An edit that changes nothing, an empty range deleted or a range replaced by what it holds, makes no undo step

A shell's : > data on an empty address, echo abc > data over abc, or
Edit s/d/d/ each pushed an undo step and a new revision, so Undo spent
a press on nothing and the pane read as edited. The splice of the 9P
writes and the Edit builtin now see the text is unchanged and stop.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 5 insertions, 2 deletions

diff --git a/src/builtins.zig b/src/builtins.zig
index edeb7ac8..cb588ba3 100644
--- a/src/builtins.zig
+++ b/src/builtins.zig
@@ -1140,8 +1140,11 @@ pub const Edit = struct {
         }
         if (res.ops.len > 0) {
             const new = sam.apply(c.p.gpa, f.content, res.ops) catch |err| return c.p.reportError(c.id, "Edit", err);
-            panes.File.pushUndo(c.p, c.pane);
-            panes.File.setContent(c.p, f, new);
+            // `s/a/a/` changes nothing: no undo step, no new revision.
+            if (std.mem.eql(u8, new, f.content)) c.p.gpa.free(new) else {
+                panes.File.pushUndo(c.p, c.pane);
+                panes.File.setContent(c.p, f, new);
+            }
         }
         ninep_pane.setDot(c.pane, sam.moveDot(res.dot, res.ops));
         if (res.printed.len > 0) _ = ninep_pane.appendErrors(c.p, c.id, res.printed);