Make MIR pass name a compile-time constant.

compiler/rustc_mir_transform/src/lib.rs

@@ -2,9 +2,11 @@
 #![deny(rustc::diagnostic_outside_of_impl)]
 #![feature(assert_matches)]
 #![feature(box_patterns)]
+#![feature(const_type_name)]
 #![feature(cow_is_borrowed)]
 #![feature(decl_macro)]
 #![feature(impl_trait_in_assoc_type)]
+#![feature(inline_const)]
 #![feature(is_sorted)]
 #![feature(let_chains)]
 #![feature(map_try_insert)]

compiler/rustc_mir_transform/src/pass_manager.rs

@@ -7,8 +7,20 @@
 /// Just like `MirPass`, except it cannot mutate `Body`.
 pub trait MirLint<'tcx> {
     fn name(&self) -> &'static str {
-        let name = std::any::type_name::<Self>();
+        // FIXME Simplify the implementation once more `str` methods get const-stable.
-        if let Some((_, tail)) = name.rsplit_once(':') { tail } else { name }
+        const {
+            let name = std::any::type_name::<Self>();
+            let bytes = name.as_bytes();
+            let mut i = bytes.len();
+            while i > 0 && bytes[i - 1] != b':' {
+                i = i - 1;
+            }
+            let (_, bytes) = bytes.split_at(i);
+            match std::str::from_utf8(bytes) {
+                Ok(name) => name,
+                Err(_) => name,
+            }
+        }
     }
 
     fn is_enabled(&self, _sess: &Session) -> bool {