Add flymake-backends defcustom

* lisp/progmodes/flymake-proc.el (flymake-proc-can-syntax-check-buffer):
Rename from flymake-can-syntax-check-file.  Suitable for adding to
flymake-backends.
(flymake-proc-start-syntax-check): Rename from
flymake-start-syntax-check.  Don't check again if buffer can be
checked.
(add-to-list flymake-backends): Hook only flymake-ui.el

* lisp/progmodes/flymake-ui.el (flymake-backends): New
defcustom.
(flymake-on-timer-event, flymake-after-change-function)
(flymake-after-save-hook, flymake-find-file-hook): Call new
flymake--start-syntax-check-buffer and
flymake--can-syntax-check-buffer.
(flymake-mode): Call flymake--can-syntax-check-buffer and set
flymake-backend.
(flymake--backend): New buffer-local variable.

2 files changed, 73 insertions, 34 deletions

diff --git a/lisp/progmodes/flymake-proc.el b/lisp/progmodes/flymake-proc.el
index 8a2fede2df5..30555559e60 100644
--- a/lisp/progmodes/flymake-proc.el
+++ b/lisp/progmodes/flymake-proc.el
@@ -120,10 +120,12 @@ NAME is the file name function to use, default `flymake-get-real-file-name'."
     (flymake-log 3 "file %s, init=%s" file-name (car mode-and-masks))
     mode-and-masks))
 
-(defun flymake-can-syntax-check-file (file-name)
-  "Determine whether we can syntax check FILE-NAME.
-Return nil if we cannot, non-nil if we can."
-  (if (flymake-get-init-function file-name) t nil))
+(defun flymake-proc-can-syntax-check-buffer ()
+  "Determine whether we can syntax check current buffer.
+Return nil if we cannot, non-nil if
+we can."
+  (and buffer-file-name
+       (if (flymake-get-init-function buffer-file-name) t nil)))
 
 (defun flymake-get-init-function (file-name)
   "Return init function to be used for the file."
@@ -714,12 +716,11 @@ Return its components if so, nil otherwise."
     (error
      (flymake-log 1 "Failed to delete dir %s, error ignored" dir-name))))
 
-(defun flymake-start-syntax-check ()
+(defun flymake-proc-start-syntax-check ()
   "Start syntax checking for current buffer."
   (interactive)
   (flymake-log 3 "flymake is running: %s" flymake-is-running)
-  (when (and (not flymake-is-running)
-             (flymake-can-syntax-check-file buffer-file-name))
+  (when (not flymake-is-running)
     (when (or (not flymake-compilation-prevents-syntax-check)
               (not (flymake-compilation-is-running))) ;+ (flymake-rep-ort-status buffer "COMP")
       (flymake-clear-buildfile-cache)
@@ -1084,5 +1085,13 @@ Use CREATE-TEMP-F for creating temp copy."
         (list "val" (flymake-init-create-temp-buffer-copy
                      'flymake-create-temp-inplace))))
 
+
+;;;; Hook onto flymake-ui
+
+(add-to-list 'flymake-backends
+             `(flymake-proc-can-syntax-check-buffer
+               .
+               flymake-proc-start-syntax-check))
+
 (provide 'flymake-proc)
 ;;; flymake-proc.el ends here
diff --git a/lisp/progmodes/flymake-ui.el b/lisp/progmodes/flymake-ui.el
index c1dffb4e7ef..3fb1ecaa7f0 100644
--- a/lisp/progmodes/flymake-ui.el
+++ b/lisp/progmodes/flymake-ui.el
@@ -108,6 +108,17 @@ See `flymake-error-bitmap' and `flymake-warning-bitmap'."
   :group 'flymake
   :type 'integer)
 
+(defcustom flymake-backends '()
+  "Ordered list of backends providing syntax check information for a buffer.
+Value is an alist of conses (PREDICATE . CHECKER). Both PREDICATE
+and CHECKER are functions called with a single argument, the
+buffer in which `flymake-mode' was enabled. PREDICATE is expected
+to (quickly) return t or nil if the buffer can be syntax checked
+by CHECKER, which in can performs more morose operations,
+possibly asynchronously."
+  :group 'flymake
+  :type 'alist)
+
 (defvar-local flymake-timer nil
   "Timer for starting syntax check.")
 
@@ -368,7 +379,7 @@ For the format of LINE-ERR-INFO, see `flymake-ler-make-ler'."
 
