Only Tty reads Word+arg as its argument

Every builtin that takes an argument split a word at its first +, so
Dump+2024.zon ran Dump with 2024.zon. A builtin now opts in with plus_arg,
read by the registry, and only Tty does.

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

1 files changed, 6 insertions, 2 deletions

diff --git a/src/exec.zig b/src/exec.zig
index 86adfeeb..86dba32a 100644
--- a/src/exec.zig
+++ b/src/exec.zig
@@ -488,8 +488,12 @@ pub fn commandText(txt: []const u8) []const u8 {
 pub fn executeBuiltinLine(p: *Pardes, id: usize, txt: []const u8) bool {
     const cmd = commandText(txt);
     if (cmd.len == 0 or p.exec_depth >= max_exec_depth) return false;
-    // `Word arg`, or as one word a tag can hold, `Word+arg` (`Tty+fish`).
-    const sp = std.mem.indexOfAny(u8, cmd, " \t") orelse std.mem.indexOfScalar(u8, cmd, '+');
+    // `Word arg`, or for a word that says so, `Word+arg` (`Tty+fish`).
+    const plus = std.mem.indexOfScalar(u8, cmd, '+');
+    var sp = std.mem.indexOfAny(u8, cmd, " \t");
+    if (sp == null) if (plus) |at| if (std.meta.stringToEnum(Builtin, cmd[0..at])) |head| {
+        if (builtins.registry.plusArg(head)) sp = at;
+    };
     const bi: ?Builtin = std.meta.stringToEnum(Builtin, cmd) orelse blk: {
         const head = std.meta.stringToEnum(Builtin, cmd[0 .. sp orelse break :blk null]) orelse break :blk null;
         break :blk if (builtins.registry.takesArg(head)) head else null;