docs(@angular-devkit/core): add preliminary overview of workspace API

packages/angular_devkit/core/README.md

@@ -56,4 +56,110 @@ export class CoreSchemaRegistry implements SchemaRegistry {
 
 # Utils
 
-# Virtual FS
+# Virtual FS
+
+# Workspaces
+
+The `workspaces` namespace provides an API for interacting with the workspace file formats.
+It provides an abstraction of the underlying storage format of the workspace and provides
+support for both reading and writing.  Currently, the only supported format is the JSON-based
+format used by the Angular CLI.  For this format, the API provides internal change tracking of values which
+enables fine-grained updates to the underlying storage of the workspace.  This allows for the
+retention of existing formatting and comments.
+
+A workspace is defined via the following object model.  Definition collection objects are specialized
+Javascript `Map` objects with an additional `add` method to simplify addition and provide more localized
+error checking of the newly added values.
+
+```ts
+export interface WorkspaceDefinition {
+    readonly extensions: Record<string, JsonValue | undefined>;
+    readonly projects: ProjectDefinitionCollection;
+}
+
+export interface ProjectDefinition {
+    readonly extensions: Record<string, JsonValue | undefined>;
+    readonly targets: TargetDefinitionCollection;
+    root: string;
+    prefix?: string;
+    sourceRoot?: string;
+}
+
+export interface TargetDefinition {
+    options?: Record<string, JsonValue | undefined>;
+    configurations?: Record<string, Record<string, JsonValue | undefined> | undefined>;
+    builder: string;
+}
+```
+
+The API is asynchronous and has two main functions to facilitate reading, creation, and modifying
+a workspace: `readWorkspace` and `writeWorkspace`.
+
+```ts
+export enum WorkspaceFormat {
+  JSON,
+}
+```
+
+```ts
+export function readWorkspace(
+  path: string,
+  host: WorkspaceHost,
+  format?: WorkspaceFormat,
+): Promise<{ workspace: WorkspaceDefinition; }>;
+```
+
+```ts
+export function writeWorkspace(
+  workspace: WorkspaceDefinition,
+  host: WorkspaceHost,
+  path?: string,
+  format?: WorkspaceFormat,
+): Promise<void>;
+```
+
+A `WorkspaceHost` abstracts the underlying data access methods from the functions.  It provides
+methods to read, write, and analyze paths.  A utility function is provided to create
+an instance of a `WorkspaceHost` from the Angular DevKit's virtual filesystem host abstraction.
+
+```ts
+export interface WorkspaceHost {
+    readFile(path: string): Promise<string>;
+    writeFile(path: string, data: string): Promise<void>;
+    isDirectory(path: string): Promise<boolean>;
+    isFile(path: string): Promise<boolean>;
+}
+
+export function createWorkspaceHost(host: virtualFs.Host): WorkspaceHost;
+```
+
+## Usage Example
+
+To demonstrate the usage of the API, the following code will show how to add a option property
+to a build target for an application.
+
+```ts
+import { NodeJsSyncHost } from '@angular-devkit/core/node';
+import { workspaces } from '@angular-devkit/core';
+
+async function demonstrate() {
+    const host = workspaces.createWorkspaceHost(new NodeJsSyncHost());
+    const workspace = await workspaces.readWorkspace('path/to/workspace/directory/', host);
+
+    const project = workspace.projects.get('my-app');
+    if (!project) {
+      throw new Error('my-app does not exist');
+    }
+
+    const buildTarget = project.targets.get('build');
+    if (!buildTarget) {
+      throw new Error('build target does not exist');
+    }
+
+    buildTarget.options.optimization = true;
+
+    await workspaces.writeWorkspace(workspace, host);
+}
+
+demonstrate();
+```

packages/angular_devkit/core/src/workspace/core.ts

@@ -13,14 +13,23 @@ import { writeJsonWorkspace } from './json/writer';
 
 const formatLookup = new WeakMap<WorkspaceDefinition, WorkspaceFormat>();
 
+/**
+ * Supported workspace formats
+ */
 export enum WorkspaceFormat {
   JSON,
 }
 
+/**
+ * @private
+ */
 export function _test_addWorkspaceFile(name: string, format: WorkspaceFormat): void {
   workspaceFiles[name] = format;
 }
 
+/**
+ * @private
+ */
 export function _test_removeWorkspaceFile(name: string): void {
   delete workspaceFiles[name];
 }
@@ -31,6 +40,22 @@ const workspaceFiles: Record<string, WorkspaceFormat> = {
   '.angular.json': WorkspaceFormat.JSON,
 };
 
+/**
+ * Reads and constructs a `WorkspaceDefinition`.  If the function is provided with a path to a
+ * directory instead of a file, a search of the directory's files will commence to attempt to
+ * locate a known workspace file.  Currently the following are considered known workspace files:
+ * - `angular.json`
+ * - `.angular.json`
+ *
+ * @param path The path to either a workspace file or a directory containing a workspace file.
+ * @param host The `WorkspaceHost` to use to access the file and directory data.
+ * @param format An optional `WorkspaceFormat` value. Used if the path specifies a non-standard
+ * file name that would prevent automatically discovering the format.
+ *
+ *
+ * @return An `Promise` of the read result object with the `WorkspaceDefinition` contained within
+ * the `workspace` property.
+ */
 export async function readWorkspace(
   path: string,
   host: WorkspaceHost,
@@ -82,6 +107,24 @@ export async function readWorkspace(
   return { workspace };
 }
 
+/**
+ * Writes a `WorkspaceDefinition` to the underlying storage via the provided `WorkspaceHost`.
+ * If the `WorkspaceDefinition` was created via the `readWorkspace` function, metadata will be
+ * used to determine the path and format of the Workspace.  In all other cases, the `path` and
+ * `format` options must be specified as they would be otherwise unknown.
+ *
+ * @param workspace The `WorkspaceDefinition` that will be written.
+ * @param host The `WorkspaceHost` to use to access/write the file and directory data.
+ * @param path The path to a file location for the output. Required if `readWorkspace` was not
+ * used to create the `WorkspaceDefinition`.  Optional otherwise; will override the
+ * `WorkspaceDefinition` metadata if provided.
+ * @param format The `WorkspaceFormat` to use for output. Required if `readWorkspace` was not
+ * used to create the `WorkspaceDefinition`.  Optional otherwise; will override the
+ * `WorkspaceDefinition` metadata if provided.
+ *
+ *
+ * @return An `Promise` of type `void`.
+ */
 export async function writeWorkspace(
   workspace: WorkspaceDefinition,
   host: WorkspaceHost,