src/vs/workbench/services/editor/browser/editorResolverService.ts/EditorResolverService/doResolveSideBySideEditor
class EditorResolverService:	private async doResolveSideBySideEditor(editor: IResourceSideBySideEditorInput, preferredGroup: PreferredGroup | undefined): Promise<ResolvedEditor> {
		const primaryResolvedEditor = await this.resolveEditor(editor.primary, preferredGroup);
		if (!isEditorInputWithOptionsAndGroup(primaryResolvedEditor)) {
			return ResolvedStatus.NONE;
		}
		const secondaryResolvedEditor = await this.resolveEditor(editor.secondary, primaryResolvedEditor.group ?? preferredGroup);
		if (!isEditorInputWithOptionsAndGroup(secondaryResolvedEditor)) {
			return ResolvedStatus.NONE;
		}
		return {
			group: primaryResolvedEditor.group ?? secondaryResolvedEditor.group,
			editor: this.instantiationService.createInstance(SideBySideEditorInput, editor.label, editor.description, secondaryResolvedEditor.editor, primaryResolvedEditor.editor),
			options: editor.options
		};
	}