refactor(router-core): improve parseSegment performance, parse without regex

[Sheraff]

parseSegment is in the hot path both for

• building the initial tree when starting the app
• every call to interpolatePath, i.e. every Link, every navigation, every preload, ...

Without the comments, this PR adds 7 lines of code in total, but increases performance by 0% to 40% depending on the type of segment we're parsing.

Because there is no enforcement of parameter name syntax at runtime anymore, we introduce

• a console warning in the generator feat(router-generator): param name syntax check and warn #6472
• an ESLint rule for CI and IDE feat(eslint-plugin-router): route param name rule #6473

bench

@tanstack/router-core new (character-based) - Static Paths (fast path) - simple static
1.06x faster than old (regex-based)
@tanstack/router-core new (character-based) - Static Paths (fast path) - deep static
1.12x faster than old (regex-based)
@tanstack/router-core new (character-based) - Simple Param Paths ($param) - simple param
1.06x faster than old (regex-based)
@tanstack/router-core new (character-based) - Simple Param Paths ($param) - multiple params
1.12x faster than old (regex-based)
@tanstack/router-core new (character-based) - Curly Brace Params ({$param}) - curly param
1.26x faster than old (regex-based)
@tanstack/router-core new (character-based) - Curly Brace Params ({$param}) - curly with prefix
1.34x faster than old (regex-based)
@tanstack/router-core new (character-based) - Curly Brace Params ({$param}) - curly with prefix+suffix
1.37x faster than old (regex-based)
@tanstack/router-core new (character-based) - Optional Params ({-$param}) - optional param
1.23x faster than old (regex-based)
@tanstack/router-core new (character-based) - Optional Params ({-$param}) - optional with prefix
1.24x faster than old (regex-based)
@tanstack/router-core new (character-based) - Optional Params ({-$param}) - optional with prefix+suffix
1.27x faster than old (regex-based)
@tanstack/router-core new (character-based) - Wildcard Paths ($) - simple wildcard
1.05x faster than old (regex-based)
@tanstack/router-core new (character-based) - Wildcard Paths ($) - wildcard with prefix
1.19x faster than old (regex-based)
@tanstack/router-core new (character-based) - Mixed Complex Paths - mixed complex
1.49x faster than old (regex-based)
@tanstack/router-core new (character-based) - all paths combined - Aggregate: All Path Types
1.26x faster than old (regex-based) - all paths combined

Summary by CodeRabbit

• Refactor
  • Reworked internal route-segment parsing to use a simpler brace-based approach, improving maintainability and parsing reliability while preserving existing public behavior.
  • Reduced complexity and optimized control flow, which should yield modest performance and validation improvements for route handling.

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

[coderabbitai]

📝 Walkthrough

Walkthrough

Replaced regex-driven parsing with brace-position detection in the router segment parser. parseSegment now uses getOpenAndCloseBraces to identify optional parameters, wildcards, and regular parameters, performing position-based validation and computing segment boundaries.

Changes

Cohort / File(s)	Summary
Parameter Parsing Optimization packages/router-core/src/new-process-route-tree.ts	Removed three precompiled regexes and added getOpenAndCloseBraces. parseSegment now branches on brace positions to handle optional params ({-$name}), wildcards ({$}), and regular params ({$name}), with explicit validation and index calculations; falls back to pathname parsing if no braces match.

Sequence Diagram(s)

(omitted — changes are internal parsing logic within a single module and do not introduce multi-component flows)

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• refactor(router-core): interpolatePath skips optional segments w/ nullish param value #5934 — adjusts interpolatePath handling of nullish optional parameter values; strongly related to the optional-segment metadata changes here.

Suggested labels

performance

Suggested reviewers

• schiller-manuel
• nlynzaad

Poem

A rabbit nibbles at tangled regex,
Finds braces instead and skips the stress.
Hops through segments, neat and spry,
Parsing paths with a brighter eye. 🐇✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: refactoring parseSegment to improve performance by eliminating regex-based parsing and using character-based parsing instead.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

• 📝 Generate docstrings

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[nx-cloud]

View your CI Pipeline Execution ↗ for commit f1f2fbf

Command	Status	Duration	Result
nx affected --targets=test:eslint,test:unit,tes...	✅ Succeeded	12m 5s	View ↗
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---

☁️ Nx Cloud last updated this comment at 2026-01-23 16:43:04 UTC

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commit: f1f2fbf

[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@packages/router-core/src/new-process-route-tree.ts`:
- Around line 119-172: The parsed brace indices (openBrace, closeBrace,
paramStart, dollarPos, afterDollar, etc.) are offsets inside part but are being
written into output as if they were absolute positions in path; add the start
offset when writing any brace-based positions into output so the output indexes
are absolute. Specifically, in the branches that set output[...] for
SEGMENT_TYPE_OPTIONAL_PARAM, SEGMENT_TYPE_WILDCARD and SEGMENT_TYPE_PARAM,
replace uses of openBrace, closeBrace, paramStart, dollarPos, afterDollar and
closeBrace + 1 with openBrace + start, closeBrace + start, paramStart + start,
dollarPos + start, afterDollar + start and (closeBrace + 1) + start respectively
(leave path.length and end as-is). Ensure all three branches (optional param,
wildcard, regular param) consistently apply the start offset so prefix/suffix
extraction uses absolute indexes.