Be more cautious in completing Eshell variable assignments

Previously, Eshell treated cases like the second argument in "tar
--directory=dir" as a variable assignment, but that prevented
'pcomplete/tar' from implementing its own completion for that
argument (bug#61778).

* lisp/eshell/esh-var.el (eshell-complete-variable-assignment): Only
handle completion when all initial arguments are variable assignments.

* test/lisp/eshell/em-cmpl-tests.el
(em-cmpl-test/variable-assign-completion/non-assignment): New test.

1 files changed, 13 insertions, 5 deletions

diff --git a/lisp/eshell/esh-var.el b/lisp/eshell/esh-var.el
index 0031324b537..5d6299af564 100644
--- a/lisp/eshell/esh-var.el
+++ b/lisp/eshell/esh-var.el
@@ -862,11 +862,19 @@ START and END."
 
 (defun eshell-complete-variable-assignment ()
   "If there is a variable assignment, allow completion of entries."
-  (let ((arg (pcomplete-actual-arg)) pos)
-    (when (string-match (concat "\\`" eshell-variable-name-regexp "=") arg)
-      (setq pos (match-end 0))
-      (if (string-match "\\(:\\)[^:]*\\'" arg)
-          (setq pos (match-end 1)))
+  (catch 'not-assignment
+    ;; The current argument can only be a variable assignment if all
+    ;; arguments leading up to it are also variable assignments.  See
+    ;; `eshell-handle-local-variables'.
+    (dotimes (offset (1+ pcomplete-index))
+      (unless (string-match (concat "\\`" eshell-variable-name-regexp "=")
+                            (pcomplete-actual-arg 'first offset))
+        (throw 'not-assignment nil)))
+    ;; We have a variable assignment.  Handle it.
+    (let ((arg (pcomplete-actual-arg))
+          (pos (match-end 0)))
+      (when (string-match "\\(:\\)[^:]*\\'" arg)
+        (setq pos (match-end 1)))
       (setq pcomplete-stub (substring arg pos))
       (throw 'pcomplete-completions (pcomplete-entries)))))