Fix Bug#40156 in Tramp

* lisp/net/tramp-sh.el (tramp-sh-handle-write-region): Copy to temp file
only if FILENAME exists.  (Bug#40156)

* test/lisp/net/tramp-tests.el (tramp-test10-write-region): Extend test.

2 files changed, 10 insertions, 2 deletions

diff --git a/lisp/net/tramp-sh.el b/lisp/net/tramp-sh.el
index 7ac41d16c8b..06dca312275 100644
--- a/lisp/net/tramp-sh.el
+++ b/lisp/net/tramp-sh.el
@@ -3306,7 +3306,8 @@ STDERR can also be a file name."
 
           ;; If `append' is non-nil, we copy the file locally, and let
           ;; the native `write-region' implementation do the job.
-          (when append (copy-file filename tmpfile 'ok))
+          (when (and append (file-exists-p filename))
+            (copy-file filename tmpfile 'ok))
 
           ;; We say `no-message' here because we don't want the
           ;; visited file modtime data to be clobbered from the temp
diff --git a/test/lisp/net/tramp-tests.el b/test/lisp/net/tramp-tests.el
index e220420d8cf..e6c6b28c58a 100644
--- a/test/lisp/net/tramp-tests.el
+++ b/test/lisp/net/tramp-tests.el
@@ -2356,7 +2356,14 @@ This checks also `file-name-as-directory', `file-name-directory',
                 (write-region nil nil tmp-name 3))
               (with-temp-buffer
                 (insert-file-contents tmp-name)
-                (should (string-equal (buffer-string) "foobaz"))))
+                (should (string-equal (buffer-string) "foobaz")))
+              (delete-file tmp-name)
+              (with-temp-buffer
+                (insert "foo")
+                (write-region nil nil tmp-name 'append))
+              (with-temp-buffer
+                (insert-file-contents tmp-name)
+                (should (string-equal (buffer-string) "foo"))))
 
             ;; Write string.
             (write-region "foo" nil tmp-name)