Don't set :foreground/background to nil to avoid font warnings in emacs29 (#15877)

Fixes https://github.com/syl20bnr/spacemacs/issues/15862

core/core-release-management.el

@@ -342,7 +342,7 @@ Returns the output of git status --porcelain."
                       (symbol-name state))
              :group 'spacemacs))
     (set-face-attribute fname nil
-                        :foreground foreground
+                        :foreground (or foreground 'unspecified)
                         :box (face-attribute 'mode-line :box))))
 
 (defun spacemacs//compute-version-score (version)

layers/+distributions/spacemacs-bootstrap/funcs.el

@@ -67,19 +67,20 @@ For evil states that also need an entry to `spacemacs-evil-cursors' use
   ;; for example treemacs: it needs no cursor since it solely uses hl-line-mode
   ;; and having an evil cursor defined anyway leads to the cursor sometimes
   ;; visibly flashing in treemacs buffers
-  (eval `(defface ,(intern (format "spacemacs-%s-face" state))
-           `((t (:background ,color
-                             :foreground ,(face-background 'mode-line)
-                             :inherit 'mode-line)))
+  (eval `(defface ,(spacemacs/state-color-face (intern state))
+           `((t (:background ,color :inherit 'mode-line)))
            (format "%s state face." state)
-           :group 'spacemacs)))
+           :group 'spacemacs))
+  ;; 'unspecified may not be used in defface, so set it via set-face-attribute.
+  (set-face-attribute (spacemacs/state-color-face (intern state)) nil
+       :foreground (face-attribute 'mode-line :background)))
 
 (defun spacemacs/set-state-faces ()
-  (cl-loop for (state color cursor) in spacemacs-evil-cursors
-           do
-           (set-face-attribute (intern (format "spacemacs-%s-face" state))
-                               nil
-                               :foreground (face-background 'mode-line))))
+  (let ((ml-bg (face-attribute 'mode-line :background)))
+    (cl-loop for (state color cursor) in spacemacs-evil-cursors
+             do
+             (set-face-attribute (spacemacs/state-color-face (intern state)) nil
+                                 :foreground ml-bg))))
 
 (defun evil-insert-state-cursor-hide ()
   (setq evil-insert-state-cursor '((hbar . 0))))

layers/+spacemacs/spacemacs-completion/funcs.el

@@ -43,8 +43,8 @@
   "Set the face of diretories for `.' and `..'"
   (set-face-attribute 'helm-ff-dotted-directory
                       nil
-                      :foreground nil
-                      :background nil
+                      :foreground 'unspecified
+                      :background 'unspecified
                       :inherit 'helm-ff-directory))
 
 (defun spacemacs//helm-find-files-enable-helm--in-fuzzy ()

layers/+spacemacs/spacemacs-defaults/packages.el

@@ -527,13 +527,13 @@
     :config
     (progn
       (set-face-attribute 'whitespace-space nil
-                          :background nil
+                          :background 'unspecified
                           :foreground (face-attribute 'font-lock-warning-face
                                                       :foreground))
       (set-face-attribute 'whitespace-tab nil
-                          :background nil)
+                          :background 'unspecified)
       (set-face-attribute 'whitespace-indentation nil
-                          :background nil)
+                          :background 'unspecified)
       (spacemacs|diminish whitespace-mode " ⓦ" " w")
       (spacemacs|diminish global-whitespace-mode " ⓦ" " w"))))
 

layers/+spacemacs/spacemacs-editing/funcs.el

@@ -115,8 +115,8 @@ If `global' is non-nil activate the respective global mode."
 (defun spacemacs//adaptive-smartparent-pair-overlay-face ()
   (set-face-attribute 'sp-pair-overlay-face nil
                       :inherit 'lazy-highlight
-                      :background nil
-                      :foreground nil))
+                      :background 'unspecified
+                      :foreground 'unspecified))
 
 (defun spacemacs//put-clean-aindent-last ()
   "Put `clean-aindent--check-last-point` to end of `post-command-hook`.

layers/+themes/theming/README.org

@@ -49,7 +49,7 @@ It should be a list of the following form:
              ;; Font locking
              (font-lock-comment-face :slant italic)
              (web-mode-html-attr-name-face :inherit font-lock-variable-name-face
-                                           :foreground nil)
+                                           :foreground 'unspecified)
              ;; Modeline
              (powerline-active1 :box (:color "#999999"
                                       :line-width 1