Question: Should this be parse error?

[fisker]

I was working on Prettier to make tests run both flow and babel-flow parser prettier/prettier#14245, and found an edge case.

flow/tests/generics/generics.js

Line 40 in f87d5bf

var fn2 : function<string> = function() { return 'foo'; } // error, arity 0

flow can parse function as identifier, but babel can't, and I found other keywords like class/while can't be used there.

Should it be valid or invalid?

[gkz]

I found it surprising and weird that function (lowercase) can be used as a type. Support for this was added when support for the Function type was added, back in 2015, but I am not aware of anyone actually using this (or even being aware of this). I would be happy to remove support for this and make this an error.

For now feel free to delete this test case from Prettier.

[fisker]

Thanks for the explanation, feel free to close if it not worth to fix.

[gkz]

I have a diff in progress to make it an error, just needs to be reviewed (internally)