Fixes #46455: Restore logical viewport when edits occur in another editor

src/vs/editor/browser/view/viewImpl.ts

@@ -321,6 +321,7 @@ export class View extends ViewEventHandler {
 	}
 	public onFocusChanged(e: viewEvents.ViewFocusChangedEvent): boolean {
 		this.domNode.setClassName(this.getEditorClassName());
+		this._context.model.setHasFocus(e.isFocused);
 		if (e.isFocused) {
 			this.outgoingEvents.emitViewFocusGained();
 		} else {

src/vs/editor/common/model.ts

@@ -1067,6 +1067,12 @@ export interface ITextModel {
 	 * @internal
 	 */
 	isAttachedToEditor(): boolean;
+
+	/**
+	 * Returns the count of editors this model is attached to.
+	 * @internal
+	 */
+	getAttachedEditorCount(): number;
 }
 
 /**

src/vs/editor/common/model/textModel.ts

@@ -551,6 +551,10 @@ export class TextModel extends Disposable implements model.ITextModel {
 		return this._attachedEditorCount > 0;
 	}
 
+	public getAttachedEditorCount(): number {
+		return this._attachedEditorCount;
+	}
+
 	public isTooLargeForHavingARichMode(): boolean {
 		return this._shouldSimplifyMode;
 	}

src/vs/editor/common/viewModel/viewModel.ts

@@ -122,6 +122,7 @@ export interface IViewModel {
 	 * Gives a hint that a lot of requests are about to come in for these line numbers.
 	 */
 	setViewport(startLineNumber: number, endLineNumber: number, centeredLineNumber: number): void;
+	setHasFocus(hasFocus: boolean): void;
 
 	getDecorationsInViewport(visibleRange: Range): ViewModelDecoration[];
 	getViewLineRenderingData(visibleRange: Range, lineNumber: number): ViewLineRenderingData;

src/vs/editor/common/viewModel/viewModelImpl.ts

@@ -23,7 +23,7 @@ import { Color } from 'vs/base/common/color';
 import { IDisposable } from 'vs/base/common/lifecycle';
 import { ITheme } from 'vs/platform/theme/common/themeService';
 import { ModelDecorationOverviewRulerOptions } from 'vs/editor/common/model/textModel';
-import { ITextModel, EndOfLinePreference } from 'vs/editor/common/model';
+import { ITextModel, EndOfLinePreference, TrackedRangeStickiness } from 'vs/editor/common/model';
 
 const USE_IDENTITY_LINES_COLLECTION = true;
 
@@ -32,6 +32,9 @@ export class ViewModel extends viewEvents.ViewEventEmitter implements IViewModel
 	private readonly editorId: number;
 	private readonly configuration: editorCommon.IConfiguration;
 	private readonly model: ITextModel;
+	private hasFocus: boolean;
+	private viewportStartLineTrackedRange: string;
+	private viewportStartLineTop: number;
 	private readonly lines: IViewModelLinesCollection;
 	public readonly coordinatesConverter: ICoordinatesConverter;
 	public readonly viewLayout: ViewLayout;
@@ -46,6 +49,9 @@ export class ViewModel extends viewEvents.ViewEventEmitter implements IViewModel
 		this.editorId = editorId;
 		this.configuration = configuration;
 		this.model = model;
+		this.hasFocus = false;
+		this.viewportStartLineTrackedRange = null;
+		this.viewportStartLineTop = 0;
 
 		if (USE_IDENTITY_LINES_COLLECTION && this.model.isTooLargeForTokenization()) {
 
@@ -114,6 +120,11 @@ export class ViewModel extends viewEvents.ViewEventEmitter implements IViewModel
 		super.dispose();
 		this.decorations.dispose();
 		this.lines.dispose();
+		this.viewportStartLineTrackedRange = this.model._setTrackedRange(this.viewportStartLineTrackedRange, null, TrackedRangeStickiness.NeverGrowsWhenTypingAtEdges);
+	}
+
+	public setHasFocus(hasFocus: boolean): void {
+		this.hasFocus = hasFocus;
 	}
 
 	private _onConfigurationChanged(eventsCollector: viewEvents.ViewEventsCollector, e: IConfigurationChangedEvent): void {
@@ -238,6 +249,16 @@ export class ViewModel extends viewEvents.ViewEventEmitter implements IViewModel
 			// Update the configuration and reset the centered view line
 			this._centeredViewLine = -1;
 			this.configuration.setMaxLineNumber(this.model.getLineCount());
+
+			// Recover viewport
+			if (!this.hasFocus && this.model.getAttachedEditorCount() >= 2 && this.viewportStartLineTrackedRange) {
+				const modelRange = this.model._getTrackedRange(this.viewportStartLineTrackedRange);
+				if (modelRange) {
+					const viewPosition = this.coordinatesConverter.convertModelPositionToViewPosition(modelRange.getStartPosition());
+					const viewPositionTop = this.viewLayout.getVerticalOffsetForLineNumber(viewPosition.lineNumber);
+					this.viewLayout.deltaScrollNow(0, viewPositionTop - this.viewportStartLineTop);
+				}
+			}
 		}));
 
 		this._register(this.model.onDidChangeTokens((e) => {
@@ -402,6 +423,10 @@ export class ViewModel extends viewEvents.ViewEventEmitter implements IViewModel
 	public setViewport(startLineNumber: number, endLineNumber: number, centeredLineNumber: number): void {
 		this._centeredViewLine = centeredLineNumber;
 		this.lines.warmUpLookupCache(startLineNumber, endLineNumber);
+
+		let position = this.coordinatesConverter.convertViewPositionToModelPosition(new Position(startLineNumber, this.getLineMinColumn(startLineNumber)));
+		this.viewportStartLineTrackedRange = this.model._setTrackedRange(this.viewportStartLineTrackedRange, new Range(position.lineNumber, position.column, position.lineNumber, position.column), TrackedRangeStickiness.NeverGrowsWhenTypingAtEdges);
+		this.viewportStartLineTop = this.viewLayout.getVerticalOffsetForLineNumber(startLineNumber);
 	}
 
 	public getLinesIndentGuides(startLineNumber: number, endLineNumber: number): number[] {