emacs: Split out the incremental json parser into its own function

This patch splits out the incremental json parser into its own
function.

It moves the main logic of the parser to happen inside the parse
buffer rather than inside the results buffer, but makes sure all
results and all errors are displayed in the results buffer.

It also changes the local parser variables from being buffer
local to the results buffer to being buffer local to the parse buffer,
and sets them up automatically so the caller does not need to.

Finally to keep the diff small this patch does not fix the whitespace,
nor complete the code movement (these are done in subsequent patches)
but it should contain all the functional changes.

emacs/notmuch.el

@@ -838,8 +838,28 @@ non-authors is found, assume that all of the authors match."
 	;; Insert new data
 	(save-excursion
 	  (goto-char (point-max))
-	  (insert string)))
+	  (insert string))
-      (with-current-buffer results-buf
+	(notmuch-json-parse-partial-list 'notmuch-search-show-result
+					 'notmuch-search-show-error
+					 results-buf)))))
+
+(defun notmuch-json-parse-partial-list (result-function error-function results-buf)
+  "Parse a partial JSON list from current buffer.
+
+This function consumes a JSON list from the current buffer,
+applying RESULT-FUNCTION in buffer RESULT-BUFFER to each complete
+value in the list.  It operates incrementally and should be
+called whenever the buffer has been extended with additional
+data.
+
+If there is a syntax error, this will attempt to resynchronize
+with the input and will apply ERROR-FUNCTION in buffer
+RESULT-BUFFER to any input that was skipped."
+  (let (done)
+    (unless (local-variable-p 'notmuch-search-json-parser)
+      (set (make-local-variable 'notmuch-search-json-parser)
+	   (notmuch-json-create-parser (current-buffer)))
+      (set (make-local-variable 'notmuch-search-process-state) 'begin))
 	(while (not done)
 	  (condition-case nil
 	      (case notmuch-search-process-state
@@ -855,7 +875,8 @@ non-authors is found, assume that all of the authors match."
 		   (case result
 		     ((retry) (setq done t))
 		     ((end) (setq notmuch-search-process-state 'end))
-		     (otherwise (notmuch-search-show-result result)))))
+			 (otherwise (with-current-buffer results-buf
+				      (funcall result-function result))))))
 		((end)
 		 ;; Any trailing data is unexpected
 		 (notmuch-json-eof notmuch-search-json-parser)
@@ -863,16 +884,13 @@ non-authors is found, assume that all of the authors match."
 	    (json-error
 	     ;; Do our best to resynchronize and ensure forward
 	     ;; progress
-	     (notmuch-search-show-error
-	      "%s"
-	      (with-current-buffer parse-buf
 		(let ((bad (buffer-substring (line-beginning-position)
 					     (line-end-position))))
 		  (forward-line)
-		  bad))))))
+	   (with-current-buffer results-buf
+	     (funcall error-function "%s" bad))))))
 	;; Clear out what we've parsed
-	(with-current-buffer parse-buf
+    (delete-region (point-min) (point))))
-	  (delete-region (point-min) (point)))))))
 
 (defun notmuch-search-tag-all (&optional tag-changes)
   "Add/remove tags from all messages in current search buffer.
@@ -984,9 +1002,6 @@ Other optional parameters are used as follows:
 	      ;; This buffer will be killed by the sentinel, which
 	      ;; should be called no matter how the process dies.
 	      (parse-buf (generate-new-buffer " *notmuch search parse*")))
-	  (set (make-local-variable 'notmuch-search-process-state) 'begin)
-	  (set (make-local-variable 'notmuch-search-json-parser)
-	       (notmuch-json-create-parser parse-buf))
 	  (process-put proc 'parse-buf parse-buf)
 	  (set-process-sentinel proc 'notmuch-search-process-sentinel)
 	  (set-process-filter proc 'notmuch-search-process-filter)