Fix a race condition when evaluating Eshell commands

* lisp/eshell/esh-cmd.el (eshell-do-eval): Don't defer when all the
processes are done.

* test/lisp/eshell/esh-cmd-tests.el
(esh-cmd-test/pipeline-wait/nested-pipes): New test.

1 files changed, 4 insertions, 2 deletions

diff --git a/lisp/eshell/esh-cmd.el b/lisp/eshell/esh-cmd.el
index dae1a77552f..57aeff59266 100644
--- a/lisp/eshell/esh-cmd.el
+++ b/lisp/eshell/esh-cmd.el
@@ -1287,13 +1287,15 @@ have been replaced by constants."
                     (setcdr form (cdr new-form)))
                   (eshell-do-eval form synchronous-p))
               (if-let (((memq (car form) eshell-deferrable-commands))
-                       (procs (eshell-make-process-list result)))
+                       (procs (eshell-make-process-list result))
+                       (active (seq-some #'eshell-process-active-p procs)))
                   (if synchronous-p
                       (apply #'eshell/wait procs)
                     (eshell-manipulate form "inserting ignore form"
                       (setcar form 'ignore)
                       (setcdr form nil))
-                    (throw 'eshell-defer procs))
+                    (when active
+                      (throw 'eshell-defer procs)))
                 (list 'quote result))))))))))))
 
 ;; command invocation