feat: add new nativeTheme API (#19656)

* feat: add new nativeTheme API

* chore: deprecate and clean up old systemPreferences theme APIs in favor of new nativeTheme module

* chore: clean up and deprecate things per feedback

* chore: add tests for deprecate and clean up invert impl

* build: when is a boolean not a boolean???

docs/api/native-theme.md

@@ -0,0 +1,35 @@
+# nativeTheme
+
+> Read and respond to changes in Chromium's native color theme.
+
+Process: [Main](../glossary.md#main-process), [Renderer](../glossary.md#renderer-process)
+
+## Events
+
+The `nativeTheme` module emits the following events:
+
+### Event: 'updated'
+
+Emitted when something in the underlying NativeTheme has changed. This normally
+means that either the value of `shouldUseDarkColors`,
+`shouldUseHighContrastColors` or `shouldUseInvertedColorScheme` has changed.
+You will have to check them to determine which one has changed.
+
+## Properties
+
+The `nativeTheme` module has the following properties:
+
+### `nativeTheme.shouldUseDarkColors` _Readonly_
+
+A `Boolean` for if the OS / Chromium currently has a dark mode enabled or is
+being instructed to show a dark-style UI.
+
+### `nativeTheme.shouldUseHighContrastColors` _macOS_ _Windows_ _Readonly_
+
+A `Boolean` for if the OS / Chromium currently has high-contrast mode enabled
+or is being instructed to show a high-constrast UI.
+
+### `nativeTheme.shouldUseInvertedColorScheme` _macOS_ _Windows_ _Readonly_
+
+A `Boolean` for if the OS / Chromium currently has an inverted color scheme
+or is being instructed to use an inverted color scheme.

docs/api/system-preferences.md

@@ -27,28 +27,34 @@ Returns:
 
 * `event` Event
 
-### Event: 'inverted-color-scheme-changed' _Windows_
+### Event: 'inverted-color-scheme-changed' _Windows_ _Deprecated_
 
 Returns:
 
 * `event` Event
 * `invertedColorScheme` Boolean - `true` if an inverted color scheme (a high contrast color scheme with light text and dark backgrounds) is being used, `false` otherwise.
 
-### Event: 'high-contrast-color-scheme-changed' _Windows_
+**Deprecated:** Should use the new [`updated`](native-theme.md#event-updated) event on the `nativeTheme` module.
+
+### Event: 'high-contrast-color-scheme-changed' _Windows_ _Deprecated_
 
 Returns:
 
 * `event` Event
 * `highContrastColorScheme` Boolean - `true` if a high contrast theme is being used, `false` otherwise.
 
+**Deprecated:** Should use the new [`updated`](native-theme.md#event-updated) event on the `nativeTheme` module.
+
 ## Methods
 
-### `systemPreferences.isDarkMode()` _macOS_ _Windows_
+### `systemPreferences.isDarkMode()` _macOS_ _Windows_ _Deprecated_
 
 Returns `Boolean` - Whether the system is in Dark Mode.
 
 **Note:** On macOS 10.15 Catalina in order for this API to return the correct value when in the "automatic" dark mode setting you must either have `NSRequiresAquaSystemAppearance=false` in your `Info.plist` or be on Electron `>=7.0.0`.  See the [dark mode guide](../tutorial/mojave-dark-mode-guide.md) for more information.
 
+**Deprecated:** Should use the new [`nativeTheme.shouldUseDarkColors`](native-theme.md#nativethemeshouldusedarkcolors-readonly) API.
+
 ### `systemPreferences.isSwipeTrackingFromScrollEventsEnabled()` _macOS_
 
 Returns `Boolean` - Whether the Swipe between pages setting is on.
@@ -342,14 +348,18 @@ Returns `String` - The standard system color formatted as `#RRGGBBAA`.
 
 Returns one of several standard system colors that automatically adapt to vibrancy and changes in accessibility settings like 'Increase contrast' and 'Reduce transparency'. See [Apple Documentation](https://developer.apple.com/design/human-interface-guidelines/macos/visual-design/color#system-colors) for  more details.
 
-### `systemPreferences.isInvertedColorScheme()` _Windows_
+### `systemPreferences.isInvertedColorScheme()` _Windows_ _Deprecated_
 
 Returns `Boolean` - `true` if an inverted color scheme (a high contrast color scheme with light text and dark backgrounds) is active, `false` otherwise.
 
