completions: add zsh completion for riverctl

build.zig

@@ -31,6 +31,12 @@ pub fn build(b: *zbs.Builder) !void {
         "Set to true to install bash completion for riverctl. Defaults to true.",
     ) orelse true;
 
+    const zsh_completion = b.option(
+        bool,
+        "zsh-completion",
+        "Set to true to install zsh completion for riverctl. Defaults to true.",
+    ) orelse true;
+
     const examples = b.option(bool, "examples", "Set to true to build examples") orelse false;
 
     const resolved_prefix = try std.fs.path.resolve(b.allocator, &[_][]const u8{b.install_prefix.?});
@@ -101,6 +107,13 @@ pub fn build(b: *zbs.Builder) !void {
         );
     }
 
+    if (zsh_completion) {
+        b.installFile(
+            "completions/zsh/_riverctl",
+            "share/zsh/site-functions/_riverctl",
+        );
+    }
+
     if (examples) {
         inline for (.{ "status", "options" }) |example_name| {
             const example = b.addExecutable(example_name, "example/" ++ example_name ++ ".zig");