refactor(@angular-devkit/core): allow creation of a host from a non-observable source

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

@@ -229,6 +229,8 @@ export declare class CoreSchemaRegistry implements SchemaRegistry {
     useXDeprecatedProvider(onUsage: (message: string) => void): void;
 }
 
+export declare function createSyncHost<StatsT extends object = {}>(handler: SyncHostHandler<StatsT>): Host<StatsT>;
+
 export declare function createWorkspaceHost(host: virtualFs.Host): WorkspaceHost;
 
 export interface CustomDimensionsAndMetricsOptions {
@@ -1048,6 +1050,18 @@ export declare class SyncDelegateHost<T extends object = {}> {
     write(path: Path, content: FileBufferLike): void;
 }
 
+export interface SyncHostHandler<StatsT extends object = {}> {
+    delete(path: Path): void;
+    exists(path: Path): boolean;
+    isDirectory(path: Path): boolean;
+    isFile(path: Path): boolean;
+    list(path: Path): PathFragment[];
+    read(path: Path): FileBuffer;
+    rename(from: Path, to: Path): void;
+    stat(path: Path): Stats<StatsT> | null;
+    write(path: Path, content: FileBufferLike): void;
+}
+
 export declare class SynchronousDelegateExpectedException extends BaseException {
     constructor();
 }

packages/angular_devkit/core/src/virtual-fs/host/create.ts

@@ -0,0 +1,82 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+import { Observable } from 'rxjs';
+import { Path, PathFragment } from '../path';
+import { FileBuffer, FileBufferLike, Host, HostCapabilities, Stats } from './interface';
+
+export interface SyncHostHandler<StatsT extends object = {}> {
+  read(path: Path): FileBuffer;
+  list(path: Path): PathFragment[];
+
+  exists(path: Path): boolean;
+  isDirectory(path: Path): boolean;
+  isFile(path: Path): boolean;
+
+  stat(path: Path): Stats<StatsT> | null;
+
+  write(path: Path, content: FileBufferLike): void;
+  delete(path: Path): void;
+  rename(from: Path, to: Path): void;
+}
+
+function wrapAction<T>(action: () => T): Observable<T> {
+  return new Observable((subscriber) => {
+    subscriber.next(action());
+    subscriber.complete();
+  });
+}
+
+export function createSyncHost<StatsT extends object = {}>(
+  handler: SyncHostHandler<StatsT>,
+): Host<StatsT> {
+  return new (class {
+    get capabilities(): HostCapabilities {
+      return { synchronous: true };
+    }
+
+    read(path: Path): Observable<FileBuffer> {
+      return wrapAction(() => handler.read(path));
+    }
+
+    list(path: Path): Observable<PathFragment[]> {
+      return wrapAction(() => handler.list(path));
+    }
+
+    exists(path: Path): Observable<boolean> {
+      return wrapAction(() => handler.exists(path));
+    }
+
+    isDirectory(path: Path): Observable<boolean> {
+      return wrapAction(() => handler.isDirectory(path));
+    }
+
+    isFile(path: Path): Observable<boolean> {
+      return wrapAction(() => handler.isFile(path));
+    }
+
+    stat(path: Path): Observable<Stats<StatsT> | null> {
+      return wrapAction(() => handler.stat(path));
+    }
+
+    write(path: Path, content: FileBufferLike): Observable<void> {
+      return wrapAction(() => handler.write(path, content));
+    }
+
+    delete(path: Path): Observable<void> {
+      return wrapAction(() => handler.delete(path));
+    }
+
+    rename(from: Path, to: Path): Observable<void> {
+      return wrapAction(() => handler.rename(from, to));
+    }
+
+    watch(): null {
+      return null;
+    }
+  })();
+}

packages/angular_devkit/core/src/virtual-fs/host/index.ts

@@ -8,6 +8,7 @@
 
 export * from './alias';
 export * from './buffer';
+export * from './create';
 export * from './empty';
 export * from './interface';
 export * from './memory';