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.

Inizia con l’ABI Playground Link e l’input TypeScript minimo mostrato nell’issue, quindi confronta il suo comportamento di emit con l’esempio collegato di una funzione non terminata. Traccia la gestione di questo input malformato da parte del compilatore e verifica che emit non aggiunga una parentesi graffa di chiusura e non produca JavaScript eseguibile.