-### `systemPreferences.isHighContrastColorScheme()` _macOS_ _Windows_
+**Deprecated:** Should use the new [`nativeTheme.shouldUseInvertedColorScheme`](native-theme.md#nativethemeshoulduseinvertedcolorscheme-macos-windows-readonly) API.
+
+### `systemPreferences.isHighContrastColorScheme()` _macOS_ _Windows_ _Deprecated_
 
 Returns `Boolean` - `true` if a high contrast theme is active, `false` otherwise.
 
+**Depreacted:** Should use the new [`nativeTheme.shouldUseHighContrastColors`](native-theme.md#nativethemeshouldusehighcontrastcolors-macos-windows-readonly) API.
+
 ### `systemPreferences.getEffectiveAppearance()` _macOS_
 
 Returns `String` - Can be `dark`, `light` or `unknown`.
@@ -365,7 +375,9 @@ using `electron-packager` or `electron-forge` just set the `enableDarwinDarkMode
 packager option to `true`.  See the [Electron Packager API](https://github.com/electron/electron-packager/blob/master/docs/api.md#darwindarkmodesupport)
 for more details.
 
-### `systemPreferences.getAppLevelAppearance()` _macOS_
+**[Deprecated](modernization/property-updates.md)**
+
+### `systemPreferences.getAppLevelAppearance()` _macOS_ _Deprecated_
 
 Returns `String` | `null` - Can be `dark`, `light` or `unknown`.
 
@@ -375,7 +387,7 @@ You can use the `setAppLevelAppearance` API to set this value.
 
 **[Deprecated](modernization/property-updates.md)**
 
-### `systemPreferences.setAppLevelAppearance(appearance)` _macOS_
+### `systemPreferences.setAppLevelAppearance(appearance)` _macOS_ _Deprecated_
 
 * `appearance` String | null - Can be `dark` or `light`
 
@@ -450,10 +462,25 @@ Returns an object with system animation settings.
 
 ### `systemPreferences.appLevelAppearance` _macOS_
 
-A `String` property that determines the macOS appearance setting for
+A `String` property that can be `dark`, `light` or `unknown`. It determines the macOS appearance setting for
 your application. This maps to values in: [NSApplication.appearance](https://developer.apple.com/documentation/appkit/nsapplication/2967170-appearance?language=objc). Setting this will override the
 system default as well as the value of `getEffectiveAppearance`.
 
 Possible values that can be set are `dark` and `light`, and possible return values are `dark`, `light`, and `unknown`.
 
 This property is only available on macOS 10.14 Mojave or newer.
+
+### `systemPreferences.effectiveAppearance` _macOS_ _Readonly_
+
+A `String` property that can be `dark`, `light` or `unknown`.
+
+Returns the macOS appearance setting that is currently applied to your application,
+maps to [NSApplication.effectiveAppearance](https://developer.apple.com/documentation/appkit/nsapplication/2967171-effectiveappearance?language=objc)
+
+Please note that until Electron is built targeting the 10.14 SDK, your application's
+`effectiveAppearance` will default to 'light' and won't inherit the OS preference. In
+the interim in order for your application to inherit the OS preference you must set the
+`NSRequiresAquaSystemAppearance` key in your apps `Info.plist` to `false`.  If you are
+using `electron-packager` or `electron-forge` just set the `enableDarwinDarkMode`
+packager option to `true`.  See the [Electron Packager API](https://github.com/electron/electron-packager/blob/master/docs/api.md#darwindarkmodesupport)
+for more details.

