fix(router-core): replaceEqualDeep max depth

[Sheraff]

Add max depth for recursive replaceEqualDeep to avoid insanely deep objects (500 nested levels) slowing/freezing the main thread. Beyond 500, we just return the new object.

The function is still callable w/ the same parameters as before. It should have now impact on users, except for those that have insanely deep objects.

Summary by CodeRabbit

• Bug Fixes
  • Improved application stability by adding safeguards to prevent performance degradation when processing deeply nested data structures.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

📝 Walkthrough

Walkthrough

Added internal depth-tracking parameter to replaceEqualDeep function with a recursion limit of 500 to prevent stack overflow when processing deeply nested object structures. The function now returns early for inputs exceeding the depth threshold.

Changes

Cohort / File(s)	Change Summary
Recursion Depth Limiting packages/router-core/src/utils.ts	Added _depth parameter (default 0) to replaceEqualDeep function with early return when depth exceeds 500; recursive calls increment depth counter

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• refactor(router-core): unify replaceEqualDeep implementation w/ query #5067 — Also modifies replaceEqualDeep in packages/router-core/src/utils.ts but refactors internal recursion logic without changing the public signature
• fix(router-core): replaceEqualDeep works w/ null prototype objects #5080 — Modifies the same replaceEqualDeep function with hardened null-prototype object checks alongside this depth-limiting change
• refactor(router-core): slightly faster replaceEqualDeep #5046 — Refactors key-enumeration and loop logic within replaceEqualDeep for performance optimization

Suggested labels

package: router-core

Suggested reviewers

• schiller-manuel

Poem

🐰 A rabbit digs deep through nested terrain,
But 500 levels cause quite the strain!
With depth-tracking walls, no more overflow—
Safe recursion now, steady and slow! 🌳

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly and concisely describes the main change: adding a maximum depth limit to the replaceEqualDeep function to fix performance issues with deeply nested objects.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing touches

• 📝 Generate docstrings

---

📜 Recent review details

Configuration used: defaults

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 1c440c3 and e19cdec.

📒 Files selected for processing (1)

• packages/router-core/src/utils.ts

🧰 Additional context used

📓 Path-based instructions (2)

**/*.{ts,tsx}

📄 CodeRabbit inference engine (AGENTS.md)

Use TypeScript strict mode with extensive type safety for all code

Files:

• packages/router-core/src/utils.ts

**/*.{js,ts,tsx}

📄 CodeRabbit inference engine (AGENTS.md)

Implement ESLint rules for router best practices using the ESLint plugin router

Files:

• packages/router-core/src/utils.ts

🧠 Learnings (2)

📓 Common learnings

Learnt from: Sheraff
Repo: TanStack/router PR: 5051
File: packages/router-core/src/utils.ts:310-315
Timestamp: 2025-08-30T09:12:13.852Z
Learning: In TanStack Router's deepEqual utility, using for..in instead of Object.keys() in getObjectKeys() when ignoreUndefined=true is acceptable because it's called only after isPlainObject() checks, which ensure objects have standard Object prototype chains with no inherited enumerable properties.

📚 Learning: 2025-08-30T09:12:13.852Z

Learnt from: Sheraff
Repo: TanStack/router PR: 5051
File: packages/router-core/src/utils.ts:310-315
Timestamp: 2025-08-30T09:12:13.852Z
Learning: In TanStack Router's deepEqual utility, using for..in instead of Object.keys() in getObjectKeys() when ignoreUndefined=true is acceptable because it's called only after isPlainObject() checks, which ensure objects have standard Object prototype chains with no inherited enumerable properties.

Applied to files:

• packages/router-core/src/utils.ts

🧬 Code graph analysis (1)

packages/router-core/src/utils.ts (1)

packages/router-core/src/index.ts (1)

• replaceEqualDeep (269-269)

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (2)

• GitHub Check: Preview
• GitHub Check: Test

🔇 Additional comments (2)

packages/router-core/src/utils.ts (2)

222-228: LGTM! Depth limit implementation is correct.

The approach is sound:

• Default parameter preserves backward compatibility for all existing callers
• The depth check after the reference equality check (line 223-225) is optimal—it avoids unnecessary depth tracking when objects are already identical
• Returning _next at depth 501+ gracefully degrades to no structural sharing rather than risking stack overflow

Consider updating the JSDoc (lines 217-221) to document this depth limit behavior for maintainability.

---

266-268: LGTM!

Depth is correctly incremented on each recursive descent, ensuring consistent depth tracking regardless of whether the nested structure is an array or object.

---

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---

☁️ Nx Cloud last updated this comment at 2026-01-13 17:01:27 UTC

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commit: e19cdec