From 13abfd01ecf2f355fb3829eb9a6352a29ca748d5 Mon Sep 17 00:00:00 2001
From: Charles Lyding <19598772+clydin@users.noreply.github.com>
Date: Wed, 10 Apr 2019 13:26:21 -0400
Subject: [PATCH] fix(@angular-devkit/schematics): fully support async rules

---
 .../angular_devkit/schematics/src/_golden-api.d.ts    |  2 +-
 .../angular_devkit/schematics/src/engine/interface.ts |  2 +-
 packages/angular_devkit/schematics/src/rules/call.ts  | 11 ++++++++++-
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/etc/api/angular_devkit/schematics/src/_golden-api.d.ts b/etc/api/angular_devkit/schematics/src/_golden-api.d.ts
index f2b35fb764..4edbf47bee 100644
--- a/etc/api/angular_devkit/schematics/src/_golden-api.d.ts
+++ b/etc/api/angular_devkit/schematics/src/_golden-api.d.ts
@@ -426,7 +426,7 @@ export interface RequiredWorkflowExecutionContext {
     schematic: string;
 }
 
-export declare type Rule = (tree: Tree, context: SchematicContext) => Tree | Observable<Tree> | Rule | Promise<void> | void;
+export declare type Rule = (tree: Tree, context: SchematicContext) => Tree | Observable<Tree> | Rule | Promise<void> | Promise<Rule> | void;
 
 export declare type RuleFactory<T extends object> = (options: T) => Rule;
 
diff --git a/packages/angular_devkit/schematics/src/engine/interface.ts b/packages/angular_devkit/schematics/src/engine/interface.ts
index 2ca66dbdff..5664780e19 100644
--- a/packages/angular_devkit/schematics/src/engine/interface.ts
+++ b/packages/angular_devkit/schematics/src/engine/interface.ts
@@ -231,4 +231,4 @@ export type AsyncFileOperator = (tree: FileEntry) => Observable<FileEntry | null
  */
 export type Source = (context: SchematicContext) => Tree | Observable<Tree>;
 export type Rule = (tree: Tree, context: SchematicContext) =>
-  Tree | Observable<Tree> | Rule | Promise<void> | void;
+  Tree | Observable<Tree> | Rule | Promise<void> | Promise<Rule> | void;
diff --git a/packages/angular_devkit/schematics/src/rules/call.ts b/packages/angular_devkit/schematics/src/rules/call.ts
index 4668d3df95..369d81cd9e 100644
--- a/packages/angular_devkit/schematics/src/rules/call.ts
+++ b/packages/angular_devkit/schematics/src/rules/call.ts
@@ -97,7 +97,16 @@ export function callRule(
         }),
       );
     } else if (isPromise(result)) {
-      return from(result).pipe(map(() => inputTree));
+      return from(result).pipe(
+        mergeMap(inner => {
+          if (typeof inner === 'function') {
+            // This is considered a Rule, chain the rule and return its output.
+            return callRule(inner, observableOf(inputTree), context);
+          } else {
+            return observableOf(inputTree);
+          }
+        }),
+      );
     } else if (TreeSymbol in result) {
       return observableOf(result);
     } else {