em-extpipe: Catch eshell-incomplete thrown while parsing

* lisp/eshell/em-extpipe.el (em-extpipe--or-with-catch): New macro.
(eshell-parse-external-pipeline): Use new macro to treat
`eshell-incomplete' as a failure of the parse function to move us
forward (Bug#54603).  Thanks to Jim Porter <jporterbugs@gmail.com> for
the report and for help isolating the problem.

* test/lisp/eshell/eshell-tests.el
(eshell-test/lisp-command-with-quote): New test for Bug#54603, thanks
to Jim Porter <jporterbugs@gmail.com> (bug#54603).

1 files changed, 18 insertions, 4 deletions

diff --git a/lisp/eshell/em-extpipe.el b/lisp/eshell/em-extpipe.el
index eb5b3bfe1df..3db1dea5955 100644
--- a/lisp/eshell/em-extpipe.el
+++ b/lisp/eshell/em-extpipe.el
@@ -49,6 +49,19 @@
   (add-hook 'eshell-pre-rewrite-command-hook
             #'eshell-rewrite-external-pipeline -20 t))
 
+(defmacro em-extpipe--or-with-catch (&rest disjuncts)
+  "Evaluate DISJUNCTS like `or' but catch `eshell-incomplete'.
+
+If `eshell-incomplete' is thrown during the evaluation of a
+disjunct, that disjunct yields nil."
+  (let ((result (gensym)))
+    `(let (,result)
+       (or ,@(cl-loop for disjunct in disjuncts collect
+                      `(if (catch 'eshell-incomplete
+                             (ignore (setq ,result ,disjunct)))
+                           nil
+                         ,result))))))
+
 (defun eshell-parse-external-pipeline ()
   "Parse a pipeline intended for execution by the external shell.
 
@@ -105,10 +118,11 @@ as though it were Eshell syntax."
                        (if (re-search-forward pat next t)
                            (throw 'found (match-beginning 1))
                          (goto-char next)
-                         (while (or (eshell-parse-lisp-argument)
-                                    (eshell-parse-backslash)
-                                    (eshell-parse-double-quote)
-                                    (eshell-parse-literal-quote)))
+                         (while (em-extpipe--or-with-catch
+                                 (eshell-parse-lisp-argument)
+                                 (eshell-parse-backslash)
+                                 (eshell-parse-double-quote)
+                                 (eshell-parse-literal-quote)))
                          ;; Guard against an infinite loop if none of
                          ;; the parsers moved us forward.
                          (unless (or (> (point) next) (eobp))