Checkbox groups fail validation with multiple selections

Possible solution:

diff --git a/node_modules/@nysds/nys-checkbox/dist/nys-checkbox.js b/node_modules/@nysds/nys-checkbox/dist/nys-checkbox.js
index 526e76f..9ecb735 100644
--- a/node_modules/@nysds/nys-checkbox/dist/nys-checkbox.js
+++ b/node_modules/@nysds/nys-checkbox/dist/nys-checkbox.js
@@ -31,7 +31,17 @@ const y = class y extends _ {
     super.disconnectedCallback(), this.removeEventListener("nys-change", this._handleCheckboxChange), this.removeEventListener("nys-other-input", this._handleOtherInput), this.removeEventListener("invalid", this._handleInvalid), this.removeEventListener("nys-error", this._handleChildError), this.removeEventListener("nys-error-clear", this._handleChildErrorClear);
   }
   firstUpdated() {
-    this._setGroupExist(), this._updateCheckboxSize(), this._updateCheckboxTile(), this._updateCheckboxShowError(), this._getSlotDescriptionForAria();
+    this._setGroupExist(), this._updateCheckboxSize(), this._updateCheckboxTile(), this._updateCheckboxShowError(), this._getSlotDescriptionForAria(), this._initFormValue();
+  }
+  // Seed the submitted value from any pre-checked children on first render.
+  // Server frameworks (Drupal, Rails, PHP) re-render the form with previously
+  // checked boxes after a validation error on another field; without this the
+  // group only sets its value on user interaction, so an untouched-but-checked
+  // group would submit nothing on the next attempt.
+  _initFormValue() {
+    this._internals.setFormValue(
+      this._buildFormValue(Array.from(this.querySelectorAll("nys-checkbox")))
+    );
   }
   updated(e) {
     e.has("required") && this.required && this._setupCheckboxRequired(), e.has("size") && this._updateCheckboxSize(), e.has("tile") && this._updateCheckboxTile(), e.has("inverted") && this._updateCheckboxInvert(), e.has("showError") && this._updateCheckboxShowError(), e.has("form") && this._updateCheckboxForm();
@@ -159,7 +169,19 @@ const y = class y extends _ {
     const t = e, { name: r } = t.detail, s = Array.from(
       this.querySelectorAll("nys-checkbox")
     ), l = s.filter((c) => c.checked).map((c) => c.value);
-    this.name = r, this._internals.setFormValue(l.join(", ")), this._checkOtherInputs(s), this._hasOtherError || this._manageRequire();
+    this.name = r, this._internals.setFormValue(this._buildFormValue(s)), this._checkOtherInputs(s), this._hasOtherError || this._manageRequire();
+  }
+  // Submit each checked child as its own form entry so server frameworks
+  // (Drupal, Rails, PHP) that expect `name[key]=value` parse multiple
+  // selections correctly, instead of one comma-joined string. Falls back to
+  // the group name when children carry no name of their own.
+  _buildFormValue(all) {
+    const checked = all.filter((c) => c.checked);
+    if (!checked.length) return null;
+    const fd = new FormData();
+    for (const c of checked)
+      fd.append(c.getAttribute("name") || this.name, c.value);
+    return fd;
   }
   async _handleChildError(e) {
     e.stopPropagation();
@@ -171,10 +193,9 @@ const y = class y extends _ {
     this._otherErrorCheckbox && r !== this._otherErrorCheckbox || (this._hasOtherError = !1, this._otherErrorCheckbox = null, this._internals.setValidity({}), this.showError = !1, this.required && !this._hasAtLeastOneChecked() && this._manageRequire());
   }
   _handleOtherInput() {
-    const t = Array.from(
-      this.querySelectorAll("nys-checkbox")
-    ).filter((r) => r.checked).map((r) => r.value);
-    this._internals.setFormValue(t.join(", "));
+    this._internals.setFormValue(
+      this._buildFormValue(Array.from(this.querySelectorAll("nys-checkbox")))
+    );
   }
   async _checkOtherInputs(e) {
     for (const t of e)

Adding the value: element['#value'], to the component seems to help it pass validation with Drupal, but when the form returns back with edits, the javascript seems upset that a value has been set.

The NYSDS adds the "name" of the selected checkbox to the fieldset every time it is clicked. In the NYSDS example, it is expected that a checkbox group will all have the same "name". In Drupal, this is not the case. It does appear that the NYSDS uses the proper method. We will have to try using the fieldset name in the indivudal checkboxes. Hopefully that does not cause data saving issues.

The merge request includes code to "patch" the existing checkboxgroup component in lit.