Fix that std was Still Required Through lazy_static

Cargo.toml

@@ -19,11 +19,24 @@ required-features = ["alloc"]
 
 [features]
 default = ["alloc"]   # default features are automatically enables (if not opt-out)
-alloc = ["hashbrown"] # requires global allocator, enables various functions such as parse_alias
+alloc = [             # requires global allocator, enables various functions such as parse_alias
+    "hashbrown",
+    "lazy_static"
+]
 doc_cfg = []          # requires nightly compiler, only intended for docs.rs builds (enables usage of doc_cfg)
 
 [dependencies]
-lazy_static = "1.4.0"
+
+[dependencies.lazy_static]
+version = "1.4.0"
+optional = true
+# The following feature on `lazy_static` would remove the transitive dependency of lazy_static on
+# std, which is necessary if targetting a platform without it. However, since the current version
+# of Cargo (1.51.0) unifies features acros crates, requiring that feature here, would make
+# lazy_static globally use spinloks instead of mutices. So, it seems more reasonable that a final
+# user (binary crate) adds this feature if they want `alloc` but not `std`.
+# Also see: https://github.com/rust-lang-nursery/lazy-static.rs/issues/150
+#features = ["spin_no_std"] # Would remove std from lazy_static, but it has side-effects
 
 [dependencies.hashbrown]
 version = "0.11"

README.md

@@ -124,14 +124,32 @@ platforms. However, some functions such as [`parse_alias`](https://docs.rs/emoji
 ad-hoc flag functions need the `alloc` crate (normally part of `std`),
 thus it is enabled by default.
 
-- `default`: (implies `alloc`) automatically enabled if not opt-out:
+- `default`: (implies `alloc`) \
+  Automatically enabled if not opt-out:
   ```toml
   [dependencies.emojic]
   version = "0.3"
   default-features = false
   ```
-- `alloc`: requires a global allocator, enables various functions such as `parse_alias` as well
-  as the ad-hoc flag functions (the flag constants are unaffected)
+- `alloc`: (implies `hashbrown` and `lazy_static`) \
+  Requires a global allocator,
+  enables various functions such as `parse_alias` as well
+  as the ad-hoc flag functions (the flag constants are unaffected).
+
+  Notice, that `lazy_static`, by default, pulls-in `std` to use mutices for waiting.
+  This is good if you do have `std` available, and bad if not. However, the alternative is
+  to instruct `lazy_static` to use spinlocks instead. Yet, since crate-features are unified by
+  Cargo, it would be bad for all user that have `std`, to requiring it by default.
+  Instead, if you want to use this `alloc` feature, but you don't have `std`
+  (e.g. in your binary crate), you can simply add `lazy_static` yourself, and make it to use
+  spinlocks, which will apply globally. E.g. add to your `Cargo.toml`:
+  ```toml
+  [dependencies.lazy_static]
+  version = "1.4"
+  features = ["spin_no_std"]
+  ```
+  Also see: <https://github.com/rust-lang-nursery/lazy-static.rs/issues/150>
+
 
 
 

src/lib.rs

@@ -142,14 +142,32 @@
 //! ad-hoc flag functions need the `alloc` crate (normally part of `std`),
 //! thus it is enabled by default.
 //!
-//! - `default`: (implies `alloc`) automatically enabled if not opt-out:
+//! - `default`: (implies `alloc`) \
+//!   Automatically enabled if not opt-out:
 //!   ```toml
 //!   [dependencies.emojic]
 //!   version = "0.3"
 //!   default-features = false
 //!   ```
-//! - `alloc`: requires a global allocator, enables various functions such as `parse_alias` as well
-//!   as the ad-hoc flag functions (the flag constants are unaffected)
+//! - `alloc`: (implies `hashbrown` and `lazy_static`) \
+//!   Requires a global allocator,
+//!   enables various functions such as `parse_alias` as well
+//!   as the ad-hoc flag functions (the flag constants are unaffected).
+//!
+//!   Notice, that `lazy_static`, by default, pulls-in `std` to use mutices for waiting.
+//!   This is good if you do have `std` available, and bad if not. However, the alternative is
+//!   to instruct `lazy_static` to use spinlocks instead. Yet, since crate-features are unified by
+//!   Cargo, it would be bad for all user that have `std`, to requiring it by default.
+//!   Instead, if you want to use this `alloc` feature, but you don't have `std`
+//!   (e.g. in your binary crate), you can simply add `lazy_static` yourself, and make it to use
+//!   spinlocks, which will apply globally. E.g. add to your `Cargo.toml`:
+//!   ```toml
+//!   [dependencies.lazy_static]
+//!   version = "1.4"
+//!   features = ["spin_no_std"]
+//!   ```
+//!   Also see: <https://github.com/rust-lang-nursery/lazy-static.rs/issues/150>
+//!
 //!
 //!