Use a list of functions for custom window number assignment

README.org

@@ -196,28 +196,39 @@ Several options are available through Emacs' Customize interface under
 
   Default: =t=
 
-- =winum-assign-func=
+- =winum-assign-functions=
 
-  Function called for each window by =winum-mode=. This is called before
-  automatic assignment begins. The function should return a number to have it
-  assigned to the current-window, =nil= otherwise.
+  List of functions called for each window by `winum-mode'.
 
-  This function along with `winum-auto-assign-0-to-minibuffer' are the only ways
-  to have 0 assigned to a window.
+  These functions allow for deterministic assignment of numbers to windows. Each
+  function is called for every window. A function should return the number to be
+  assigned to a window or nil. The /first/ function to output a number for
+  a given window will determine this window's number (if more than 1 function
+  assigns a number a warning will be logged in the messages buffer).
+
+  If the list is empty or if every function returns nil for a given window winum
+  will proceed to automatic number assignment.
+
+  Since this list is meant to allow custom window assignment for /mutiple/
+  packages at once it should never be directly set, only added to and removed
+  from.
+
+  These functions, along with ~winum-auto-assign-0-to-minibuffer~, are the only
+  way to have 0 assigned to a window.
 
   Example: always assign *Calculator* the number 9 and *NeoTree* the number 0:
 
   #+BEGIN_SRC emacs-lisp
-  (defun my-winum-assign-func ()
+    (defun winum-assign-9-to-calculator-8-to-flycheck-errors ()
       (cond
-     ((equal (buffer-name) "*Calculator*")
-      9)
-     ((string-match-p (buffer-name) ".*\\*NeoTree\\*.*")
-      0)
-     (t
-      nil)))
+       ((equal (buffer-name) "*Calculator*") 9)
+       ((equal (buffer-name) "*Flycheck errors*") 8)))
 
-  (setq winum-assign-func 'my-winum-assign-func)
+    (defun winum-assign-0-to-neotree-and ()
+      (when (string-match-p (buffer-name) ".*\\*NeoTree\\*.*") 10))
+
+    (add-to-list 'winum-assign-functions #'winum-assign-9-to-calculator-8-to-flycheck-errors)
+    (add-to-list 'winum-assign-functions #'winum-assign-0-to-neotree)
   #+END_SRC
 
   Default: =nil=
@@ -268,14 +279,16 @@ available winum options.
 
   (require 'winum)
 
-  (defun my-winum-assign-func ()
+  (defun winum-assign-9-to-calculator-8-to-flycheck-errors ()
     (cond
-     ((equal (buffer-name) "*Calculator*")
-      9)
-     ((string-match-p (buffer-name) ".*\\*NeoTree\\*.*")
-      0)
-     (t
-      nil)))
+     ((equal (buffer-name) "*Calculator*") 9)
+     ((equal (buffer-name) "*Flycheck errors*") 8)))
+
+  (defun winum-assign-0-to-neotree-and ()
+    (when (string-match-p (buffer-name) ".*\\*NeoTree\\*.*") 10))
+
+  (add-to-list 'winum-assign-functions #'winum-assign-9-to-calculator-8-to-flycheck-errors)
+  (add-to-list 'winum-assign-functions #'winum-assign-0-to-neotree)
 
   (set-face-attribute 'winum-face nil :weight 'bold)
 

winum.el

@@ -22,7 +22,7 @@
 ;; URL: http://github.com/deb0ch/winum.el
 ;; Created: 2016
 ;; Compatibility: GNU Emacs 24.x
-;; Package-requires: ((cl-lib "0.5"))
+;; Package-requires: ((cl-lib "0.5") (dash "2.13.0"))
 ;;
 ;; This file is NOT part of GNU Emacs.
 ;;
@@ -43,6 +43,7 @@
 ;;
 
 (eval-when-compile (require 'cl-lib))
+(require 'dash)
 
 ;; Configuration variables -----------------------------------------------------
 
@@ -92,6 +93,44 @@ Example: always assign *Calculator* the number 9 and *NeoTree* the number 0:
   :group 'winum
   :type  'function)
 
+(make-obsolete-variable 'winum-assign-func 'winum-assign-functions "28.05.2017")
+
+(defcustom winum-assign-functions nil
+  "List of functions called for each window by `winum-mode'.
+
+These functions allow for deterministic assignment of numbers to windows. Each
+function is called for every window. A function should return the number to be
+assigned to a window or nil. The *first* function to output a number for
+a given window will determine this window's number.
+
+If the list is empty or if every functions returns nil for a given window winum
+will proceed to automatic number assignment.
+
+Since this list is meant to allow custom window assignment for *mutiple*
+packages at once it should never be directly set, only added to and removed
+from.
+
+These functions, along with `winum-auto-assign-0-to-minibuffer', are the only
+way to have 0 assigned to a window.
+
+Example: always assign *Calculator* the number 9, *Flycheck-errors* the number 8
+and *NeoTree* the number 0:
+
+  (defun winum-assign-9-to-calculator-8-to-flycheck-errors ()
+    (cond
+     ((equal (buffer-name) \"*Calculator*\") 9)
+     ((equal (buffer-name) \"*Flycheck errors*\") 8)))
+
+  (defun winum-assign-0-to-neotree ()
+    (when (string-match-p (buffer-name) \".*\\*NeoTree\\*.*\") 10))
+
+  (add-to-list
+    'winum-assign-functions #'winum-assign-9-to-calculator-8-to-flycheck-errors)
+  (add-to-list
+    'winum-assign-functions #'winum-assign-0-to-neotree)"
+  :group 'winum
+  :type  'list)
+
 (defcustom winum-auto-setup-mode-line t
   "When nil, `winum-mode' will not display window numbers in the mode-line.
 You might want this to be nil if you use a package that already manages window
@@ -398,14 +437,8 @@ POSITION: position in the mode-line."
           winum--remaining (winum--available-numbers))
     (winum--set-window-vector (make-vector (1+ winum--window-count) nil))
     (clrhash (winum--get-numbers-table))
-    (when winum-assign-func
-      (mapc (lambda (w)
-              (with-selected-window w
-                (with-current-buffer (window-buffer w)
-                  (let ((num (funcall winum-assign-func)))
-                    (when num
-                      (winum--assign w num))))))
-            windows))
+    (when winum-assign-functions
+      (-each windows #'winum--try-to-find-custom-number))
     (when (and winum-auto-assign-0-to-minibuffer
                (active-minibuffer-window)
                (not (winum-get-window-by-number 0)))
@@ -413,6 +446,23 @@ POSITION: position in the mode-line."
     (dolist (w windows)
       (winum--assign w))))
 
+(defun winum--try-to-find-custom-number (window)
+  "Try to find and assign a custom number for WINDOW.
+Do so by trying every function in `winum-assign-functions' and assign the
+*first* non nil integer.
+When multiple functions assign a number to a window log a warning and use the
+first number anyway."
+  (with-selected-window window
+    (with-current-buffer (window-buffer window)
+      (let* ((nums (->> winum-assign-functions
+                        (--map (cons it (funcall it)))
+                        (--remove (null (cdr it)))))
+             (num (-> nums (cl-first) (cdr))))
+        (when (> (length nums) 1)
+          (message "Winum conflict - window %s was assigned a number by multiple custom assign functions: '%s'"
+                   window (--map (format "%s -> %s" (car it) (cdr it)) nums)))
+        (when (integerp num) (winum--assign window num))))))
+
 (defun winum--assign (window &optional number)
   "Assign to window WINDOW the number NUMBER.
 If NUMBER is not specified, determine it first based on `winum--remaining'.