Fix tp-text reactive variable synchronization when initial value is nil

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

.gitignore

@@ -7,3 +7,4 @@ dash.el
 # Backup files
 *~
 \#*\#
+dash.el

tp-tests.el

@@ -3044,6 +3044,49 @@ preserving the native text property behavior."
       ;; Cleanup
       (makunbound 'tp-test-reactive-text))))
 
+(ert-deftest tp-test-tp-text-reactive-nil-initializes-variable ()
+  "Test tp-text with nil reactive variable initializes the variable to source text.
+When tp-text is bound to a reactive variable and that variable is nil,
+the source text should be used and the reactive variable should be updated."
+  (tp-test-with-temp-buffer
+    (defvar tp-test-text-var nil "Test variable for tp-text initialization.")
+    (setq tp-test-text-var nil)
+    (unwind-protect
+        (progn
+          ;; Define layer with tp-text bound to a reactive variable
+          (tp-define-layer 'test-init-text-layer
+            :props '(face bold tp-text $tp-test-text-var))
+          ;; Apply layer to string - variable is nil, so source text should be used
+          (let ((result (tp-set "2" 'test-init-text-layer)))
+            ;; Result should be the source text "2"
+            (should (equal result "2"))
+            ;; tp-test-text-var should now be "2"
+            (should (equal tp-test-text-var "2"))
+            ;; tp-text property should be "2"
+            (should (equal (tp-at 0 'tp-text result) "2")))
+          ;; Now set the variable to a different value and test again
+          (setq tp-test-text-var "18")
+          ;; Redefine layer to reset resolved props
+          (tp-define-layer 'test-init-text-layer
+            :props '(face bold tp-text $tp-test-text-var))
+          (let ((result (tp-set "2" 'test-init-text-layer)))
+            ;; Result should be the variable value "18", not source "2"
+            (should (equal result "18"))
+            ;; Variable should remain "18"
+            (should (equal tp-test-text-var "18"))))
+      ;; Cleanup
+      (makunbound 'tp-test-text-var))))
+
+(ert-deftest tp-test-tp-text-direct-string-uses-specified-text ()
+  "Test tp-text with direct string value uses that string, not source text.
+When tp-text is set directly to a string (not a reactive variable),
+the inserted text should be that string, not the source text."
+  (let ((result (tp-set "2" 'tp-text "23")))
+    ;; Result should be "23", not "2"
+    (should (equal result "23"))
+    ;; tp-text property should be "23"
+    (should (equal (tp-at 0 'tp-text result) "23"))))
+
 (ert-deftest tp-test-tp-text-reactive-computed ()
   "Test tp-text with computed reactive variable."
   (tp-test-with-temp-buffer

tp.el

@@ -576,6 +576,26 @@ WHERE specifies which buffers to update:
 ;;; Layer 4: Reactive Text (tp-text property)
 ;;;============================================================================
 
+(defun tp--find-tp-text-reactive-var (layer-name)
+  "Find the reactive variable symbol used for tp-text in LAYER-NAME.
+Returns the variable symbol (e.g., tp-test-counter) if tp-text uses a
+reactive variable (e.g., $tp-test-counter), or nil if not found.
+Searches through `tp-reactive-deps' to find the original reactive props."
+  (catch 'found
+    (dolist (dep tp-reactive-deps)
+      (let* ((var-sym (car dep))
+             (layer-entry (assoc layer-name (cdr dep))))
+        (when layer-entry
+          (let ((reactive-props (cdr layer-entry)))
+            ;; Check if tp-text in reactive-props uses this variable
+            (when (plist-member reactive-props 'tp-text)
+              (let ((tp-text-val (plist-get reactive-props 'tp-text)))
+                ;; Check if tp-text-val is a reactive symbol for this variable
+                (when (and (tp--reactive-symbol-p tp-text-val)
+                           (eq (tp--reactive-var-symbol tp-text-val) var-sym))
+                  (throw 'found var-sym))))))))
+    nil))
+
 (defun tp--update-reactive-text (layer-name &optional where)
   "Update text regions that have tp-text property with LAYER-NAME applied.
 This is called when a reactive variable bound to tp-text changes.
@@ -644,6 +664,17 @@ NEW-OBJECT is the new string object (only different for strings with tp-text)."
                      (with-current-buffer object
                        (buffer-substring-no-properties start end))
                    (buffer-substring-no-properties start end)))))
+          ;; If tp-text uses a reactive variable, update that variable to match
+          ;; This ensures the reactive variable and buffer text stay in sync
+          (when-let ((layer-name (plist-get props 'tp-name)))
+            (when-let ((reactive-var (tp--find-tp-text-reactive-var layer-name)))
+              ;; Update the reactive variable with the current text (buffer-local)
+              (set reactive-var current-text)
+              ;; Also update the layer definition so future accesses see the new value
+              (let ((layer-props (cdr (assoc layer-name tp-layer-alist))))
+                (when layer-props
+                  (setf (cdr (assoc layer-name tp-layer-alist))
+                        (plist-put layer-props 'tp-text current-text))))))
           (list (plist-put props 'tp-text current-text) end object)))
        ;; tp-text has a string value - replace the text in the region
        ((stringp tp-text-val)