Fix wrong value of `when` and `unless` with empty body (bug#74215)

* lisp/subr.el (when, unless): Return nil when the body is empty.
Reported by Brennan Vincent.
* test/lisp/subr-tests.el (subr-test-when): Add test cases.

(cherry picked from commit 9ee9154247454c18f9f75d0d32592b817d7e977a)

2 files changed, 7 insertions, 3 deletions

diff --git a/lisp/subr.el b/lisp/subr.el
index b849d8d1b16..465795c7555 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -299,7 +299,7 @@ value of last one, or nil if there are none."
   (if body
       (list 'if cond (cons 'progn body))
     (macroexp-warn-and-return (format-message "`when' with empty body")
-                              cond '(empty-body when) t)))
+                              (list 'progn cond nil) '(empty-body when) t)))
 
 (defmacro unless (cond &rest body)
   "If COND yields nil, do BODY, else return nil.
@@ -309,7 +309,7 @@ value of last one, or nil if there are none."
   (if body
       (cons 'if (cons cond (cons nil body)))
     (macroexp-warn-and-return (format-message "`unless' with empty body")
-                              cond '(empty-body unless) t)))
+                              (list 'progn cond nil) '(empty-body unless) t)))
 
 (defsubst subr-primitive-p (object)
   "Return t if OBJECT is a built-in primitive written in C.
diff --git a/test/lisp/subr-tests.el b/test/lisp/subr-tests.el
index 6f28e057342..e12e3c62e0c 100644
--- a/test/lisp/subr-tests.el
+++ b/test/lisp/subr-tests.el
@@ -454,7 +454,11 @@
                    x)))
     (should (= x 2)))
   (should (equal (macroexpand-all '(when a b c d))
-                 '(if a (progn b c d)))))
+                 '(if a (progn b c d))))
+  (with-suppressed-warnings ((empty-body when unless))
+    (should (equal (when t) nil))
+    (should (equal (unless t) nil))
+    (should (equal (unless nil) nil))))
 
 (ert-deftest subr-test-xor ()
   "Test `xor'."