feat(select): add helperText and errorText properties (#30143)

Issue number: resolves #29205

---------

## What is the current behavior?
Select does not support helper and error text.

## What is the new behavior?
- Adds support for `helperText` and `errorText`
- Adds parts for `helper-text`, `error-text` and `supporting-text`
- Adds an e2e test for helper and error text with functional tests and
screenshot tests

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

## Other information


[Preview](https://ionic-framework-git-rou-11551-ionic1.vercel.app/src/components/select/test/bottom-content)

---------

Co-authored-by: swimer11 <[email protected]>

---------

Co-authored-by: Brandy Smith <[email protected]>

Author: brandyscarney

core/api.txt

@@ -1626,8 +1626,10 @@ ion-select,prop,cancelText,string,'Cancel',false,false
 ion-select,prop,color,"danger" | "dark" | "light" | "medium" | "primary" | "secondary" | "success" | "tertiary" | "warning" | string & Record<never, never> | undefined,undefined,false,true
 ion-select,prop,compareWith,((currentValue: any, compareValue: any) => boolean) | null | string | undefined,undefined,false,false
 ion-select,prop,disabled,boolean,false,false,false
+ion-select,prop,errorText,string | undefined,undefined,false,false
 ion-select,prop,expandedIcon,string | undefined,undefined,false,false
 ion-select,prop,fill,"outline" | "solid" | undefined,undefined,false,false
+ion-select,prop,helperText,string | undefined,undefined,false,false
 ion-select,prop,interface,"action-sheet" | "alert" | "modal" | "popover",'alert',false,false
 ion-select,prop,interfaceOptions,any,{},false,false
 ion-select,prop,justify,"end" | "space-between" | "start" | undefined,undefined,false,false
@@ -1682,9 +1684,12 @@ ion-select,css-prop,--placeholder-opacity,md
 ion-select,css-prop,--ripple-color,ios
 ion-select,css-prop,--ripple-color,md
 ion-select,part,container
+ion-select,part,error-text
+ion-select,part,helper-text
 ion-select,part,icon
 ion-select,part,label
 ion-select,part,placeholder
+ion-select,part,supporting-text
 ion-select,part,text
 
 ion-select-modal,scoped

core/src/components.d.ts

@@ -2771,6 +2771,10 @@ 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.
          */
@@ -2779,6 +2783,10 @@ 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`.
          */
@@ -7616,6 +7624,10 @@ 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.
          */
@@ -7624,6 +7636,10 @@ 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

@@ -275,6 +275,71 @@ 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`.
    */
@@ -1014,6 +1029,8 @@ export class Select implements ComponentInterface {
         aria-label={this.ariaLabel}
         aria-haspopup="dialog"
         aria-expanded={`${isExpanded}`}
+        aria-describedby={this.getHintTextID()}
+        aria-invalid={this.getHintTextID() === this.errorTextId}
         aria-required={`${required}`}
         onFocus={this.onFocus}
         onBlur={this.onBlur}
@@ -1022,6 +1039,55 @@ export class Select implements ComponentInterface {
     );
   }
 
+  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;
@@ -1101,6 +1167,7 @@ export class Select implements ComponentInterface {
           {hasFloatingOrStackedLabel && this.renderSelectIcon()}
           {shouldRenderHighlight && <div class="select-highlight"></div>}
         </label>
+        {this.renderBottomContent()}
       </Host>
     );
   }