feature/eglot2emacs 4f1f06375a 045/120: Prevent empty diagnostic tags vector hiding main fontification

[João Távora]

branch: feature/eglot2emacs
commit 4f1f06375a219178ba681a6101af1fece73024b0
Author: Brian Leung <bkleung89@gmail.com>
Commit: João Távora <joaotavora@gmail.com>

    Prevent empty diagnostic tags vector hiding main fontification
    
    * eglot.el (eglot-handle-notification): Require that the resulting
    list of faces is non-empty and that each face corresponds only to a
    known tag.
    
    For unknown tags, we don't pass any additional face information to
    Flymake, and instead expect it to make the appropriate overlay with
    the "severity" property of the Diagnostic.
    
    Co-authored-by: João Távora <joaotavora@gmail.com>
    GitHub-reference: fix https://github.com/joaotavora/eglot/issues/851
---
 lisp/progmodes/eglot.el | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/lisp/progmodes/eglot.el b/lisp/progmodes/eglot.el
index 5a0a8caba4..3f84b3b7a2 100644
--- a/lisp/progmodes/eglot.el
+++ b/lisp/progmodes/eglot.el
@@ -1866,11 +1866,11 @@ COMMAND is a symbol naming the command."
                         (current-buffer) beg end
                         (eglot--diag-type severity)
                         message `((eglot-lsp-diag . ,diag-spec))
-                        (and tags
-                             `((face
-                                . ,(mapcar (lambda (tag)
-                                             (alist-get tag eglot--tag-faces))
-                                           tags)))))))
+                        (when-let ((faces
+                                    (cl-loop for tag across tags
+                                             when (alist-get tag 
eglot--tag-faces)
+                                             collect it)))
+                          `((face . ,faces))))))
            into diags
            finally (cond (eglot--current-flymake-report-fn
                           (eglot--report-to-flymake diags))