Need control over trivia when replacing nodes

[amcasey]

Consider the following code:

// a
var q = /*b*/ //c
    /*d*/ 1 /*e*/ //f
    /*g*/ + /*h*/ //i
    /*j*/ 2 /*k*/ //l
    /*m*/; /*n*/ //o

Suppose we extract the range from 1 to 2 (inclusive) into a separate function. We would like comments e-j to move to the new function and the others to remain where they are:

// a
var q = /*b*/ //c
    /*d*/ newFunction() /*k*/ //l
    /*m*/; /*n*/ //o

function newFunction() {
    return 1 /*e*/ //f
    /*g*/ + /*h*/ //i
    /*j*/ 2;
}

Presently, there doesn't seem to be a way to express this. We can cause the leading and trailing trivia to remain at the call site by replacing a range ({pos: expr.getStart(), end: expr.end}), rather than a node (expr), but there doesn't seem to be a way to strip the leading and trailing trivia in the body of the extracted function.

[amcasey]

FYI Mohamed Hegazy (@mhegazy) Nathan Shively-Sanders (@sandersn)

[amcasey]

We think the solution is to introduce a clone function that replaces the leftmost token of a node and re-spines accordingly (roughly "left deep-clone").

[amcasey]

That didn't work because (a) the trailing trivia of the leftmost token was also dropped and (b) the trailing trivia of the rightmost token was not dropped.

[amcasey]

I have a PR prepared, but I'd like to build it on top of #18997, so it's on hold for now.