A refused write to dot after a shell's truncation changes nothing: the truncation waits for the write, as limit's does

echo /nomatch/ > dot truncated dot to an empty range at the top before
the write was refused, so a failed address still moved the selection
and scrolled. The truncation is now held until the write that follows
it: that write sets dot, or, refused, leaves it as it was. A truncation
with no write after it (: > dot) empties it when its open goes.

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

1 files changed, 12 insertions, 2 deletions

diff --git a/src/ninep/pane.zig b/src/ninep/pane.zig
index 78bec09f..71484538 100644
--- a/src/ninep/pane.zig
+++ b/src/ninep/pane.zig
@@ -44,6 +44,10 @@ pub const State = struct {
     /// The limit a truncation cleared, kept until the write that follows it
     /// on that open (a shell's `>`): a write that fails puts it back.
     limit_truncated: ?Range = null,
+    /// `dot` was truncated and nothing written since: the write that
+    /// follows sets it or, refused, leaves it as it was; with none, the
+    /// open's release empties it (tree.zig releaseHandle).
+    dot_truncated: bool = false,
     /// Opens of `event`, which hold the pane scripted.
     readers: u16 = 0,
     /// One of `readers` reads `event`; a second reading open is refused.
@@ -800,9 +804,11 @@ fn writeRange(req: Req, pane: *Pane, file: PaneFile) Reply {
             pf.limit = kept;
             pf.limit_truncated = null;
         };
+        if (file == .dot) pf.dot_truncated = false;
         return tree.failText(req.tag, E.INVAL, a.err);
     };
     if (file == .limit) pf.limit_truncated = null;
+    if (file == .dot) pf.dot_truncated = false;
     switch (file) {
         .addr => {
             pf.addr = range;
@@ -1000,7 +1006,7 @@ pub fn truncate(p: *Pardes, pane: *Pane, file: PaneFile) tree.Status {
             pf.limit_truncated = pf.limit;
             pf.limit = null;
         },
-        .dot => if (fileOf(pane) != null) setDot(pane, .{}),
+        .dot => pf.dot_truncated = fileOf(pane) != null,
         else => {},
     }
     return .ok;
@@ -1211,8 +1217,12 @@ test "sel reads the selection and writing sel replaces it" {
     try testing.expectEqual(@as(u32, 0), p.panes[0].?.fs.addr.q0);
     try testing.expectEqual(@as(u32, 3), p.panes[0].?.fs.addr.q1);
 
-    // A truncation empties dot; an address expression addresses it.
+    // A truncation empties dot once its open goes, nothing written after
+    // it; an address expression addresses it.
+    const h = call(p, .{ .tag = 8, .op = .open, .node = dot, .omode = 1 }).reply.handle;
     _ = call(p, .{ .tag = 9, .op = .setattr, .node = dot, .truncate = true });
+    try testing.expectEqualStrings("one", rd(p, sel, 0, 100).bytes);
+    _ = call(p, .{ .tag = 10, .op = .release, .node = dot, .handle = h, .opened = true });
     try testing.expectEqualStrings("", rd(p, sel, 0, 100).bytes);
     try testing.expectEqual(Status.ok, wr(p, dot, "#0,#3").reply.status);