Fix tp-text property detection to scan entire string

Use tp--string-has-properties-p helper function instead of checking
only position 0. This properly detects text properties that start at
non-zero positions in the string.

Added test tp-test-tp-text-with-properties-starting-at-nonzero to
verify this fix.

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

tp-tests.el

@@ -3124,6 +3124,26 @@ the inserted text should be that string, not the source text."
     ;; The embedded custom-prop from tp-text should be preserved
     (should (equal (tp-at 0 'custom-prop result) 'value))))
 
+(ert-deftest tp-test-tp-text-with-properties-starting-at-nonzero ()
+  "Test that tp-text with properties starting at non-zero position are preserved."
+  ;; This tests the fix for the issue where only position 0 was checked
+  (let* ((propertized-text (copy-sequence "Hello"))
+         ;; Set properties starting at position 2, not 0
+         (_ (put-text-property 2 5 'custom-prop 'value propertized-text))
+         (result (tp-set "X" 'tp-text propertized-text 'face 'bold)))
+    ;; The text content should be from tp-text
+    (should (equal result "Hello"))
+    ;; The face from props should be applied uniformly
+    (should (equal (tp-at 0 'face result) 'bold))
+    (should (equal (tp-at 2 'face result) 'bold))
+    ;; Position 0-1 should NOT have custom-prop
+    (should (null (tp-at 0 'custom-prop result)))
+    (should (null (tp-at 1 'custom-prop result)))
+    ;; Position 2-4 should have custom-prop
+    (should (equal (tp-at 2 'custom-prop result) 'value))
+    (should (equal (tp-at 3 'custom-prop result) 'value))
+    (should (equal (tp-at 4 'custom-prop result) 'value))))
+
 ;;; ============================================================
 ;;; New define-tp Format Tests (Parameterized and Non-Parameterized)
 ;;; ============================================================

tp.el

@@ -252,6 +252,13 @@ NEW values override BASE values."
                   (t val))))))
     result))
 
+(defun tp--string-has-properties-p (str)
+  "Return non-nil if string STR has any text properties.
+Scans the entire string, not just position 0."
+  (and (stringp str)
+       (> (length str) 0)
+       (not (null (object-intervals str)))))
+
 (defun tp--apply-string-props-to-region (str start &optional object)
   "Apply text properties from string STR to buffer region starting at START.
 For each character position in STR, its text properties are applied to
@@ -929,8 +936,8 @@ Text properties embedded in NEW-TEXT are preserved."
   (goto-char (point-min))
   (let ((match (text-property-search-forward 'tp-name layer-name t))
         ;; Check if new-text has embedded text properties
-        (new-text-has-props (and (stringp new-text)
+        ;; Use tp--string-has-properties-p to scan the entire string
-                                 (text-properties-at 0 new-text))))
+        (new-text-has-props (tp--string-has-properties-p new-text)))
     (while match
       (let* ((m-start (prop-match-beginning match))
              (m-end (prop-match-end match))
@@ -1006,8 +1013,8 @@ NEW-OBJECT is the new string object (only different for strings with tp-text)."
                        tp-text-val))
                   tp-text-val))
                ;; Check if final-text has text properties that should be preserved
-               (tp-text-has-props (and (stringp final-text)
+               ;; Use tp--string-has-properties-p to scan the entire string
-                                       (text-properties-at 0 final-text))))
+               (tp-text-has-props (tp--string-has-properties-p final-text)))
           (if (stringp object)
               ;; For strings: create a new string with tp-text content
               ;; Preserve any text properties from the tp-text value itself