fix: diff display edge cases for empty patches and hunks

[bonerush]

• FileEditToolDiff: show "No changes to display" when patch is empty

• FileWriteToolDiff: guard against empty hunks array

• getPatchForDisplay: skip replace when old_string is empty

Summary by CodeRabbit

• Bug Fixes
  • Improved handling of empty diffs by displaying a clear "No changes to display" message instead of an empty list.
  • Enhanced diff display logic to gracefully render original code when no hunks are available.
  • Fixed edit application for insert-only operations to properly handle empty source content.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: b7ba6b97-d1be-4458-8f19-cd1ebee3b746

📥 Commits

Reviewing files that changed from the base of the PR and between c982104 and 56828e1.

📒 Files selected for processing (3)

• src/components/FileEditToolDiff.tsx
• src/components/permissions/FileWritePermissionRequest/FileWriteToolDiff.tsx
• src/utils/diff.ts

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📝 Walkthrough

Walkthrough

This PR adds edge-case handling for empty and insert-only diffs. The utility function now correctly handles edits where old content is empty, and the diff rendering components gracefully display placeholders or fall back to syntax highlighting when no hunks exist.

Changes

Empty diff handling and insert-only edits

Layer / File(s)	Summary
Patch generation for insert-only edits src/utils/diff.ts	When an edit's old string is empty after escaping, getPatchForDisplay now returns the escaped new string directly instead of attempting a replace operation.
Component rendering for empty diffs src/components/FileEditToolDiff.tsx, src/components/permissions/FileWritePermissionRequest/FileWriteToolDiff.tsx	DiffBody and FileWriteToolDiff now check for empty patch or hunk lists, rendering "No changes to display" placeholders or falling back to HighlightedCode instead of rendering empty diff structures.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 A diff with nothing to compare,
No hunks, no patches in the air—
Now shows a message calm and bright:
"No changes," whispered soft and light.
Insert-only edits find their way,
Through empty strings to save the day! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'fix: diff display edge cases for empty patches and hunks' accurately and specifically describes the main changes: handling empty patches in FileEditToolDiff, empty hunks in FileWriteToolDiff, and empty old_string in getPatchForDisplay.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

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