Fix varlock binary resolution for monorepo sub-packages (#547)

* Initial plan

* Fix monorepo binary resolution in varlock/auto-load

- Extract findVarlockBin() helper that walks up without premature throw
  when node_modules/.bin exists but lacks varlock (monorepo scenario)
- Add callerDir option to execSyncVarlock for additional search start point
- auto-load.ts passes import.meta.dirname as callerDir so binary search
  starts from inside the varlock package itself in node_modules

Agent-Logs-Url: https://github.com/dmno-dev/varlock/sessions/b32f0fb8-9a46-4a26-9f47-8ec85420b88c

Co-authored-by: philmillman <3722211+philmillman@users.noreply.github.com>

* Fix import.meta.dirname fallback and Windows binary name

- Add fallback to `new URL('.', import.meta.url).pathname` for older
  Node versions where `import.meta.dirname` is undefined
- Use `varlock.exe` on Windows when searching node_modules/.bin

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: philmillman <3722211+philmillman@users.noreply.github.com>
Co-authored-by: Theo Ephraim <theo@dmno.dev>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 4 people

.changeset/fix-monorepo-binary-resolution.md

@@ -0,0 +1,13 @@
+---
+"varlock": patch
+---
+
+Fix binary resolution in monorepos when `cwd` differs from the package root.
+
+When importing `varlock/auto-load` (e.g. from a `playwright.config.ts` in a monorepo sub-package), VS Code and similar tools may set `process.cwd()` to the workspace root rather than the sub-package directory. This caused `execSyncVarlock` to search for the `varlock` binary starting at the workspace root and fail to find it when it was only installed in a sub-package's `node_modules/.bin`.
+
+Two fixes are applied:
+
+1. `execSyncVarlock` now accepts a `callerDir` option. When provided, the binary search walks up from `callerDir` before falling back to `process.cwd()`. `auto-load.ts` passes `import.meta.dirname` so the search always starts from inside the varlock package itself, which is already in the correct sub-package's `node_modules`.
+
+2. The walk-up logic no longer throws immediately when it finds a `node_modules/.bin` directory that does not contain varlock. It now continues walking up, allowing the search to find varlock installed at a higher or lower level of a monorepo.

packages/varlock/src/auto-load.ts

@@ -14,6 +14,10 @@ import { patchGlobalResponse } from './runtime/patch-response';
 const execResult = execSyncVarlock('load --format json-full --compact', {
   exitOnError: true,
   showLogsOnError: true,
+  // Pass the directory of this module so that in monorepos the binary search
+  // starts from inside the varlock package (e.g. apps/web/node_modules/varlock)
+  // rather than from process.cwd(), which may be an unrelated workspace root.
+  callerDir: import.meta.dirname ?? new URL('.', import.meta.url).pathname,
 });
 process.env.__VARLOCK_ENV = execResult;
 

packages/varlock/src/lib/exec-sync-varlock.ts

@@ -11,6 +11,30 @@ const platform = os.platform();
 const isWindows = platform.match(/^win/i);
 
 
+/**
+ * Walk up the directory tree from startDir looking for a node_modules/.bin/varlock binary.
+ * Returns the full path to the binary if found, or null if not found.
+ */
+function findVarlockBin(startDir: string): string | null {
+  let currentDir = startDir;
+  while (currentDir) {
+    const possibleBinPath = path.join(currentDir, 'node_modules', '.bin');
+    if (fs.existsSync(possibleBinPath)) {
+      const possibleVarlockPath = path.join(possibleBinPath, isWindows ? 'varlock.exe' : 'varlock');
+      if (fs.existsSync(possibleVarlockPath)) {
+        return possibleVarlockPath;
+      }
+      // Found a .bin directory but varlock is not in it - keep walking up.
+      // In a monorepo the root node_modules/.bin may exist without varlock,
+      // which is installed only in a sub-package.
+    }
+    const parentDir = path.dirname(currentDir);
+    if (parentDir === currentDir) break;
+    currentDir = parentDir;
+  }
+  return null;
+}
+
 /**
  * small helper to call execSync and call the varlock cli
  *
@@ -22,6 +46,13 @@ export function execSyncVarlock(
   opts?: (Parameters<typeof execSyncType>[1] & {
     exitOnError?: boolean,
     showLogsOnError?: boolean,
+    /**
+     * Additional directory to start searching for the varlock binary from.
+     * Searched before process.cwd(). Pass `import.meta.dirname` from the
+     * call-site so that in monorepos the binary installed next to the
+     * importing package is found even when cwd is an unrelated workspace root.
+     */
+    callerDir?: string,
   }),
 ) {
   try {
@@ -41,27 +72,25 @@ export function execSyncVarlock(
     }
 
     // if varlock was not found, it either means it is not installed
-    // or we must find the path to node_modules/.bin ourselves
-    // so we'll walk up the directory tree looking for it
-    let currentDir = process.cwd();
-    while (currentDir) {
-      const possibleBinPath = path.join(currentDir, 'node_modules', '.bin');
-      if (fs.existsSync(possibleBinPath)) {
-        const possibleVarlockPath = path.join(possibleBinPath, 'varlock');
-        if (fs.existsSync(possibleVarlockPath)) {
-          const result = execFileSync(possibleVarlockPath, command.split(' '), {
-            ...opts,
-            stdio: 'pipe',
-          });
-          return result.toString();
-        } else {
-          throw new Error('Unable to find varlock executable');
-        }
+    // or we must find the path to node_modules/.bin ourselves.
+    // Search from callerDir first (if provided), then from process.cwd().
+    // This handles monorepo setups where cwd may be an unrelated workspace
+    // root while varlock is only installed in a sub-package - the callerDir
+    // supplied by auto-load.ts points inside that sub-package's node_modules.
+    const searchDirs = [
+      ...(opts?.callerDir ? [opts.callerDir] : []),
+      process.cwd(),
+    ];
+
+    for (const startDir of searchDirs) {
+      const varlockPath = findVarlockBin(startDir);
+      if (varlockPath) {
+        const result = execFileSync(varlockPath, command.split(' '), {
+          ...opts,
+          stdio: 'pipe',
+        });
+        return result.toString();
       }
-      // when we reach the root, it will stop
-      const parentDir = path.dirname(currentDir);
-      if (parentDir === currentDir) break;
-      currentDir = path.dirname(currentDir);
     }
     throw new Error('Unable to find varlock executable');
   } catch (err) {