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, 22 insertions, 0 deletions

diff --git a/src/ninep/addr.zig b/src/ninep/addr.zig
index df2cfaf0..b78c46e7 100644
--- a/src/ninep/addr.zig
+++ b/src/ninep/addr.zig
@@ -498,6 +498,28 @@ test "regular expressions search lines as sam's do, and a search wraps" {
     try testing.expectEqual(@as(u32, 5), q.panes[0].?.fs.addr.q0);
 }
 
+test "a refused write to dot after a truncation changes nothing; a truncation with no write empties it at close" {
+    const p = try th.withFile(testing.allocator, "one\ntwo\nthree\n");
+    defer p.deinit();
+    const serial = th.serialOf(p);
+    const dot = Node.of(serial, .dot);
+    try testing.expectEqual(Status.ok, th.wr(p, dot, "2").reply.status);
+    const was = th.rd(p, dot, 0, 64).bytes;
+    var kept: [64]u8 = undefined;
+    @memcpy(kept[0..was.len], was);
+    // A shell's `echo /nomatch/ > dot`: truncate, then the refused write.
+    const h = th.call(p, .{ .tag = 1, .op = .open, .node = dot, .omode = 1 }).reply.handle;
+    _ = th.call(p, .{ .tag = 2, .op = .setattr, .node = dot, .truncate = true });
+    try testing.expectEqual(Status.err, th.call(p, .{ .tag = 3, .op = .write, .node = dot, .handle = h, .data = "/nomatch/" }).reply.status);
+    _ = th.call(p, .{ .tag = 4, .op = .release, .node = dot, .handle = h, .opened = true });
+    try testing.expectEqualStrings(kept[0..was.len], th.rd(p, dot, 0, 64).bytes);
+    // `: > dot`: the truncation alone empties it once its open goes.
+    const h2 = th.call(p, .{ .tag = 5, .op = .open, .node = dot, .omode = 1 }).reply.handle;
+    _ = th.call(p, .{ .tag = 6, .op = .setattr, .node = dot, .truncate = true });
+    _ = th.call(p, .{ .tag = 7, .op = .release, .node = dot, .handle = h2, .opened = true });
+    try testing.expectEqualStrings("          0           0 ", th.rd(p, dot, 0, 64).bytes);
+}
+
 test "a failed address leaves none, so data refuses rather than act at the last one" {
     const p = try th.withFile(testing.allocator, "one\ntwo\n");
     defer p.deinit();