Compiler warning for unused local top-level variables

[Ludovic Courtès]

Hello,

With the new ‘-Wunused-toplevel’ the compiler warns about unused
module-local top-level variables [0].

It works well, but has the following limitations:

  - Public variables exported with ‘define-public’, ‘export’, or anything
    other than the ‘#:export’ option of ‘define-module’ is considered
    private, and thus possibly misdiagnosed as unused.

    This is because ‘export’ et al. are only evaluated at run-time, not
    at compile-time, unlike ‘define-module’.  This is something we could
    change, though.

  - Local variables used only by a macro are incorrectly flagged as
    unused.  Example:

          (define (bar) 'foo)
          (define-syntax baz
            (syntax-rules () ((_) (bar))))

    Here ‘bar’ is incorrectly flagged as unused.  This is because the
    definition of ‘baz’ expands to ‘(define baz (make-syntax-transformer
    ...))’ and this code doesn’t contain any literal
    ‘(toplevel-ref bar)’.  Instead, the reference to ‘bar’ is buried in
    an opaque syntax object.

    Andy: any idea how to work around this?

Thanks,
Ludo’.

[0] 
http://git.sv.gnu.org/cgit/guile.git/commit/?id=bcae9a98b0dd82b7be93e90134a01a03b44b4af7