Make core_maths optional.

Cargo.toml

@@ -13,11 +13,12 @@ edition = "2018"
 exclude = ["benches/**"]
 
 [dependencies]
-core_maths = { version = "0.1.0" } # No-op for `std` builds.
+core_maths = { version = "0.1.0", optional = true } # only for no_std builds
 
 [features]
 default = ["std", "opentype-layout", "apple-layout", "variable-fonts", "glyph-names"]
 # Enables the use of the standard library.
+# When disabled, the `core_maths` feature must be enabled instead.
 std = []
 # Enables variable fonts support. Increases binary size almost twice.
 # Includes avar, CFF2, fvar, gvar, HVAR, MVAR and VVAR tables.

src/lib.rs

@@ -49,8 +49,11 @@ Font parsing starts with a [`Face`].
 #[macro_use]
 extern crate std;
 
-#[allow(unused_imports)]
-use core_maths::*;
+#[cfg(not(any(feature = "std", feature = "core_maths")))]
+compile_error!("You have to activate either the `std` or the `core_maths` feature.");
+
+#[cfg(not(feature = "std"))]
+use core_maths::CoreFloat;
 
 #[cfg(feature = "apple-layout")]
 mod aat;