1 files changed, 21 insertions, 2 deletions
diff --git a/src/ninep/pane.zig b/src/ninep/pane.zig
index d276b771..14877f0f 100644
--- a/src/ninep/pane.zig
+++ b/src/ninep/pane.zig
@@ -304,6 +304,21 @@ pub fn spliceBody(p: *Pardes, pane: *Pane, q0: usize, q1: usize, bytes: []const
     return take;
 }
 
+test "a shell's > into an empty pane's body is one undo step, as into any other" {
+    const p = try withFile(testing.allocator, "");
+    defer p.deinit();
+    const pane = p.panes[0].?;
+    const f = &pane.file.?;
+    const body = Node.of(pane.serial, .body);
+    const steps = f.history.undo_len;
+    const h = call(p, .{ .tag = 1, .op = .open, .node = body, .omode = 1 }).reply.handle;
+    _ = call(p, .{ .tag = 2, .op = .setattr, .node = body, .truncate = true });
+    try testing.expectEqual(tree.Status.ok, call(p, .{ .tag = 3, .op = .write, .node = body, .handle = h, .data = "fresh\n" }).reply.status);
+    _ = call(p, .{ .tag = 4, .op = .release, .node = body, .handle = h, .opened = true });
+    try testing.expectEqualStrings("fresh\n", f.content);
+    try testing.expectEqual(steps + 1, f.history.undo_len);
+}
+
 test "a write that changes nothing, an empty range deleted or a range replaced by itself, makes no undo step" {
     const p = try withFile(testing.allocator, "abc\ndef\n");
     defer p.deinit();
@@ -1017,8 +1032,11 @@ pub fn truncate(p: *Pardes, pane: *Pane, file: PaneFile) tree.Status {
     switch (file) {
         .body => if (fileOf(pane) != null) {
             pf.joined = null;
+            const was = fileOf(pane).?.revision;
             _ = spliceBody(p, pane, 0, bodyOf(pane).len, "") orelse return .err;
-            pf.joined = fileOf(pane).?.revision;
+            // An empty body truncated is no edit: the write after it makes
+            // the step, rather than join one that was never pushed.
+            pf.joined = if (fileOf(pane).?.revision != was) fileOf(pane).?.revision else null;
             pf.joined_by = 0;
             pf.addr = .{};
             setDot(pane, .{});
@@ -1029,8 +1047,9 @@ pub fn truncate(p: *Pardes, pane: *Pane, file: PaneFile) tree.Status {
             const q1 = @max(q0, pf.addr.q1);
             const before = dotOf(pane);
             pf.joined = null;
+            const was = fileOf(pane).?.revision;
             _ = spliceBody(p, pane, q0, q1, "") orelse return .err;
-            pf.joined = fileOf(pane).?.revision;
+            pf.joined = if (fileOf(pane).?.revision != was) fileOf(pane).?.revision else null;
             pf.joined_by = 0;
             setDot(pane, .{ .q0 = shiftOne(before.q0, q0, q1 - q0, 0), .q1 = shiftOne(before.q1, q0, q1 - q0, 0) });
             pf.addr = .{ .q0 = q0, .q1 = q0 };