Block Fields: Fix crash resolving pattern overrides bindings

[cbravobernal]

What?

Fixes the Block Fields inspector panel crashing with TypeError: Cannot read properties of null (reading '__default') whenever a selected block carries a core/pattern-overrides binding.

Fixes #79090.

Why?

With the gutenberg-content-only-inspector-fields experiment enabled, selecting any fields-declaring block (paragraph, heading, image, button, list-item — 20 block types) that has a pattern overrides binding crashes the panel and trips BlockCrashBoundary. Both the raw __default binding and an expanded per-attribute binding reproduce it (the latter fails with reading 'content').

How?

The BlockFields attributes selector had two defects, fixed here:

• It iterated raw bindings, so the __default placeholder reached the source's getValues() as if it were a real attribute. It is now expanded through replacePatternOverridesDefaultBinding() using the server-provided bindable attributes, like every other bindings consumer; a __default that cannot be expanded is skipped.
• It called getValues() without clientId, so the pattern overrides source did getBlockAttributes( undefined ) → null → null[ attributeName ]. The clientId is now passed through, and the source itself is additionally null-safe (currentBlockAttributes?.[ attributeName ]) since it is the only source that resolves block attributes by clientId.

Test plan (TDD)

The first commit adds the tests; they fail on trunk:

• packages/editor/src/bindings/test/pattern-overrides.js — unit tests for getValues, including the null-block-attributes case (fails on trunk with the TypeError; the two behavior-pinning cases pass before and after).
• test/e2e/specs/editor/various/block-bindings/block-fields-pattern-overrides.spec.js — renders the Block Fields panel for a paragraph with a raw __default binding and with an expanded binding; the e2e fixtures fail any test that logs a console error, and both tests fail on an unfixed build with the two TypeError variants.

The second commit applies the fix; all three unit tests and both e2e tests pass, and the full custom-sources.spec.js bindings suite stays green.

Testing Instructions

1. npm run test:unit -- packages/editor/src/bindings/test/pattern-overrides.js
2. npm run test:e2e -- test/e2e/specs/editor/various/block-bindings/block-fields-pattern-overrides.spec.js
3. Manual: enable the Content only inspector fields experiment, add a paragraph with metadata.bindings.__default = { source: 'core/pattern-overrides' } and a metadata.name, select it, open the inspector — the panel renders instead of crashing.

Testing Instructions for Keyboard

No new keyboard interactions.

Use of AI Tools

Claude was used to investigate the crash, author the fix and the test coverage, and draft this description and the linked issue. The bug was reproduced and the fix verified bidirectionally against real builds (tests fail on an unfixed build with the reported TypeError variants and pass with the fix), and the full block bindings e2e suite was run locally before pushing. All changes were reviewed by the PR author.

🤖 Generated with Claude Code

[github-actions]

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Co-authored-by: cbravobernal <cbravobernal@git.wordpress.org>
Co-authored-by: ramonjd <ramonopoly@git.wordpress.org>

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[Copilot]

Pull request overview

Fixes a crash in the Block Fields inspector panel when resolving core/pattern-overrides bindings (notably the __default placeholder) by expanding default bindings before value resolution and ensuring the source receives clientId, with additional null-safety in the pattern overrides bindings source.

Changes:

• Expand __default pattern override bindings to bindable attributes (or skip if not expandable) before resolving values in BlockFields.
• Pass clientId through to bindings sources and make the core/pattern-overrides source null-safe when block attributes are unavailable.
• Add unit and E2E coverage for BlockFields rendering with both __default and expanded pattern override bindings.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
test/e2e/specs/editor/various/block-bindings/block-fields-pattern-overrides.spec.js	Adds E2E regression coverage to ensure the Block Fields panel renders without crashing for pattern overrides bindings.
packages/editor/src/bindings/test/pattern-overrides.js	Adds unit tests for core/pattern-overrides getValues() behavior, including the previously-crashing null-attributes case.
packages/editor/src/bindings/pattern-overrides.js	Makes getValues() resilient to missing block attributes via optional chaining.
packages/block-editor/src/hooks/block-fields/index.js	Expands __default bindings before resolving values and passes clientId into getValues() to prevent null-attribute crashes.

[ramonjd]

This tests well for me and matches the logic in the PR. Thanks for the fix.

Before	After

The existing Copilot comment appears valid as a test-hardening measure.

[cbravobernal]

This tests well for me and matches the logic in the PR. Thanks for the fix.

Before After

The existing Copilot comment appears valid as a test-hardening measure.

Yes. I will review it and merge it then.