Span for reserved keywords

[magic-akari]

Is it worth saving span for reserved keywords?

I found this issue when I was investigating the comments of export default.

Input

/*1*/ export /*2*/ default /*3*/ function /*4*/ foo /*5*/() /*6*/ {} /*7*/

SWC

/*1*/ export default /*3*/ function /*4*/ foo() /*6*/ {}; /*7*/

Babel

/*1*/
export default
/*3*/
function
/*4*/
foo
/*5*/
()
/*6*/
{}
/*7*/

tsc

/*1*/ export /*2*/ default /*3*/ function foo /*5*/() { } /*7*/

Rome

/*1*/ export /*2*/ default /*3*/ function /*4*/ foo /*5*/ () /*6*/ {} /*7*/

What the Rome tool shows is the clearest, and you can see directly that it stores information about the default keyword in the AST.

If we expect the comments surrounding the keywords to be output, then we would have to store some additional span information.

Is this worth it?

And I found more unit test cases in tsc repo. For example

/*a*/ do /*b*/ {} /*c*/ while /*d*/ ( /*e*/ true /*f*/ );

The comments around the while are lost in SWC output.

---

Note: esbuild always drops comments for performance concern.

[kdy1]

Maybe? I considered changing bools to Option<Span> at the past but I forgot about it