Make second arg to defvar-local optional

This change allows declaring a variable both special
and buffer-local like so:

    (defvar-local foo)

* lisp/subr.el (defvar-local): Make second argument optional.
* test/lisp/subr-tests.el (subr-test-defvar-local): New test.
* doc/lispref/variables.texi (Creating Buffer-Local): Document above change.
* etc/NEWS:

* lisp/mb-depth.el (minibuffer-depth-overlay):
* lisp/minibuf-eldef.el (minibuf-eldef-initial-input)
(minibuf-eldef-initial-buffer-length)
(minibuf-eldef-showing-default-in-prompt, minibuf-eldef-overlay):
* lisp/misc.el (list-dynamic-libraries--loaded-only-p):
* lisp/simple.el (minibuffer-history-isearch-message-overlay): Use
above new one-argument form of 'defvar-local'.

doc/lispref/variables.texi

@@ -1649,7 +1649,7 @@ on having separate values in separate buffers, then using
 @code{make-variable-buffer-local} can be the best solution.
 @end deffn
 
-@defmac defvar-local variable value &optional docstring
+@defmac defvar-local variable &optional value docstring
 This macro defines @var{variable} as a variable with initial value
 @var{value} and @var{docstring}, and marks it as automatically
 buffer-local.  It is equivalent to calling @code{defvar} followed by

etc/NEWS

@@ -1565,6 +1565,11 @@ and signal an error if they are given a non-number.
 They return non-nil if an integer is odd or even, respectively, and
 signal an error if they are given a non-integer.
 
++++
+** The 'defvar-local' macro second argument is now optional.
+This means that you can now call it with just one argument, like
+'defvar', to declare a variable both special, and buffer-local.
+
 ** ERT
 
 *** Some experimental ERT macros are now considered stable.

lisp/mb-depth.el

@@ -50,8 +50,7 @@ the `minibuffer-depth-indicator' face."
 ;; An overlay covering the prompt.  This is a buffer-local variable in
 ;; each affected minibuffer.
 ;;
-(defvar minibuffer-depth-overlay)
-(make-variable-buffer-local 'minibuffer-depth-overlay)
+(defvar-local minibuffer-depth-overlay)
 
 ;; This function goes on minibuffer-setup-hook
 (defun minibuffer-depth-setup ()

lisp/minibuf-eldef.el

@@ -88,19 +88,16 @@ should be displayed in its place.")
 ;;; The following are all local variables in the minibuffer
 
 ;; Input pre-inserted into the minibuffer before the user can edit it.
-(defvar minibuf-eldef-initial-input)
-(make-variable-buffer-local 'minibuf-eldef-initial-input)
+(defvar-local minibuf-eldef-initial-input)
+
 ;; and the length of the buffer with it inserted.
-(defvar minibuf-eldef-initial-buffer-length)
-(make-variable-buffer-local 'minibuf-eldef-initial-buffer-length)
+(defvar-local minibuf-eldef-initial-buffer-length)
 
 ;; True if the current minibuffer prompt contains the default spec.
-(defvar minibuf-eldef-showing-default-in-prompt)
-(make-variable-buffer-local 'minibuf-eldef-showing-default-in-prompt)
+(defvar-local minibuf-eldef-showing-default-in-prompt)
 
 ;; An overlay covering the default portion of the prompt
-(defvar minibuf-eldef-overlay)
-(make-variable-buffer-local 'minibuf-eldef-overlay)
+(defvar-local minibuf-eldef-overlay)
 
 
 ;;; Hook functions

lisp/misc.el

@@ -262,8 +262,7 @@ variation of `C-x M-c M-butterfly' from url `https://xkcd.com/378/'."
 ;; A command to list dynamically loaded libraries.  This useful in
 ;; environments where dynamic-library-alist is used, i.e., Windows
 
-(defvar list-dynamic-libraries--loaded-only-p)
-(make-variable-buffer-local 'list-dynamic-libraries--loaded-only-p)
+(defvar-local list-dynamic-libraries--loaded-only-p)
 
 (defun list-dynamic-libraries--loaded (from)
   "Compute the \"Loaded from\" column.

lisp/simple.el

@@ -3235,8 +3235,7 @@ Return 0 if current buffer is not a minibuffer."
 ;; isearch minibuffer history
 (add-hook 'minibuffer-setup-hook 'minibuffer-history-isearch-setup)
 
-(defvar minibuffer-history-isearch-message-overlay)
-(make-variable-buffer-local 'minibuffer-history-isearch-message-overlay)
+(defvar-local minibuffer-history-isearch-message-overlay)
 
 (defun minibuffer-history-isearch-setup ()
   "Set up a minibuffer for using isearch to search the minibuffer history.

lisp/subr.el

@@ -192,14 +192,20 @@ pair.
       (setq pairs (cdr (cdr pairs))))
     (macroexp-progn (nreverse expr))))
 
-(defmacro defvar-local (var val &optional docstring)
-  "Define VAR as a buffer-local variable with default value VAL.
+(defmacro defvar-local (symbol &rest args)
+  "Define SYMBOL as a buffer-local variable with default value VALUE.
 Like `defvar' but additionally marks the variable as being automatically
-buffer-local wherever it is set."
+buffer-local wherever it is set.
+\n(fn symbol &optional value docstring)"
   (declare (debug defvar) (doc-string 3) (indent 2))
   ;; Can't use backquote here, it's too early in the bootstrap.
-  (list 'progn (list 'defvar var val docstring)
-        (list 'make-variable-buffer-local (list 'quote var))))
+  (let ((value (car-safe args))
+        (docstring (car-safe (cdr-safe args))))
+    (list 'progn
+          (if (zerop (length args))
+              (list 'defvar symbol)
+            (list 'defvar symbol value docstring))
+          (list 'make-variable-buffer-local (list 'quote symbol)))))
 
 (defun buffer-local-boundp (symbol buffer)
   "Return non-nil if SYMBOL is bound in BUFFER.

test/lisp/subr-tests.el

@@ -30,6 +30,16 @@
 (require 'ert-x)
 (eval-when-compile (require 'cl-lib))
 
+(defvar-local subr-tests--local-var1)
+(defvar-local subr-tests--local-var2 'hello)
+(defvar-local subr-tests--local-var3 nil "Doc.")
+(ert-deftest subr-test-defvar-local ()
+  (should (local-variable-if-set-p 'subr-tests--local-var1))
+  (should (local-variable-if-set-p 'subr-tests--local-var2))
+  (should (eq subr-tests--local-var2 'hello))
+  (should (local-variable-if-set-p 'subr-tests--local-var3))
+  (should (get 'subr-tests--local-var3 'variable-documentation)))
+
 (ert-deftest subr-test-apply-partially ()
   (should (functionp (apply-partially #'identity)))
   (should (functionp (apply-partially #'list 1 2 3)))