In Eshell, allow an escaped newline at the end of a command

Normally, "echo<RET>" runs the command "echo".  Likewise,
"echo\<RET><RET>" should too: we escape the first newline, and then
the second one is unescaped and should send the command input to
Eshell.  Previously, you had to press RET a third time, but now it
works as expected.

* lisp/eshell/esh-arg.el (eshell-looking-at-backslash-return): Make
obsolete.
(eshell-parse-backslash): A backslash sequence is only incomplete if
there's nothing at all after it.

* test/lisp/eshell/esh-arg-tests.el (esh-arg-test/escape/newline)
(esh-arg-test/escape-quoted/newline): Remove inaccurate comment;
escaped newlines are always special.
(esh-arg-test/escape/trailing-newline): New test.

2 files changed, 11 insertions, 8 deletions

diff --git a/lisp/eshell/esh-arg.el b/lisp/eshell/esh-arg.el
index 1880cc03885..97ddac58629 100644
--- a/lisp/eshell/esh-arg.el
+++ b/lisp/eshell/esh-arg.el
@@ -440,6 +440,7 @@ Point is left at the end of the arguments."
 
 (defsubst eshell-looking-at-backslash-return (pos)
   "Test whether a backslash-return sequence occurs at POS."
+  (declare (obsolete nil "30.1"))
   (and (eq (char-after pos) ?\\)
        (or (= (1+ pos) (point-max))
            (and (eq (char-after (1+ pos)) ?\n)
@@ -464,8 +465,8 @@ backslash is ignored and the character after is returned.  If the
 backslash is in a quoted string, the backslash and the character
 after are both returned."
   (when (eq (char-after) ?\\)
-    (when (eshell-looking-at-backslash-return (point))
-        (throw 'eshell-incomplete "\\"))
+    (when (= (1+ (point)) (point-max))
+      (throw 'eshell-incomplete "\\"))
     (forward-char 2) ; Move one char past the backslash.
     (let ((special-chars (if eshell-current-quoted
                              eshell-special-chars-inside-quoting
diff --git a/test/lisp/eshell/esh-arg-tests.el b/test/lisp/eshell/esh-arg-tests.el
index b626cf10bf1..b748c5ab4c0 100644
--- a/test/lisp/eshell/esh-arg-tests.el
+++ b/test/lisp/eshell/esh-arg-tests.el
@@ -60,13 +60,17 @@ chars."
                                 "he\\\\llo\n")))
 
 (ert-deftest esh-arg-test/escape/newline ()
-  "Test that an escaped newline is equivalent to the empty string.
-When newlines are *nonspecial*, an escaped newline should be
-treated as just a newline."
+  "Test that an escaped newline is equivalent to the empty string."
   (with-temp-eshell
    (eshell-match-command-output "echo hi\\\nthere"
                                 "hithere\n")))
 
+(ert-deftest esh-arg-test/escape/trailing-newline ()
+  "Test that an escaped newline is equivalent to the empty string."
+  (with-temp-eshell
+   (eshell-match-command-output "echo hi\\\n"
+                                "hi\n")))
+
 (ert-deftest esh-arg-test/escape/newline-conditional ()
   "Test invocation of an if/else statement using line continuations."
   (let ((eshell-test-value t))
@@ -95,9 +99,7 @@ chars."
                                 "\\\"hi\\\\\n")))
 
 (ert-deftest esh-arg-test/escape-quoted/newline ()
-  "Test that an escaped newline is equivalent to the empty string.
-When newlines are *nonspecial*, an escaped newline should be
-treated literally, as a backslash and a newline."
+  "Test that an escaped newline is equivalent to the empty string."
   (with-temp-eshell
    (eshell-match-command-output "echo \"hi\\\nthere\""
                                 "hithere\n")))