To customize the appearance of error types, the user must set properties on the symbols associated with each diagnostic type.
The three standard diagnostic keyword symbols – :error,
:warning and :note – have pre-configured appearances.
However a backend may define more (see Backend functions).
The following properties can be set:
flymake-bitmap, an image displayed in the fringe according to
flymake-fringe-indicator-position. The value actually follows
the syntax of flymake-error-bitmap (see Customizable variables). It is overridden by any before-string overlay
property.
flymake-overlay-control, an alist ((OVPROP . VALUE)
...) of further properties used to affect the appearance of
Flymake annotations. With the exception of category and
evaporate, these properties are applied directly to the created
overlay (see Overlay Properties in The Emacs Lisp Reference
Manual).
As an example, here’s how to make diagnostics of the type :note
stand out more prominently:
(push '(face . highlight) (get :note 'flymake-overlay-control))
If you push another alist entry in front, it overrides the previous
one. So this effectively removes the face from :note
diagnostics:
(push '(face . nil) (get :note 'flymake-overlay-control))
To restore the original look for :note types, empty or remove
its flymake-overlay-control property:
(put :note 'flymake-overlay-control '())
flymake-severity is a non-negative integer specifying the
diagnostic’s severity. The higher the value, the more serious is the
error. If the overlay property priority is not specified in
flymake-overlay-control, flymake-severity is used to set
it and help sort overlapping overlays.
flymake-type-name is a string used to succinctly name the error
type, in case the name of the symbol associated with it is very long.
flymake-category is a symbol whose property list is considered
the default for missing values of any other properties.
Three default diagnostic types are predefined: :error,
:warning, and :note. By default, each one of them has a
flymake-category property whose value is, respectively, the
category symbol flymake-error, flymake-warning and
flymake-note.
These category symbols’ plist is where the values of customizable
variables and faces (such as flymake-error-bitmap) are found.
Thus, if you change their plists, Flymake may stop honoring these user
customizations.
The flymake-category special property is especially useful for
backends which create diagnostics objects with non-default types that
differ from an existing type by only a few properties (see Flymake utility functions).
As an example, consider configuring a new diagnostic type
:low-priority-note that behaves much like :note, but
without an overlay face.
(put :low-priority-note 'flymake-overlay-control '((face . nil))) (put :low-priority-note 'flymake-category 'flymake-note)
As you might have guessed, Flymake’s annotations are implemented as
overlays (see Overlays in The Emacs Lisp Reference Manual).
Along with the properties that you specify for the specific type of
diagnostic, Flymake adds the property flymake-diagnostic to
these overlays, and sets it to the object that the backend created
with flymake-make-diagnostic.
Since overlays also support arbitrary keymaps, you can use this along
with the functions flymake-diagnostics and
flymake-diagnostic-text (see Flymake utility functions) to
create interactive annotations, such as in the following example of
binding a mouse-3 event (middle mouse button click) to an
Internet search for the text of a :warning or :error.
(defun my-search-for-message (event)
(interactive "e")
(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))
(push '(mouse-face . highlight) (get type 'flymake-overlay-control))
(push `(keymap . ,(let ((map (make-sparse-keymap)))
(define-key map [mouse-2]
'my-search-for-message)
map))
(get type 'flymake-overlay-control)))