Augment Flymake API for third-party extensions

See
https://lists.gnu.org/archive/html/emacs-devel/2017-10/msg00619.html

* doc/misc/flymake.texi (Flymake error types): Rewrite
example.
(Flymake utility functions): Augment with new API.

* lisp/progmodes/flymake.el (flymake-diagnostics): New function.
(flymake--diag-accessor): New helper macro.
(flymake-diagnostic-buffer, flymake-diagnostic-text)
(flymake-diagnostic-beg, flymake-diagnostic-end)
(flymake-diagnostic-backend): Accessors for diagnostic objects.
(flymake--overlays): Use flymake-diagnostic property.
(flymake--highlight-line): Simplify.  Only set
flymake-diagnostic property.
(flymake--handle-report, flymake-goto-next-error): Use
flymake-diagnostic property.
(flymake-show-diagnostic): Use diagnostic object.
(flymake--diagnostics-buffer-entries): Use
flymake-diagnostics.

doc/misc/flymake.texi

@@ -361,34 +361,38 @@ priority but without an overlay face.
                          (flymake-category . flymake-note))))
 @end example
 
-@vindex flymake-text
+@vindex flymake-diagnostics
+@vindex flymake-diagnostic-backend
+@vindex flymake-diagnostic-buffer
+@vindex flymake-diagnostic-text
+@vindex flymake-diagnostic-beg
+@vindex flymake-diagnostic-end
 As you might have guessed, Flymake's annotations are implemented as
 overlays (@pxref{Overlays,,, elisp, The Emacs Lisp Reference Manual}).
 Along with the properties that you specify for the specific type of
-diagnostic, Flymake adds the property @code{flymake-text} to these
-overlays, and sets it to the message string that the backend used to
-describe the diagnostic.
+diagnostic, Flymake adds the property @code{flymake-diagnostic} to
+these overlays, and sets it to the object that the backend created
+with @code{flymake-make-diagnostic}.
 
-Since overlays also support arbitrary keymaps, you can use this
-property @code{flymake-text} to create interactive annotations, such
-as in the following example of binding a @kbd{mouse-3} event (middle
-mouse button click) to an Internet search for the text of a
-@code{:warning} or @code{:error}.
+Since overlays also support arbitrary keymaps, you can use this along
+with the functions @code{flymake-diagnostics} and
+@code{flymake-diagnostic-text} (@pxref{Flymake utility functions}) to
+create interactive annotations, such as in the following example of
+binding a @code{mouse-3} event (middle mouse button click) to an
+Internet search for the text of a @code{:warning} or @code{:error}.
 
 @example
 (defun my-search-for-message (event)
   (interactive "e")
-  (let ((ovs (overlays-at (posn-point (event-start event))))
-        ov)
-    ;; loop until flymake overlay we clicked on is recovered
-    (while (not (overlay-get (setq ov (pop ovs)) 'flymake-text)))
-    (when ov
-      (eww-browse-url
-       (concat "https://duckduckgo.com/?q="
-               (replace-regexp-in-string " "
-                                         "+"
-                                         (overlay-get ov 'flymake-text)))
-       t))))
+  (let* ((diags (flymake-diagnostics (posn-point (event-start event))))
+         (topmost-diag (car diags)))
+    (eww-browse-url
+       (concat
+        "https://duckduckgo.com/?q="
+        (replace-regexp-in-string " "
+                                  "+"
+                                  (flymake-diagnostic-text topmost-diag)))
+       t)))
 
 (dolist (type '(:warning :error))
   (let ((a (assoc type flymake-diagnostic-types-alist)))
@@ -513,6 +517,24 @@ Make a Flymake diagnostic for @var{buffer}'s region from @var{beg} to
 of the problem detected in this region.
 @end deffn
 
+@cindex access diagnostic object
+These objects' properties can be accessed with the functions
+@code{flymake-diagnostic-backend}, @code{flymake-diagnostic-buffer},
+@code{flymake-diagnostic-text}, @code{flymake-diagnostic-beg},
+@code{flymake-diagnostic-end} and @code{flymake-diagnostic-type}.
+
+Additionally, the function @code{flymake-diagnostics} will collect
+such objects in the region you specify.
+
+@cindex collect diagnostic objects
+@deffn Function flymake-diagnostics beg end
+Get a list of Flymake diagnostics in the region determined by
+@var{beg} and @var{end}.  If neither @var{beg} or @var{end} is
+supplied, use the whole buffer, otherwise if @var{beg} is
+non-@code{nil} and @var{end} is @code{nil}, consider only diagnostics
+at @var{beg}.
+@end deffn
+
 @cindex buffer position from line and column number
 It is often the case with external syntax tools that a diagnostic's
 position is reported in terms of a line number, and sometimes a column
@@ -520,9 +542,10 @@ number.  To convert this information into a buffer position, backends
 can use the following function:
 
 @deffn Function flymake-diag-region buffer line &optional col
-Compute @var{buffer}'s region (@var{beg} .  @var{end}) corresponding to
-@var{line} and @var{col}.  If @var{col} is nil, return a region just
-for @var{line}.  Return nil if the region is invalid.
+Compute @var{buffer}'s region (@var{beg} .  @var{end}) corresponding
+to @var{line} and @var{col}.  If @var{col} is @code{nil}, return a
+region just for @var{line}.  Return @code{nil} if the region is
+invalid.
 @end deffn
 
