A shell's > on addr no longer resets it, so echo /re/ > addr searches on

Truncating addr reset it to #0, so a shell's find-and-replace loop matched the first hit for ever, .+#1 read 1 1 each time, and foo x foo y foo became foobarbarbar... acme resets addr on the first open (xfid.c:105-108), for clients that hold the fid; a shell cannot. Here neither an open nor a truncation resets it: the address written is evaluated from the last one, and 0 or , starts over. Documented as a departure from acme.

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

1 files changed, 10 insertions, 9 deletions

diff --git a/src/ninep/pane.zig b/src/ninep/pane.zig
index f87e43a6..714a2566 100644
--- a/src/ninep/pane.zig
+++ b/src/ninep/pane.zig
@@ -29,14 +29,15 @@ const Node = tree.Node;
 /// Filesystem state a pane carries beside its editor state.
 pub const State = struct {
     /// The range `data` and `xdata` read and write through. acme clears it
-    /// when the first client opens `addr` (editors/acme/xfid.c:105), which
-    /// suits a client that holds the fid open and leaves a shell reading back
-    /// `0 0` from the address it just wrote. Here it is the pane's own
-    /// register, cleared by truncating the file, so that `cp addr dot` and
+    /// when the first client opens `addr` (editors/acme/xfid.c:105-108),
+    /// which suits a client that holds the fid open; a shell cannot, and
+    /// would evaluate every `echo /re/ > addr` from #0 and never advance.
+    /// Here it is the pane's own register, cleared by neither an open nor
+    /// a truncation: `0` or `,` starts over, and `cp addr dot` and
     /// `cat addr` answer what was written.
     addr: Range = .{},
     /// The last address written to `addr` failed, so there is none: `data`
-    /// and `xdata` refuse until one is written or `addr` is truncated,
+    /// and `xdata` refuse until a good one is written,
     /// rather than act at the address before it, which acme would do.
     addr_failed: bool = false,
     limit: ?Range = null,
@@ -634,10 +635,10 @@ pub fn truncate(p: *Pardes, pane: *Pane, file: PaneFile) tree.Status {
             pane.tag.vsel.active = false;
             pane.tag.nsel = 0;
         },
-        .addr => {
-            pf.addr = .{};
-            pf.addr_failed = false;
-        },
+        // A shell's `>` truncates before it writes: the address written
+        // is evaluated from where the last one left off, as with `>>`.
+        // `0` (or `,`) is how to start over. See State.addr.
+        .addr => {},
         .limit => pf.limit = null,
         .dot => if (fileOf(pane) != null) setDot(pane, .{}),
         else => {},