feat(@angular-devkit/schematics): use CordHost as the backend for HostTree

This removes the need for VirtualTree although it is not yet removed. This should fix
a lot of merging/branching bugs seen in VirtualTree, AND align the branch/merging with
what is actually _meant_ to be. It will also streamline documentation.

Author: hansl

packages/angular_devkit/schematics/src/index.ts

@@ -25,6 +25,7 @@ export * from './rules/template';
 export * from './rules/url';
 export * from './tree/delegate';
 export * from './tree/empty';
+export * from './tree/host-tree';
 export * from './tree/filesystem';
 export * from './tree/virtual';
 export {UpdateRecorder} from './tree/interface';

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

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 import { Observable, of as observableOf } from 'rxjs';
-import { concatMap, map } from 'rxjs/operators';
+import { concatMap, last, map } from 'rxjs/operators';
 import { FileOperator, Rule, SchematicContext, Source } from '../engine/interface';
 import { FilteredTree } from '../tree/filtered';
 import { FileEntry, FilePredicate, MergeStrategy, Tree } from '../tree/interface';
@@ -81,7 +81,7 @@ export function mergeWith(source: Source, strategy: MergeStrategy = MergeStrateg
   return (tree: Tree, context: SchematicContext) => {
     const result = callSource(source, context);
 
-    return result.pipe(map(other => VirtualTree.merge(tree, other, strategy || context.strategy)));
+    return result.pipe(map(other => staticMerge(tree, other, strategy || context.strategy)));
   };
 }
 
@@ -106,7 +106,10 @@ export function branchAndMerge(rule: Rule, strategy = MergeStrategy.Default): Ru
     const branchedTree = branch(tree);
 
     return callRule(rule, observableOf(branchedTree), context)
-      .pipe(map(t => staticMerge(tree, t, strategy)));
+      .pipe(
+        last(),
+        map(t => staticMerge(tree, t, strategy)),
+      );
   };
 }
 

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

@@ -6,8 +6,9 @@
  * found in the LICENSE file at https://angular.io/license
  */
 import { of as observableOf } from 'rxjs';
+import { last, map } from 'rxjs/operators';
 import { Rule, SchematicContext } from '../engine/interface';
-import { Tree } from '../tree/interface';
+import { MergeStrategy, Tree } from '../tree/interface';
 import { branch } from '../tree/static';
 
 
@@ -41,6 +42,15 @@ export function schematic<OptionT extends object>(schematicName: string, options
     const collection = context.schematic.collection;
     const schematic = collection.createSchematic(schematicName, true);
 
-    return schematic.call(options, observableOf(branch(input)), context);
+    return schematic.call(options, observableOf(branch(input)), context).pipe(
+      last(),
+      map(x => {
+        // We allow overwrite conflict here because they're the only merge conflict we particularly
+        // don't want to deal with; the input tree might have an OVERWRITE which the sub
+        input.merge(x, MergeStrategy.AllowOverwriteConflict);
+
+        return input;
+      }),
+    );
   };
 }

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

@@ -173,9 +173,6 @@ export class FileSystemTree extends VirtualTree {
 }
 
 
-export class HostTree extends FileSystemTree {}
-
-
 export class FileSystemCreateTree extends FileSystemTree {
   constructor(host: virtualFs.Host) {
     super(host);