Preserve face text properties in comint prompt.

Fixes: debbugs:20084

* lisp/font-lock.el (font-lock--remove-face-from-text-property): New
function.  Adapted from the previously commented out
remove-single-text-property.
Remove previously unused and commented out auxiliary function
remove-text-property and obsolete comment.
* lisp/comint.el (comint-output-filter): Use it to remove
comint-highlight-prompt.
(comint-snapshot-last-prompt, comint-output-filter): Use
font-lock-prepend-text-property for comint-highlight-prompt.
* test/automated/textprop-tests.el: New file.
(textprop-tests-font-lock--remove-face-from-text-property): New test.

Thus, the original face text property of a prompt "candidate" (the
last line of an output chunk not ending with a newline) is
preserved.  This amends the fix for bug#14744.

3 files changed, 53 insertions, 39 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 0cc7bc6f702..b2d431c62cf 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,16 @@
+2015-03-27  Wolfgang Jenkner  <wjenkner@inode.at>
+
+        * font-lock.el (font-lock--remove-face-from-text-property): New
+        function.  Adapted from the previously commented out
+        remove-single-text-property.
+        Remove previously unused and commented out auxiliary function
+        remove-text-property and obsolete comment.
+        * comint.el (comint-output-filter): Use it to remove
+        comint-highlight-prompt.
+        (comint-snapshot-last-prompt, comint-output-filter): Use
+        font-lock-prepend-text-property for comint-highlight-prompt.
+        (Bug#20084)
+
 2015-03-26  Daniel Colascione  <dancol@dancol.org>
         * progmodes/python.el
         (python-indent-guess-indent-offset-verbose): New defcustom.
diff --git a/lisp/comint.el b/lisp/comint.el
index b6944da355c..31649ff31ca 100644
--- a/lisp/comint.el
+++ b/lisp/comint.el
@@ -1930,10 +1930,10 @@ the start, the cdr to the end of the last prompt recognized.")
 Freezes the `font-lock-face' text property in place."
   (when comint-last-prompt
     (with-silent-modifications
-      (add-text-properties
+      (font-lock-prepend-text-property
        (car comint-last-prompt)
        (cdr comint-last-prompt)
-       '(font-lock-face comint-highlight-prompt)))
+       'font-lock-face 'comint-highlight-prompt))
     ;; Reset comint-last-prompt so later on comint-output-filter does
     ;; not remove the font-lock-face text property of the previous
     ;; (this) prompt.
@@ -2084,14 +2084,19 @@ Make backspaces delete the previous character."
                   (add-text-properties prompt-start (point)
                                        '(read-only t front-sticky (read-only)))))
               (when comint-last-prompt
-                (remove-text-properties (car comint-last-prompt)
-                                        (cdr comint-last-prompt)
-                                        '(font-lock-face)))
+                (with-silent-modifications
+                  (font-lock--remove-face-from-text-property
+                   (car comint-last-prompt)
+                   (cdr comint-last-prompt)
+                   'font-lock-face
+                   'comint-highlight-prompt)))
               (setq comint-last-prompt
                     (cons (copy-marker prompt-start) (point-marker)))
-              (add-text-properties prompt-start (point)
-                                   '(rear-nonsticky t
-                                     font-lock-face comint-highlight-prompt)))
+              (with-silent-modifications
+                (font-lock-prepend-text-property prompt-start (point)
+                                                 'font-lock-face
+                                                 'comint-highlight-prompt)
+                (add-text-properties prompt-start (point) '(rear-nonsticky t))))
             (goto-char saved-point)))))))
 
 (defun comint-preinput-scroll-to-bottom ()
diff --git a/lisp/font-lock.el b/lisp/font-lock.el
index 1838a0f02b4..6c8392bc090 100644
--- a/lisp/font-lock.el
+++ b/lisp/font-lock.el
@@ -1418,37 +1418,33 @@ Optional argument OBJECT is the string or buffer containing the text."
       (put-text-property start next prop value object)
       (setq start (text-property-any next end prop nil object)))))
 
-;; For completeness: this is to `remove-text-properties' as `put-text-property'
-;; is to `add-text-properties', etc.
-;;(defun remove-text-property (start end property &optional object)
-;;  "Remove a property from text from START to END.
-;;Argument PROPERTY is the property to remove.
-;;Optional argument OBJECT is the string or buffer containing the text.
-;;Return t if the property was actually removed, nil otherwise."
-;;  (remove-text-properties start end (list property) object))
-
-;; For consistency: maybe this should be called `remove-single-property' like
-;; `next-single-property-change' (not `next-single-text-property-change'), etc.
-;;(defun remove-single-text-property (start end prop value &optional object)
-;;  "Remove a specific property value from text from START to END.
-;;Arguments PROP and VALUE specify the property and value to remove.  The
-;;resulting property values are not equal to VALUE nor lists containing VALUE.
-;;Optional argument OBJECT is the string or buffer containing the text."
-;;  (let ((start (text-property-not-all start end prop nil object)) next prev)
-;;    (while start
-;;      (setq next (next-single-property-change start prop object end)
-;;          prev (get-text-property start prop object))
-;;      (cond ((and (symbolp prev) (eq value prev))
-;;           (remove-text-property start next prop object))
-;;          ((and (listp prev) (memq value prev))
-;;           (let ((new (delq value prev)))
-;;             (cond ((null new)
-;;                    (remove-text-property start next prop object))
-;;                   ((= (length new) 1)
-;;                    (put-text-property start next prop (car new) object))
-;;                   (t
-;;                    (put-text-property start next prop new object))))))
-;;      (setq start (text-property-not-all next end prop nil object)))))
+(defun font-lock--remove-face-from-text-property (start
+                                                  end
+                                                  prop value &optional object)
+  "Remove a specific property value from text from START to END.
+Arguments PROP and VALUE specify the property and value to remove.  The
+resulting property values are not `eq' to VALUE nor lists containing VALUE.
+Optional argument OBJECT is the string or buffer containing the text."
+  (let ((start (text-property-not-all start end prop nil object)) next prev)
+    (while start
+      (setq next (next-single-property-change start prop object end)
+            prev (get-text-property start prop object))
+      (cond ((or (atom prev)
+                 (keywordp (car prev))
+                 (eq (car prev) 'foreground-color)
+                 (eq (car prev) 'background-color))
+             (when (eq value prev)
+               (remove-list-of-text-properties start next (list prop) object)))
+            ((memq value prev)          ;Assume prev is not dotted.
+             (let ((new (remq value prev)))
+               (cond ((null new)
+                      (remove-list-of-text-properties start next (list prop)
+                                                      object))
+                     ((= (length new) 1)
+                      (put-text-property start next prop (car new) object))
+                     (t
+                      (put-text-property start next prop new object))))))
+      (setq start (text-property-not-all next end prop nil object)))))
 
 ;;; End of Additional text property functions.