Allows editor options to override how new config updates are applied.

src/vs/editor/common/config/commonEditorConfig.ts

@@ -112,12 +112,15 @@ class EditorConfiguration2 {
 	}
 
 	private static _deepEquals<T>(a: T, b: T): boolean {
-		if (typeof a !== 'object' || typeof b !== 'object') {
-			return (a === b);
+		if (typeof a !== 'object' || typeof b !== 'object' || !a || !b) {
+			return a === b;
 		}
 		if (Array.isArray(a) || Array.isArray(b)) {
 			return (Array.isArray(a) && Array.isArray(b) ? arrays.equals(a, b) : false);
 		}
+		if (Object.keys(a).length !== Object.keys(b).length) {
+			return false;
+		}
 		for (let key in a) {
 			if (!EditorConfiguration2._deepEquals(a[key], b[key])) {
 				return false;
@@ -138,6 +141,22 @@ class EditorConfiguration2 {
 		}
 		return (somethingChanged ? new ConfigurationChangedEvent(result) : null);
 	}
+
+	/**
+	 * Returns true if something changed.
+	 * Modifies `options`.
+	*/
+	public static applyUpdate(options: IEditorOptions, update: Readonly<IEditorOptions>): boolean {
+		let changed = false;
+		for (const editorOption of editorOptionsRegistry) {
+			if (update.hasOwnProperty(editorOption.name)) {
+				const result = editorOption.applyUpdate((options as any)[editorOption.name], (update as any)[editorOption.name]);
+				(options as any)[editorOption.name] = result.newValue;
+				changed = changed || result.didChange;
+			}
+		}
+		return changed;
+	}
 }
 
 /**
@@ -382,43 +401,17 @@ export abstract class CommonEditorConfiguration extends Disposable implements IC
 		return EditorConfiguration2.computeOptions(this._validatedOptions, env);
 	}
 
-	private static _subsetEquals(base: { [key: string]: any }, subset: { [key: string]: any }): boolean {
-		for (const key in subset) {
-			if (hasOwnProperty.call(subset, key)) {
-				const subsetValue = subset[key];
-				const baseValue = base[key];
-
-				if (baseValue === subsetValue) {
-					continue;
-				}
-				if (Array.isArray(baseValue) && Array.isArray(subsetValue)) {
-					if (!arrays.equals(baseValue, subsetValue)) {
-						return false;
-					}
-					continue;
-				}
-				if (baseValue && typeof baseValue === 'object' && subsetValue && typeof subsetValue === 'object') {
-					if (!this._subsetEquals(baseValue, subsetValue)) {
-						return false;
-					}
-					continue;
-				}
-
-				return false;
-			}
-		}
-		return true;
-	}
-
 	public updateOptions(_newOptions: Readonly<IEditorOptions>): void {
 		if (typeof _newOptions === 'undefined') {
 			return;
 		}
 		const newOptions = deepCloneAndMigrateOptions(_newOptions);
-		if (CommonEditorConfiguration._subsetEquals(this._rawOptions, newOptions)) {
+
+		const didChange = EditorConfiguration2.applyUpdate(this._rawOptions, newOptions);
+		if (!didChange) {
 			return;
 		}
-		this._rawOptions = objects.mixin(this._rawOptions, newOptions || {});
+
 		this._readOptions = EditorConfiguration2.readOptions(this._rawOptions);
 		this._validatedOptions = EditorConfiguration2.validateOptions(this._readOptions);
 

src/vs/editor/common/config/editorOptions.ts

@@ -12,6 +12,8 @@ import { USUAL_WORD_SEPARATORS } from 'vs/editor/common/model/wordHelper';
 import { AccessibilitySupport } from 'vs/platform/accessibility/common/accessibility';
 import { IConfigurationPropertySchema } from 'vs/platform/configuration/common/configurationRegistry';
 import { IJSONSchema } from 'vs/base/common/jsonSchema';
+import * as arrays from 'vs/base/common/arrays';
+import * as objects from 'vs/base/common/objects';
 
 //#region typed options
 
@@ -806,6 +808,11 @@ export interface IEditorOption<K1 extends EditorOption, V> {
 	 * @internal
 	 */
 	compute(env: IEnvironmentalOptions, options: IComputedEditorOptions, value: V): V;
+
+	/**
+	 * Might modify `value`.
+	*/
+	applyUpdate(value: V, update: V): ApplyUpdateResult<V>;
 }
 
 type PossibleKeyName0<V> = { [K in keyof IEditorOptions]: IEditorOptions[K] extends V | undefined ? K : never }[keyof IEditorOptions];
@@ -828,6 +835,10 @@ abstract class BaseEditorOption<K1 extends EditorOption, V> implements IEditorOp
 		this.schema = schema;
 	}
 
