Fail if generate_docs feature is not enabled and ROS_DISTRO is not set

rclrs/Cargo.toml

@@ -16,7 +16,9 @@ path = "src/lib.rs"
 [dependencies]
 # Needed for dynamically finding type support libraries 
 ament_rs = { version = "0.2", optional = true }
+# Needed for uploading documentation to docs.rs
 cfg-if = "1.0.0"
+
 # Needed for clients
 futures = "0.3"
 # Needed for dynamic messages
@@ -31,6 +33,8 @@ tempfile = "3.3.0"
 [build-dependencies]
 # Needed for FFI
 bindgen = "0.66.1"
+# Needed for uploading documentation to docs.rs
+cfg-if = "1.0.0"
 
 [features]
 dyn_msg = ["ament_rs", "libloading"]

rclrs/build.rs

@@ -21,11 +21,16 @@ fn main() {
     let ros_distro = if let Ok(value) = env::var(ROS_DISTRO) {
         value
     } else {
-        println!(
-            "{} environment variable not set - please source ROS 2 installation first.",
-            ROS_DISTRO
-        );
-        return;
+        let error_msg =
+            "ROS_DISTRO environment variable not set - please source ROS 2 installation first.";
+        cfg_if::cfg_if! {
+            if #[cfg(feature="generate_docs")] {
+                println!(error_msg);
+                return;
+            } else {
+                panic!(error_msg);
+            }
+        }
     };
 
     println!("cargo:rustc-cfg=ros_distro=\"{ros_distro}\"");