feat: Add --chromium-pref flag

src/cmd/run.js

@@ -48,6 +48,7 @@ export default async function run(
     firefoxApkComponent,
     // Chromium CLI options.
     chromiumBinary,
+    chromiumPref,
     chromiumProfile,
   },
   {
@@ -80,6 +81,11 @@ export default async function run(
   // Create an alias for --pref since it has been transformed into an
   // object containing one or more preferences.
   const customPrefs = { ...pref };
+
+  // Create an alias for --chromium-pref since it has been transformed into an
+  // object containing one or more preferences.
+  const customChromiumPrefs = { ...chromiumPref };
+
   const manifestData = await getValidatedManifest(sourceDir);
 
   const profileDir = firefoxProfile || chromiumProfile;
@@ -187,6 +193,7 @@ export default async function run(
       ...commonRunnerParams,
       chromiumBinary,
       chromiumProfile,
+      customChromiumPrefs,
     };
 
     const chromiumRunner = await createExtensionRunner({

src/extension-runners/chromium.js

@@ -17,6 +17,7 @@ import { createLogger } from '../util/logger.js';
 import { TempDir } from '../util/temp-dir.js';
 import isDirectory from '../util/is-directory.js';
 import fileExists from '../util/file-exists.js';
+import expandPrefs from '../util/expand-prefs.js';
 
 const log = createLogger(import.meta.url);
 
@@ -26,6 +27,10 @@ export const DEFAULT_CHROME_FLAGS = ChromeLauncher.defaultFlags().filter(
   (flag) => !EXCLUDED_CHROME_FLAGS.includes(flag),
 );
 
+const DEFAULT_PREFS = {
+  'extensions.ui.developer_mode': true,
+};
+
 /**
  * Implements an IExtensionRunner which manages a Chromium instance.
  */
@@ -210,6 +215,7 @@ export class ChromiumExtensionRunner {
       userDataDir,
       // Ignore default flags to keep the extension enabled.
       ignoreDefaultFlags: true,
+      prefs: this.getPrefs(),
     });
 
     this.chromiumInstance.process.once('close', () => {
@@ -414,4 +420,15 @@ export class ChromiumExtensionRunner {
       }
     }
   }
+
+  /**
+   * Returns a deep preferences object based on a set of flat preferences, like
+   * "extensions.ui.developer_mode".
+   */
+  getPrefs() {
+    return expandPrefs({
+      ...DEFAULT_PREFS,
+      ...(this.params.customChromiumPrefs || {}),
+    });
+  }
 }

src/program.js

@@ -14,6 +14,7 @@ import {
   consoleStream as defaultLogStream,
 } from './util/logger.js';
 import { coerceCLICustomPreference } from './firefox/preferences.js';
+import { coerceCLICustomChromiumPreference } from './util/chromium-preferences.js';
 import { checkForUpdates as defaultUpdateChecker } from './util/updates.js';
 import {
   discoverConfigFiles as defaultConfigDiscovery,
@@ -616,6 +617,18 @@ Example: $0 --help run.
         demandOption: false,
         type: 'string',
       },
+      'chromium-pref': {
+        describe:
+          'Launch chromium with a custom preference ' +
+          '(example: --chromium-pref=browser.theme.follows_system_colors=false). ' +
+          'You can repeat this option to set more than one ' +
+          'preference.',
+        demandOption: false,
+        requiresArg: true,
+        type: 'array',
+        coerce: (arg) =>
+          arg != null ? coerceCLICustomChromiumPreference(arg) : undefined,
+      },
       'chromium-profile': {
         describe: 'Path to a custom Chromium profile',
         demandOption: false,

src/util/chromium-preferences.js

@@ -0,0 +1,33 @@
+import { UsageError } from '../errors.js';
+
+export function coerceCLICustomChromiumPreference(cliPrefs) {
+  const customPrefs = {};
+
+  for (const pref of cliPrefs) {
+    const prefsAry = pref.split('=');
+
+    if (prefsAry.length < 2) {
+      throw new UsageError(
+        `Incomplete custom preference: "${pref}". ` +
+          'Syntax expected: "prefname=prefvalue".',
+      );
+    }
+
+    const key = prefsAry[0];
+    let value = prefsAry.slice(1).join('=');
+
+    if (/[^\w_.]/.test(key)) {
+      throw new UsageError(`Invalid custom preference name: ${key}`);
+    }
+
+    if (value === `${parseInt(value)}`) {
+      value = parseInt(value, 10);
+    } else if (value === 'true' || value === 'false') {
+      value = value === 'true';
+    }
+
+    customPrefs[`${key}`] = value;
+  }
+
+  return customPrefs;
+}

src/util/expand-prefs.js

@@ -0,0 +1,32 @@
+/**
+ * Given an object where the keys are the flattened path to a
+ * preference, and the value is the value to set at that path, return
+ * an object where the paths are fully expanded.
+ */
+export default function expandPrefs(prefs) {
+  const prefsMap = new Map();
+  for (const [key, value] of Object.entries(prefs)) {
+    let submap = prefsMap;
+    const props = key.split('.');
+    const lastProp = props.pop();
+    for (const prop of props) {
+      if (!submap.has(prop)) {
+        submap.set(prop, new Map());
+      }
+      submap = submap.get(prop);
+      if (!(submap instanceof Map)) {
+        throw new Error(
+          `Cannot set ${key} because a value already exists at ${prop}`,
+        );
+      }
+    }
+    submap.set(lastProp, value);
+  }
+  return mapToObject(prefsMap);
+}
+
+function mapToObject(map) {
+  return Object.fromEntries(
+    Array.from(map, ([k, v]) => [k, v instanceof Map ? mapToObject(v) : v]),
+  );
+}

