td: Add a check_knob util

Summary: It's a little annoying to write all the `cfg` boilerplate again and again.

Reviewed By: Acesine

Differential Revision: D55648146

fbshipit-source-id: ab30c9714dfd8a40861ee7ec39ef15fa8de04e6d

td_util/src/knobs.rs

@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under both the MIT license found in the
+ * LICENSE-MIT file in the root directory of this source tree and the Apache
+ * License, Version 2.0 found in the LICENSE-APACHE file in the root directory
+ * of this source tree.
+ */
+
+#[cfg(any(not(fbcode_build), not(target_os = "linux")))]
+pub fn check_boolean_knob(name: &str) -> bool {
+    false
+}
+
+#[cfg(all(fbcode_build, target_os = "linux"))]
+pub fn check_boolean_knob(name: &str) -> bool {
+    justknobs::eval(name, None, None).unwrap_or(false)
+}

td_util/src/lib.rs

@@ -13,6 +13,7 @@ pub mod cli;
 pub mod command;
 pub mod directives;
 pub mod json;
+pub mod knobs;
 pub mod no_hash;
 pub mod prelude;
 pub mod project;