Don't load submodules with not installed optional dependencies

See: metarhia#1937

Author: DmitryScaletta

lib/deps.js

@@ -54,8 +54,16 @@ const loadModule = (name) => {
   const subKeys = Object.keys(pkg.exports).map((key) => key.substring(2));
   const subNames = subKeys.filter(validSubmodules);
   for (const subName of subNames) {
-    const sub = appRequire(name + '/' + subName);
-    lib[subName] = sub;
+    try {
+      const sub = appRequire(name + '/' + subName);
+      lib[subName] = sub;
+    } catch (e) {
+      if (e.message.startsWith("Cannot find module '")) {
+        const moduleName = e.message.substring(20, e.message.indexOf("'\n"));
+        const optional = pkg.peerDependenciesMeta?.[moduleName].optional;
+        if (optional) continue; else throw e;
+      }
+    }
   }
   return lib;
 };