filenames.auto.gni

@@ -34,6 +34,7 @@ auto_filenames = {
     "docs/api/menu.md",
     "docs/api/modernization",
     "docs/api/native-image.md",
+    "docs/api/native-theme.md",
     "docs/api/net-log.md",
     "docs/api/net.md",
     "docs/api/notification.md",
@@ -131,6 +132,7 @@ auto_filenames = {
     "lib/common/api/deprecate.ts",
     "lib/common/api/module-list.js",
     "lib/common/api/native-image.js",
+    "lib/common/api/native-theme.ts",
     "lib/common/api/shell.js",
     "lib/common/buffer-utils.ts",
     "lib/common/clipboard-utils.ts",
@@ -229,7 +231,7 @@ auto_filenames = {
     "lib/browser/api/protocol.ts",
     "lib/browser/api/screen.ts",
     "lib/browser/api/session.js",
-    "lib/browser/api/system-preferences.js",
+    "lib/browser/api/system-preferences.ts",
     "lib/browser/api/top-level-window.js",
     "lib/browser/api/touch-bar.js",
     "lib/browser/api/tray.js",
@@ -262,6 +264,7 @@ auto_filenames = {
     "lib/common/api/exports/electron.js",
     "lib/common/api/module-list.js",
     "lib/common/api/native-image.js",
+    "lib/common/api/native-theme.ts",
     "lib/common/api/shell.js",
     "lib/common/buffer-utils.ts",
     "lib/common/clipboard-utils.ts",
@@ -287,6 +290,7 @@ auto_filenames = {
     "lib/common/api/exports/electron.js",
     "lib/common/api/module-list.js",
     "lib/common/api/native-image.js",
+    "lib/common/api/native-theme.ts",
     "lib/common/api/shell.js",
     "lib/common/buffer-utils.ts",
     "lib/common/clipboard-utils.ts",
@@ -337,6 +341,7 @@ auto_filenames = {
     "lib/common/api/exports/electron.js",
     "lib/common/api/module-list.js",
     "lib/common/api/native-image.js",
+    "lib/common/api/native-theme.ts",
     "lib/common/api/shell.js",
     "lib/common/buffer-utils.ts",
     "lib/common/clipboard-utils.ts",

filenames.gni

@@ -419,6 +419,8 @@ filenames = {
     "shell/common/api/atom_api_native_image.cc",
     "shell/common/api/atom_api_native_image.h",
     "shell/common/api/atom_api_native_image_mac.mm",
+    "shell/common/api/atom_api_native_theme.cc",
+    "shell/common/api/atom_api_native_theme.h",
     "shell/common/api/atom_api_shell.cc",
     "shell/common/api/atom_api_v8_util.cc",
     "shell/common/api/electron_bindings.cc",

lib/browser/api/system-preferences.js

@@ -1,15 +0,0 @@
-'use strict'
-
-const { EventEmitter } = require('events')
-const { deprecate } = require('electron')
-const { systemPreferences, SystemPreferences } = process.electronBinding('system_preferences')
-
-// SystemPreferences is an EventEmitter.
-Object.setPrototypeOf(SystemPreferences.prototype, EventEmitter.prototype)
-EventEmitter.call(systemPreferences)
-
-if ('appLevelAppearance' in systemPreferences) {
-  deprecate.fnToProperty(SystemPreferences.prototype, 'appLevelAppearance', '_getAppLevelAppearance', '_setAppLevelAppearance')
-}
-
-module.exports = systemPreferences

lib/browser/api/system-preferences.ts

@@ -0,0 +1,42 @@
+import { EventEmitter } from 'events'
+import { deprecate } from 'electron'
+const { systemPreferences, SystemPreferences } = process.electronBinding('system_preferences')
+
+// SystemPreferences is an EventEmitter.
+Object.setPrototypeOf(SystemPreferences.prototype, EventEmitter.prototype)
+EventEmitter.call(systemPreferences)
+
+if ('appLevelAppearance' in systemPreferences) {
+  deprecate.fnToProperty(
+    SystemPreferences.prototype,
+    'appLevelAppearance',
+    '_getAppLevelAppearance',
+    '_setAppLevelAppearance'
+  )
+}
+
+if ('effectiveAppearance' in systemPreferences) {
+  deprecate.fnToProperty(
+    SystemPreferences.prototype,
+    'effectiveAppearance',
+    '_getEffectiveAppearance'
+  )
+}
+
+SystemPreferences.prototype.isDarkMode = deprecate.moveAPI(
+  SystemPreferences.prototype.isDarkMode,
+  'systemPreferences.isDarkMode()',
+  'nativeTheme.shouldUseDarkColors'
+)
+SystemPreferences.prototype.isInvertedColorScheme = deprecate.moveAPI(
+  SystemPreferences.prototype.isInvertedColorScheme,
+  'systemPreferences.isInvertedColorScheme()',
+  'nativeTheme.shouldUseInvertedColorScheme'
+)
+SystemPreferences.prototype.isHighContrastColorScheme = deprecate.moveAPI(
+  SystemPreferences.prototype.isHighContrastColorScheme,
+  'systemPreferences.isHighContrastColorScheme()',
+  'nativeTheme.shouldUseHighContrastColors'
+)
+
+module.exports = systemPreferences

