fix: throw if the same pattern resolves to multiple screens

packages/core/src/__tests__/getStateFromPath.test.tsx

@@ -2673,6 +2673,47 @@ it('uses nearest parent wildcard match for unmatched paths', () => {
   );
 });
 
+it('throws if two screens map to the same pattern', () => {
+  const path = '/bar/42/baz/test';
+
+  expect(() =>
+    getStateFromPath(path, {
+      screens: {
+        Foo: {
+          screens: {
+            Bar: {
+              path: '/bar/:id/',
+              screens: {
+                Baz: 'baz',
+              },
+            },
+            Bax: '/bar/:id/baz',
+          },
+        },
+      },
+    })
+  ).toThrow(
+    "Found conflicting screens with the same pattern. The pattern 'bar/:id/baz' resolves to both 'Foo > Bax' and 'Foo > Bar > Baz'. Patterns must be unique and cannot resolve to more than one screen."
+  );
+
+  expect(() =>
+    getStateFromPath(path, {
+      screens: {
+        Foo: {
+          screens: {
+            Bar: {
+              path: '/bar/:id/',
+              screens: {
+                Baz: '',
+              },
+            },
+          },
+        },
+      },
+    })
+  ).not.toThrow();
+});
+
 it('throws if wildcard is specified with legacy config', () => {
   const path = '/bar/42/baz/test';
   const config = {

packages/core/src/getPathFromState.tsx

@@ -239,6 +239,10 @@ export default function getPathFromState(
 // Object.fromEntries is not available in older iOS versions
 const fromEntries = <K extends string, V>(entries: (readonly [K, V])[]) =>
   entries.reduce((acc, [k, v]) => {
+    if (acc.hasOwnProperty(k)) {
+      throw new Error(`A value for key '${k}' already exists in the object.`);
+    }
+
     acc[k] = v;
     return acc;
   }, {} as Record<K, V>);

packages/core/src/getStateFromPath.tsx

@@ -119,6 +119,12 @@ export default function getStateFromPath(
       // - the most exhaustive ones are always at the beginning
       // - patterns with wildcard are always at the end
 
+      // If 2 patterns are same, move the one with less route names up
+      // This is an error state, so it's only useful for consistent error messages
+      if (a.pattern === b.pattern) {
+        return b.routeNames.join('>').localeCompare(a.routeNames.join('>'));
+      }
+
       // If one of the patterns starts with the other, it's more exhaustive
       // So move it up
       if (a.pattern.startsWith(b.pattern)) {
@@ -155,6 +161,35 @@ export default function getStateFromPath(
       return bWildcardIndex - aWildcardIndex;
     });
 
+  // Check for duplicate patterns in the config
+  configs.reduce<Record<string, RouteConfig>>((acc, config) => {
+    if (acc[config.pattern]) {
+      const a = acc[config.pattern].routeNames;
+      const b = config.routeNames;
+
+      // It's not a problem if the path string omitted from a inner most screen
+      // For example, it's ok if a path resolves to `A > B > C` or `A > B`
+      const intersects =
+        a.length > b.length
+          ? b.every((it, i) => a[i] === it)
+          : a.every((it, i) => b[i] === it);
+
+      if (!intersects) {
+        throw new Error(
+          `Found conflicting screens with the same pattern. The pattern '${
+            config.pattern
+          }' resolves to both '${a.join(' > ')}' and '${b.join(
+            ' > '
+          )}'. Patterns must be unique and cannot resolve to more than one screen.`
+        );
+      }
+    }
+
+    return Object.assign(acc, {
+      [config.pattern]: config,
+    });
+  }, {});
+
   if (remaining === '/') {
     // We need to add special handling of empty path so navigation to empty path also works
     // When handling empty path, we should only look at the root level config