New grid rows share reference of previous row when sub-fields have object-type values

[morhi]

Bug description

When a Grid field has sub-fields with object-type default values (e.g., a Group fieldtype), adding a new row after editing an existing row causes the new row to inherit the edited row's values instead of clean defaults.

This happens because Grid.addRow() copies this.meta.defaults values by reference instead of deep-cloning them. When data_set() later mutates a nested field value in-place, it traverses through the shared reference back to this.meta.defaults, polluting defaults for all subsequent rows.

The Replicator and Bard fieldtypes already deep-clone their defaults:

• Replicator.vue:223: ...JSON.parse(JSON.stringify(data.defaults))
• BardFieldtype.vue:503: const deepCopy = JSON.parse(JSON.stringify(data.defaults))

The Grid is missing this deep clone.

How to reproduce

1. Create a blueprint with a Grid field containing a Group sub-field:

fields:
 -
 handle: my_grid
 field:
 type: grid
 display: 'My Grid'
 fields:
 -
 handle: my_group
 field:
 type: group
 display: 'My Group'
 fields:
 -
 handle: my_text
 field:
 type: text
 display: 'My Text'

2. Create an entry using this blueprint
3. Add a row to the Grid
4. Type something in the text field (e.g., "hello")
5. Add another row
6. The new row shows "hello" in the text field instead of being empty

Expected behavior

New rows should always start with clean default values, regardless of what was entered in previous rows.

Bug location

resources/js/components/fieldtypes/grid/Grid.vue, addRow() method (line ~175):

addRow() {
 const id = uniqid();

 const row = Object.fromEntries(
 this.fields.map((field) => [field.handle, this.meta.defaults[field.handle]]),
 );
 // ...
}

Object.fromEntries copies object-type values (from Group sub-fields) by reference. When data_set() later mutates a nested property in-place, the shared reference pollutes this.meta.defaults.

Suggested fix

Deep-clone the defaults when creating a new row:

addRow() {
 const id = uniqid();

 const row = JSON.parse(JSON.stringify(
 Object.fromEntries(
 this.fields.map((field) => [field.handle, this.meta.defaults[field.handle]]),
 ),
 ));

 row._id = id;

 this.updateRowMeta(id, this.meta.new);
 this.update([...this.value, row]);
}

The same pattern in removed() (used for comparison) should also be deep-cloned.

Logs

No response

Environment

Statamic: 6.x

Installation

Existing Laravel application

Additional details

No response