Fields named "text" on custom block objects breaks preview reactivity

[fvieira]

Disclaimer: I detected the issue in a Sanity Portable Text, that whenever I wrote into the field named "text", the preview would stop working after the first character, and I checked that it happened only to fields named "text". But then I threw Claude Code at Sanity's repo, then this one, until it supposedly found the issue, and the explanation below was written by it and not validated by me, since I don't know the code well enough to do it, just thought it might help (assuming it's right).

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Bug: field named text on custom block objects causes set_node updates to be silently dropped

Summary

When a custom object type used as a block in a Portable Text array has a field named text, changes to that field are silently dropped from editor.value after the initial insertion. This causes preview reactivity to break -- the preview shows the first character typed and then freezes. All other field names work correctly.

Root cause

isPartialSpanNode() in packages/editor/src/internal-utils/portable-text-node.ts identifies any object with a string text property as a partial span node, regardless of _type:

export function isPartialSpanNode(node: unknown): node is PartialSpanNode {
  return (
    typeof node === 'object' &&
    node !== null &&
    'text' in node &&
    typeof node.text === 'string'
  )
}

A block object like {_type: "quote", _key: "abc", text: "hello"} in editor.value matches this check, which causes isObjectNode() to return false (since it checks !isPartialSpanNode(node)).

In apply-operation-to-portable-text.ts, the set_node handler then:

1. Skips the isObjectNode branch (line ~370) -- the correct handler that processes value property changes
2. Enters the isPartialSpanNode branch (line ~471) -- the wrong handler
3. Skips the text key explicitly (if (key === 'text') { continue } at line ~475)

Result: updates to the text field on block objects are silently dropped from editor.value. Since render.element.tsx reads block object values from editor.value, the render callback receives stale data.

Reproduction

Minimal schema:

const quote = defineType({
  name: "quote",
  type: "object",
  fields: [
    defineField({
      name: "text",       // <-- this field name triggers the bug
      type: "string",
      title: "Quote Text",
    }),
    defineField({
      name: "source",     // <-- this field works fine
      type: "string",
      title: "Source",
    }),
  ],
  preview: {
    select: {
      title: "text",
      subtitle: "source",
    },
  },
})

const body = defineType({
  name: "body",
  type: "array",
  of: [
    defineArrayMember({ type: "block" }),
    defineArrayMember({ type: "quote" }),
  ],
})

Steps:

1. Add a quote block to the PTE
2. Open the block and type in the text field -- preview shows the first character only and freezes
3. Type in the source field -- preview updates correctly on every keystroke
4. Navigate away from the document and come back -- preview now shows the full text value

Renaming the field from text to anything else (e.g. quoteText) immediately fixes the issue.

What was ruled out (on the Sanity Studio side)

• Custom PTE input components
• Custom PTE options, decorators, annotations, styles
• Custom preview components
• The preview select key name (renaming the select key doesn't help -- the actual field name must change)
• Field type (type: "text" and type: "string" are both affected)
• Other document fields / other PTE members

Suggested fix

isPartialSpanNode should not match nodes that have a _type explicitly set to something other than span. A node with _type: "quote" and text: "hello" is clearly not a span:

export function isPartialSpanNode(node: unknown): node is PartialSpanNode {
  return (
    typeof node === 'object' &&
    node !== null &&
    'text' in node &&
    typeof node.text === 'string' &&
    !('_type' in node && node._type !== 'span')
  )
}

This ensures block objects with a text field are correctly identified as object nodes, and their text property updates are processed in the isObjectNode branch of applyOperationToPortableText.

Environment

• Sanity Studio v3 (latest)
• @portabletext/editor ^4.3.7
• Affects both type: "text" and type: "string" field types on the block object

[christianhg]

Thank you for finding, researching and reporting this! I've now fixed it in #2168 and cut a new release with the fix.