lib/common/api/deprecate.ts

@@ -51,7 +51,15 @@ const deprecate: ElectronInternal.DeprecationUtil = {
     const warn = warnOnce(`${fn.name} function`, `${newName} function`)
     return function (this: any) {
       warn()
-      fn.apply(this, arguments)
+      return fn.apply(this, arguments)
+    }
+  },
+
+  moveAPI: (fn: Function, oldUsage: string, newUsage: string) => {
+    const warn = warnOnce(oldUsage, newUsage)
+    return function (this: any) {
+      warn()
+      return fn.apply(this, arguments)
     }
   },
 
@@ -69,7 +77,7 @@ const deprecate: ElectronInternal.DeprecationUtil = {
   },
 
   // deprecate a getter/setter function pair in favor of a property
-  fnToProperty: (prototype: any, prop: string, getter: string, setter: string) => {
+  fnToProperty: (prototype: any, prop: string, getter: string, setter?: string) => {
     const withWarnOnce = function (obj: any, key: any, oldName: string, newName: string) {
       const warn = warnOnce(oldName, newName)
       const method = obj[key]
@@ -80,7 +88,9 @@ const deprecate: ElectronInternal.DeprecationUtil = {
     }
 
     prototype[getter.substr(1)] = withWarnOnce(prototype, getter, `${getter.substr(1)} function`, `${prop} property`)
+    if (setter) {
       prototype[setter.substr(1)] = withWarnOnce(prototype, setter, `${setter.substr(1)} function`, `${prop} property`)
+    }
   },
 
   // remove a property with no replacement

lib/common/api/module-list.js

@@ -4,6 +4,7 @@
 module.exports = [
   { name: 'clipboard', loader: () => require('./clipboard') },
   { name: 'nativeImage', loader: () => require('./native-image') },
+  { name: 'nativeTheme', loader: () => require('./native-theme') },
   { name: 'shell', loader: () => require('./shell') },
   // The internal modules, invisible unless you know their names.
   { name: 'deprecate', loader: () => require('./deprecate'), private: true }

lib/common/api/native-theme.ts

@@ -0,0 +1,8 @@
+import { EventEmitter } from 'events'
+
+const { NativeTheme, nativeTheme } = process.electronBinding('native_theme')
+
+Object.setPrototypeOf(NativeTheme.prototype, EventEmitter.prototype)
+EventEmitter.call(nativeTheme as any)
+
+module.exports = nativeTheme

shell/browser/api/atom_api_system_preferences.cc

@@ -99,7 +99,7 @@ void SystemPreferences::BuildPrototype(
       .SetMethod("removeUserDefault", &SystemPreferences::RemoveUserDefault)
       .SetMethod("isSwipeTrackingFromScrollEventsEnabled",
                  &SystemPreferences::IsSwipeTrackingFromScrollEventsEnabled)
-      .SetMethod("getEffectiveAppearance",
+      .SetMethod("_getEffectiveAppearance",
                  &SystemPreferences::GetEffectiveAppearance)
       .SetMethod("_getAppLevelAppearance",
                  &SystemPreferences::GetAppLevelAppearance)
@@ -108,6 +108,8 @@ void SystemPreferences::BuildPrototype(
       .SetProperty("appLevelAppearance",
                    &SystemPreferences::GetAppLevelAppearance,
                    &SystemPreferences::SetAppLevelAppearance)
+      .SetProperty("effectiveAppearance",
+                   &SystemPreferences::GetEffectiveAppearance)
       .SetMethod("getSystemColor", &SystemPreferences::GetSystemColor)
       .SetMethod("canPromptTouchID", &SystemPreferences::CanPromptTouchID)
       .SetMethod("promptTouchID", &SystemPreferences::PromptTouchID)

