internal: introduce minicore -- a subset of libcore for testing

crates/test_utils/src/minicore.rs

@@ -0,0 +1,69 @@
+//! This is a fixture we use for tests that need lang items.
+//!
+//! We want to include the minimal subset of core for each test, so this file
+//! supports "conditional compilation". Tests use the following syntax to include minicore:
+//!
+//!  //- minicore: flag1, flag2
+//!
+//! We then strip all the code marked with other flags.
+//!
+//! Available flags:
+//!     sized:
+//!     coerce_unsized: sized
+
+pub mod marker {
+    // region:sized
+    #[lang = "sized"]
+    #[fundamental]
+    #[rustc_specialization_trait]
+    pub trait Sized {}
+
+    #[lang = "unsize"]
+    pub trait Unsize<T: ?Sized> {}
+    // endregion:sized
+}
+
+pub mod ops {
+    mod unsize {
+        // region:coerce_unsized
+        use crate::marker::Unsize;
+
+        #[lang = "coerce_unsized"]
+        pub trait CoerceUnsized<T: ?Sized> {}
+
+        impl<'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<&'a mut U> for &'a mut T {}
+        impl<'a, 'b: 'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<&'a U> for &'b mut T {}
+        impl<'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*mut U> for &'a mut T {}
+        impl<'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*const U> for &'a mut T {}
+
+        impl<'a, 'b: 'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<&'a U> for &'b T {}
+        impl<'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*const U> for &'a T {}
+
+        impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*mut U> for *mut T {}
+        impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*const U> for *mut T {}
+        impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*const U> for *const T {}
+        // endregion:coerce_unsized
+    }
+}
+
+pub mod prelude {
+    pub mod v1 {
+        pub use crate::marker::Sized; // :sized
+    }
+
+    pub mod rust_2015 {
+        pub use super::v1::*;
+    }
+
+    pub mod rust_2018 {
+        pub use super::v1::*;
+    }
+
+    pub mod rust_2021 {
+        pub use super::v1::*;
+    }
+}
+
+#[prelude_import]
+#[allow(unused)]
+use prelude::v1::*;