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, 11 insertions, 0 deletions

diff --git a/src/builtins.zig b/src/builtins.zig
index 02787cf5..4815a114 100644
--- a/src/builtins.zig
+++ b/src/builtins.zig
@@ -145,6 +145,16 @@ pub const registry = struct {
         return true;
     }
 
+    /// Whether the word takes its argument joined by a `+` as one word a
+    /// tag can hold and a click take whole (`Tty+fish`). Only a builtin
+    /// that says `pub const plus_arg = true;`: others have arguments a `+`
+    /// may be in (`Dump+2024.zon` is a name, not Dump's argument).
+    pub fn plusArg(b: Builtin()) bool {
+        inline for (manualBuiltinList(), 0..) |T, i|
+            if (@intFromEnum(b) == i) return @hasDecl(T, "plus_arg") and T.plus_arg;
+        return false;
+    }
+
     /// Whether the word means nothing without its argument (`Mount`,
     /// `Msg`, a setting's value), or would ask for it at a prompt (`Find`):
     /// a ctl refuses it bare before any line of the write runs. A builtin
@@ -822,6 +832,7 @@ pub const DelBelow = struct {
 /// the one named, `Tty fish`, as a terminal's own tag word `Tty+fish` says.
 pub const Tty = struct {
     pub const takes_arg = true;
+    pub const plus_arg = true;
     pub fn run(c: Ctx) void {
         exec.spawnTty(c.p, c.id);
         const arg = c.arg orelse return;