Make hygiene private to hir

crates/hir/src/lib.rs

@@ -52,8 +52,12 @@ pub use hir_def::{
     type_ref::{Mutability, TypeRef},
 };
 pub use hir_expand::{
-    hygiene::Hygiene, name::Name, HirFileId, InFile, MacroCallId, MacroCallLoc,
-    MacroDefId, /* FIXME */
+    name::Name, HirFileId, InFile, MacroCallId, MacroCallLoc, /* FIXME */ MacroDefId,
     MacroFile, Origin,
 };
 pub use hir_ty::display::HirDisplay;
+
+// These are negative re-exports: pub using these names is forbidden, they
+// should remain private to hir internals.
+#[allow(unused)]
+use hir_expand::hygiene::Hygiene;