Tolerate invalid identifier syntax errors in list parsing

Search Terms

parser variable name list identifiers

Suggestion

Instead of aborting parsing a list when an invalid identifier is reached, have the parser emit a syntax error but otherwise parsing. In other words: it should successfully parse lists such as variable declarations as if the identifiers were valid, with the one difference of emitting a syntax error that doesn't affect parsing.

Use Cases

Issues such as #11648 and #19352 pop up from situations where the parser attempts to read in a list, such as one of variable declarations, and cannot because an identifier is invalid.

const case = 123;
//    ~~~~ 'case' is not allowed as a variable declaration name.(1389)
//         ~ Variable declaration expected.(1134)
//           ~~~ Variable declaration expected.(1134)

Although #40105 improved the first error message (previously it was also Variable declaration expected.), the underlying issue remains: the parser aborts reading in the list, resulting in an odd error message and surprising emitted JavaScript.

const ;
123;

Examples

Collecting a few examples from the linked issues...

const data = { in: 1 };
const { in } = data;

for (const case of [1, 2, 3]) console.log(case);

const case = 123;

let delete = true;

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

issue では実装ファイルやテストが指定されていません。まず、TypeScript parser で列挙された invalid-identifier のケースを再現し、リストのパースが最初の syntax error をどのように処理するかを追跡してください。完了条件は、parser が identifier エラーを報告しつつ、現在の不正な出力を生成せずに、周囲の宣言またはリストのパースを続行することです。