May I use a _directory_ as a prerequisite?

[Eric Hanchrow]

I have a script that generates interface bindings by reading header
files.  (It's sort of a crude homemade version of `swig'.)  I want
this script to run not just when any of the files changes, but also
if any of those files _gets deleted_.  So I decided to write a rule
like this:

bindings: $(wildcard $(header_dir)/*.h) $(header_dir)
          ./make-bindings

It seems to work -- that is, the rule runs not only when one of the
header files changes, but also after I delete or add a header file.

The question is: can I depend upon this behavior?  That is, can I
depend upon `make' reading the last-mod time of a directory?  The
documentation doesn't say anything about this; it only refers to
prerequisites as files.

-- 
Always code as if the guy who ends up maintaining your code will
    be a violent psychopath who knows where you live.  John F. Woods