
           {shouldRenderHighlight && <div class="select-highlight"></div>}
         </label>
+        {this.renderBottomContent()}
       </Host>
     );
   }

packages/angular/src/directives/proxies.ts

@@ -2060,15 +2060,15 @@ export declare interface IonSegmentView extends Components.IonSegmentView {
 
 
 @ProxyCmp({
-  inputs: ['cancelText', 'color', 'compareWith', 'disabled', 'expandedIcon', 'fill', 'interface', 'interfaceOptions', 'justify', 'label', 'labelPlacement', 'mode', 'multiple', 'name', 'okText', 'placeholder', 'selectedText', 'shape', 'toggleIcon', 'value'],
+  inputs: ['cancelText', 'color', 'compareWith', 'disabled', 'errorText', 'expandedIcon', 'fill', 'helperText', 'interface', 'interfaceOptions', 'justify', 'label', 'labelPlacement', 'mode', 'multiple', 'name', 'okText', 'placeholder', 'selectedText', 'shape', 'toggleIcon', 'value'],
   methods: ['open']
 })
 @Component({
   selector: 'ion-select',
   changeDetection: ChangeDetectionStrategy.OnPush,
   template: '<ng-content></ng-content>',
   // eslint-disable-next-line @angular-eslint/no-inputs-metadata-property
-  inputs: ['cancelText', 'color', 'compareWith', 'disabled', 'expandedIcon', 'fill', 'interface', 'interfaceOptions', 'justify', 'label', 'labelPlacement', 'mode', 'multiple', 'name', 'okText', 'placeholder', 'selectedText', 'shape', 'toggleIcon', 'value'],
+  inputs: ['cancelText', 'color', 'compareWith', 'disabled', 'errorText', 'expandedIcon', 'fill', 'helperText', 'interface', 'interfaceOptions', 'justify', 'label', 'labelPlacement', 'mode', 'multiple', 'name', 'okText', 'placeholder', 'selectedText', 'shape', 'toggleIcon', 'value'],
 })
 export class IonSelect {
   protected el: HTMLElement;

packages/vue/src/proxies.ts

@@ -771,6 +771,8 @@ export const IonSelect = /*@__PURE__*/ defineContainer<JSX.IonSelect, JSX.IonSel
   'compareWith',
   'disabled',
   'fill',
+  'errorText',
+  'helperText',
   'interface',
   'interfaceOptions',
   'justify',