WIP: Add two-pass resolve is missing package.json:main

lib/package.js

@@ -51,33 +51,71 @@ const getLastPackageSegment = (filePath) => {
   return relPath || null;
 };
 
-// TODO: ADD TESTS!!!
 // Get path up to and including the package name (but no further).
 const getLastPackageRoot = (filePath) => {
   if (!filePath) { return null; }
 
   // Iterate all normalized parts of the file path and extract packages.
   const parts = path.normalize(filePath).split(path.sep);
   const lastModsIdx = parts.lastIndexOf("node_modules");
-  // Not within node_modules.
-  if (lastModsIdx === -1) { return null; }
 
-  // Scoped.
-  if ((parts[lastModsIdx + 1] || "")[0] === "@" && parts[lastModsIdx + 2]) {
-    return parts.slice(0, lastModsIdx + 3).join(path.sep);
+  // Not within node_modules or potential path possibility.
+  if (lastModsIdx === -1 || lastModsIdx + 1 === parts.length) { return null; }
+
+  // Find package root index. Start with unscoped.
+  let pkgRootIdx = lastModsIdx + 1;
+  if (parts[pkgRootIdx][0] === "@") {
+    // Check possible scoped path possibility.
+    if (pkgRootIdx + 1 === parts.length) { return null; }
+    // Scoped.
+    pkgRootIdx++;
+  }
+
+  return parts.slice(0, pkgRootIdx + 1).join(path.sep);
+};
+
+// Return module name and relative path (as array of path parts).
+const getDependencyParts = (dep) => {
+  if (
+    !dep
+    || path.isAbsolute(dep)
+    || dep.startsWith(".")
+  ) {
+    return null;
+  }
+
+  // Note that `package.json:exports` don't normalize/resolve `..` or file
+  // paths, so leave them intact (which means manually replace `\\` instead
+  // of using `toPosixPath`).
+  let parts = dep
+    .replace(/\\/g, "/")
+    .split("/")
+    .filter(Boolean);
+
+  let name;
+  if (parts.length > 0) {
+    if (parts[0][0] === "@") {
+      if (parts[1]) {
+        name = `${parts[0]}/${parts[1]}`;
+        parts = parts.slice(2); // eslint-disable-line no-magic-numbers
+      }
+    } else if (parts[0]) {
+      name = parts[0];
+      parts = parts.slice(1);
+    }
   }
 
-  // Unscoped
-  if (parts[lastModsIdx + 1]) {
-    return parts.slice(0, lastModsIdx + 2).join(path.sep);
+  if (!name) {
+    return null;
   }
 
-  return null;
+  return { name, parts };
 };
 
 module.exports = {
   getPackages,
   getLastPackage,
   getLastPackageSegment,
-  getLastPackageRoot
+  getLastPackageRoot,
+  getDependencyParts
 };

lib/path.js

@@ -0,0 +1,9 @@
+"use strict";
+
+const path = require("path");
+
+const toPosixPath = (file) => !file ? file : path.normalize(file).replace(/\\/g, "/");
+
+module.exports = {
+  toPosixPath
+};