[racket-dev] expand, local-expand, and syntax-procedure-converted-arguments-property

Hi all,

I'm currently trying to fix the Typed Racket unit tests. I think I've
narrowed down the issue to a certain syntax property for keyword
functions.

The issue is illustrated by the following example:

  #lang racket

  (require racket/file
           (for-syntax racket/file
                       racket/keyword-transform))

  ;; the property is #f
  (begin-for-syntax
   (displayln
     (syntax-case (expand-syntax #'(copy-directory/files 1 2)) ()
       [(let-values (((temp1) _)
                     ((temp2) _))
          (if _
              (#%plain-app1 copy-directory/files15 e1 ...)
              (#%plain-app2 copy-directory/files17 e2 ...)))
        (syntax-procedure-converted-arguments-property #'copy-directory/files15)])))

  ;; property is syntax
  (begin-for-syntax
   (displayln
     (syntax-case (local-expand #'(copy-directory/files 1 2) 'expression null) ()
       [(let-values (((temp1) _)
                     ((temp2) _))
          (if _
              (#%plain-app1 copy-directory/files15 e1 ...)
              (#%plain-app2 copy-directory/files17 e2 ...)))
        (syntax-procedure-converted-arguments-property #'copy-directory/files15)])))

There are two syntax-time computations here. Both are expanding an
application of a keyword function (one with local-expand, one with
expand) and looking at the resulting syntax.

The key point here is that I want to find the property looked up by
`syntax-procedure-converted-arguments-property` on an output identifier
because Typed Racket needs it to type-check the expansion.

Unfortunately, as the comments indicate, only the second piece of code
can find the property. The reason appears to be that the property key is
actually a private `gensym`ed symbol and the two pieces of code appear
to get separate instantiations of the kw.rkt module (perhaps at different
phases).

To check that, if I modify kw.rkt to use a plain symbol, both of the
snippets above return the same property value.

Anyone have any idea how I can keep using `expand` but still be able to
look up the property?

Cheers,
Asumu