import<T> is valid syntax in nightly

[evanw]

Bug Report

Context: I'm trying to figure out how to update esbuild to handle the latest ASI-related behavior changes that just landed (#48755 and #48659). In the process, I discovered this weird TypeScript behavior that I believe was an oversight. I assume #47607 introduced the regression since it landed around the same time.

I tried to dig through code history to understand this better. It looks like isStartOfLeftHandSideExpression allows < after import due to #16544, although no tests were added for import followed by < in that PR. So I'm assuming TypeScript only allows < after import for parser recovery, which I don't need to support in esbuild.

🔎 Search Terms

regression import expression type parameters missing arguments

🕗 Version & Regression Information

• This changed between versions 4.7.0-dev.20220216 and 4.7.0-dev.20220217

⏯ Playground Link

Playground link with relevant code

💻 Code

import<T>;
let foo = import<foo, bar>;

🙁 Actual behavior

The nightly TypeScript compiler converts the above TypeScript code into the following JavaScript without any errors:

"use strict";
import;
let foo = (import);

🙂 Expected behavior

I either expected the TypeScript compiler to consider this invalid syntax, or if it's valid syntax I expected it to give type errors for the missing type names.

[fatcerberus]

4.6.2 produces this error for a dynamic import with type arguments:

Dynamic import cannot have type arguments.

let foo = import; is also not valid JS, so this definitely looks like an oversight.

[DanielRosenwasser]

Thanks @a-tarasyuk!