fix(@angular/cli): handle duplicate arguments

packages/angular/cli/src/command-builder/command-runner.ts

@@ -33,6 +33,7 @@ import { PackageManagerUtils } from '../utilities/package-manager';
 import { CommandContext, CommandModuleError, CommandScope } from './command-module';
 import { addCommandModuleToYargs, demandCommandFailureMessage } from './utilities/command';
 import { jsonHelpUsage } from './utilities/json-help';
+import { normalizeOptionsMiddleware } from './utilities/normalize-options-middleware';
 
 const COMMANDS = [
   VersionCommandModule,
@@ -145,6 +146,7 @@ export async function runCommand(args: string[], logger: logging.Logger): Promis
     })
     .demandCommand(1, demandCommandFailureMessage)
     .recommendCommands()
+    .middleware(normalizeOptionsMiddleware)
     .version(false)
     .showHelpOnFail(false)
     .strict()

packages/angular/cli/src/command-builder/utilities/normalize-options-middleware.ts

@@ -0,0 +1,37 @@
+/**
+ * @license
+ * Copyright Google LLC 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 * as yargs from 'yargs';
+
+/**
+ * A Yargs middleware that normalizes non Array options when the argument has been provided multiple times.
+ *
+ * By default, when an option is non array and it is provided multiple times in the command line, yargs
+ * will not override it's value but instead it will be changed to an array unless `duplicate-arguments-array` is disabled.
+ * But this option also have an effect on real array options which isn't desired.
+ *
+ * See: https://github.com/yargs/yargs-parser/pull/163#issuecomment-516566614
+ */
+export function normalizeOptionsMiddleware(args: yargs.Arguments): void {
+  // `getOptions` is not included in the types even though it's public API.
+  // https://github.com/yargs/yargs/issues/2098
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  const { array } = (yargs as any).getOptions();
+  const arrayOptions = new Set(array);
+
+  for (const [key, value] of Object.entries(args)) {
+    if (key !== '_' && Array.isArray(value) && !arrayOptions.has(key)) {
+      const newValue = value.pop();
+      // eslint-disable-next-line no-console
+      console.warn(
+        `Option '${key}' has been specified multiple times. The value '${newValue}' will be used.`,
+      );
+      args[key] = newValue;
+    }
+  }
+}

tests/legacy-cli/e2e/tests/misc/duplicate-command-line-option.ts

@@ -0,0 +1,19 @@
+import { ng } from '../../utils/process';
+import { expectFileToExist } from '../../utils/fs';
+
+export default async function () {
+  const { stderr } = await ng(
+    'generate',
+    'component',
+    'test-component',
+    '--style=scss',
+    '--style=sass',
+  );
+
+  const warningMatch = `Option 'style' has been specified multiple times. The value 'sass' will be used`;
+  if (!stderr.includes(warningMatch)) {
+    throw new Error(`Expected stderr to contain: "${warningMatch}".`);
+  }
+
+  await expectFileToExist('src/app/test-component/test-component.component.sass');
+}