feat(checkbox)!: remove top level subcomponents

src/components/Checkbox/Checkbox.module.css

@@ -1,4 +1,76 @@
+@import '../../design-tokens/mixins.css';
+
 .checkbox {
   display: flex;
   gap: var(--eds-size-1);
 }
+
+.checkbox__input {
+  height: 18px;
+  width: 18px;
+
+  /* The parent Checkbox component is a flex container. Make sure the input doesn't shrink. */
+  flex-shrink: 0;
+
+  /* Remove the browser's checkbox styles, allowing us to provide our own. */
+  appearance: none;
+
+  /* Magic value to center the checkbox on its label. */
+  margin: 3px;
+
+  color: var(--eds-theme-color-checkbox-brand-background);
+  border: 2px solid currentColor;
+
+  /* Place the ::before content smack in the middle of the input. */
+  display: grid;
+  place-content: center;
+}
+
+.checkbox__input:checked::before {
+  background-color: currentColor;
+  content: '';
+
+  /* Clip this element in the shape of a checkbox. The element's background color will be visible
+  anywhere the svg path is solid. Whatever is behind the checkbox will show through wherever the
+  svg is transparent. See https://developer.mozilla.org/en-US/docs/Web/CSS/clip-path */
+  clip-path: path(
+    'M10.6 16.2L17.65 9.15L16.25 7.75L10.6 13.4L7.75 10.55L6.35 11.95L10.6 16.2ZM3 21V3H21V21H3Z'
+  );
+
+  /* Because the path does not have an explicit viewbox, this element's bounding box establishes
+  one. In other words, the height/width here need to match the expected viewbox for the path. */
+  height: 24px;
+  width: 24px;
+}
+
+.checkbox__input:indeterminate::before {
+  background-color: currentColor;
+  content: '';
+
+  clip-path: path('M7 13H17V11H7V13ZM3 21V3H21V21H3Z');
+
+  height: 24px;
+  width: 24px;
+}
+
+.checkbox__input:focus-visible {
+  @mixin focus;
+}
+
+@supports not selector(:focus-visible) {
+  .checkbox__input:focus {
+    @mixin focus;
+    outline-offset: 1px;
+  }
+}
+
+.checkbox__input:disabled {
+  color: var(--eds-theme-color-icon-disabled);
+  cursor: not-allowed;
+}
+
+.checkbox__label--md {
+  /* Center the first line of the medium label with the checkbox. */
+  position: relative;
+  top: 0.0625rem;
+}

src/components/Checkbox/Checkbox.stories.tsx

@@ -1,8 +1,6 @@
 import type { StoryObj, Meta } from '@storybook/react';
 import React from 'react';
 import { Checkbox } from './Checkbox';
-import CheckboxInput from '../CheckboxInput';
-import CheckboxLabel from '../CheckboxLabel';
 
 const defaultArgs = {
   disabled: false,
@@ -157,10 +155,10 @@ export const LongLabels = {
 export const WithCustomPositioning = {
   render: () => (
     <div className="flex items-center">
-      <CheckboxLabel className="mr-2" htmlFor="test">
+      <Checkbox.Label className="mr-2" htmlFor="test">
         Label on Left
-      </CheckboxLabel>
-      <CheckboxInput id="test" />
+      </Checkbox.Label>
+      <Checkbox.Input id="test" />
     </div>
   ),
 };

src/components/Checkbox/Checkbox.tsx

@@ -1,19 +1,41 @@
 import clsx from 'clsx';
 import React, { forwardRef } from 'react';
+import useForwardedRef from '../../util/useForwardedRef';
 import { useId } from '../../util/useId';
-import type {
-  EitherInclusive,
-  ForwardedRefComponent,
-} from '../../util/utility-types';
-import type { CheckboxInputProps } from '../CheckboxInput';
-import CheckboxInput from '../CheckboxInput';
-import type { CheckboxLabelProps } from '../CheckboxLabel';
-import CheckboxLabel from '../CheckboxLabel';
+import type { EitherInclusive } from '../../util/utility-types';
+import { InputLabel, type InputLabelProps } from '../InputLabel/InputLabel';
+
 import styles from './Checkbox.module.css';
 
