Fix Eshell call to 'string-suffix-p' when checking for trailing newline

* lisp/eshell/esh-io.el (eshell--output-maybe-n): Fix call.

* test/lisp/eshell/esh-io-tests.el
(esh-io-test/output-newline/add-newline)
(esh-io-test/output-newline/no-newline)
(esh-io-test/output-newline/no-extra-newline): New tests (bug#79063).

2 files changed, 23 insertions, 1 deletions

diff --git a/lisp/eshell/esh-io.el b/lisp/eshell/esh-io.el
index ff275560a04..1b474d988a7 100644
--- a/lisp/eshell/esh-io.el
+++ b/lisp/eshell/esh-io.el
@@ -569,7 +569,7 @@ ends in a newline."
   (eshell-output-object object handle)
   (when (and eshell-ensure-newline-p
              (not (and (stringp object)
-                       (string-suffix-p object "\n"))))
+                       (string-suffix-p "\n" object))))
     (eshell-maybe-output-newline handle)))
 
 (defsubst eshell-print-maybe-n (object)
diff --git a/test/lisp/eshell/esh-io-tests.el b/test/lisp/eshell/esh-io-tests.el
index 0b25ad812fa..e6bc5c9809c 100644
--- a/test/lisp/eshell/esh-io-tests.el
+++ b/test/lisp/eshell/esh-io-tests.el
@@ -42,6 +42,28 @@
 ;;; Tests:
 
 
+;; Newlines
+
+(ert-deftest esh-io-test/output-newline/add-newline ()
+  "Ensure we add a newline when writing a string to stdout."
+  (with-temp-eshell
+    (eshell-match-command-output "(concat \"hello\")" "\\`hello\n\\'")))
+
+(ert-deftest esh-io-test/output-newline/no-newline ()
+  "Ensure we don't add a newline when writing a string to a buffer."
+  (eshell-with-temp-buffer bufname ""
+    (with-temp-eshell
+      (eshell-match-command-output
+       (format "(concat \"hello\") > #<%s>" bufname)
+       "\\`\\'"))
+    (should (equal (buffer-string) "hello"))))
+
+(ert-deftest esh-io-test/output-newline/no-extra-newline ()
+  "Ensure we don't add an extra newline when writing to stdout."
+  (with-temp-eshell
+    (eshell-match-command-output "(concat \"hello\n\")" "\\`hello\n\\'")))
+
+
 ;; Basic redirection
 
 (ert-deftest esh-io-test/redirect-file/overwrite ()