refactor(react-router): extract helper functions from computeParentPath

Author: ShaneK

packages/react-router/src/ReactRouter/utils/computeParentPath.ts

@@ -125,6 +125,103 @@ interface ComputeParentPathOptions {
   hasWildcardRoute: boolean;
 }
 
+/**
+ * Checks if any route matches as a specific (non-wildcard, non-index) route.
+ */
+const findSpecificMatch = (routeChildren: React.ReactElement[], remainingPath: string): boolean => {
+  return routeChildren.some(
+    (route) => isSpecificRouteMatch(route, remainingPath) || matchesEmbeddedWildcardRoute(route, remainingPath)
+  );
+};
+
+/**
+ * Checks if any specific route could plausibly match the remaining path.
+ * Used to determine if we should fall back to a wildcard match.
+ */
+const couldSpecificRouteMatch = (routeChildren: React.ReactElement[], remainingPath: string): boolean => {
+  const remainingFirstSegment = remainingPath.split('/')[0];
+  return routeChildren.some((route) => {
+    const routePath = route.props.path as string | undefined;
+    if (!routePath || routePath === '*' || routePath === '/*') return false;
+    if (route.props.index) return false;
+
+    const routeFirstSegment = routePath.split('/')[0].replace(/[*:]/g, '');
+    if (!routeFirstSegment) return false;
+
+    // Check for prefix overlap (either direction)
+    return (
+      routeFirstSegment.startsWith(remainingFirstSegment.slice(0, 3)) ||
+      remainingFirstSegment.startsWith(routeFirstSegment.slice(0, 3))
+    );
+  });
+};
+
+/**
+ * Checks for index route match when remaining path is empty.
+ * Index routes only match at the outlet's mount path level.
+ */
+const checkIndexMatch = (
+  parentPath: string,
+  remainingPath: string,
+  hasIndexRoute: boolean,
+  outletMountPath: string | undefined
+): string | undefined => {
+  if ((remainingPath === '' || remainingPath === '/') && hasIndexRoute) {
+    if (outletMountPath) {
+      // Index should only match at the existing mount path
+      return parentPath === outletMountPath ? parentPath : undefined;
+    }
+    // No mount path yet - this would establish it
+    return parentPath;
+  }
+  return undefined;
+};
+
+/**
+ * Determines the best parent path from the available matches.
+ * Priority: specific > wildcard > index
+ */
+const selectBestMatch = (
+  specificMatch: string | undefined,
+  wildcardMatch: string | undefined,
+  indexMatch: string | undefined
+): string | undefined => {
+  return specificMatch ?? wildcardMatch ?? indexMatch;
+};
+
+/**
+ * Handles outlets with only absolute routes by computing their common prefix.
+ */
+const computeAbsoluteRoutesParentPath = (
+  routeChildren: React.ReactElement[],
+  currentPathname: string,
+  outletMountPath: string | undefined
+): ParentPathResult | undefined => {
+  const absolutePathRoutes = routeChildren.filter((route) => {
+    const path = route.props.path;
+    return path && path.startsWith('/');
+  });
+
+  if (absolutePathRoutes.length === 0) {
+    return undefined;
+  }
+
+  const absolutePaths = absolutePathRoutes.map((r) => r.props.path as string);
+  const commonPrefix = computeCommonPrefix(absolutePaths);
+
+  if (!commonPrefix || commonPrefix === '/') {
+    return undefined;
+  }
+
+  const newOutletMountPath = outletMountPath || commonPrefix;
+
+  if (!currentPathname.startsWith(commonPrefix)) {
+    return { parentPath: undefined, outletMountPath: newOutletMountPath };
+  }
+
+  return { parentPath: commonPrefix, outletMountPath: newOutletMountPath };
+};
+
 /**
  * Computes the parent path for a nested outlet based on the current pathname
  * and the outlet's route configuration.
@@ -139,9 +236,7 @@ export const computeParentPath = (options: ComputeParentPathOptions): ParentPath
   const { currentPathname, outletMountPath, routeChildren, hasRelativeRoutes, hasIndexRoute, hasWildcardRoute } =
     options;
 
