src/vs/editor/common/languages/autoIndent.ts/getIndentMetadata
export function getIndentMetadata(
	model: ITextModel,
	lineNumber: number,
	languageConfigurationService: ILanguageConfigurationService
): number | null {
	const indentRulesSupport = languageConfigurationService.getLanguageConfiguration(model.getLanguageId()).indentRulesSupport;
	if (!indentRulesSupport) {
		return null;
	}
	if (lineNumber < 1 || lineNumber > model.getLineCount()) {
		return null;
	}
	return indentRulesSupport.getIndentMetadata(model.getLineContent(lineNumber));
}