Erase existing duplicates in eshell-history-ring

Erase all existing duplicates instead of just the last duplicate entry
when 'eshell-hist-ignoredups' is set to 'erase'.  Multiple duplicates
can exist in case 'eshell-hist-ignoredups' was set to something else
than 'erase' in the past or if the history file contains duplicates
(bug#71107).

* lisp/eshell/em-hist.el (eshell-add-input-to-history): Remove all
duplicates from history ring.

* test/lisp/eshell/em-hist-tests.el
(em-hist-test/add-to-history/erase-existing-dups): New test.

2 files changed, 20 insertions, 5 deletions

diff --git a/lisp/eshell/em-hist.el b/lisp/eshell/em-hist.el
index 21029eae1bc..b171a2850ff 100644
--- a/lisp/eshell/em-hist.el
+++ b/lisp/eshell/em-hist.el
@@ -398,11 +398,9 @@ input."
              (pcase eshell-hist-ignoredups
                ('nil t)                 ; Always add to history
                ('erase                  ; Add, removing any old occurrences
-                (when-let ((old-index (ring-member eshell-history-ring input)))
-                  ;; Remove the old occurrence of this input so we can
-                  ;; add it to the end.  FIXME: Should we try to
-                  ;; remove multiple old occurrences, e.g. if the user
-                  ;; recently changed to using `erase'?
+                (while-let ((old-index (ring-member eshell-history-ring input)))
+                  ;; Remove the old occurrences of this input so we can
+                  ;; add it to the end.
                   (ring-remove eshell-history-ring old-index))
                 t)
                (_                       ; Add if not already the latest entry
diff --git a/test/lisp/eshell/em-hist-tests.el b/test/lisp/eshell/em-hist-tests.el
index a4e1e01b124..40e6f90478d 100644
--- a/test/lisp/eshell/em-hist-tests.el
+++ b/test/lisp/eshell/em-hist-tests.el
@@ -163,6 +163,23 @@ elements against that; if t (the default), check against EXPECTED."
      (should (equal (ring-elements eshell-history-ring)
                     '("echo hi" "echo bye"))))))
 
+(ert-deftest em-hist-test/add-to-history/erase-existing-dups ()
+  "Test adding to history, erasing any old dups after switching to 'erase."
+  (let ((eshell-hist-ignoredups nil))
+    (with-temp-eshell
+     (eshell-insert-command "echo hi")
+     (eshell-insert-command "echo bye")
+     (eshell-insert-command "echo bye")
+     (eshell-insert-command "echo hi")
+     (eshell-insert-command "echo bye")
+     (setq eshell-hist-ignoredups 'erase)
+     (eshell-insert-command "echo hi")
+     (should (equal (ring-elements eshell-history-ring)
+                    '("echo hi" "echo bye" "echo bye" "echo bye")))
+     (eshell-insert-command "echo bye")
+     (should (equal (ring-elements eshell-history-ring)
+                    '("echo bye" "echo hi"))))))
+
 (provide 'em-hist-test)
 
 ;;; em-hist-tests.el ends here