Ignore string properties when saving eshell history (Bug#28700)

* lisp/eshell/em-hist.el (eshell-write-history): Remove properties
before inserting history strings.
(eshell-read-history): Remove obsolete comment.
* test/lisp/eshell/em-hist-tests.el (eshell-write-readonly-history):
New test.

lisp/eshell/em-hist.el

@@ -444,7 +444,6 @@ line, with the most recent command last.  See also
 	     (ignore-dups eshell-hist-ignoredups))
 	(with-temp-buffer
 	  (insert-file-contents file)
-	  ;; Save restriction in case file is already visited...
 	  ;; Watch for those date stamps in history files!
 	  (goto-char (point-max))
 	  (while (and (< count size)
@@ -488,7 +487,9 @@ See also `eshell-read-history'."
 	  (while (> index 0)
 	    (setq index (1- index))
 	    (let ((start (point)))
-	      (insert (ring-ref ring index) ?\n)
+              ;; Remove properties before inserting, to avoid trouble
+              ;; with read-only strings (Bug#28700).
+              (insert (substring-no-properties (ring-ref ring index)) ?\n)
 	      (subst-char-in-region start (1- (point)) ?\n ?\177)))
 	  (eshell-with-private-file-modes
 	   (write-region (point-min) (point-max) file append

test/lisp/eshell/em-hist-tests.el

@@ -0,0 +1,39 @@
+;;; tests/em-hist-tests.el --- em-hist test suite
+
+;; Copyright (C) 2017 Free Software Foundation, Inc.
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Code:
+
+(require 'ert)
+(require 'em-hist)
+
+(ert-deftest eshell-write-readonly-history ()
+  "Test that having read-only strings in history is okay."
+  (let ((histfile (make-temp-file "eshell-history"))
+        (eshell-history-ring (make-ring 2)))
+    (ring-insert eshell-history-ring
+                 (propertize "echo foo" 'read-only t))
+    (ring-insert eshell-history-ring
+                 (propertize "echo bar" 'read-only t))
+    (unwind-protect
+        (eshell-write-history histfile)
+      (delete-file histfile))))
+
+(provide 'em-hist-test)
+
+;;; em-hist-tests.el ends here

test/lisp/eshell/eshell-tests.el

@@ -247,6 +247,6 @@ chars"
    (goto-char eshell-last-input-start)
    (string= (eshell-get-old-input) "echo alpha")))
 
-(provide 'esh-test)
+(provide 'eshell-tests)
 
 ;;; tests/eshell-tests.el ends here