-  // If this outlet previously established a mount path and the current
-  // pathname is outside of that scope, do not attempt to re-compute a new
-  // parent path.
+  // If pathname is outside the established mount path scope, skip computation
   if (outletMountPath && !currentPathname.startsWith(outletMountPath)) {
     return { parentPath: undefined, outletMountPath };
   }
@@ -150,105 +245,49 @@ export const computeParentPath = (options: ComputeParentPathOptions): ParentPath
     const segments = currentPathname.split('/').filter(Boolean);
 
     if (segments.length >= 1) {
-      // Find matches at each level, keeping track of the FIRST (shortest) match
-      let firstSpecificMatch: string | undefined = undefined;
-      let firstWildcardMatch: string | undefined = undefined;
-      let indexMatchAtMount: string | undefined = undefined;
+      let firstSpecificMatch: string | undefined;
+      let firstWildcardMatch: string | undefined;
+      let indexMatchAtMount: string | undefined;
 
-      // Start at i = 1 (normal case: strip at least one segment for parent path)
+      // Iterate through path segments to find the shortest matching parent path
       for (let i = 1; i <= segments.length; i++) {
         const parentPath = '/' + segments.slice(0, i).join('/');
         const remainingPath = segments.slice(i).join('/');
 
-        // Check for specific route matches (non-wildcard-only, non-index)
-        // Also check routes with embedded wildcards (e.g., "tab1/*")
-        const hasSpecificMatch = routeChildren.some(
-          (route) => isSpecificRouteMatch(route, remainingPath) || matchesEmbeddedWildcardRoute(route, remainingPath)
-        );
-        if (hasSpecificMatch && !firstSpecificMatch) {
+        // Check for specific route match (highest priority)
+        if (!firstSpecificMatch && findSpecificMatch(routeChildren, remainingPath)) {
           firstSpecificMatch = parentPath;
-          // Found a specific match - this is our answer for non-index routes
           break;
         }
 
-        // Check if wildcard would match this remaining path
-        // Only if remaining is non-empty (wildcard needs something to match)
-        if (remainingPath !== '' && remainingPath !== '/' && hasWildcardRoute && !firstWildcardMatch) {
-          // Check if any specific route could plausibly match this remaining path
-          const remainingFirstSegment = remainingPath.split('/')[0];
-          const couldAnyRouteMatch = routeChildren.some((route) => {
-            const routePath = route.props.path as string | undefined;
-            if (!routePath || routePath === '*' || routePath === '/*') return false;
-            if (route.props.index) return false;
-
-            const routeFirstSegment = routePath.split('/')[0].replace(/[*:]/g, '');
-            if (!routeFirstSegment) return false;
-
-            // Check for prefix overlap (either direction)
-            return (
-              routeFirstSegment.startsWith(remainingFirstSegment.slice(0, 3)) ||
-              remainingFirstSegment.startsWith(routeFirstSegment.slice(0, 3))
-            );
-          });
-
-          // Only save wildcard match if no specific route could match
-          if (!couldAnyRouteMatch) {
+        // Check for wildcard match (only if remaining path is non-empty)
+        const hasNonEmptyRemaining = remainingPath !== '' && remainingPath !== '/';
+        if (!firstWildcardMatch && hasNonEmptyRemaining && hasWildcardRoute) {
+          if (!couldSpecificRouteMatch(routeChildren, remainingPath)) {
             firstWildcardMatch = parentPath;
-            // Continue looking - might find a specific match at a longer path
           }
         }
 
