Parser treats comma expression as type arguments

[mheiber]

Bug Report

The last line below evaluates to true but is rejected by TS due to < b, c > being parsed as a type parameter list:

const a = 1;
const b = 2;
const c = 3;
const d = 4;
   (a < b, c > (d));  // Error: c refers to a value, but is being used as a type here

Adapted from rust-lang/rfcs#2527 (comment).

Sorry if this issue was known already.

🔎 Search Terms

turbofish
ambiguity
generics
"refers to a value"

🕗 Version & Regression Information

3.5.1 through 4.5.0-beta

This is the behavior in every version I tried, and I reviewed the FAQ for entries about parsing and generics.
3.33 has a slightly different error message.

Note: when using // @ts-check on a JS file the only error is that the left side of the comma expression is unused (good).

⏯ Playground Link

playground

ts-ast-viewer

💻 Code

const a = 1;
const b = 2;
const c = 3;
const d = 4;
   (a < b, c > (d)); 
//  |   |  ^ Error: e refers to a value, but is being used as a type here
//  |   ^ Error: c refers to a value, but is being used as a type here
//  ^ Error: This expression is not callable

🙁 Actual behavior

• Errors:

  • Error: This expression is not callable
  • Error: c refers to a value, but is being used as a type here
  • e refers to a value, but is being used as a type here

• And the AST contains CallExpression

🙂 Expected behavior

• No errors
• The AST contains BinaryExpression with LessThanToken etc. instead of CallExpression.

[whzx5byb]

It seems similar to #33639

[mheiber]

It seems similar to #33639

Looks like a duplicate. Thanks, closing

[MartinJohns]

Is there any legit reason to write code like this?

[mheiber]

Is there any legit reason to write code like this?

Humans no, machines maybe: #36662