492996 - JSParseTrees should be trees

Status: RESOLVED WONTFIX

(Core :: JavaScript Engine, defect, P3)

Description

[Jason Orendorff [:jorendorff]]

+++ This bug was initially created as a clone of Bug #492714 +++

Walking a parse tree should not visit any node more than once.  Currently the syntax

  var {x} = obj;

creates a parse node like,

  let (x = NameDef('x')) Binary(':', x, x)

Using CloneParseTree I could easily change this to

  let (x = NameDef('x'))
    Binary(':', x, NameUse(x))

but this isn't clearly better, as now the definition node x has a spurious use.

I think I'll look up what we do for the rhs of `obj.x` and try doing the same here.

Comment 1

[Brendan Eich [:brendan]]

Srsly, what was I thinking? Hack hack hack.

/be

Comment 2

[Brendan Eich [:brendan]]

Oops, didn't mean to steal this if you wanted it, Jason. Please do assign to yourself if  that's what you meant at the end of comment 0.

/be

Comment 3

[Brendan Eich [:brendan]]

Bug 496134 comment 26 points to infelicitous PN_NAME arity for destructuring shorthands, e.g. var {x} = {x:42}; where PN_NULLARY would be used for the full var {x:x} = {x:42}. Not sure why this was done. Seems worth minimizing if we can.

/be