master b9e8474a447 3/4: Repair miscompilation of single-arg `apply` (bug#69533)

[Mattias Engdegård]

branch: master
commit b9e8474a4470f71c30a4b89651fd3c5f2ef92ba2
Author: Mattias Engdegård <mattiase@acm.org>
Commit: Mattias Engdegård <mattiase@acm.org>

    Repair miscompilation of single-arg `apply` (bug#69533)
    
    * lisp/emacs-lisp/byte-opt.el (byte-optimize-apply):
    Don't optimise single-argument `apply`; it's a legacy construct.
    * test/lisp/emacs-lisp/bytecomp-tests.el (bytecomp-tests--test-cases):
    Add test case.
---
 lisp/emacs-lisp/byte-opt.el            | 3 ++-
 test/lisp/emacs-lisp/bytecomp-tests.el | 3 +++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/lisp/emacs-lisp/byte-opt.el b/lisp/emacs-lisp/byte-opt.el
index add13a5c312..f75be3f71ad 100644
--- a/lisp/emacs-lisp/byte-opt.el
+++ b/lisp/emacs-lisp/byte-opt.el
@@ -1448,7 +1448,8 @@ See Info node `(elisp) Integer Basics'."
 
 (defun byte-optimize-apply (form)
   (let ((len (length form)))
-    (if (>= len 2)
+    ;; Single-arg `apply' is an abomination that we don't bother optimizing.
+    (if (> len 2)
         (let ((fn (nth 1 form))
              (last (nth (1- len) form)))
           (cond
diff --git a/test/lisp/emacs-lisp/bytecomp-tests.el 
b/test/lisp/emacs-lisp/bytecomp-tests.el
index 8ccac492141..26408e8685a 100644
--- a/test/lisp/emacs-lisp/bytecomp-tests.el
+++ b/test/lisp/emacs-lisp/bytecomp-tests.el
@@ -800,6 +800,9 @@ inner loops respectively."
     ;; Aristotelian identity optimization
     (let ((x (bytecomp-test-identity 1)))
       (list (eq x x) (eql x x) (equal x x)))
+
+    ;; Legacy single-arg `apply' call
+    (apply '(* 2 3))
     )
   "List of expressions for cross-testing interpreted and compiled code.")