Grudgingly accept function values in the function position

* lisp/emacs-lisp/cconv.el (cconv-convert):
Warn about (F ...) where F is a non-symbol function value (bytecode
object etc), but let it pass for compatibility's sake (bug#68931).
* test/lisp/emacs-lisp/bytecomp-tests.el (bytecomp--fun-value-as-head):
New test.

1 files changed, 8 insertions, 4 deletions

diff --git a/lisp/emacs-lisp/cconv.el b/lisp/emacs-lisp/cconv.el
index e210cfdf5ce..4ff47971351 100644
--- a/lisp/emacs-lisp/cconv.el
+++ b/lisp/emacs-lisp/cconv.el
@@ -621,12 +621,16 @@ places where they originally did not directly appear."
        (cconv-convert exp env extend))
 
       (`(,func . ,forms)
-       (if (symbolp func)
+       (if (or (symbolp func) (functionp func))
            ;; First element is function or whatever function-like forms are:
            ;; or, and, if, catch, progn, prog1, while, until
-           `(,func . ,(mapcar (lambda (form)
-                                (cconv-convert form env extend))
-                              forms))
+           (let ((args (mapcar (lambda (form) (cconv-convert form env extend))
+                               forms)))
+             (unless (symbolp func)
+               (byte-compile-warn-x
+                form
+                "Use `funcall' instead of `%s' in the function position" func))
+             `(,func . ,args))
          (byte-compile-warn-x form "Malformed function `%S'" func)
          nil))