Fix tp-add to override embedded face sub-properties with new values

When tp-add merges face properties, new props values should now
override embedded values for the same sub-properties (e.g., if
new face has :foreground "green" and embedded has :foreground "red",
result should be :foreground "green").

Updated tp--merge-string-props-into-plist to pass props as the
override value when merging faces.

Updated tp--merge-face-values to properly handle mixed face lists
(symbols + plists) when the base face is a plist.

Added test tp-test-tp-add-face-override-subprops to verify this behavior.

Co-authored-by: Kinneyzhang <38454496+Kinneyzhang@users.noreply.github.com>

tp-tests.el

@@ -3165,6 +3165,32 @@ the inserted text should be that string, not the source text."
                                        (equal (plist-get f :foreground) "red")))
                                 face-val)))))))
 
+(ert-deftest tp-test-tp-add-face-override-subprops ()
+  "Test that tp-add with tp-text overrides same face sub-properties."
+  ;; When new props have same sub-property as embedded, new value should override
+  ;; Example: new (:foreground "green") should override embedded (:foreground "red")
+  (let ((result (tp-add "emacs" 'face '(:foreground "green")
+                        'tp-text (propertize "vim" 'face '(:foreground "red")))))
+    (should (equal result "vim"))
+    ;; Face should be (:foreground "green") - new overrides old
+    (let ((face-val (tp-at 0 'face result)))
+      (should (equal face-val '(:foreground "green")))))
+  ;; More complex case: new (bold (:foreground "green")) with embedded (:foreground "red")
+  (let ((result (tp-add "emacs" 'face '(bold (:foreground "green"))
+                        'tp-text (propertize "vim" 'face '(:foreground "red")))))
+    (should (equal result "vim"))
+    ;; Face should be (bold (:foreground "green")) - new overrides old
+    (let ((face-val (tp-at 0 'face result)))
+      (should (member 'bold (if (listp face-val) face-val (list face-val))))
+      ;; Should have green, not red
+      (should (cl-some (lambda (f)
+                         (and (listp f)
+                              (keywordp (car-safe f))
+                              (equal (plist-get f :foreground) "green")))
+                       (if (and (listp face-val) (not (keywordp (car-safe face-val))))
+                           face-val
+                         (list face-val)))))))
+
 ;;; ============================================================
 ;;; New define-tp Format Tests (Parameterized and Non-Parameterized)
 ;;; ============================================================

tp.el

@@ -260,24 +260,30 @@ Scans the entire string, not just position 0."
 
 (defun tp--merge-string-props-into-plist (str props)
   "Merge text properties from string STR into PROPS plist.
-Properties from STR are merged with proper face handling using
+Properties from PROPS take precedence over those in STR.
-`tp--merge-face-values'. Returns the merged plist.
+Returns the merged plist where new props override embedded props.
 For simplicity, only considers properties at position 0 of STR."
   (if (not (tp--string-has-properties-p str))
       props
     (let ((str-props (text-properties-at 0 str))
           (result (copy-sequence props)))
       ;; Merge each property from the string into result
+      ;; Props values take precedence over embedded string values
       (cl-loop for (key val) on str-props by #'cddr
                do (let ((existing (plist-get result key)))
+                    (if existing
+                        ;; Props already has this key - merge with props taking precedence
                         (setq result
                               (plist-put result key
                                          (cond
                                           ;; Face properties need special merging
+                                          ;; Pass embedded val as face1 (base), existing as face2 (override)
                                           ((memq key '(face font-lock-face mouse-face))
-                                       (tp--merge-face-values existing val))
+                                           (tp--merge-face-values val existing))
-                                      ;; Other properties - string value takes precedence
+                                          ;; Other properties - props value takes precedence
-                                      (t val))))))
+                                          (t existing))))
+                      ;; Props doesn't have this key - add from string
+                      (setq result (plist-put result key val)))))
       result)))
 
 (defun tp--merge-face-values (face1 face2)
@@ -326,6 +332,20 @@ Returns the merged face value."
       (if (member face1 face2)
           face2
         (append face2 (list face1))))
+     ;; face1 is a plist - need to merge any plist in face2 with face1
+     ((and (listp face1) (keywordp (car-safe face1)))
+      ;; Extract plist and symbols from face2
+      (let ((symbols nil)
+            (plist nil))
+        (dolist (f face2)
+          (if (and (listp f) (keywordp (car-safe f)))
+              (setq plist (if plist (tp--deep-merge-plist plist f) f))
+            (push f symbols)))
+        ;; Merge face2's plist with face1, then prepend symbols
+        (let ((merged-plist (if plist (tp--deep-merge-plist face1 plist) face1)))
+          (if symbols
+              (append (nreverse symbols) (list merged-plist))
+            merged-plist))))
      ((listp face1)
       (append face2
               (cl-remove-if (lambda (f) (member f face2)) face1)))