         (setq flymake-last-change-time nil)
         (flymake-log 3 "starting syntax check as more than 1 second passed since last change")
-        (flymake-start-syntax-check)))))
+        (flymake--start-syntax-check)))))
 
 (define-obsolete-function-alias 'flymake-display-err-menu-for-current-line
   'flymake-popup-current-error-menu "24.4")
@@ -442,6 +453,20 @@ For the format of LINE-ERR-INFO, see `flymake-ler-make-ler'."
   (flymake-log 0 "switched OFF Flymake mode for buffer %s due to fatal status %s, warning %s"
                (buffer-name) status warning))
 
+(defvar-local flymake--backend nil
+  "The currently active backend selected by `flymake-mode'")
+
+(defun flymake--can-syntax-check-buffer (buffer)
+  (let ((all flymake-backends)
+        (candidate))
+    (catch 'done
+      (while (setq candidate (pop all))
+        (when (with-current-buffer buffer (funcall (car candidate)))
+          (throw 'done (cdr candidate)))))))
+
+(defun flymake--start-syntax-check ()
+  (funcall flymake--backend))
+
 ;;;###autoload
 (define-minor-mode flymake-mode nil
   :group 'flymake :lighter flymake-mode-line
@@ -449,31 +474,36 @@ For the format of LINE-ERR-INFO, see `flymake-ler-make-ler'."
 
    ;; Turning the mode ON.
    (flymake-mode
-    (cond
-     ((not buffer-file-name)
-      (message "Flymake unable to run without a buffer file name"))
-     ((not (flymake-can-syntax-check-file buffer-file-name))
-      (flymake-log 2 "flymake cannot check syntax in buffer %s" (buffer-name)))
-     (t
-      (add-hook 'after-change-functions 'flymake-after-change-function nil t)
-      (add-hook 'after-save-hook 'flymake-after-save-hook nil t)
-      (add-hook 'kill-buffer-hook 'flymake-kill-buffer-hook nil t)
-      ;;+(add-hook 'find-file-hook 'flymake-find-file-hook)
-
-      (flymake-report-status "" "")
-
-      (setq flymake-timer
-            (run-at-time nil 1 'flymake-on-timer-event (current-buffer)))
-
-      (when (and flymake-start-syntax-check-on-find-file
-                 ;; Since we write temp files in current dir, there's no point
-                 ;; trying if the directory is read-only (bug#8954).
-                 (file-writable-p (file-name-directory buffer-file-name)))
-        (with-demoted-errors
-          (flymake-start-syntax-check))))))
+    (let* ((backend (flymake--can-syntax-check-buffer (current-buffer))))
+      (cond
+       ((not backend)
+        (flymake-log 2 "flymake cannot check syntax in buffer %s" (buffer-name)))
+       (t
+        (setq flymake--backend backend)
+
+        (add-hook 'after-change-functions 'flymake-after-change-function nil t)
+        (add-hook 'after-save-hook 'flymake-after-save-hook nil t)
+        (add-hook 'kill-buffer-hook 'flymake-kill-buffer-hook nil t)
+        ;;+(add-hook 'find-file-hook 'flymake-find-file-hook)
+
+        (flymake-report-status "" "")
+
+        (setq flymake-timer
+              (run-at-time nil 1 'flymake-on-timer-event (current-buffer)))
+
+        (when (and flymake-start-syntax-check-on-find-file
+                   ;; Since we write temp files in current dir, there's no point
+                   ;; trying if the directory is read-only (bug#8954).
+                   (file-writable-p (file-name-directory buffer-file-name)))
+          (with-demoted-errors
+              (flymake--start-syntax-check)))))
+      )
+    )
 
    ;; Turning the mode OFF.
    (t
+    (setq flymake--backend nil)
+
     (remove-hook 'after-change-functions 'flymake-after-change-function t)
     (remove-hook 'after-save-hook 'flymake-after-save-hook t)
     (remove-hook 'kill-buffer-hook 'flymake-kill-buffer-hook t)
@@ -505,14 +535,14 @@ For the format of LINE-ERR-INFO, see `flymake-ler-make-ler'."
   (let((new-text (buffer-substring start stop)))
     (when (and flymake-start-syntax-check-on-newline (equal new-text "\n"))
       (flymake-log 3 "starting syntax check as new-line has been seen")
-      (flymake-start-syntax-check))
+      (flymake--start-syntax-check))
     (setq flymake-last-change-time (float-time))))
 
 (defun flymake-after-save-hook ()
   (if (local-variable-p 'flymake-mode (current-buffer)) ; (???) other way to determine whether flymake is active in buffer being saved?
       (progn
         (flymake-log 3 "starting syntax check as buffer was saved")
-        (flymake-start-syntax-check)))) ; no more mode 3. cannot start check if mode 3 (to temp copies) is active - (???)
+        (flymake--start-syntax-check)))) ; no more mode 3. cannot start check if mode 3 (to temp copies) is active - (???)
 
 (defun flymake-kill-buffer-hook ()
   (when flymake-timer
@@ -523,10 +553,10 @@ For the format of LINE-ERR-INFO, see `flymake-ler-make-ler'."
 (defun flymake-find-file-hook ()
   ;;+(when flymake-start-syntax-check-on-find-file
   ;;+    (flymake-log 3 "starting syntax check on file open")
-  ;;+    (flymake-start-syntax-check)
+  ;;+    (flymake--start-syntax-check)
   ;;+)
   (when (and (not (local-variable-p 'flymake-mode (current-buffer)))
-             (flymake-can-syntax-check-file buffer-file-name))
+             (flymake--can-syntax-check-buffer (current-buffer)))
     (flymake-mode)
     (flymake-log 3 "automatically turned ON flymake mode")))