1 files changed, 19 insertions, 0 deletions
diff --git a/src/ninep/ctl.zig b/src/ninep/ctl.zig
index 98980f2c..e44368ea 100644
--- a/src/ninep/ctl.zig
+++ b/src/ninep/ctl.zig
@@ -239,6 +239,14 @@ pub fn captured(p: *Pardes, req: Req, id: usize, exec: bool, text: []const u8, i
             p.fs.results_len = 0;
             return refuse(p, req, "wrong #args in control message", cmd);
         };
+        // ...and one that takes none, written with one (`Config extra`):
+        // refused as a ctl's is, not run as a shell command of that name.
+        if (std.mem.indexOfAny(u8, cmd, " \t")) |sp| if (std.meta.stringToEnum(Builtin, cmd[0..sp])) |b| {
+            if (!builtins.registry.takesArg(b) and config.Runtime.find(cmd[0..sp]) == null) {
+                p.fs.results_len = 0;
+                return refuse(p, req, "wrong #args in control message", cmd);
+            }
+        };
     }
     p.fs.capturing = true;
     p.fs.failure_len = 0;
@@ -2435,6 +2443,17 @@ test "a look that misses file:/re/ names the file, and is logged as its pane's"
     try testing.expect(th.logHas(p, try std.fmt.bufPrint(&want, "err {d} look: {s}/f.txt: no match for regexp", .{ f_serial, dir })));
 }
 
+test "a builtin that takes no argument, written with one to an exec, is refused wrong #args, as at a ctl" {
+    const p = try withFile(testing.allocator, "x\n");
+    defer p.deinit();
+    const serial = serialOf(p);
+    for ([_]u64{ @intFromEnum(tree.TopFile.exec), Node.of(serial, .exec) }) |node| for ([_][]const u8{ "Config extra\n", "DumpConfig extra\n" }) |line| {
+        const r = wr(p, node, line);
+        try testing.expectEqual(E.INVAL, r.errno());
+        try testing.expectStringStartsWith(r.reply.ename, "wrong #args in control message");
+    };
+}
+
 test "acme's words run as pardes's (Put is Save, Delete a Del that does not ask) or are refused, never run as commands" {
     const p = try withFile(testing.allocator, "x\n");
     defer p.deinit();