[nongnu] elpa/undo-fu 49cca61343 56/82: Fix unconstrained redo trapping the user at the end of the chain

[ELPA Syncer]

branch: elpa/undo-fu
commit 49cca61343e5fc80347a7b1f7d8692a49752575d
Author: Campbell Barton <ideasman42@gmail.com>
Commit: Campbell Barton <ideasman42@gmail.com>

    Fix unconstrained redo trapping the user at the end of the chain
    
    Add a special check for this, allowing you to undo out of this state.
---
 changelog.rst |  2 ++
 undo-fu.el    | 10 ++++++++++
 2 files changed, 12 insertions(+)

diff --git a/changelog.rst b/changelog.rst
index 57787c5684..9ed97ea73b 100644
--- a/changelog.rst
+++ b/changelog.rst
@@ -5,6 +5,8 @@ Change Log
 
 - In development
 
+  - Fix continual redo in unconstrained mode trapping the user in a state
+    where neither undo or redo can be performed.
   - Fix undo checkpoint initialization when running for the first with 
existing undo data.
     This could happen when running undo immediately upon loading a file with 
undo data from ``undo-fu-session``.
   - Undo in *unconstrained* mode no longer uses ``undo-only``,
diff --git a/undo-fu.el b/undo-fu.el
index ac70a1ef67..120fd1b39d 100644
--- a/undo-fu.el
+++ b/undo-fu.el
@@ -353,6 +353,7 @@ Optional argument ARG the number of steps to undo."
   (let*
     ( ;; Assign for convenience.
       (was-undo-or-redo (undo-fu--was-undo-or-redo))
+      (was-redo (and was-undo-or-redo undo-fu--was-redo))
       (undo-fu-quit-command
         (if undo-fu-ignore-keyboard-quit
           'undo-fu-disable-checkpoint
@@ -399,6 +400,15 @@ Optional argument ARG the number of steps to undo."
         (steps (or arg 1))
         (last-command
           (cond
+            ;; Special case, to avoid being locked out of the undo-redo chain.
+            ;; Without this, continuously redoing will end up in a state where 
undo & redo fails.
+            ;;
+            ;; Detect this case and break the chain. Only do this when 
previously redoing
+            ;; otherwise undo will reverse immediately once it reaches the 
beginning,
+            ;; which we don't want even when unconstrained,
+            ;; as we don't want to present the undo chain as infinite in 
either direction.
+            ((and was-redo (null undo-fu--respect) (eq t pending-undo-list))
+              'ignore)
             (was-undo-or-redo
               ;; Checked by the undo function.
               'undo)