pardes --wait with no FILE says it needs one; --detach over a name another session's socket holds (a plain session is named by its pid) says so plainly, and any other failure of it in words, never a Zig error trace

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

2 files changed, 19 insertions, 1 deletions

diff --git a/src/main.zig b/src/main.zig
index f6a3a3ec..ed70b624 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -466,6 +466,10 @@ fn nativeMain(init: std.process.Init) !void {
     opts.mounts = mounts[0..mounts_len];
     if (detach != null and attach != null)
         badArgs(init.io, "--detach and --attach are opposites: one runs the session, the other joins one", .{});
+    // --wait waits on the pane a FILE opens: with none there is nothing to
+    // wait for (EDITOR=pardes --wait is given the file).
+    if (wait and positional == null)
+        badArgs(init.io, "--wait needs a FILE: it returns when that file's pane is closed", .{});
     if (opts.ninep_name.len != 0 and attach != null)
         badArgs(init.io, "--9p names a session's own socket, and --attach has none of its own", .{});
     if (opts.ninep_tcp != null and attach != null)
@@ -709,7 +713,18 @@ fn nativeMain(init: std.process.Init) !void {
             name
         else
             try std.fmt.allocPrint(arena, "{d}", .{@as(u32, @intCast(std.c.getpid()))});
-        return @import("detached/server.zig").run(init, opts, named);
+        // Said plainly, never a Zig error trace: a name another session's
+        // socket holds already (a plain session is named by its pid too).
+        return @import("detached/server.zig").run(init, opts, named) catch |err| {
+            var words: [128]u8 = undefined;
+            var said: [512]u8 = undefined;
+            const why = if (err == error.ListenFailed)
+                "its socket is taken: another session (a plain one is named by its pid) holds that name; choose another"
+            else
+                pardes.Messages.errorWords(err, &words);
+            std.Io.File.stderr().writeStreamingAll(init.io, std.fmt.bufPrint(&said, "pardes: --detach={s}: {s}\n", .{ named, why }) catch "pardes: --detach failed\n") catch {};
+            std.process.exit(1);
+        };
     }
     if (attach != null and pardes.platform != .tty and pardes.platform != .gui) {
         try std.Io.File.stderr().writeStreamingAll(init.io, "pardes: --attach needs the tty or gui shell\n");
diff --git a/test/fs.py b/test/fs.py
index f954b508..97af9e6b 100644
--- a/test/fs.py
+++ b/test/fs.py
@@ -1595,6 +1595,9 @@ def test(binary, quic=False):
             dead_env = dict(outside_env, PARDES_9P=str(root / 'pardes-9p-gone.sock'))
             gone = subprocess.run([binary, '--wait', str(far)], cwd=root, env=dead_env, capture_output=True, timeout=10)
             assert gone.returncode == 1 and b'does not answer' in gone.stderr, gone
+            # --wait with no FILE says it needs one, and waits on nothing.
+            bare = subprocess.run([binary, '--wait'], cwd=root, env=env, capture_output=True, timeout=10)
+            assert bare.returncode == 1 and b'--wait needs a FILE' in bare.stderr, bare
             # `--` ends the options: a name starting with a dash is a name.
             dash = root / '-dash.txt'
             dash.write_bytes(b'dash\n')