src/vs/workbench/contrib/mergeEditor/browser/commands/commands.ts/mergeEditorCompare
function mergeEditorCompare(editorService: IEditorService, commandService: ICommandService, inputNumber: 1 | 2) {
	const { activeEditorPane } = editorService;
	if (activeEditorPane instanceof MergeEditor) {
		if (!activeEditorPane.model) {
			return;
		}

		const base = activeEditorPane.model.base.uri;
		const input = inputNumber === 1 ? activeEditorPane.model.input1.uri : activeEditorPane.model.input2.uri;

		openDiffEditor(commandService, base, input);
	}
}