[generic_assert] "Constify" the Debug trait

Author: c410-f3r

library/core/src/fmt/mod.rs

@@ -845,6 +845,8 @@ impl Display for Arguments<'_> {
 /// assert_eq!(format!("The origin is: {origin:#?}"), expected);
 /// ```
 
+#[const_trait]
+#[rustc_const_unstable(feature = "const_debug", issue = "none")]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_on_unimplemented(
     on(

tests/ui/traits/const-traits/debug.rs

@@ -0,0 +1,16 @@
+//@ check-pass
+
+#![feature(const_debug, const_trait_impl)]
+
+use std::fmt::Debug;
+use std::fmt::Formatter;
+
+pub struct Foo;
+
+impl const Debug for Foo {
+    fn fmt(&self, _: &mut Formatter<'_>) -> Result<(), std::fmt::Error> {
+        Ok(())
+    }
+}
+
+fn main() {}