Add static-when, static-unless like static-if

* lisp/subr.el (static-when, static-unless): define
* doc/lispref/control.texi (Conditional Compilation): document
* etc/NEWS: mention

doc/lispref/control.texi

@@ -2841,6 +2841,19 @@ Test @var{condition} at macro-expansion time.  If its value is
 non-@code{nil}, expand the macro to @var{then-form}, otherwise expand
 it to @var{else-forms} enclosed in a @code{progn}.  @var{else-forms}
 may be empty.
+@end defmac
+
+@defmac static-when condition body...
+Test @var{condition} at macro-expansion time.  If its value is
+non-@code{nil}, expand the macro to evaluate all @var{body} forms
+sequentially and return the value of the last one, or @code{nil} if there
+are none.
+@end defmac
+
+@defmac static-unless condition body...
+Test @var{condition} at macro-expansion time.  If its value is @code{nil},
+expand the macro to evaluate all @var{body} forms sequentially and return
+the value of the last one, or @code{nil} if there are none.
 
 Here is an example of its use from CC Mode, which prevents a
 @code{defadvice} form being compiled in newer versions of Emacs:

etc/NEWS

@@ -1507,6 +1507,12 @@ Previously, its argument was always evaluated using dynamic binding.
 
 * Lisp Changes in Emacs 31.1
 
++++
+** New macros 'static-when' and 'static-unless' implement conditional
+compilation like 'static-if'.
+These macros evaluate their condition at macro-expansion time and are useful
+for writing code that can work across different Emacs versions.
+
 ---
 ** You can change the default value of 'lexical-binding'.
 While the default is still the use dynamic binding dialect of ELisp

lisp/subr.el

@@ -301,6 +301,19 @@ value of last one, or nil if there are none."
     (macroexp-warn-and-return (format-message "`when' with empty body")
                               (list 'progn cond nil) '(empty-body when) t)))
 
+(defmacro static-when (condition &rest body)
+  "A conditional compilation macro.
+Evaluate CONDITION at macro-expansion time.  If it is non-nil,
+expand the macro to evaluate all BODY forms sequentially and return
+the value of the last one, or nil if there are none."
+  (declare (indent 1) (debug t))
+  (if body
+      (if (eval condition lexical-binding)
+          (cons 'progn body)
+        nil)
+    (macroexp-warn-and-return (format-message "`static-when' with empty body")
+                              (list 'progn nil nil) '(empty-body static-when) t)))
+
 (defmacro unless (cond &rest body)
   "If COND yields nil, do BODY, else return nil.
 When COND yields nil, eval BODY forms sequentially and return
@@ -311,6 +324,19 @@ value of last one, or nil if there are none."
     (macroexp-warn-and-return (format-message "`unless' with empty body")
                               (list 'progn cond nil) '(empty-body unless) t)))
 
+(defmacro static-unless (condition &rest body)
+  "A conditional compilation macro.
+Evaluate CONDITION at macro-expansion time.  If it is nil,
+expand the macro to evaluate all BODY forms sequentially and return
+the value of the last one, or nil if there are none."
+  (declare (indent 1) (debug t))
+  (if body
+      (if (eval condition lexical-binding)
+          nil
+        (cons 'progn body))
+    (macroexp-warn-and-return (format-message "`static-unless' with empty body")
+                              (list 'progn nil nil) '(empty-body static-unless) t)))
+
 (defsubst subr-primitive-p (object)
   "Return t if OBJECT is a built-in primitive written in C.
 Such objects can be functions or special forms."