misc/emacs: Refactor coverage code into multiple functions

Also fixes color gradient being calculated against the wrong maximum.

R=adonovan
CC=golang-dev
https://golang.org/cl/12968043

misc/emacs/go-mode.el

@@ -1014,22 +1014,49 @@ current coverage buffer or by prompting for it."
       go--coverage-origin-buffer
     (current-buffer)))
 
-(defun go-coverage (&optional coverage-file)
-  "Open a clone of the current buffer and overlay it with
-coverage information gathered via go test -coverprofile=COVERAGE-FILE.
-
-If COVERAGE-FILE is nil, it will either be infered from the
-current buffer if it's already a coverage buffer, or be prompted
-for."
-  (interactive)
-  (setq coverage-file (or coverage-file (go--coverage-file)))
-  (let* ((ranges '())
-         (cur-buffer (current-buffer))
-         (origin-buffer (go--coverage-origin-buffer))
-         (file-name (file-name-nondirectory (buffer-file-name origin-buffer)))
-         (gocov-buffer-name (concat (buffer-name origin-buffer) "<gocov>"))
-         (max-count 0)
-         divisor)
+(defun go--coverage-face (count divisor)
+  "Return the intensity face for COUNT when using DIVISOR
+to scale it to a range [0,10].
+
+DIVISOR scales the absolute cover count to values from 0 to 10.
+For DIVISOR = 0 the count will always translate to 8."
+  (let* ((count (go--covered-count range))
+         (norm (cond
+                ((= count 0)
+                 -0.1) ;; Uncovered code, set to -0.1 so n becomes 0.
+                ((= divisor 0)
+                 0.8) ;; covermode=set, set to 0.8 so n becomes 8.
+                (t
+                 (/ (log count) divisor))))
+         (n (1+ (floor (* norm 9))))) ;; Convert normalized count [0,1] to intensity [0,10]
+    (concat "go-coverage-" (number-to-string n))))
+
+(defun go--coverage-make-overlay (range divisor)
+  "Create a coverage overlay for a RANGE of covered/uncovered
+code. Uses DIVISOR to scale absolute counts to a [0,10] scale."
+  (let* ((count (go--covered-count range))
+         (face (go--coverage-face count divisor))
+         (ov (make-overlay (go--line-column-to-point (go--covered-start-line range)
+                                                     (go--covered-start-column range))
+                           (go--line-column-to-point (go--covered-end-line range)
+                                                     (go--covered-end-column range)))))
+
+    (overlay-put ov 'face face)
+    (overlay-put ov 'help-echo (format "Count: %d" count))))
+
+(defun go--coverage-clear-overlays ()
+  "Remove existing overlays and put a single untracked overlay
+over the entire buffer."
+  (remove-overlays)
+  (overlay-put (make-overlay (point-min) (point-max))
+               'face
+               'go-coverage-untracked))
+
+(defun go--coverage-parse-file (coverage-file file-name)
+  "Parse COVERAGE-FILE and extract coverage information and
+divisor for FILE-NAME."
+  (let (ranges
+        (max-count 0))
     (with-temp-buffer
       (insert-file-contents coverage-file)
       (go--goto-line 2) ;; Skip over mode
@@ -1040,62 +1067,48 @@ for."
 
           (destructuring-bind
               (start-line start-column end-line end-column num count)
-              (mapcar 'string-to-number rest)
-
-            (if (> count max-count)
-                (setq max-count count))
-
-            (if (and (string= (file-name-nondirectory file) file-name))
-                (push
-                 (make-go--covered
-                  :start-line start-line
-                  :start-column start-column
-                  :end-line end-line
-                  :end-column end-column
-                  :covered (/= count 0)
-                  :count count)
-                 ranges)))
+              (mapcar #'string-to-number rest)
+
+            (when (and (string= (file-name-nondirectory file) file-name))
+              (if (> count max-count)
+                  (setq max-count count))
+              (push (make-go--covered :start-line start-line
+                                      :start-column start-column
+                                      :end-line end-line
+                                      :end-column end-column
+                                      :covered (/= count 0)
+                                      :count count)
+                    ranges)))
 
           (forward-line)))
 
-      (if (> max-count 0)
-          (setq divisor (log max-count))))
+      (list ranges (if (> max-count 0) (log max-count) 0)))))
 
-    (with-current-buffer (or
-                          (get-buffer gocov-buffer-name)
-                          (make-indirect-buffer origin-buffer gocov-buffer-name t))
+(defun go-coverage (&optional coverage-file)
+  "Open a clone of the current buffer and overlay it with
+coverage information gathered via go test -coverprofile=COVERAGE-FILE.
+
+If COVERAGE-FILE is nil, it will either be infered from the
+current buffer if it's already a coverage buffer, or be prompted
+for."
+  (interactive)
+  (let* ((cur-buffer (current-buffer))
+         (origin-buffer (go--coverage-origin-buffer))
+         (gocov-buffer-name (concat (buffer-name origin-buffer) "<gocov>"))
+         (coverage-file (or coverage-file (go--coverage-file)))
+         (ranges-and-divisor (go--coverage-parse-file
+                              coverage-file
+                              (file-name-nondirectory (buffer-file-name origin-buffer)))))
+    (with-current-buffer (or (get-buffer gocov-buffer-name)
+                             (make-indirect-buffer origin-buffer gocov-buffer-name t))
       (set (make-local-variable 'go--coverage-origin-buffer) origin-buffer)
       (set (make-local-variable 'go--coverage-current-file-name) coverage-file)
 
       (save-excursion
-        (remove-overlays)
-        (overlay-put
-         (make-overlay
-          (point-min)
-          (point-max))
-         'face 'go-coverage-untracked)
-
-        (dolist (range ranges)
-          (let* ((count (go--covered-count range))
-                 (norm (cond
-                        ((= count 0)
-                         -0.1)
-                        ((= max-count 1)
-                         0.8)
-                        (t
-                         (/ (log count) divisor))))
-                 (n (1+ (floor (* norm 9))))
-                 (face (concat "go-coverage-" (number-to-string n)))
-                 (ov (make-overlay
-                      (go--line-column-to-point
-                       (go--covered-start-line range)
-                       (go--covered-start-column range))
-                      (go--line-column-to-point
-                       (go--covered-end-line range)
-                       (go--covered-end-column range)))))
-
-            (overlay-put ov 'face face)
-            (overlay-put ov 'help-echo (format "Count: %d" count)))))
+        (go--coverage-clear-overlays)
+        (dolist (range (car ranges-and-divisor))
+          (go--coverage-make-overlay range (cadr ranges-and-divisor))))
+
       (if (not (eq cur-buffer (current-buffer)))
           (display-buffer (current-buffer) 'display-buffer-reuse-window)))))