tests/unit/test-extension-runners/test.chromium.js

@@ -47,7 +47,7 @@ function prepareExtensionRunnerParams({ params } = {}) {
 
 describe('util/extension-runners/chromium', async () => {
   it('uses the expected chrome flags', () => {
-    // Flags from chrome-launcher v0.14.0
+    // Flags from chrome-launcher v1.1.2
     const expectedFlags = [
       '--disable-features=Translate,OptimizationHints,MediaRouter,DialMediaRouteProvider,CalculateNativeWinOcclusion,InterestFeedContentSuggestions,CertificateTransparencyComponentUpdater,AutofillServerCommunication,PrivacySandboxSettings4',
       '--disable-component-extensions-with-background-pages',
@@ -619,6 +619,56 @@ describe('util/extension-runners/chromium', async () => {
       }),
   );
 
+  it('does pass default prefs to chrome', async () => {
+    const { params } = prepareExtensionRunnerParams();
+
+    const runnerInstance = new ChromiumExtensionRunner(params);
+    await runnerInstance.run();
+
+    sinon.assert.calledOnce(params.chromiumLaunch);
+    sinon.assert.calledWithMatch(params.chromiumLaunch, {
+      prefs: {
+        extensions: {
+          ui: {
+            developer_mode: true,
+          },
+        },
+      },
+    });
+
+    await runnerInstance.exit();
+  });
+
+  it('does pass custom prefs to chrome', async () => {
+    const { params } = prepareExtensionRunnerParams({
+      params: {
+        customChromiumPrefs: {
+          'download.default_directory': '/some/directory',
+          'extensions.ui.developer_mode': false,
+        },
+      },
+    });
+
+    const runnerInstance = new ChromiumExtensionRunner(params);
+    await runnerInstance.run();
+
+    sinon.assert.calledOnce(params.chromiumLaunch);
+    sinon.assert.calledWithMatch(params.chromiumLaunch, {
+      prefs: {
+        download: {
+          default_directory: '/some/directory',
+        },
+        extensions: {
+          ui: {
+            developer_mode: false,
+          },
+        },
+      },
+    });
+
+    await runnerInstance.exit();
+  });
+
   describe('reloadAllExtensions', () => {
     let runnerInstance;
     let wsClient;

tests/unit/test-util/test.expand-prefs.js

@@ -0,0 +1,68 @@
+import { assert, expect } from 'chai';
+import { describe, it } from 'mocha';
+
+import expandPrefs from '../../../src/util/expand-prefs.js';
+
+describe('utils/expand-prefs', () => {
+  it('expands dot-deliminated preferences into a deep object', () => {
+    const input = {
+      a: 'a',
+      'b.c': 'c',
+      'd.e.f': 'f',
+    };
+    const expected = {
+      a: 'a',
+      b: {
+        c: 'c',
+      },
+      d: {
+        e: {
+          f: 'f',
+        },
+      },
+    };
+    const actual = expandPrefs(input);
+
+    assert.deepEqual(actual, expected);
+  });
+
+  it("doesn't pollute the object prototype", () => {
+    const call = 'overriden';
+    const input = {
+      'hasOwnProperty.call': call,
+    };
+    const expected = {
+      hasOwnProperty: {
+        call,
+      },
+    };
+    const actual = expandPrefs(input);
+
+    assert.notEqual(Object.prototype.hasOwnProperty.call, call);
+    assert.deepEqual(actual, expected);
+  });
+
+  it('throws an error when setting the child property of an already set parent', () => {
+    const input = {
+      a: 'a',
+      'a.b': 'b',
+    };
+
+    expect(() => expandPrefs(input)).to.throw(
+      'Cannot set a.b because a value already exists at a',
+    );
+  });
+
+  it('allows overriding a parent even if a child has already been set', () => {
+    const input = {
+      'a.b': 'b',
+      a: 'a',
+    };
+    const expected = {
+      a: 'a',
+    };
+    const actual = expandPrefs(input);
+
+    assert.deepEqual(actual, expected);
+  });
+});

tests/unit/test.program.js

@@ -627,6 +627,27 @@ describe('program.main', () => {
     });
   });
 
+  it('converts custom chromium preferences into an object', () => {
+    const fakeCommands = fake(commands, {
+      run: () => Promise.resolve(),
+    });
+    return execProgram(
+      [
+        'run',
+        '--chromium-pref',
+        'prop=true',
+        '--chromium-pref',
+        'prop2=value2',
+      ],
+      { commands: fakeCommands },
+    ).then(() => {
+      const { chromiumPref } = fakeCommands.run.firstCall.args[0];
+      assert.isObject(chromiumPref);
+      assert.equal(chromiumPref.prop, true);
+      assert.equal(chromiumPref.prop2, 'value2');
+    });
+  });
+
   it('passes shouldExitProgram option to commands', () => {
     const fakeCommands = fake(commands, {
       lint: () => Promise.resolve(),