application-package: refine configuration typings

Typings now support both a `partial` and `resolved` version for our
configurations. A `resolved` configuration has `undefined` values
replaced by available defaults, a `partial` configuration does not.

Co-Authored-By: Nathanael Demacon <[email protected]>

dev-packages/application-package/src/application-props.ts

@@ -16,6 +16,27 @@
 
 import type { BrowserWindowConstructorOptions } from 'electron';
 
+/**
+ * Base configuration for the Theia application.
+ */
+export interface ApplicationConfig {
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    readonly [key: string]: any;
+}
+
+/**
+ * Helper interface that generates two versions of an interface given two inputs:
+ * @param WithDefault key/values that may be left undefined but will be resolved to a default when missing.
+ * @param Rest key/values that may or may not be left undefined but will stay that way.
+ * @returns a pseudo-interface you can query 'resolved' or 'partial' to get different versions of the same interface.
+ */
+interface ConfigHelper<WithDefault extends object, Rest extends object> {
+    /** Query this field like `Config['partial']` to get the type with optional fields. */
+    partial: Partial<WithDefault> & Rest & ApplicationConfig
+    /** Query this field like `Config['resolved']` to get the type without undefined values for fields with defaults. */
+    resolved: Required<WithDefault> & Rest & ApplicationConfig
+}
+
 export interface NpmRegistryProps {
 
     /**
@@ -76,37 +97,22 @@ export namespace ApplicationProps {
         ...NpmRegistryProps.DEFAULT,
         target: 'browser',
         backend: {
-            config: {}
+            config: BackendApplicationConfig.DEFAULT,
         },
         frontend: {
-            config: {
-                applicationName: 'Eclipse Theia',
-                defaultTheme: 'dark',
-                defaultIconTheme: 'none'
-            }
+            config: FrontendApplicationConfig.DEFAULT,
         },
         generator: {
-            config: {
-                preloadTemplate: ''
-            }
+            config: GeneratorConfig.DEFAULT,
         }
     };
-
-}
-
-/**
- * Base configuration for the Theia application.
- */
-export interface ApplicationConfig {
-    // eslint-disable-next-line @typescript-eslint/no-explicit-any
-    readonly [key: string]: any;
 }
 
 /**
  * Application configuration for the frontend. The following properties will be injected into the `index.html`.
  */
-export interface FrontendApplicationConfig extends ApplicationConfig {
-
+export type FrontendApplicationConfig = _FrontendApplicationConfig['resolved'];
+type _FrontendApplicationConfig = ConfigHelper<{
     /**
      * The default theme for the application. If not given, defaults to `dark`. If invalid theme is given, also defaults to `dark`.
      */
@@ -121,47 +127,69 @@ export interface FrontendApplicationConfig extends ApplicationConfig {
      * The name of the application. `Eclipse Theia` by default.
      */
     readonly applicationName: string;
-
+}, {
     /**
      * Electron specific configuration.
      */
     readonly electron?: Readonly<ElectronFrontendApplicationConfig>;
+}>;
+export namespace FrontendApplicationConfig {
+    export const DEFAULT: FrontendApplicationConfig = {
+        applicationName: 'Eclipse Theia',
+        defaultTheme: 'dark',
+        defaultIconTheme: 'none'
+    };
+    export type Partial = _FrontendApplicationConfig['partial'];
 }
 
-export interface ElectronFrontendApplicationConfig {
-
+export type ElectronFrontendApplicationConfig = _ElectronFrontendApplicationConfig['resolved'];
+type _ElectronFrontendApplicationConfig = ConfigHelper<{
     /**
      * If set to `true`, reloading the current browser window won't be possible with the `Ctrl/Cmd + R` keybinding.
      * It is `false` by default. Has no effect if not in an electron environment.
      */
-    readonly disallowReloadKeybinding?: boolean;
-
+    readonly disallowReloadKeybinding: boolean;
+}, {
     /**
      * Override or add properties to the electron `windowOptions`.
      */
     readonly windowOptions?: BrowserWindowConstructorOptions;
+}>;
+export namespace ElectronFrontendApplicationConfig {
+    export const DEFAULT: ElectronFrontendApplicationConfig = {
+        disallowReloadKeybinding: false,
+    };
+    export type Partial = _ElectronFrontendApplicationConfig['partial'];
 }
 
 /**
  * Application configuration for the backend.
  */
-export interface BackendApplicationConfig extends ApplicationConfig {
-
+export type BackendApplicationConfig = _BackendApplicationConfig['resolved'];
+type _BackendApplicationConfig = ConfigHelper<{}, {
     /**
      * If true and in Electron mode, only one instance of the application is allowed to run at a time.
      */
-    singleInstance?: boolean;
-
+    readonly singleInstance?: boolean;
+}>;
+export namespace BackendApplicationConfig {
+    export const DEFAULT: BackendApplicationConfig = {};
+    export type Partial = _BackendApplicationConfig['partial'];
 }
 
 /**
  * Configuration for the generator.
  */
-export interface GeneratorConfig {
-
+export type GeneratorConfig = _GeneratorConfig['resolved'];
+type _GeneratorConfig = ConfigHelper<{
     /**
-     * Template to use for extra preload content markup (file path or HTML)
+     * Template to use for extra preload content markup (file path or HTML). Defaults to `''`.
      */
     readonly preloadTemplate: string;
-
+}, {}>;
+export namespace GeneratorConfig {
+    export const DEFAULT: GeneratorConfig = {
+        preloadTemplate: ''
+    };
+    export type Partial = _GeneratorConfig['partial'];
 }

packages/core/src/browser/frontend-application-config-provider.ts

@@ -28,14 +28,18 @@ export class FrontendApplicationConfigProvider {
         return config;
     }
 
-    static set(config: FrontendApplicationConfig): void {
+    static set(config: FrontendApplicationConfig.Partial): void {
         if (FrontendApplicationConfigProvider.doGet() !== undefined) {
             throw new Error('The configuration is already set.');
         }
+        const resolved: FrontendApplicationConfig = {
+            ...FrontendApplicationConfig.DEFAULT,
+            ...config
+        };
         // eslint-disable-next-line @typescript-eslint/no-explicit-any
         const globalObject = window as any;
         const key = FrontendApplicationConfigProvider.KEY;
-        globalObject[key] = config;
+        globalObject[key] = resolved;
     }
 
     private static doGet(): FrontendApplicationConfig | undefined {

packages/core/src/node/backend-application-config-provider.ts

@@ -28,14 +28,18 @@ export class BackendApplicationConfigProvider {
         return config;
     }
 
-    static set(config: BackendApplicationConfig): void {
+    static set(config: BackendApplicationConfig.Partial): void {
         if (BackendApplicationConfigProvider.doGet() !== undefined) {
             throw new Error('The configuration is already set.');
         }
+        const resolved: BackendApplicationConfig = {
+            ...BackendApplicationConfig.DEFAULT,
+            ...config
+        };
         // eslint-disable-next-line @typescript-eslint/no-explicit-any
         const globalObject = global as any;
         const key = BackendApplicationConfigProvider.KEY;
-        globalObject[key] = config;
+        globalObject[key] = resolved;
     }
 
     private static doGet(): BackendApplicationConfig | undefined {