If --no-default-features is used, either std or hashbrown must be ena…

…bled.

Cargo.toml

@@ -17,6 +17,7 @@ exclude = ["dev/**"]
 maintenance = { status = "experimental" }
 
 [features]
+# If using no default features, you must enable either hashbrown or std.
 default = ["simd", "hashbrown"]
 # Enable this flag to use std::HashMap instead of hashbrown::HashMap
 std = []

src/lib.rs

@@ -2,7 +2,7 @@
 //!
 //! This is a no_std crate, but still requires the alloc crate.
 
-#![cfg_attr(all(not(test), not(feature = "std")), no_std)]
+#![cfg_attr(all(not(test), not(feature = "std"), not(feature = "hashbrown")), no_std)]
 #![allow(dead_code)]
 #![allow(clippy::style)]
 #![allow(clippy::complexity)]