make std feature conflict with hashbrown in compile error

src/allocator/free_list_allocator/mod.rs

@@ -5,12 +5,15 @@ use alloc::{
     string::{String, ToString},
     vec::Vec,
 };
-#[cfg(all(feature = "std", not(feature = "hashbrown")))]
-use std::collections::{HashMap, HashSet};
+
 #[cfg(feature = "std")]
-use std::{backtrace::Backtrace, sync::Arc};
+use std::{
+    backtrace::Backtrace,
+    collections::{HashMap, HashSet},
+    sync::Arc,
+};
 
-#[cfg(all(not(feature = "std"), feature = "hashbrown"))]
+#[cfg(feature = "hashbrown")]
 use hashbrown::{HashMap, HashSet};
 use log::{log, Level};
 

src/allocator/mod.rs

@@ -10,7 +10,9 @@ use crate::result::*;
 pub(crate) mod dedicated_block_allocator;
 pub(crate) use dedicated_block_allocator::DedicatedBlockAllocator;
 
+#[cfg(any(feature = "std", feature = "hashbrown"))]
 pub(crate) mod free_list_allocator;
+#[cfg(any(feature = "std", feature = "hashbrown"))]
 pub(crate) use free_list_allocator::FreeListAllocator;
 
 #[derive(PartialEq, Copy, Clone, Debug)]

src/lib.rs

@@ -222,8 +222,8 @@
 #[macro_use]
 extern crate alloc;
 
-#[cfg(all(not(feature = "std"), not(feature = "hashbrown")))]
-compile_error!("\"hashbrown\" feature should be enabled in \"no_std\" environment.");
+#[cfg(all(feature = "std", feature = "hashbrown"))]
+compile_error!("\"hashbrown\" feature should not be enabled in \"std\" environment.");
 
 #[cfg(all(not(feature = "std"), feature = "visualizer"))]
 compile_error!("Cannot enable \"visualizer\" feature in \"no_std\" environment.");