fix(@angular-devkit/schematics): running external schematics with yarn pnp

This change addresses an issue encountered when running external schematics from
a yarn pnp workspace.  The function used to resolve a collection json using node
used recursion in a way that it effectively walked itself into an exception. Then
if the exception is the type it expected, it would keep going.  This was flawed
in that yarn with pnp throws a different type of error when it failed to load
the mis-constructed collection path (e.g. `/node_modules/@schematics/angular/collection.json/package.json`).  `ENOTDIR` instead of `MODULE_NOT_FOUND`.

This process of intentionally / knowingly walking into an exception seems problematic in
general.  So, I addressed it by removing the recursion that was used mainly because
there's a similar need to construct the collection path from a relative path in the
package.json as there is to construct the collection path from a relative path that's
passed in.  Rather than leaning on the recursion to do this, I added the logic
at the time we pull the schematics path from the package, and move on.

Since the recursion was removed, the infinite recursion safety check at the start wasn't
needed anymore.

I've tested this in both yarn pnp and non-pnp environments.

packages/angular_devkit/schematics/tools/node-module-engine-host.ts

@@ -33,18 +33,7 @@ export class NodeModulesEngineHost extends FileSystemEngineHostBase {
     super();
   }
 
-  private resolve(name: string, requester?: string, references = new Set<string>()): string {
+  private resolve(name: string, requester?: string): string {
-    if (requester) {
-      if (references.has(requester)) {
-        references.add(requester);
-        throw new Error(
-          'Circular schematic reference detected: ' + JSON.stringify(Array.from(references)),
-        );
-      } else {
-        references.add(requester);
-      }
-    }
-
     const relativeBase = requester ? dirname(requester) : process.cwd();
     let collectionPath: string | undefined = undefined;
 
@@ -57,6 +46,7 @@ export class NodeModulesEngineHost extends FileSystemEngineHostBase {
     };
 
     // Try to resolve as a package
+    let possibleCollectionPath = name;
     try {
       const packageJsonPath = require.resolve(join(name, 'package.json'), resolveOptions);
       const { schematics } = require(packageJsonPath);
@@ -65,7 +55,16 @@ export class NodeModulesEngineHost extends FileSystemEngineHostBase {
         throw new NodePackageDoesNotSupportSchematics(name);
       }
 
-      collectionPath = this.resolve(schematics, packageJsonPath, references);
+      // If this is a relative path to the collection, then create the collection
+      // path in relation to the package path
+      if (schematics.startsWith('.')) {
+        const packageDirectory = dirname(packageJsonPath);
+        collectionPath = resolve(packageDirectory, schematics);
+      }
+      // Otherwise use the path as-is to attempt resolution
+      else {
+        possibleCollectionPath = schematics;
+      }
     } catch (e) {
       if ((e as NodeJS.ErrnoException).code !== 'MODULE_NOT_FOUND') {
         throw e;
@@ -75,7 +74,7 @@ export class NodeModulesEngineHost extends FileSystemEngineHostBase {
     // If not a package, try to resolve as a file
     if (!collectionPath) {
       try {
-        collectionPath = require.resolve(name, resolveOptions);
+        collectionPath = require.resolve(possibleCollectionPath, resolveOptions);
       } catch (e) {
         if ((e as NodeJS.ErrnoException).code !== 'MODULE_NOT_FOUND') {
           throw e;