 @cindex add a log message

lisp/progmodes/flymake.el

@@ -228,6 +228,29 @@ TYPE is a key to `flymake-diagnostic-types-alist' and TEXT is a
 description of the problem detected in this region."
   (flymake--diag-make :buffer buffer :beg beg :end end :type type :text text))
 
+;;;###autoload
+(defun flymake-diagnostics (&optional beg end)
+  "Get Flymake diagnostics in region determined by BEG and END.
+
+If neither BEG or END is supplied, use the whole buffer,
+otherwise if BEG is non-nil and END is nil, consider only
+diagnostics at BEG."
+  (mapcar (lambda (ov) (overlay-get ov 'flymake-diagnostic))
+          (flymake--overlays :beg beg :end end)))
+
+(defmacro flymake--diag-accessor (public internal thing)
+  "Make PUBLIC an alias for INTERNAL, add doc using THING."
+  `(defsubst ,public (diag)
+     ,(format "Get Flymake diagnostic DIAG's %s." (symbol-name thing))
+     (,internal diag)))
+
+(flymake--diag-accessor flymake-diagnostic-buffer flymake--diag-buffer buffer)
+(flymake--diag-accessor flymake-diagnostic-text flymake--diag-text text)
+(flymake--diag-accessor flymake-diagnostic-type flymake--diag-type type)
+(flymake--diag-accessor flymake-diagnostic-beg flymake--diag-beg beg)
+(flymake--diag-accessor flymake-diagnostic-end flymake--diag-end end)
+(flymake--diag-accessor flymake-diagnostic-backend flymake--diag-backend backend)
+
 (cl-defun flymake--overlays (&key beg end filter compare key)
   "Get flymake-related overlays.
 If BEG is non-nil and END is nil, consider only `overlays-at'
@@ -238,7 +261,7 @@ verify FILTER, a function, and sort them by COMPARE (using KEY)."
     (widen)
     (let ((ovs (cl-remove-if-not
                 (lambda (ov)
-                  (and (overlay-get ov 'flymake)
+                  (and (overlay-get ov 'flymake-diagnostic)
                        (or (not filter)
                            (funcall filter ov))))
                 (if (and beg (null end))
@@ -498,18 +521,15 @@ associated `flymake-category' return DEFAULT."
       (default-maybe 'help-echo
         (lambda (_window _ov pos)
           (mapconcat
-           (lambda (ov)
-             (overlay-get ov 'flymake-text))
-           (flymake--overlays :beg pos)
+           #'flymake--diag-text
+           (flymake-diagnostics pos)
            "\n")))
       (default-maybe 'severity (warning-numeric-level :error))
       (default-maybe 'priority (+ 100 (overlay-get ov 'severity))))
     ;; Some properties can't be overridden.
     ;;
     (overlay-put ov 'evaporate t)
-    (overlay-put ov 'flymake t)
-    (overlay-put ov 'flymake-text (flymake--diag-text diagnostic))
-    (overlay-put ov 'flymake--diagnostic diagnostic)))
+    (overlay-put ov 'flymake-diagnostic diagnostic)))
 
 ;; Nothing in Flymake uses this at all any more, so this is just for
 ;; third-party compatibility.
@@ -600,7 +620,7 @@ not expected."
              (lambda (ov)
                (eq backend
                    (flymake--diag-backend
-                    (overlay-get ov 'flymake--diagnostic))))))
+                    (overlay-get ov 'flymake-diagnostic))))))
           (mapc (lambda (diag)
                   (flymake--highlight-line diag)
                   (setf (flymake--diag-backend diag) backend))
@@ -899,7 +919,7 @@ applied."
                                  (lambda (ov)
                                    (let ((diag (overlay-get
                                                 ov
-                                                'flymake--diagnostic)))
+                                                'flymake-diagnostic)))
                                      (and diag
                                           (or (not filter)
                                               (memq (flymake--diag-type diag)
@@ -1089,13 +1109,13 @@ applied."
   (interactive (list (point) t))
   (let* ((id (or (tabulated-list-get-id pos)
                  (user-error "Nothing at point")))
-         (overlay (plist-get id :overlay)))
-    (with-current-buffer (overlay-buffer overlay)
+         (diag (plist-get id :diagnostic)))
+    (with-current-buffer (flymake--diag-buffer diag)
       (with-selected-window
           (display-buffer (current-buffer) other-window)
-        (goto-char (overlay-start overlay))
-        (pulse-momentary-highlight-region (overlay-start overlay)
-                                          (overlay-end overlay)
+        (goto-char (flymake--diag-beg diag))
+        (pulse-momentary-highlight-region (flymake--diag-beg diag)
+                                          (flymake--diag-end diag)
                                           'highlight))
       (current-buffer))))
 
@@ -1108,18 +1128,16 @@ POS can be a buffer position or a button"
 
 (defun flymake--diagnostics-buffer-entries ()
   (with-current-buffer flymake--diagnostics-buffer-source
-    (cl-loop for ov in (flymake--overlays)
-             for diag = (overlay-get ov
-                                     'flymake--diagnostic)
+    (cl-loop for diag in (flymake-diagnostics)
              for (line . col) =
              (save-excursion
-               (goto-char (overlay-start ov))
+               (goto-char (flymake--diag-beg diag))
                (cons (line-number-at-pos)
                      (- (point)
                         (line-beginning-position))))
              for type = (flymake--diag-type diag)
              collect
-             (list (list :overlay ov
+             (list (list :diagnostic diag
                          :line line
                          :severity (flymake--lookup-type-property
                                     type