Fixes #188284 - Adds diffEditor.switchSide command

src/vs/editor/browser/widget/diffEditorWidget2/diffEditorWidget2.contribution.ts

@@ -5,8 +5,12 @@
 
 import { Codicon } from 'vs/base/common/codicons';
 import { ThemeIcon } from 'vs/base/common/themables';
-import { ServicesAccessor } from 'vs/editor/browser/editorExtensions';
+import { ICodeEditor } from 'vs/editor/browser/editorBrowser';
+import { EditorAction2, ServicesAccessor } from 'vs/editor/browser/editorExtensions';
+import { findFocusedDiffEditor } from 'vs/editor/browser/widget/diffEditor.contribution';
+import { DiffEditorWidget2 } from 'vs/editor/browser/widget/diffEditorWidget2/diffEditorWidget2';
 import { localize } from 'vs/nls';
+import { ILocalizedString } from 'vs/platform/action/common/action';
 import { Action2, MenuId, MenuRegistry, registerAction2 } from 'vs/platform/actions/common/actions';
 import { IConfigurationService } from 'vs/platform/configuration/common/configuration';
 import { ContextKeyEqualsExpr, ContextKeyExpr } from 'vs/platform/contextkey/common/contextkey';
@@ -88,3 +92,29 @@ MenuRegistry.appendMenuItem(MenuId.EditorTitle, {
 	group: '1_diff',
 	when: ContextKeyEqualsExpr.create('diffEditorVersion', 2)
 });
+
+const diffEditorCategory: ILocalizedString = {
+	value: localize('diffEditor', 'Diff Editor'),
+	original: 'Diff Editor',
+};
+export class SwitchSide extends EditorAction2 {
+	constructor() {
+		super({
+			id: 'diffEditor.switchSide',
+			title: { value: localize('switchSide', "Switch Side"), original: 'Switch Side' },
+			icon: Codicon.arrowSwap,
+			precondition: ContextKeyExpr.and(ContextKeyEqualsExpr.create('diffEditorVersion', 2), ContextKeyExpr.has('isInDiffEditor')),
+			f1: true,
+			category: diffEditorCategory,
+		});
+	}
+
+	runEditorCommand(accessor: ServicesAccessor, editor: ICodeEditor, ...args: unknown[]): void {
+		const diffEditor = findFocusedDiffEditor(accessor);
+		if (diffEditor instanceof DiffEditorWidget2) {
+			diffEditor.switchSide();
+		}
+	}
+}
+
+registerAction2(SwitchSide);

src/vs/editor/browser/widget/diffEditorWidget2/diffEditorWidget2.ts

@@ -44,6 +44,8 @@ import { DiffEditorViewModel, DiffMapping, DiffState } from './diffEditorViewMod
 import { AccessibleDiffViewer } from 'vs/editor/browser/widget/diffEditorWidget2/accessibleDiffViewer';
 import { CursorChangeReason } from 'vs/editor/common/cursorEvents';
 import { AudioCue, IAudioCueService } from 'vs/platform/audioCues/browser/audioCueService';
+import { LengthObj } from 'vs/editor/common/model/bracketPairsTextModelPart/bracketPairsTree/length';
+import { Range } from 'vs/editor/common/core/range';
 
 export class DiffEditorWidget2 extends DelegatingEditor implements IDiffEditor {
 	private readonly elements = h('div.monaco-diff-editor.side-by-side', { style: { position: 'relative', height: '100%' } }, [
@@ -479,6 +481,71 @@ export class DiffEditorWidget2 extends DelegatingEditor implements IDiffEditor {
 		if (!diffModel) { return; }
 		await diffModel.waitForDiff();
 	}
+
+	switchSide(): void {
+		const isModifiedFocus = this._editors.modified.hasWidgetFocus();
+		const source = isModifiedFocus ? this._editors.modified : this._editors.original;
+		const destination = isModifiedFocus ? this._editors.original : this._editors.modified;
+
+		const sourceSelection = source.getSelection();
+		if (sourceSelection) {
+			const mappings = this._diffModel.get()?.diff.get()?.mappings.map(m => isModifiedFocus ? m.lineRangeMapping.flip() : m.lineRangeMapping);
+			if (mappings) {
+				const newRange1 = translatePosition(sourceSelection.getStartPosition(), mappings);
+				const newRange2 = translatePosition(sourceSelection.getEndPosition(), mappings);
+				const range = Range.plusRange(newRange1, newRange2);
+				destination.setSelection(range);
+			}
+		}
+		destination.focus();
+	}
+}
+
+function translatePosition(posInOriginal: Position, mappings: LineRangeMapping[]): Range {
+	const mapping = findLast(mappings, m => m.originalRange.startLineNumber <= posInOriginal.lineNumber);
+	if (!mapping) {
+		// No changes before the position
+		return Range.fromPositions(posInOriginal);
+	}
+
+	if (mapping.originalRange.endLineNumberExclusive <= posInOriginal.lineNumber) {
+		const newLineNumber = posInOriginal.lineNumber - mapping.originalRange.endLineNumberExclusive + mapping.modifiedRange.endLineNumberExclusive;
+		return Range.fromPositions(new Position(newLineNumber, posInOriginal.column));
+	}
+
+	if (!mapping.innerChanges) {
+		// Only for legacy algorithm
+		return Range.fromPositions(new Position(mapping.modifiedRange.startLineNumber, 1));
+	}
+
+	const innerMapping = findLast(mapping.innerChanges, m => m.originalRange.getStartPosition().isBeforeOrEqual(posInOriginal));
+	if (!innerMapping) {
+		const newLineNumber = posInOriginal.lineNumber - mapping.originalRange.startLineNumber + mapping.modifiedRange.startLineNumber;
+		return Range.fromPositions(new Position(newLineNumber, posInOriginal.column));
+	}
+
+	if (innerMapping.originalRange.containsPosition(posInOriginal)) {
+		return innerMapping.modifiedRange;
+	} else {
+		const l = lengthBetweenPositions(innerMapping.originalRange.getEndPosition(), posInOriginal);
+		return Range.fromPositions(addLength(innerMapping.modifiedRange.getEndPosition(), l));
+	}
+}
+
+function lengthBetweenPositions(position1: Position, position2: Position): LengthObj {
+	if (position1.lineNumber === position2.lineNumber) {
+		return new LengthObj(0, position2.column - position1.column);
+	} else {
+		return new LengthObj(position2.lineNumber - position1.lineNumber, position2.column - 1);
+	}
+}
+
+function addLength(position: Position, length: LengthObj): Position {
+	if (length.lineCount === 0) {
+		return new Position(position.lineNumber, position.column + length.columnCount);
+	} else {
+		return new Position(position.lineNumber + length.lineCount, length.columnCount + 1);
+	}
 }
 
 function toLineChanges(state: DiffState): ILineChange[] {