shell/common/api/atom_api_native_theme.cc

@@ -0,0 +1,97 @@
+// Copyright (c) 2019 Slack Technologies, Inc.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+#include "shell/common/api/atom_api_native_theme.h"
+
+#include "native_mate/dictionary.h"
+#include "native_mate/object_template_builder.h"
+#include "shell/common/node_includes.h"
+#include "ui/gfx/color_utils.h"
+#include "ui/native_theme/native_theme.h"
+
+namespace electron {
+
+namespace api {
+
+NativeTheme::NativeTheme(v8::Isolate* isolate, ui::NativeTheme* theme)
+    : theme_(theme) {
+  theme_->AddObserver(this);
+  Init(isolate);
+}
+
+NativeTheme::~NativeTheme() {
+  theme_->RemoveObserver(this);
+}
+
+void NativeTheme::OnNativeThemeUpdated(ui::NativeTheme* theme) {
+  Emit("updated");
+}
+
+bool NativeTheme::ShouldUseDarkColors() {
+  return theme_->SystemDarkModeEnabled();
+}
+
+bool NativeTheme::ShouldUseHighContrastColors() {
+  return theme_->UsesHighContrastColors();
+}
+
+#if defined(OS_MACOSX)
+const CFStringRef WhiteOnBlack = CFSTR("whiteOnBlack");
+const CFStringRef UniversalAccessDomain = CFSTR("com.apple.universalaccess");
+#endif
+
+// TODO(MarshallOfSound): Implement for Linux
+bool NativeTheme::ShouldUseInvertedColorScheme() {
+#if defined(OS_MACOSX)
+  CFPreferencesAppSynchronize(UniversalAccessDomain);
+  Boolean keyExistsAndHasValidFormat = false;
+  Boolean is_inverted = CFPreferencesGetAppBooleanValue(
+      WhiteOnBlack, UniversalAccessDomain, &keyExistsAndHasValidFormat);
+  if (!keyExistsAndHasValidFormat)
+    return false;
+  return is_inverted;
+#else
+  return color_utils::IsInvertedColorScheme();
+#endif
+}
+
+// static
+v8::Local<v8::Value> NativeTheme::Create(v8::Isolate* isolate) {
+  ui::NativeTheme* theme = ui::NativeTheme::GetInstanceForNativeUi();
+  return mate::CreateHandle(isolate, new NativeTheme(isolate, theme)).ToV8();
+}
+
+// static
+void NativeTheme::BuildPrototype(v8::Isolate* isolate,
+                                 v8::Local<v8::FunctionTemplate> prototype) {
+  prototype->SetClassName(mate::StringToV8(isolate, "NativeTheme"));
+  mate::ObjectTemplateBuilder(isolate, prototype->PrototypeTemplate())
+      .SetProperty("shouldUseDarkColors", &NativeTheme::ShouldUseDarkColors)
+      .SetProperty("shouldUseHighContrastColors",
+                   &NativeTheme::ShouldUseHighContrastColors)
+      .SetProperty("shouldUseInvertedColorScheme",
+                   &NativeTheme::ShouldUseInvertedColorScheme);
+}
+
+}  // namespace api
+
+}  // namespace electron
+
+namespace {
+
+void Initialize(v8::Local<v8::Object> exports,
+                v8::Local<v8::Value> unused,
+                v8::Local<v8::Context> context,
+                void* priv) {
+  v8::Isolate* isolate = context->GetIsolate();
+  mate::Dictionary dict(isolate, exports);
+  dict.Set("nativeTheme", electron::api::NativeTheme::Create(isolate));
+  dict.Set("NativeTheme", electron::api::NativeTheme::GetConstructor(isolate)
+                              ->GetFunction(context)
+                              .ToLocalChecked());
+}
+
+}  // namespace
+
+NODE_LINKED_MODULE_CONTEXT_AWARE(atom_common_native_theme, Initialize)

