1 files changed, 28 insertions, 0 deletions
diff --git a/src/builtins.zig b/src/builtins.zig
index 5fdabd87..da87ba37 100644
--- a/src/builtins.zig
+++ b/src/builtins.zig
@@ -575,6 +575,22 @@ fn warnModifiedIn(c: Ctx, asking: Pane.Discarding, which: Asked) bool {
             .column => |col| if ((layout.findPane(c.p, id) orelse continue).col != col) continue,
         }
         const f = pane.file orelse continue;
+        // Twins (Zerox) hold one text: closing one while another stays
+        // loses nothing, and the text is asked about once.
+        if (f.twin != 0) {
+            const asked_elsewhere = for (c.p.panes, 0..) |other_slot, other_id| {
+                const other = other_slot orelse continue;
+                const of = other.file orelse continue;
+                if (other_id == id or of.twin != f.twin) continue;
+                const closing = switch (which) {
+                    .all => true,
+                    .pane => |only| other_id == only,
+                    .column => |col| if (layout.findPane(c.p, other_id)) |at| at.col == col else false,
+                };
+                if (!closing or other_id < id) break true;
+            } else false;
+            if (asked_elsewhere) continue;
+        }
         // A +New scratch saves nowhere, but what is typed in it is as lost;
         // under 100 bytes it is not asked about, as acme's winclean does not
         // whine about a small unnamed window, nor about a command's output.
@@ -1196,6 +1212,18 @@ pub const Incl = struct {
     }
 };
 
+/// acme's Zerox: a second pane on this pane's file, the same text, undo and
+/// unsaved state, with a scroll and a cursor of its own (File.zerox).
+pub const Zerox = struct {
+    pub fn run(c: Ctx) void {
+        const f = c.pane.file orelse return c.p.reportFailure(c.id, "Zerox: only a file pane takes it");
+        if (f.output != null or f.listing != null or f.mini != null) return c.p.reportFailure(c.id, "Zerox: only a file pane takes it");
+        const free = c.p.freeSlot() orelse return c.p.reportError(c.id, "Zerox", error.NoPaneSlots);
+        _ = panes.File.zerox(c.p, c.id, free) catch |err| return c.p.reportError(c.id, "Zerox", err);
+        exec.placeNew(c.p, c.id, c.id, free, .doc);
+    }
+};
+
 /// Write the pane's text to its file, or to the file its argument names.
 pub const Save = struct {
     pub const takes_arg = true;