feat: add parseNodeModulePath and lookupNodeModuleSubpath utils

README.md

@@ -491,6 +491,40 @@ import { sanitizeFilePath } from "mlly";
 console.log(sanitizeFilePath("C:\\te#st\\[...slug].jsx"));
 ```
 
+### `parseNodeModulePath`
+
+Parses an absolute file path in `node_modules` to three segments:
+
+- `dir`: Path to main directory of package
+- `name`: Package name
+- `subpath`: The optional package subpath
+
+It returns an empty object (with partial keys) if parsing fails.
+
+```js
+import { parseNodeModulePath } from "mlly";
+
+// dir: "/src/a/node_modules/"
+// name: "lib"
+// subpath: "./dist/index.mjs"
+const { dir, name, subpath } = parseNodeModulePath(
+  "/src/a/node_modules/lib/dist/index.mjs"
+);
+```
+
+### `lookupNodeModuleSubpath`
+
+Parses an absolute file path in `node_modules` and tries to reverse lookup (or guess) the original package exports subpath for it.
+
+```js
+import { lookupNodeModuleSubpath } from "mlly";
+
+// subpath: "./utils"
+const subpath = lookupNodeModuleSubpath(
+  "/src/a/node_modules/lib/dist/utils.mjs"
+);
+```
+
 ## License
 
 [MIT](./LICENSE) - Made with ❤️

src/resolve.ts

@@ -1,8 +1,9 @@
 import { existsSync, realpathSync } from "node:fs";
 import { pathToFileURL } from "node:url";
 import { joinURL } from "ufo";
-import { isAbsolute } from "pathe";
+import { isAbsolute, join, normalize } from "pathe";
 import { moduleResolve } from "import-meta-resolve";
+import { PackageJson, readPackageJSON } from "pkg-types";
 import { fileURLToPath, normalizeid } from "./utils";
 import { pcall, BUILTIN_MODULES } from "./_utils";
 
@@ -148,3 +149,77 @@
     return resolve(id, { url, ...defaults });
   };
 }
+
+const NODE_MODULES_RE = /^(.+\/node_modules\/)([^/@]+|@[^/]+\/[^/]+)(\/?.*?)?$/;
+
+export function parseNodeModulePath(path: string) {
+  if (!path) {
+    return {};
+  }
+  path = normalize(fileURLToPath(path));
+  const match = NODE_MODULES_RE.exec(path);
+  if (!match) {
+    return {};
+  }
+  const [, dir, name, subpath] = match;
+  return {
+    dir,
+    name,
+    subpath: subpath ? `.${subpath}` : undefined,
+  };
+}
+
+/** Reverse engineer a subpath export if possible */
+export async function lookupNodeModuleSubpath(
+  path: string
+): Promise<string | undefined> {
+  path = normalize(fileURLToPath(path));
+  const { name, subpath } = parseNodeModulePath(path);
+
+  if (!name || !subpath) {
+    return subpath;
+  }
+
+  const { exports } = (await readPackageJSON(path).catch(() => {})) || {};
+  if (exports) {
+    const resolvedSubpath = _findSubpath(subpath, exports);
+    if (resolvedSubpath) {
+      return resolvedSubpath;
+    }
+  }
+
+  return subpath;
+}
+
+// --- Internal ---
+
+function _findSubpath(subpath: string, exports: PackageJson["exports"]) {
+  if (typeof exports === "string") {
+    exports = { ".": exports };
+  }
+
+  if (!subpath.startsWith(".")) {
+    subpath = subpath.startsWith("/") ? `.${subpath}` : `./${subpath}`;
+  }
+
+  if (subpath in exports) {
+    return subpath;
+  }
+
+  const flattenedExports = _flattenExports(exports);
+  const [foundPath] =
+    flattenedExports.find(([_, resolved]) => resolved === subpath) || [];
+
+  return foundPath;
+}
+
+function _flattenExports(
+  exports: Exclude<PackageJson["exports"], string>,
+  path?: string
+) {
+  return Object.entries(exports).flatMap(([key, value]) =>
+    typeof value === "string"
+      ? [[path ?? key, value]]
+      : _flattenExports(value, path ?? key)
+  );
+}

test/utils.test.ts

@@ -1,5 +1,13 @@
+import { fileURLToPath } from "node:url";
 import { describe, it, expect } from "vitest";
-import { isNodeBuiltin, sanitizeFilePath, getProtocol } from "../src";
+
+import {
+  isNodeBuiltin,
+  sanitizeFilePath,
+  getProtocol,
+  parseNodeModulePath,
+  lookupNodeModuleSubpath,
+} from "../src";
 
 describe("isNodeBuiltin", () => {
   const cases = {
@@ -58,3 +66,80 @@
     expect(getProtocol("file:///C:/src/a.ts")).to.equal("file");
   });
 });
+
+describe("parseNodeModulePath", () => {
+  const tests = [
+    {
+      input: "/foo/bar",
+      output: {},
+    },
+    {
+      input: "/src/a/node_modules/thing",
+      output: {
+        dir: "/src/a/node_modules/",
+        name: "thing",
+      },
+    },
+    {
+      input: "/src/a/node_modules/thing/dist/index.mjs",
+      output: {
+        dir: "/src/a/node_modules/",
+        name: "thing",
+        subpath: "./dist/index.mjs",
+      },
+    },
+    {
+      input: "C:\\src\\a\\node_modules\\thing\\dist\\index.mjs",
+      output: {
+        dir: "C:/src/a/node_modules/",
+        name: "thing",
+        subpath: "./dist/index.mjs",
+      },
+    },
+  ];
+  for (const t of tests) {
+    it(t.input, () => {
+      expect(parseNodeModulePath(t.input)).toMatchObject(t.output);
+    });
+  }
+});
+
+describe("lookupNodeModuleSubpath", () => {
+  // eslint-disable-next-line unicorn/consistent-function-scoping
+  const r = (p: string) => new URL(p, import.meta.url).toString();
+
+  const tests = [
+    {
+      name: "resolves with exports field",
+      input: r("fixture/package/node_modules/subpaths/lib/subpath.mjs"),
+      output: "./subpath",
+    },
+    {
+      name: "resolves with fallback subpath guess",
+      input: r("fixture/package/node_modules/alien/lib/subpath.json5"),
+      output: "./lib/subpath.json5",
+    },
+    {
+      name: "ignores invalid paths",
+      input: r("/foo/bar/lib/subpath.mjs"),
+      output: undefined,
+    },
+    {
+      name: "resolves main export",
+      input: r("fixture/package/node_modules/subpaths/foo/bar.mjs"),
+      output: "./foo/bar.mjs",
+    },
+    {
+      name: "resolves main export",
+      input: r("fixture/package/node_modules/subpaths/"),
+      output: "./",
+    },
+  ];
+
+  for (const t of tests) {
+    it(t.name, async () => {
+      const result = await lookupNodeModuleSubpath(t.input);
+      expect(result).toBe(t.output);
+    });
+  }
+});