Strange behaviour of subtypep with undefined types

[Syll]

With attached code file :
    (load "code")
    (f)
    (with-compilation-unit () (f))

=> subtypep signals a style-warning after execution of (with-compilation-unit () (f)).
   (but not while loading/compiling the file, calling (f), nor during execution of f itself)

Discussion on this bug (https://bugs.launchpad.net/sbcl/+bug/716819) concluded that subtypep should not signal an error when types don't exist.

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SBCL 2.0.5

[Douglas Katzman (dougk)]

Wrapping a compilation unit around code that you're trying to compile causes the compiler to "notice" that code will possibly be compiled suboptimally if you references types that are unknown.
In your minimal example there is no code that actually causes bad assembly code to be emitted, nor would it necessarily be construed as style-warning-worthy, but that's the effect that the compilation unit has.

But *NOT* wrapping a compilation-unit does *not* ask the compiler to notice such things.

For further details see the handler in
 (defun %with-compilation-unit ...
  (handler-bind ((parse-unknown-type
                   (lambda (c)
                     (note-undefined-reference (parse-unknown-type-specifier c)
                                               :type))))

You may not desire this behavior, but it is what it is.

[Douglas Katzman (dougk)]

(launchpad doesn't have "working as designed" as a status, so I've marked it as "won't fix", but feel free to submit a patch if you feel that there is a better behavior)