Prefer module filenames instead of mod.rs

Summary:
> Note: Prior to rustc 1.30, using `mod.rs` files was the way to load a
> module with nested children. It is encouraged to use the new naming
> convention as it is more consistent, and avoids having many files
> named `mod.rs` within a project.

https://doc.rust-lang.org/reference/items/modules.html#module-source-filenames

Reviewed By: davidbarsky

Differential Revision: D55921363

fbshipit-source-id: 31cdc981117649c9d8a64f7239429ca40cdfc1e0

common/rust/shed/hostcaps/src/facebook.rs

@@ -0,0 +1,53 @@
+// (c) Meta Platforms, Inc. and affiliates. Confidential and proprietary.
+
+use fbwhoami::FbWhoAmI;
+
+#[derive(PartialEq)]
+#[repr(u8)]
+pub enum Env {
+    Prod = 0,
+    Corp = 1,
+    Lab = 2,
+}
+
+pub fn get_env() -> Env {
+    let whoami = if let Ok(whoami) = FbWhoAmI::get() {
+        whoami
+    } else {
+        // default to corp env if no fbwhoami
+        return Env::Corp;
+    };
+
+    // Corp host e.g. a lab
+    if let Some(hostname_scheme) = &whoami.hostname_scheme {
+        if hostname_scheme.starts_with("corp_") {
+            return Env::Corp;
+        }
+        if hostname_scheme.starts_with("lab_") {
+            return Env::Lab;
+        }
+    }
+
+    // Cloud hosts e.g. AWS are treated like corp
+    if whoami.cloud_provider.is_some() {
+        return Env::Corp;
+    }
+
+    // Default to prod
+    Env::Prod
+}
+
+/// Returns true if the running host is on the production network.
+pub fn is_prod() -> bool {
+    get_env() == Env::Prod
+}
+
+/// Returns true if the running host is on the corp network.
+pub fn is_corp() -> bool {
+    get_env() == Env::Corp
+}
+
+/// Returns true if the running host is on the lab network.
+pub fn is_lab() -> bool {
+    get_env() == Env::Lab
+}