+	public applyUpdate(value: V, update: V): ApplyUpdateResult<V> {
+		return applyUpdate(value, update);
+	}
+
 	public abstract validate(input: any): V;
 
 	public compute(env: IEnvironmentalOptions, options: IComputedEditorOptions, value: V): V {
@@ -835,6 +846,34 @@ abstract class BaseEditorOption<K1 extends EditorOption, V> implements IEditorOp
 	}
 }
 
+export class ApplyUpdateResult<T> {
+	constructor(
+		public readonly newValue: T,
+		public readonly didChange: boolean
+	) { }
+}
+
+function applyUpdate<T>(value: T, update: T): ApplyUpdateResult<T> {
+	if (typeof value !== 'object' || typeof update !== 'object') {
+		return new ApplyUpdateResult(update, value === update);
+	}
+	if (Array.isArray(value) || Array.isArray(update)) {
+		const arrayEquals = Array.isArray(value) && Array.isArray(update) && arrays.equals(value, update);
+		return new ApplyUpdateResult(update, arrayEquals);
+	}
+	let didChange = false;
+	for (let key in update) {
+		if ((value as T & object).hasOwnProperty(key)) {
+			const result = applyUpdate(value[key], update[key]);
+			if (result.didChange) {
+				value[key] = result.newValue;
+				didChange = true;
+			}
+		}
+	}
+	return new ApplyUpdateResult(value, didChange);
+}
+
 /**
  * @internal
  */
@@ -853,6 +892,10 @@ abstract class ComputedEditorOption<K1 extends EditorOption, V> implements IEdit
 		this.deps = deps;
 	}
 
+	public applyUpdate(value: V, update: V): ApplyUpdateResult<V> {
+		return applyUpdate(value, update);
+	}
+
 	public validate(input: any): V {
 		return this.defaultValue;
 	}
@@ -874,6 +917,10 @@ class SimpleEditorOption<K1 extends EditorOption, V> implements IEditorOption<K1
 		this.schema = schema;
 	}
 
+	public applyUpdate(value: V, update: V): ApplyUpdateResult<V> {
+		return applyUpdate(value, update);
+	}
+
 	public validate(input: any): V {
 		if (typeof input === 'undefined') {
 			return this.defaultValue;

src/vs/editor/standalone/browser/standaloneEditor.ts

@@ -10,7 +10,7 @@ import { ICodeEditor } from 'vs/editor/browser/editorBrowser';
 import { ICodeEditorService } from 'vs/editor/browser/services/codeEditorService';
 import { OpenerService } from 'vs/editor/browser/services/openerService';
 import { DiffNavigator, IDiffNavigator } from 'vs/editor/browser/widget/diffNavigator';
-import { EditorOptions, ConfigurationChangedEvent } from 'vs/editor/common/config/editorOptions';
+import { EditorOptions, ConfigurationChangedEvent, ApplyUpdateResult } from 'vs/editor/common/config/editorOptions';
 import { BareFontInfo, FontInfo } from 'vs/editor/common/config/fontInfo';
 import { Token } from 'vs/editor/common/core/token';
 import { IEditor, EditorType } from 'vs/editor/common/editorCommon';
@@ -393,6 +393,7 @@ export function createMonacoEditorAPI(): typeof monaco.editor {
 		FontInfo: <any>FontInfo,
 		TextModelResolvedOptions: <any>TextModelResolvedOptions,
 		FindMatch: <any>FindMatch,
+		ApplyUpdateResult: <any>ApplyUpdateResult,
 
 		// vars
 		EditorType: EditorType,

src/vs/monaco.d.ts

@@ -3378,6 +3378,16 @@ declare namespace monaco.editor {
 		readonly id: K1;
 		readonly name: string;
 		defaultValue: V;
+		/**
+		 * Might modify `value`.
+		*/
+		applyUpdate(value: V, update: V): ApplyUpdateResult<V>;
+	}
+
+	export class ApplyUpdateResult<T> {
+		readonly newValue: T;
+		readonly didChange: boolean;
+		constructor(newValue: T, didChange: boolean);
 	}
 
 	/**