+type CheckboxLabelProps = InputLabelProps;
+type CheckboxHTMLElementProps = Omit<
+  React.InputHTMLAttributes<HTMLInputElement>,
+  'checked' | 'id' | 'size'
+>;
+
+type CheckboxInputProps = CheckboxHTMLElementProps & {
+  /**
+   * Whether checkbox is checked.
+   */
+  checked?: boolean;
+  /**
+   * Additional classnames passed in for styling.
+   */
+  className?: string;
+  /**
+   * Checkbox ID. Used to connect the input with a label for accessibility purposes.
+   */
+  id: string;
+  /**
+   * Whether the checkbox is "indeterminate". Neither checked nor unchecked. The most common use
+   * case for this is when a checkbox has sub-checkboxes, to represent a "partially checked" state.
+   */
+  indeterminate?: boolean;
+};
+
 // id is required in CheckboxInputProps but optional in CheckboxProps, so we
 // first remove `id` from CheckboxInputProps before intersecting.
-export type CheckboxProps = Omit<CheckboxInputProps, 'id'> & {
+type CheckboxProps = Omit<CheckboxInputProps, 'id'> & {
   /**
    * HTML id attribute. If not passed, this component
    * will generate an id to use for accessibility.
@@ -38,37 +60,81 @@ export type CheckboxProps = Omit<CheckboxInputProps, 'id'> & {
     }
   >;
 
-type CheckboxType = ForwardedRefComponent<HTMLInputElement, CheckboxProps> & {
-  Input?: typeof CheckboxInput;
+/**
+ * Checkbox input element, exported for greater flexibility.
+ * You must provide an `id` prop and connect it to a visible label.
+ */
+const CheckboxInput = React.forwardRef<HTMLInputElement, CheckboxInputProps>(
+  ({ checked, className, disabled, indeterminate, ...other }, ref) => {
+    const forwardedRef = useForwardedRef(ref);
+
+    // Make this checkbox indeterminate. Can only be done with JS for some reason.
+    // See https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/checkbox#indeterminate_state_checkboxes.
+    React.useEffect(() => {
+      if (forwardedRef.current) {
+        forwardedRef.current.indeterminate = !!indeterminate;
+      }
+    }, [forwardedRef, indeterminate]);
+
+    return (
+      <input
+        checked={checked}
+        className={clsx(className, styles['checkbox__input'])}
+        disabled={disabled}
+        ref={forwardedRef}
+        type="checkbox"
+        {...other}
+      />
+    );
+  },
+);
+
+CheckboxInput.displayName = 'CheckboxInput';
+
+const CheckboxLabel = ({ className, size, ...other }: CheckboxLabelProps) => {
+  const componentClassName = clsx(
+    size === 'md' && styles['checkbox__label--md'],
+    className,
+  );
+
+  return <InputLabel className={componentClassName} size={size} {...other} />;
 };
 
 /**
  * `import {Checkbox} from "@chanzuckerberg/eds";`
  *
- * `import {CheckboxInput, CheckboxLabel} from '@chanzuckerberg/eds';`
- *
  * Checkbox control indicating if something is selected or unselected.
  *
  * NOTE: Requires either a visible label or `aria-label` prop.
  */
-export const Checkbox: CheckboxType = forwardRef((props, ref) => {
-  // All remaining props are passed to the `input` element
-  const { className, id, label, size = 'lg', disabled, ...other } = props;
+export const Checkbox = Object.assign(
+  forwardRef<HTMLInputElement, CheckboxProps>((props, ref) => {
+    // All remaining props are passed to the `input` element
+    const { className, id, label, size = 'lg', disabled, ...other } = props;
 
-  const generatedId = useId();
-  const checkboxId = id || generatedId;
+    const generatedId = useId();
+    const checkboxId = id || generatedId;
 
-  return (
-    <div className={clsx(className, styles.checkbox)}>
-      <CheckboxInput disabled={disabled} id={checkboxId} ref={ref} {...other} />
-      {label && (
-        <CheckboxLabel disabled={disabled} htmlFor={checkboxId} size={size}>
-          {label}
-        </CheckboxLabel>
-      )}
-    </div>
-  );
-});
+    return (
+      <div className={clsx(className, styles.checkbox)}>
+        <CheckboxInput
+          disabled={disabled}
+          id={checkboxId}
+          ref={ref}
+          {...other}
+        />
+        {label && (
+          <CheckboxLabel disabled={disabled} htmlFor={checkboxId} size={size}>
+            {label}
+          </CheckboxLabel>
+        )}
+      </div>
+    );
+  }),
+  {
+    Input: CheckboxInput,
+    Label: CheckboxLabel,
+  },
+);
 
 Checkbox.displayName = 'Checkbox';
-Checkbox.Input = CheckboxInput;

src/components/Checkbox/index.ts

@@ -1,2 +1 @@
 export { Checkbox as default } from './Checkbox';
-export type { CheckboxProps } from './Checkbox';