Rollup merge of #47892 - Badel2:const_type_id_of, r=oli-obk

Turn `type_id` into a constant intrinsic

https://github.com/rust-lang/rust/issues/27745

The method `get_type_id` in `Any` is intended to support reflection. It's currently unstable in favor of using an associated constant instead. This PR makes the `type_id` intrinsic a constant intrinsic, the same as `size_of` and `align_of`, allowing `TypeId::of` to be a `const fn`, which will allow using an associated constant in `Any`.

2 files changed, 28 insertions, 0 deletions

diff --git a/src/libcore/any.rs b/src/libcore/any.rs
index 338e5c7fd95..566bfe2a3fb 100644
--- a/src/libcore/any.rs
+++ b/src/libcore/any.rs
@@ -367,9 +367,36 @@ impl TypeId {
     /// }
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg(stage0)]
     pub fn of<T: ?Sized + 'static>() -> TypeId {
         TypeId {
             t: unsafe { intrinsics::type_id::<T>() },
         }
     }
+
+    /// Returns the `TypeId` of the type this generic function has been
+    /// instantiated with.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::any::{Any, TypeId};
+    ///
+    /// fn is_string<T: ?Sized + Any>(_s: &T) -> bool {
+    ///     TypeId::of::<String>() == TypeId::of::<T>()
+    /// }
+    ///
+    /// fn main() {
+    ///     assert_eq!(is_string(&0), false);
+    ///     assert_eq!(is_string(&"cookie monster".to_string()), true);
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_unstable(feature="const_type_id")]
+    #[cfg(not(stage0))]
+    pub const fn of<T: ?Sized + 'static>() -> TypeId {
+        TypeId {
+            t: unsafe { intrinsics::type_id::<T>() },
+        }
+    }
 }
diff --git a/src/libcore/lib.rs b/src/libcore/lib.rs
index 2e1f925c49a..59a296c2a76 100644
--- a/src/libcore/lib.rs
+++ b/src/libcore/lib.rs
@@ -91,6 +91,7 @@
 #![feature(untagged_unions)]
 #![feature(unwind_attributes)]
 #![feature(doc_spotlight)]
+#![feature(rustc_const_unstable)]
 
 #[prelude_import]
 #[allow(unused)]