fix(@angular-devkit/schematics): improve tree type checking

Fixes #11683

Author: clydin

packages/angular_devkit/schematics/src/rules/base.ts

@@ -96,9 +96,9 @@ export function noop(): Rule {
 export function filter(predicate: FilePredicate<boolean>): Rule {
   return ((tree: Tree) => {
     // TODO: Remove VirtualTree usage in 7.0
-    if (tree instanceof VirtualTree) {
+    if (VirtualTree.isVirtualTree(tree)) {
       return new FilteredTree(tree, predicate);
-    } else if (tree instanceof HostTree) {
+    } else if (HostTree.isHostTree(tree)) {
       return new FilterHostTree(tree, predicate);
     } else {
       throw new SchematicsException('Tree type is not supported.');

packages/angular_devkit/schematics/src/tree/host-tree.ts

@@ -109,6 +109,18 @@ export class HostTree implements Tree {
     return this;
   }
 
+  static isHostTree(tree: Tree): tree is HostTree {
+    if (tree instanceof HostTree) {
+      return true;
+    }
+
+    if (typeof tree === 'object' && typeof (tree as HostTree)._ancestry === 'object') {
+      return true;
+    }
+
+    return false;
+  }
+
   constructor(protected _backend: virtualFs.ReadonlyHost<{}> = new virtualFs.Empty()) {
     this._record = new virtualFs.CordHost(new virtualFs.SafeReadonlyHost(_backend));
     this._recordSync = new virtualFs.SyncDelegateHost(this._record);

packages/angular_devkit/schematics/src/tree/virtual.ts

@@ -104,7 +104,6 @@ export class VirtualDirEntry implements DirEntry {
   }
 }
 
-
 /**
  * The root class of most trees.
  */
@@ -114,6 +113,18 @@ export class VirtualTree implements Tree {
   protected _root = new VirtualDirEntry(this);
   protected _tree = new Map<Path, FileEntry>();
 
+  static isVirtualTree(tree: Tree): tree is VirtualTree {
+    if (tree instanceof VirtualTree) {
+      return true;
+    }
+
+    if (typeof tree === 'object' && typeof (tree as VirtualTree)._copyTo === 'function') {
+      return true;
+    }
+
+    return false;
+  }
+
   /**
    * Normalize the path. Made available to subclasses to overload.
    * @param path The path to normalize.