refactor(metro): share the babel plugin's test for this package's own modules

The resolver computed the package root and the own-module test the babel
import plugin already computes, and its copy dropped the trailing path
separator, so a directory beside the package whose name merely begins
with dist or src counted as the package's own and its imports were left
unrewritten. Both now import one isFromThisModule.

Author: YevheniiKotyrlo

src/__tests__/metro/resolver.test.ts

@@ -144,6 +144,28 @@ describe("nativeResolver", () => {
     });
   });
 
+  test.each([
+    ["dist", join(packageRoot, "distribution", "index.js")],
+    ["src", join(packageRoot, "src-generated", "index.js")],
+  ])(
+    "rewrites an import from a directory whose name only begins with %s",
+    (_prefix, originModulePath) => {
+      const { resolver, calls } = recordingResolver();
+
+      nativeResolver(
+        resolver,
+        contextFor(originModulePath),
+        "react-native-gesture-handler",
+        "ios",
+      );
+
+      expect(calls).toEqual([
+        ["react-native-gesture-handler", "ios"],
+        ["react-native-css/components/react-native-gesture-handler", "ios"],
+      ]);
+    },
+  );
+
   test("leaves a resolution that is not a source file alone", () => {
     const calls: [string, string | null][] = [];
     const resolver: CustomResolver = (_context, moduleName, platform) => {

src/babel/import-plugin.ts

@@ -1,5 +1,3 @@
-import { basename, dirname, resolve, sep } from "path";
-
 import { type PluginObj } from "@babel/core";
 import type { Statement } from "@babel/types";
 
@@ -19,6 +17,7 @@ import {
   handleReactNativeWebInteropRequireDefault,
   handleReactNativeWebObjectPatternRequire,
 } from "./react-native-web";
+import { isFromThisModule } from "./this-module";
 
 export default function ({
   types: t,
@@ -27,19 +26,6 @@ export default function ({
 }): PluginObj<PluginState> {
   const processed = new WeakSet();
 
-  const packageRoot = resolve(
-    __dirname,
-    basename(dirname(__dirname)) === "src" ? "../.." : "../../..",
-  );
-  const thisModuleDist = resolve(packageRoot, "dist") + sep;
-  const thisModuleSrc = resolve(packageRoot, "src") + sep;
-
-  function isFromThisModule(filename: string): boolean {
-    return (
-      filename.startsWith(thisModuleDist) || filename.startsWith(thisModuleSrc)
-    );
-  }
-
   return {
     name: "Rewrite react-native to react-native-css",
     visitor: {

src/babel/this-module.ts

@@ -0,0 +1,16 @@
+import { basename, dirname, resolve, sep } from "node:path";
+
+// Anchored on the layout segment, since this runs from src/babel under the source condition and from dist/<format>/babel once built
+const packageRoot = resolve(
+  __dirname,
+  basename(dirname(__dirname)) === "src" ? "../.." : "../../..",
+);
+const thisModuleDist = resolve(packageRoot, "dist") + sep;
+const thisModuleSrc = resolve(packageRoot, "src") + sep;
+
+/** Whether `filename` is one of this package's own modules, which import the libraries it rewrites */
+export function isFromThisModule(filename: string): boolean {
+  return (
+    filename.startsWith(thisModuleDist) || filename.startsWith(thisModuleSrc)
+  );
+}

src/metro/resolver.ts

@@ -1,4 +1,4 @@
-import { basename, dirname, join, resolve, sep } from "node:path";
+import { basename, sep } from "node:path";
 
 import type {
   CustomResolutionContext,
@@ -7,20 +7,7 @@ import type {
 } from "metro-resolver";
 
 import { allowedModules } from "../babel/allowedModules";
-
-// Anchored on the layout segment, since this runs from src/metro under the source condition and from dist/<format>/metro once built
-const packageRoot = resolve(
-  __dirname,
-  basename(dirname(__dirname)) === "src" ? "../.." : "../../..",
-);
-const thisModuleDist = join(packageRoot, "dist");
-const thisModuleSrc = join(packageRoot, "src");
-
-function isFromThisModule(filename: string): boolean {
-  return (
-    filename.startsWith(thisModuleDist) || filename.startsWith(thisModuleSrc)
-  );
-}
+import { isFromThisModule } from "../babel/this-module";
 
 export function nativeResolver(
   resolver: CustomResolver,