awk macro: warn about invalid var use in rng forms.

The awk macro abruptly relocates rng forms out of their
apparent scope. Therefore, code like this is wrong:

  (awk ((let ((x t))
          (rng t x))
        (action)))

The rng form is transformed and relocated to a scope in which
the let is not visible. This is a problem worth warning about.

In the above case, there will also be a warning about the
variable x being unbound, which might alerts the programmer
to the problem. However, in cases where there is yet another
binding of x introduced via :let or outside of awk, that
warning wll not occur: the code motion will silently cause
x to refer to the wrong x:

  (awk (:let (x nil))
       ((let ((x t))
          (rng 1 x)) ;; refers to the (x nil) binding!!!
        (action)))

  (let ((x nil))
    (awk ((let ((x t))
            (rng 1 x)) ;; refers to the (x 4) binding!!!
          (action))))

Now there is a warning for this situation.

* share/txr/stdlib/awk.tl (sys:awk-compile-time): New slot,
outer-env.
(sys:awk-expander): Takes an env parameter, which is stored
into the new slot of the awk-compile-time structure.
(sys:awk-code-move-check): New function.
(sys:awk-mac-let): Use sys:expand-with-free-refs to expand
the rng forms, capturing the extra information which enables
the implementation of the warning. The rng variants are
refactored to pass the original form to the sys:rng
expander. This allows the diagnostic to display the original
rng form.
(awk): Parameter e renamed to outer-env, and passed to
sys:awk-expander.

0 files changed, 0 insertions, 0 deletions