Make it possible to mark generalized variables as obsolete

* doc/lispref/variables.texi (Adding Generalized Variables):
Document it.

* lisp/emacs-lisp/bytecomp.el (byte-compile-warn-obsolete): Alter
the interface so that it can also be used by generalized variable
warnings.
(byte-compile-function-warn): Adjust caller.
(byte-compile-check-variable): Adjust caller.

* lisp/emacs-lisp/gv.el (gv-get): Warn about obsolete generalized
variables (bug#49730).
(make-obsolete-generalized-variable): New function.

doc/lispref/variables.texi

@@ -2822,6 +2822,16 @@ expression manipulating @var{place} via @var{getter} and @var{setter}.
 
 Consult the source file @file{gv.el} for more details.
 
+@defun make-obsolete-generalized-variable obsolete-name current-name when
+This function makes the byte compiler warn that the generalized
+variable @var{obsolete-name} is obsolete.  If @var{current-name} is a
+symbol, then the warning message says to use @var{current-name}
+instead of @var{obsolete-name}.  If @var{current-name} is a string,
+this is the message.  @var{when} should be a string indicating when
+the variable was first made obsolete (usually a version number
+string).
+@end defun
+
 @cindex CL note---no @code{setf} functions
 @quotation
 @b{Common Lisp note:} Common Lisp defines another way to specify the

etc/NEWS

@@ -2588,6 +2588,11 @@ patcomp.el, pc-mode.el, pc-select.el, s-region.el, and sregex.el.
 
 * Lisp Changes in Emacs 29.1
 
++++
+** New function 'make-obsolete-generalized-variable'.
+This can be used to mark setters used by 'setf' as obsolete, and the
+byte-compiler will then warn about using them.
+
 +++
 ** New functions 'pos-eol' and 'pos-bol'.
 These are like 'line-end-position' and 'line-beginning-position'

lisp/emacs-lisp/byte-run.el

@@ -568,7 +568,6 @@ ACCESS-TYPE if non-nil should specify the kind of access that will trigger
        (purecopy (list current-name access-type when)))
   obsolete-name)
 
-
 (defmacro define-obsolete-variable-alias ( obsolete-name current-name when
                                            &optional docstring)
   "Make OBSOLETE-NAME a variable alias for CURRENT-NAME and mark it obsolete.

lisp/emacs-lisp/bytecomp.el

@@ -1355,16 +1355,22 @@ FORMAT and ARGS are as in `byte-compile-warn'."
   (let ((byte-compile-form-stack (cons arg byte-compile-form-stack)))
     (apply #'byte-compile-warn format args)))
 
-(defun byte-compile-warn-obsolete (symbol)
-  "Warn that SYMBOL (a variable or function) is obsolete."
+(defun byte-compile-warn-obsolete (symbol type)
+  "Warn that SYMBOL (a variable, function or generalized variable) is obsolete.
+TYPE is a string that say which one of these three types it is."
   (when (byte-compile-warning-enabled-p 'obsolete symbol)
-    (let* ((funcp (get symbol 'byte-obsolete-info))
-           (msg (macroexp--obsolete-warning
-                 symbol
-                 (or funcp (get symbol 'byte-obsolete-variable))
-                 (if funcp "function" "variable"))))
-      (unless (and funcp (memq symbol byte-compile-not-obsolete-funcs))
-	(byte-compile-warn-x symbol "%s" msg)))))
+    (byte-compile-warn-x
+     symbol "%s"
+     (macroexp--obsolete-warning
+      symbol
+      (pcase type
+        ("function"
+         (get symbol 'byte-obsolete-info))
+        ("variable"
+         (get symbol 'byte-obsolete-variable))
+        ("generalized variable"
+         (get symbol 'byte-obsolete-generalized-variable)))
+      type))))
 
 (defun byte-compile-report-error (error-info &optional fill)
   "Report Lisp error in compilation.
@@ -1468,8 +1474,8 @@ when printing the error message."
 
 (defun byte-compile-function-warn (f nargs def)
   (when (and (get f 'byte-obsolete-info)
-             (byte-compile-warning-enabled-p 'obsolete f))
-    (byte-compile-warn-obsolete f))
+             (not (memq f byte-compile-not-obsolete-funcs)))
+    (byte-compile-warn-obsolete f "function"))
 
   ;; Check to see if the function will be available at runtime
   ;; and/or remember its arity if it's unknown.
@@ -3604,7 +3610,7 @@ lambda-expression."
                   ('set (not (eq access-type 'reference)))
                   ('get (eq access-type 'reference))
                   (_ t))))
-	 (byte-compile-warn-obsolete var))))
+	 (byte-compile-warn-obsolete var "variable"))))
 
 (defsubst byte-compile-dynamic-variable-op (base-op var)
   (let ((tmp (assq var byte-compile-variables)))

lisp/emacs-lisp/gv.el

@@ -92,6 +92,9 @@ DO must return an Elisp expression."
    (t
     (let* ((head (car place))
            (gf (function-get head 'gv-expander 'autoload)))
+      (when (and (symbolp head)
+                 (get head 'byte-obsolete-generalized-variable))
+        (byte-compile-warn-obsolete head "generalized variable"))
       (if gf (apply gf do (cdr place))
         (let ((me (macroexpand-1 place
                                  ;; (append macroexpand-all-environment
@@ -616,6 +619,18 @@ REF must have been previously obtained with `gv-ref'."
 
 ;;; Generalized variables.
 
+(defun make-obsolete-generalized-variable (obsolete-name current-name when)
+  "Make byte-compiler warn that generalized variable OBSOLETE-NAME is obsolete.
+The warning will say that CURRENT-NAME should be used instead.
+
+If CURRENT-NAME is a string, that is the `use instead' message.
+
+WHEN should be a string indicating when the variable was first
+made obsolete, for example a date or a release number."
+  (put obsolete-name 'byte-obsolete-generalized-variable
+       (purecopy (list current-name when)))
+  obsolete-name)
+
 ;; Some Emacs-related place types.
 (gv-define-simple-setter buffer-file-name set-visited-file-name t)
 (gv-define-setter buffer-modified-p (flag &optional buf)