Warn about too specific type declarations

[Moritz Heidkamp]

The following program produces code that may segfault when compiled with specialization:

(: foo (-> string))

(define (foo) (read))

(print (string-ref (foo) 0))

$ csc -specialize foo.scm
echo '"foo"' | ./foo
f

$ echo 123 | ./foo             

Error: segmentation violation

	Call history:

	baz.scm:5: foo	  
	baz.scm:3: read	  	<--

I think the root cause is that the declared return type of foo is more specific than that of read. Perhaps this could be detected by the scrutinizer and warned about accordingly.

[evhan]

I added this feature, but it produces far too many warnings. Stuff like this:

Note: at toplevel:
  declared type `(procedure chicken.base#error (* #!rest *) noreturn)' of toplevel variable `chicken.base#error' is more specific than inferred type `(procedure chicken.base#error (#!rest) . *)'

Note: at toplevel:
  declared type `(procedure chicken.base#void (#!rest *) undefined)' of toplevel variable `chicken.base#void' is more specific than inferred type `(procedure chicken.base#void (#!rest) *)'

Note: at toplevel:
  declared type `(procedure chicken.base#sleep (fixnum) undefined)' of toplevel variable `chicken.base#sleep' is more specific than inferred type `(procedure chicken.base#sleep (*) *)'

We could add all sorts of rules about whether to issue a warning or not in order to cut down on the noise, but I'm not sure this feature would be worth the added complexity. Plus, we already issue a warning when the types are incompatible, so I'm more inclined to just close this wontfix.