feat(@angular-devkit/schematics): add applyToSubTree rule

This rule allows a group of rules to be applied to a scoped subdirectory of the current tree.

etc/api/angular_devkit/schematics/src/_golden-api.d.ts

@@ -30,6 +30,8 @@ export declare function applyPathTemplate<T extends PathTemplateData>(data: T, o
 
 export declare function applyTemplates<T>(options: T): Rule;
 
+export declare function applyToSubtree(path: string, rules: Rule[]): Rule;
+
 export declare function asSource(rule: Rule): Source;
 
 export declare type AsyncFileOperator = (tree: FileEntry) => Observable<FileEntry | null>;

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

@@ -12,6 +12,7 @@ import { SchematicsException } from '../exception/exception';
 import { FilteredTree } from '../tree/filtered';
 import { FilterHostTree, HostTree } from '../tree/host-tree';
 import { FileEntry, FilePredicate, MergeStrategy, Tree } from '../tree/interface';
+import { ScopedTree } from '../tree/scoped';
 import {
   branch,
   empty as staticEmpty,
@@ -202,3 +203,21 @@ export function composeFileOperators(operators: FileOperator[]): FileOperator {
     return current;
   };
 }
+
+export function applyToSubtree(path: string, rules: Rule[]): Rule {
+  return (tree, context) => {
+    const scoped = new ScopedTree(tree, path);
+
+    return callRule(chain(rules), observableOf(scoped), context).pipe(
+      map(result => {
+        if (result === scoped) {
+          return tree;
+        } else {
+          throw new SchematicsException(
+            'Original tree must be returned from all rules when using "applyToSubtree".',
+          );
+        }
+      }),
+    );
+  };
+}

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

@@ -17,8 +17,9 @@ import { of as observableOf } from 'rxjs';
 import { Rule, SchematicContext, Source } from '../engine/interface';
 import { Tree } from '../tree/interface';
 import { empty } from '../tree/static';
-import { apply, chain } from './base';
+import { apply, applyToSubtree, chain } from './base';
 import { callRule, callSource } from './call';
+import { move } from './move';
 
 
 const context: SchematicContext = {
@@ -163,3 +164,21 @@ describe('partitionApplyMerge', () => {
       .then(done, done.fail);
   });
 });
+
+describe('applyToSubtree', () => {
+  it('works', done => {
+    const tree = new HostTree();
+    tree.create('a/b/file1', 'hello world');
+    tree.create('a/b/file2', 'hello world');
+    tree.create('a/c/file3', 'hello world');
+
+    callRule(applyToSubtree('a/b', [move('x')]), observableOf(tree), context)
+      .toPromise()
+      .then(result => {
+        expect(result.exists('a/b/x/file1')).toBe(true);
+        expect(result.exists('a/b/x/file2')).toBe(true);
+        expect(result.exists('a/c/file3')).toBe(true);
+      })
+      .then(done, done.fail);
+  });
+});