master 949dd41: Fix mistake in switch-case generation of `null` (bug#49746)

[Mattias Engdegård]

branch: master
commit 949dd41c31dab69f7a5067bba324c28bb2cfbf8e
Author: Mattias Engdegård <mattiase@acm.org>
Commit: Mattias Engdegård <mattiase@acm.org>

    Fix mistake in switch-case generation of `null` (bug#49746)
    
    Reported by Gregor Zattler.
    
    * lisp/emacs-lisp/bytecomp.el (byte-compile--cond-switch-prefix):
    Be more careful in the selection of equality.
    * test/lisp/emacs-lisp/bytecomp-tests.el (bytecomp-tests--test-cases):
    Add test case.
---
 lisp/emacs-lisp/bytecomp.el            | 3 ++-
 test/lisp/emacs-lisp/bytecomp-tests.el | 6 ++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index f615006..1b64a06 100644
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -4362,7 +4362,8 @@ Return (TAIL VAR TEST CASES), where:
               (and (or (eq var switch-var) (not switch-var))
                    (progn
                      (setq switch-var var)
-                     (setq switch-test 'eq)
+                     (setq switch-test
+                           (byte-compile--common-test switch-test 'eq))
                      (unless (memq nil keys)
                        (push nil keys)
                        (push (cons (list nil) (or body '(t))) cases))
diff --git a/test/lisp/emacs-lisp/bytecomp-tests.el 
b/test/lisp/emacs-lisp/bytecomp-tests.el
index 7c40f7e..ee0f931 100644
--- a/test/lisp/emacs-lisp/bytecomp-tests.el
+++ b/test/lisp/emacs-lisp/bytecomp-tests.el
@@ -503,6 +503,12 @@
                  (:success 'good))
                (1+ x))))
       (funcall f 3))
+
+    ;; Check `not' in cond switch (bug#49746).
+    (mapcar (lambda (x) (cond ((equal x "a") 1)
+                              ((member x '("b" "c")) 2)
+                              ((not x) 3)))
+            '("a" "b" "c" "d" nil))
     )
   "List of expressions for cross-testing interpreted and compiled code.")