-        // Check for index route match when remaining path is empty
-        // BUT only at the outlet's mount path level
-        if ((remainingPath === '' || remainingPath === '/') && hasIndexRoute) {
-          // Index route matches when current path exactly matches the mount path
-          // If we already have an outletMountPath, index should only match there
-          if (outletMountPath) {
-            if (parentPath === outletMountPath) {
-              indexMatchAtMount = parentPath;
-            }
-          } else {
-            // No mount path set yet - index would establish this as mount path
-            // But only if we haven't found a better match
-            indexMatchAtMount = parentPath;
-          }
+        // Check for index route match
+        const indexMatch = checkIndexMatch(parentPath, remainingPath, hasIndexRoute, outletMountPath);
+        if (indexMatch) {
+          indexMatchAtMount = indexMatch;
         }
       }
 
-      // Fallback: check at root level (i = 0) for embedded wildcard routes.
-      // This handles outlets inside root-level splat routes where routes like
-      // "tab1/*" need to match the full pathname.
+      // Fallback: check root level for embedded wildcard routes (e.g., "tab1/*")
       if (!firstSpecificMatch) {
         const fullRemainingPath = segments.join('/');
-        const hasRootLevelMatch = routeChildren.some((route) => matchesEmbeddedWildcardRoute(route, fullRemainingPath));
-        if (hasRootLevelMatch) {
+        if (routeChildren.some((route) => matchesEmbeddedWildcardRoute(route, fullRemainingPath))) {
           firstSpecificMatch = '/';
         }
       }
 
-      // Determine the best parent path:
-      // 1. Specific match (routes like tabs/*, favorites) - highest priority
-      // 2. Wildcard match (route path="*") - catches unmatched segments
-      // 3. Index match - only valid at the outlet's mount point, not deeper
-      let bestPath: string | undefined = undefined;
-
-      if (firstSpecificMatch) {
-        bestPath = firstSpecificMatch;
-      } else if (firstWildcardMatch) {
-        bestPath = firstWildcardMatch;
-      } else if (indexMatchAtMount) {
-        // Only use index match if no specific or wildcard matched
-        // This handles the case where pathname exactly matches the mount path
-        bestPath = indexMatchAtMount;
-      }
+      const bestPath = selectBestMatch(firstSpecificMatch, firstWildcardMatch, indexMatchAtMount);
 
-      // Store the mount path when we first successfully match a route
-      let newOutletMountPath = outletMountPath;
-      if (!outletMountPath && bestPath) {
-        newOutletMountPath = bestPath;
-      }
+      // Establish mount path on first successful match
+      const newOutletMountPath = outletMountPath || bestPath;
 
-      // If we have a mount path, verify the current pathname is within scope
       if (newOutletMountPath && !currentPathname.startsWith(newOutletMountPath)) {
         return { parentPath: undefined, outletMountPath: newOutletMountPath };
       }
@@ -257,29 +296,11 @@ export const computeParentPath = (options: ComputeParentPathOptions): ParentPath
     }
   }
 
-  // Handle outlets with ONLY absolute routes (no relative routes or index routes)
-  // Compute the common prefix of all absolute routes to determine the outlet's scope
+  // Handle outlets with only absolute routes
   if (!hasRelativeRoutes && !hasIndexRoute) {
-    const absolutePathRoutes = routeChildren.filter((route) => {
-      const path = route.props.path;
-      return path && path.startsWith('/');
-    });
-
-    if (absolutePathRoutes.length > 0) {
-      const absolutePaths = absolutePathRoutes.map((r) => r.props.path as string);
-      const commonPrefix = computeCommonPrefix(absolutePaths);
-
-      if (commonPrefix && commonPrefix !== '/') {
-        // Set the mount path based on common prefix of absolute routes
-        const newOutletMountPath = outletMountPath || commonPrefix;
-
-        // Check if current pathname is within scope
-        if (!currentPathname.startsWith(commonPrefix)) {
-          return { parentPath: undefined, outletMountPath: newOutletMountPath };
-        }
-
-        return { parentPath: commonPrefix, outletMountPath: newOutletMountPath };
-      }
+    const result = computeAbsoluteRoutesParentPath(routeChildren, currentPathname, outletMountPath);
+    if (result) {
+      return result;
     }
   }