Be more allowing when looking for menu-bar items

Don't merge to master.  This is a safe-for-release fix for Bug#50752.

* src/keymap.c (lookup_key_1): Factor out function from
Flookup_key.
(Flookup_key): Be case insensitive when looking for Qmenu_bar
items.  (Bug#50752)

* test/src/keymap-tests.el
(keymap-lookup-key/mixed-case)
(keymap-lookup-key/mixed-case-multibyte): New tests.

etc/NEWS

@@ -4343,6 +4343,14 @@ The new optional "," parameter has been added, and
 ** 'parse-time-string' can now parse ISO 8601 format strings.
 These have a format like "2020-01-15T16:12:21-08:00".
 
+---
+** 'lookup-key' is more allowing when searching for extended menu items.
+When looking for a menu item '[menu-bar Foo-Bar]', first try to find
+an exact match, then look for the lowercased '[menu-bar foo-bar]'.
+It will only try to downcase ASCII characters in the range "A-Z".
+This improves backwards-compatibility when converting menus to use
+'easy-menu-define'.
+
 ---
 ** 'make-network-process', 'make-serial-process' ':coding' behavior change.
 Previously, passing ':coding nil' to either of these functions would

src/keymap.c

@@ -1183,27 +1183,8 @@ remapping in all currently active keymaps.  */)
   return FIXNUMP (command) ? Qnil : command;
 }
 
-/* Value is number if KEY is too long; nil if valid but has no definition.  */
-/* GC is possible in this function.  */
-
-DEFUN ("lookup-key", Flookup_key, Slookup_key, 2, 3, 0,
-       doc: /* Look up key sequence KEY in KEYMAP.  Return the definition.
-A value of nil means undefined.  See doc of `define-key'
-for kinds of definitions.
-
-A number as value means KEY is "too long";
-that is, characters or symbols in it except for the last one
-fail to be a valid sequence of prefix characters in KEYMAP.
-The number is how many characters at the front of KEY
-it takes to reach a non-prefix key.
-KEYMAP can also be a list of keymaps.
-
-Normally, `lookup-key' ignores bindings for t, which act as default
-bindings, used when nothing else in the keymap applies; this makes it
-usable as a general function for probing keymaps.  However, if the
-third optional argument ACCEPT-DEFAULT is non-nil, `lookup-key' will
-recognize the default bindings, just as `read-key-sequence' does.  */)
-  (Lisp_Object keymap, Lisp_Object key, Lisp_Object accept_default)
+static Lisp_Object
+lookup_key_1 (Lisp_Object keymap, Lisp_Object key, Lisp_Object accept_default)
 {
   bool t_ok = !NILP (accept_default);
 
@@ -1243,6 +1224,63 @@ recognize the default bindings, just as `read-key-sequence' does.  */)
     }
 }
 
+/* Value is number if KEY is too long; nil if valid but has no definition.  */
+/* GC is possible in this function.  */
+
+DEFUN ("lookup-key", Flookup_key, Slookup_key, 2, 3, 0,
+       doc: /* Look up key sequence KEY in KEYMAP.  Return the definition.
+A value of nil means undefined.  See doc of `define-key'
+for kinds of definitions.
+
+A number as value means KEY is "too long";
+that is, characters or symbols in it except for the last one
+fail to be a valid sequence of prefix characters in KEYMAP.
+The number is how many characters at the front of KEY
+it takes to reach a non-prefix key.
+KEYMAP can also be a list of keymaps.
+
+Normally, `lookup-key' ignores bindings for t, which act as default
+bindings, used when nothing else in the keymap applies; this makes it
+usable as a general function for probing keymaps.  However, if the
+third optional argument ACCEPT-DEFAULT is non-nil, `lookup-key' will
+recognize the default bindings, just as `read-key-sequence' does.  */)
+  (Lisp_Object keymap, Lisp_Object key, Lisp_Object accept_default)
+{
+  Lisp_Object found = lookup_key_1 (keymap, key, accept_default);
+  if (!NILP (found) && !NUMBERP (found))
+    return found;
+
+  /* Menu definitions might use mixed case symbols (notably in old
+     versions of `easy-menu-define').  We accept this variation for
+     backwards-compatibility.  (Bug#50752)  */
+  ptrdiff_t key_len = ASIZE (key);
+  if (VECTORP (key) && key_len > 0 && EQ (AREF (key, 0), Qmenu_bar))
+    {
+      Lisp_Object new_key = make_vector (key_len, Qnil);
+      for (int i = 0; i < key_len; ++i)
+	{
+	  Lisp_Object sym = Fsymbol_name (AREF (key, i));
+	  USE_SAFE_ALLOCA;
+	  unsigned char *dst = SAFE_ALLOCA (SBYTES (sym) + 1);
+	  memcpy (dst, SSDATA (sym), SBYTES (sym));
+	  /* We can walk the string data byte by byte, because UTF-8
+	     encoding ensures that no other byte of any multibyte
+	     sequence will ever include a 7-bit byte equal to an ASCII
+	     single-byte character.  */
+	  for (int j = 0; j < SBYTES (sym); ++j)
+	    if (dst[j] >= 'A' && dst[j] <= 'Z')
+	      dst[j] += 'a' - 'A';  /* Convert to lower case.  */
+	  ASET (new_key, i, Fintern (make_multibyte_string ((char *) dst,
+							    SCHARS (sym),
+							    SBYTES (sym)),
+				     Qnil));
+	  SAFE_FREE ();
+	}
+      found = lookup_key_1 (keymap, new_key, accept_default);
+    }
+  return found;
+}
+
 /* Make KEYMAP define event C as a keymap (i.e., as a prefix).
    Assume that currently it does not define C at all.
    Return the keymap.  */

test/src/keymap-tests.el

@@ -124,6 +124,16 @@
 ;; (ert-deftest keymap-lookup-key/accept-default ()
 ;;   ...)
 
+(ert-deftest keymap-lookup-key/mixed-case ()
+  "Backwards compatibility behaviour (Bug#50752)."
+  (let ((map (make-keymap)))
+    (define-key map [menu-bar foo bar] 'foo)
+    (should (eq (lookup-key map [menu-bar foo bar]) 'foo))
+    (should (eq (lookup-key map [menu-bar Foo Bar]) 'foo)))
+  (let ((map (make-keymap)))
+    (define-key map [menu-bar i-bar] 'foo)
+    (should (eq (lookup-key map [menu-bar I-bar]) 'foo))))
+
 (ert-deftest describe-buffer-bindings/header-in-current-buffer ()
   "Header should be inserted into the current buffer.
 https://debbugs.gnu.org/39149#31"