sbcl - Incorrect arglist returned on low debug levels

[Zulu-Inuoe]

On SBCL 2.0.9:

(trivial-arguments:arglist (locally (declare (optimize (debug 0)))
                             (lambda (x y z) (+ x y z))))

returns nil, whereas upping debug:

(trivial-arguments:arglist (locally (declare (optimize (debug 3)))
                             (lambda (x y z) (+ x y z))))

gives me the expected result of (x y z)

I would instead expect :unknown, in order to detect that the lambda list couldn't be determined

[phoe]

I asked on #sbcl whether there is a way to tell whether the value returned by sb-introspect:function-lambda-list is NIL because the information was not saved from the situation where the lambda list is an empty list.

[Shinmera]

I don't believe SBCL gives us any way to distinguish the two.

[phoe]

Submitted upstream to https://bugs.launchpad.net/sbcl/+bug/1901781

[snuglas]

You may want to add your thoughts to https://groups.google.com/g/sbcl-devel/c/bCqU3TYyqxo/m/0YWwfkyoBQAJ which has attracted some criticism. I think I'll make sb-introspect return NIL for :UNKNOWN, but suggest to you that sb-kernel:%fun-lambda-list be used to detect the actual unknown case. The issue was internally we could not detect unknown, and now we can.

[Zulu-Inuoe]

@snuglas you may want to hold on that, as that change has been reverted partially and is still pending impl details.

Regardless you likely want to wait until the new SBCL version is officially out

[stassats]

I made it return two values, as using the internal sb-kernel:%fun-lambda-list is not a great idea.

[Zulu-Inuoe]

Oh oops. I misread what you suggested. I thought you'd be updating trivial-arguments to return nil rather than :unknown. Disregard