Automatic Brace Insertion (ABI) is undesirable

TypeScript Version: 3.7-beta

Search Terms: automatic brace insertion ABI syntax error

Code:

function a() {
    "Automatic Brace Insertion! (ABI)";

Expected behavior:

The input is syntactically invalid, so emit should fail regardless of the state of noEmitOnError. Other forms of un-parsable input already do this, e.g. function a(

Actual behavior:

A closing brace is inserted in the emitted JS code.

function a() {
    "Automatic Brace Insertion! (ABI)";
}

This means that users who are not using noEmitOnError are silently having invalid code transformed into valid code. I can confirm this actually happened to someone shipping something to production.

Playground Link: ABI Playground Link

Related Issues: https://github.com/microsoft/TypeScript/issues/34870 , https://github.com/microsoft/TypeScript/issues/34871 , Lazy Twitter report

I would suggest this bug deserves to be fixed based on Design Goal 7 (Preserve runtime behavior of all JavaScript code) and Design Non-Goal 7 (Introduce behaviour that is likely to surprise users).

Tagline: If the braces don't fit, you must not emit.

Commencez par le ABI Playground Link et l’entrée TypeScript minimale présentée dans l’issue, puis comparez son comportement d’emit avec l’exemple lié d’une fonction non terminée. Suivez le traitement de cette entrée malformée par le compilateur et vérifiez que emit n’ajoute pas d’accolade fermante et ne produit pas de JavaScript exécutable.