feature/syntax-checker: redesign tooltip support

Use flycheck-posframe in GUI Emacs (26+) and flycheck-popup-tip
everywhere else.

modules/feature/syntax-checker/autoload.el

@@ -0,0 +1,41 @@
+;;; feature/syntax-checker/autoload.el -*- lexical-binding: t; -*-
+
+(defun +syntax-checker-show-popup (errors)
+  "TODO"
+  (if (and EMACS26+ (display-graphic-p))
+      (flycheck-posframe-show-posframe errors)
+    (flycheck-popup-tip-show-popup errors)))
+
+(defun +syntax-checker-cleanup-popup ()
+  "TODO"
+  (when (display-graphic-p)
+    (flycheck-popup-tip-delete-popup)))
+
+;;;###autoload
+(define-minor-mode +syntax-checker-popup-mode
+  "TODO"
+  :lighter nil
+  :group 'doom
+  (let ((hooks '(post-command-hook focus-out-hook)))
+    (cond
+     ;; Use our display function and remember the old one but only if we haven't
+     ;; yet configured it, to avoid activating twice.
+     ((and +syntax-checker-popup-mode
+           (not (eq flycheck-display-errors-function
+                    #'+syntax-checker-show-popup)))
+      (setq flycheck-popup-tip-old-display-function
+            flycheck-display-errors-function
+            flycheck-display-errors-function
+            #'+syntax-checker-show-popup)
+      (dolist (hook hooks)
+        (add-hook hook #'+syntax-checker-cleanup-popup nil t)))
+     ;; Reset the display function and remove ourselves from all hooks but only
+     ;; if the mode is still active.
+     ((and (not +syntax-checker-popup-mode)
+           (eq flycheck-display-errors-function
+               #'+syntax-checker-show-popup))
+      (setq flycheck-display-errors-function
+            flycheck-popup-tip-old-display-function
+            flycheck-popup-tip-old-display-function nil)
+      (dolist (hook hooks)
+        (remove-hook hook '+syntax-checker-cleanup-popup t))))))