refactor: make the cli testable

packages/angular_devkit/schematics_cli/bin/schematics.ts

@@ -17,7 +17,7 @@ import {
   terminal,
   virtualFs,
 } from '@angular-devkit/core';
-import { NodeJsSyncHost, createConsoleLogger } from '@angular-devkit/core/node';
+import { NodeJsSyncHost, ProcessOutput, createConsoleLogger } from '@angular-devkit/core/node';
 import {
   DryRunEvent,
   SchematicEngine,
@@ -31,42 +31,6 @@ import {
 import * as minimist from 'minimist';
 
 
-/**
- * Show usage of the CLI tool, and exit the process.
- */
-function usage(exitCode = 0): never {
-  logger.info(tags.stripIndent`
-    schematics [CollectionName:]SchematicName [options, ...]
-
-    By default, if the collection name is not specified, use the internal collection provided
-    by the Schematics CLI.
-
-    Options:
-        --debug             Debug mode. This is true by default if the collection is a relative
-                            path (in that case, turn off with --debug=false).
-
-        --allowPrivate      Allow private schematics to be run from the command line. Default to
-                            false.
-
-        --dry-run           Do not output anything, but instead just show what actions would be
-                            performed. Default to true if debug is also true.
-
-        --force             Force overwriting files that would otherwise be an error.
-
-        --list-schematics   List all schematics from the collection, by name. A collection name
-                            should be suffixed by a colon. Example: '@schematics/schematics:'.
-
-        --verbose           Show more information.
-
-        --help              Show this message.
-
-    Any additional option is passed to the Schematics depending on
-  `);
-
-  return process.exit(exitCode);
-}
-
-
 /**
  * Parse the name of schematic passed in argument, and return a {collection, schematic} named
  * tuple. The user can pass in `collection-name:schematic-name`, and this function will either
@@ -93,6 +57,18 @@ function parseSchematicName(str: string | null): { collection: string, schematic
 }
 
 
+export interface MainOptions {
+  args: string[];
+  stdout?: ProcessOutput;
+  stderr?: ProcessOutput;
+}
+
+export async function main({
+  args,
+  stdout = process.stdout,
+  stderr = process.stderr,
+}: MainOptions): Promise<0 | 1> {
+
   /** Parse the command line. */
   const booleanArgs = [
     'allowPrivate',
@@ -103,7 +79,7 @@ const booleanArgs = [
     'list-schematics',
     'verbose',
   ];
-const argv = minimist(process.argv.slice(2), {
+  const argv = minimist(args, {
     boolean: booleanArgs,
     default: {
       'debug': null,
@@ -113,10 +89,12 @@ const argv = minimist(process.argv.slice(2), {
   });
 
   /** Create the DevKit Logger used through the CLI. */
-const logger = createConsoleLogger(argv['verbose']);
+  const logger = createConsoleLogger(argv['verbose'], stdout, stderr);
 
   if (argv.help) {
-  usage();
+    logger.info(getUsage());
+
+    return 0;
   }
 
   /** Get the collection an schematic name from the first argument. */
@@ -137,12 +115,13 @@ if (argv['list-schematics']) {
     const collection = engine.createCollection(collectionName);
     logger.info(engine.listSchematicNames(collection).join('\n'));
 
-  process.exit(0);
+    return 0;
   }
 
   if (!schematicName) {
-  usage(1);
-  throw 0; // TypeScript doesn't know that process.exit() never returns.
+    logger.info(getUsage());
+
+    return 1;
   }
 
   /** Gather the arguments for later use. */
@@ -225,10 +204,10 @@ workflow.lifeCycle.subscribe(event => {
   /**
    * Remove every options from argv that we support in schematics itself.
    */
-const args = Object.assign({}, argv);
-delete args['--'];
+  const parsedArgs = Object.assign({}, argv);
+  delete parsedArgs['--'];
   for (const key of booleanArgs) {
-  delete args[key];
+    delete parsedArgs[key];
   }
 
   /**
@@ -236,7 +215,7 @@ for (const key of booleanArgs) {
    */
   const argv2 = minimist(argv['--']);
   for (const key of Object.keys(argv2)) {
-  args[key] = argv2[key];
+    parsedArgs[key] = argv2[key];
   }
 
   // Pass the rest of the arguments as the smart default "argv". Then delete it.
@@ -247,7 +226,7 @@ workflow.registry.addSmartDefaultProvider('argv', (schema: JsonObject) => {
       return argv._;
     }
   });
-delete args._;
+  delete parsedArgs._;
 
 
   /**
@@ -258,17 +237,24 @@ delete args._;
    *  step of the workflow failed (sink or task), with details included, and will only complete
    *  when everything is done.
    */
-workflow.execute({
+  try {
+    await workflow.execute({
       collection: collectionName,
       schematic: schematicName,
-  options: args,
+      options: parsedArgs,
       allowPrivate: allowPrivate,
       debug: debug,
       logger: logger,
     })
-.subscribe({
-  error(err: Error) {
-    // In case the workflow was not successful, show an appropriate error message.
+      .toPromise();
+
+    if (nothingDone) {
+      logger.info('Nothing to be done.');
+    }
+
+    return 0;
+
+  } catch (err) {
     if (err instanceof UnsuccessfulWorkflowExecution) {
       // "See above" because we already printed the error.
       logger.fatal('The Schematic workflow failed. See above.');
@@ -278,11 +264,46 @@ workflow.execute({
       logger.fatal(err.stack || err.message);
     }
 
-    process.exit(1);
-  },
-  complete() {
-    if (nothingDone) {
-      logger.info('Nothing to be done.');
+    return 1;
+  }
+}
+
+ /**
+ * Get usage of the CLI tool.
+ */
+function getUsage(): string {
+  return tags.stripIndent`
+  schematics [CollectionName:]SchematicName [options, ...]
+
+  By default, if the collection name is not specified, use the internal collection provided
+  by the Schematics CLI.
+
+  Options:
+      --debug             Debug mode. This is true by default if the collection is a relative
+                          path (in that case, turn off with --debug=false).
+
+      --allowPrivate      Allow private schematics to be run from the command line. Default to
+                          false.
+
+      --dry-run           Do not output anything, but instead just show what actions would be
+                          performed. Default to true if debug is also true.
+
+      --force             Force overwriting files that would otherwise be an error.
+
+      --list-schematics   List all schematics from the collection, by name. A collection name
+                          should be suffixed by a colon. Example: '@schematics/schematics:'.
+
+      --verbose           Show more information.
+
+      --help              Show this message.
+
+  Any additional option is passed to the Schematics depending on
+  `;
+}
+
+if (require.main === module) {
+  const args = process.argv.slice(2);
+  main({ args })
+    .then(exitCode => process.exitCode = exitCode)
+    .catch(e => { throw (e); });
 }
-  },
-});