Add a note

Author: compiler-errors

compiler/rustc_next_trait_solver/src/lib.rs

@@ -1,3 +1,9 @@
+//! Crate containing the implementation of the next-generation trait solver.
+//!
+//! This crate may also contain things that are used by the old trait solver,
+//! but were uplifted in the process of making the new trait solver generic.
+//! So if you got to this crate from the old solver, it's totally normal.
+
 pub mod canonicalizer;
 pub mod resolve;
 pub mod solve;