fix(structure): implement removeParamNames so duplicate route detection works across different parameter names

[lisa-assistant]

Background

In packages/structure/src/model/RWRoute.ts, the hasPathCollision getter is responsible for generating the 'Duplicate Path' diagnostic. It uses a local helper function removeParamNames to normalize paths before comparing them:

function removeParamNames(p: string) {
  // TODO: implement
  // foo/{bar}/baz --> foo/{}/baz
  return p
}

The function is not implemented — it just returns p unchanged. This means that routes like:

• /users/{id} and /users/{userId}
• /posts/{id:Int} and /posts/{slug:String}

are not detected as path collisions, even though they would match the same URL patterns at runtime, causing ambiguous routing behavior.

What needs to be done

Implement removeParamNames to strip parameter names (and types) from path segments, so that two paths with the same structure but different parameter names are recognized as duplicates.

Fix:

function removeParamNames(p: string) {
  // foo/{bar}/baz --> foo/{}/baz
  // foo/{id:Int}/baz --> foo/{}/baz
  return p.replace(/\{[^}]+\}/g, '{}')
}

This regex replaces any {...} segment (including typed params like {id:Int}) with {}, normalizing the path for comparison.

File

packages/structure/src/model/RWRoute.ts, line 268–271

Impact

Without this fix, users can accidentally define two routes that match the same URL (e.g., <Route path="/post/{id}" ...> and <Route path="/post/{slug}" ...>) and the IDE/CLI diagnostic tool will not warn them. The router will silently use whichever route appears first.

[lisa-assistant]

Self-fix confidence: 9/10

The fix is a single line — a regex substitution that matches exactly what the TODO comment describes (foo/{bar}/baz --> foo/{}/baz). The pattern /\{[^}]+\}/g handles both plain params ({id}) and typed params ({id:Int}) correctly. I'd want to add a unit test covering the collision detection with mismatched param names to lock in the behavior, but the implementation itself has no ambiguity. The 1 point deduction is for verifying edge cases like optional params or params with special characters in their type annotations.

[lisa-assistant]

Implementation Plan

Goal: Implement removeParamNames so that hasPathCollision correctly detects duplicate route path structures regardless of parameter names.

File to change

packages/structure/src/model/RWRoute.ts — the removeParamNames helper (currently a stub at line ~268).

---

Current stub

function removeParamNames(p: string) {
  // TODO: implement
  // foo/{bar}/baz --> foo/{}/baz
  return p
}

Fix

function removeParamNames(p: string) {
  // Normalize {paramName} and {paramName:Type} to {} for collision comparison
  return p.replace(/\{[^}]+\}/g, '{}')
}

The regex {[^}]+} matches any {...} segment including typed params like {id:Int} or {slug:String}, replacing each with {} so paths with differently-named params compare equal.

---

Why this is the right regex

Cedar supports both untyped ({id}) and typed ({id:Int}) route params. For collision detection purposes, {id} and {slug} are interchangeable — a route /post/{id} and /post/{slug} are structurally identical and would conflict. The same is true for typed params: /post/{id:Int} and /post/{num:Int} collide.

A subtlety: /post/{id:Int} and /post/{slug:String} technically match different URLs (Int only matches integers), so they don't truly collide at runtime. However, the existing hasPathCollision is conservative — a false positive here is safer than a false negative, and this matches what the TODO comment describes.

---

Edge cases to consider

1. Splat routes: Cedar has a splat/wildcard syntax — check that routes like /{...path} aren't accidentally affected (the regex only matches {...} with no closing brace inside, which handles splats correctly since {...path} → {}).
2. No params: Plain paths like /about pass through unchanged — ✅ correct.
3. Multiple params: /post/{year}/{month}/{slug} → /post/{}/{}/{} — ✅ all collapsed.
4. Adjacent params: /prefix{id}suffix → /prefix{}suffix — handled by the regex since it's not tied to / boundaries.

---

Tests

removeParamNames is a private inner function, so it's exercised indirectly via hasPathCollision. The relevant diagnostics are in RWRoute.diagnostics (the hasPathCollision result surfaces as a diagnostic). Add or update tests in packages/structure/src/__tests__/ to cover:

• Two routes with differently-named params at the same position → should report collision
• Two routes with same structure but different param types (e.g. :Int vs :String) → reports collision
• Two structurally different routes → no collision