shell/common/api/atom_api_native_theme.h

@@ -0,0 +1,45 @@
+// Copyright (c) 2019 Slack Technologies, Inc.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+#ifndef SHELL_COMMON_API_ATOM_API_NATIVE_THEME_H_
+#define SHELL_COMMON_API_ATOM_API_NATIVE_THEME_H_
+
+#include "native_mate/handle.h"
+#include "shell/browser/api/event_emitter.h"
+#include "ui/native_theme/native_theme_observer.h"
+
+namespace electron {
+
+namespace api {
+
+class NativeTheme : public mate::EventEmitter<NativeTheme>,
+                    public ui::NativeThemeObserver {
+ public:
+  static v8::Local<v8::Value> Create(v8::Isolate* isolate);
+
+  static void BuildPrototype(v8::Isolate* isolate,
+                             v8::Local<v8::FunctionTemplate> prototype);
+
+ protected:
+  NativeTheme(v8::Isolate* isolate, ui::NativeTheme* theme);
+  ~NativeTheme() override;
+
+  bool ShouldUseDarkColors();
+  bool ShouldUseHighContrastColors();
+  bool ShouldUseInvertedColorScheme();
+
+  // ui::NativeThemeObserver:
+  void OnNativeThemeUpdated(ui::NativeTheme* theme) override;
+
+ private:
+  ui::NativeTheme* theme_;
+
+  DISALLOW_COPY_AND_ASSIGN(NativeTheme);
+};
+
+}  // namespace api
+
+}  // namespace electron
+
+#endif  // SHELL_COMMON_API_ATOM_API_NATIVE_THEME_H_

shell/common/node_bindings.cc

@@ -61,6 +61,7 @@
   V(atom_common_crash_reporter)      \
   V(atom_common_features)            \
   V(atom_common_native_image)        \
+  V(atom_common_native_theme)        \
   V(atom_common_notification)        \
   V(atom_common_screen)              \
   V(atom_common_shell)               \

spec-main/api-native-theme-spec.ts

@@ -0,0 +1,22 @@
+import { expect } from 'chai'
+import { nativeTheme } from 'electron'
+
+describe('nativeTheme module', () => {
+  describe('nativeTheme.shouldUseDarkColors', () => {
+    it('returns a boolean', () => {
+      expect(nativeTheme.shouldUseDarkColors).to.be.a('boolean')
+    })
+  })
+
+  describe('nativeTheme.shouldUseInvertedColorScheme', () => {
+    it('returns a boolean', () => {
+      expect(nativeTheme.shouldUseInvertedColorScheme).to.be.a('boolean')
+    })
+  })
+
+  describe('nativeTheme.shouldUseHighContrastColors', () => {
+    it('returns a boolean', () => {
+      expect(nativeTheme.shouldUseHighContrastColors).to.be.a('boolean')
+    })
+  })
+})

spec/api-deprecate-spec.js

@@ -168,6 +168,37 @@ describe('deprecate', () => {
     expect(warnings[1]).to.include(newProp)
   })
 
+  describe('moveAPI', () => {
+    beforeEach(() => {
+      deprecate.setHandler(null)
+    })
+
+    it('should call the original method', () => {
+      const warnings = []
+      deprecate.setHandler(warning => warnings.push(warning))
+
+      let called = false
+      const fn = () => {
+        called = true
+      }
+      const deprecated = deprecate.moveAPI(fn, 'old', 'new')
+      deprecated()
+      expect(called).to.equal(true)
+    })
+
+    it('should log the deprecation warning once', () => {
+      const warnings = []
+      deprecate.setHandler(warning => warnings.push(warning))
+
+      const deprecated = deprecate.moveAPI(() => null, 'old', 'new')
+      deprecated()
+      expect(warnings).to.have.lengthOf(1)
+      deprecated()
+      expect(warnings).to.have.lengthOf(1)
+      expect(warnings[0]).to.equal('\'old\' is deprecated and will be removed. Please use \'new\' instead.')
+    })
+  })
+
   describe('promisify', () => {
     const expected = 'Hello, world!'
     let promiseFunc

typings/internal-electron.d.ts

@@ -89,9 +89,10 @@ declare namespace ElectronInternal {
     removeFunction(fn: Function, removedName: string): Function;
     renameFunction(fn: Function, newName: string): Function;
     event(emitter: NodeJS.EventEmitter, oldName: string, newName: string): void;
-    fnToProperty(module: any, prop: string, getter: string, setter: string): void;
+    fnToProperty(module: any, prop: string, getter: string, setter?: string): void;
     removeProperty<T, K extends (keyof T & string)>(object: T, propertyName: K): T;
     renameProperty<T, K extends (keyof T & string)>(object: T, oldName: string, newName: K): T;
+    moveAPI(fn: Function, oldUsage: string, newUsage: string): Function;
 
     promisify<T extends (...args: any[]) => any>(fn: T): T;