Warning message if guards without allocator enabled

examples/release_mode.rs

@@ -14,6 +14,7 @@ fn does_allocate() -> Box<u8> {
 fn main() {
     // If you were to run `cargo run --example release_mode`, this program blows up.
     // If, however, you ran `cargo run --release --example release_mode`,
-    // nothing interesting will happen.
+    // nothing interesting will happen since panic-related code is stripped
+    // for release builds.
     does_allocate();
 }

examples/setup_warning.rs

@@ -0,0 +1,21 @@
+extern crate env_logger;
+extern crate qadapt;
+
+use qadapt::allocate_panic;
+
+// Note that we're missing the `#[global_allocator]` attribute
+
+#[allocate_panic]
+fn does_allocate() -> Box<u8> {
+    Box::new(0)
+}
+
+fn main() {
+    // This code will warn that QADAPT isn't being used, but won't trigger a panic.
+    // Run with `RUST_LOG=warn cargo run --example setup_warning`
+    env_logger::init();
+    does_allocate();
+
+    // The warning will only trigger once though
+    does_allocate();
+}