AST of import declaration without attributes

[sosukesuzuki]

The following AST is defined for import attributes:

extend interface ImportDeclaration {
    attributes: [ ImportAttribute ];
}

This means import foo from "mod"; and import foo from "mod" with {}; have the same AST.

This isn't good for implementing code formatters. For example, Prettier's implementation reads the original text of the input to print attributes( https://github.com/prettier/prettier/blob/f5e339351e792cea0e8a6b111b336d5efa6441ea/src/language-js/print/module.js#L251-L272 ).

So I propose representing attributes as an empty array in import foo from "mod" with {}; and as null in import foo from "mod";.

What do you think?

[bradzacher]

One point against doing this is that the import specifiers follow the same pattern - the array is always defined, regardless of the presence of the braces. So keeping it like this is standardised with that, at least, for better or worse.

Another point against this is that there are already implementations of the current spec. Things can change though and (AFAIK) acorn/eslint don't have support yet.

[sosukesuzuki]

One point against doing this is that the import specifiers follow the same pattern - the array is always defined, regardless of the presence of the braces. So keeping it like this is standardised with that, at least, for better or worse.

Yes, Prettier actually determines whether to print {} for import specifiers in the same way ( https://github.com/prettier/prettier/blob/6db66c53d948d0a70dbc7abfa3f7d6f01f544242/src/language-js/print/module.js#L233-L249 ). If it's still possible to change the spec at this point, as someone implementing a code formatter, I would appreciate it if the import specifiers for import {} from "mod"; and import "mod"; could be distinguished as an empty array and null.

Another point against this is that there are already implementations of the current spec. Things can change though and (AFAIK) acorn/eslint don't have support yet.

Since import attributes is still stage 3 syntax, I think we can still be able to change the estree spec.

[sosukesuzuki]

@JLHwung What do you think?

[JLHwung]

I agree with @bradzacher, like he said the import specifiers follows the always-array pattern even if the empty braces {} are optional in the syntax.

This rule is not limited to empty braces. For example ESTree does not differentiate new A with new A() as both of them provide an empty arguments array. In this case, Prettier formats new A into new A(). Can prettier prefer import foo from "foo" over import foo from "foo" with {}?

[nzakas]

Agree with @bradzacher and @JLHwung here. ESTree is an abstract syntax tree, which necessarily means that not every token is represented, but rather, the meaning of the syntax is represented. I think the meaning is properly conveyed with the empty array.