Replace early-bound normalization hack with per-query key/value type aliases.

Author: eddyb

src/librustc_metadata/rmeta/decoder/cstore_impl.rs

@@ -17,7 +17,6 @@ use rustc_middle::middle::cstore::{CrateSource, CrateStore, EncodedMetadata};
 use rustc_middle::middle::exported_symbols::ExportedSymbol;
 use rustc_middle::middle::stability::DeprecationEntry;
 use rustc_middle::ty::query::Providers;
-use rustc_middle::ty::query::QueryConfig;
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_session::utils::NativeLibKind;
 use rustc_session::{CrateDisambiguator, Session};
@@ -32,12 +31,10 @@ macro_rules! provide {
     (<$lt:tt> $tcx:ident, $def_id:ident, $other:ident, $cdata:ident,
       $($name:ident => $compute:block)*) => {
         pub fn provide_extern<$lt>(providers: &mut Providers<$lt>) {
-            // HACK(eddyb) `$lt: $lt` forces `$lt` to be early-bound, which
-            // allows the associated type in the return type to be normalized.
-            $(fn $name<$lt: $lt, T: IntoArgs>(
+            $(fn $name<$lt>(
                 $tcx: TyCtxt<$lt>,
-                def_id_arg: T,
-            ) -> <ty::queries::$name<$lt> as QueryConfig<TyCtxt<$lt>>>::Value {
+                def_id_arg: ty::query::query_keys::$name<$lt>,
+            ) -> ty::query::query_values::$name<$lt> {
                 let _prof_timer =
                     $tcx.prof.generic_activity("metadata_decode_entry");
 

src/librustc_middle/ty/query/plumbing.rs

@@ -318,15 +318,34 @@ macro_rules! define_queries_inner {
             }
         }
 
+        #[allow(nonstandard_style)]
         pub mod queries {
             use std::marker::PhantomData;
 
-            $(#[allow(nonstandard_style)]
-            pub struct $name<$tcx> {
+            $(pub struct $name<$tcx> {
                 data: PhantomData<&$tcx ()>
             })*
         }
 
+        // HACK(eddyb) this is like the `impl QueryConfig for queries::$name`
+        // below, but using type aliases instead of associated types, to bypass
+        // the limitations around normalizing under HRTB - for example, this:
+        // `for<'tcx> fn(...) -> <queries::$name<'tcx> as QueryConfig<TyCtxt<'tcx>>>::Value`
+        // doesn't currently normalize to `for<'tcx> fn(...) -> query_values::$name<'tcx>`.
+        // This is primarily used by the `provide!` macro in `rustc_metadata`.
+        #[allow(nonstandard_style, unused_lifetimes)]
+        pub mod query_keys {
+            use super::*;
+
+            $(pub type $name<$tcx> = $($K)*;)*
+        }
+        #[allow(nonstandard_style, unused_lifetimes)]
+        pub mod query_values {
+            use super::*;
+
+            $(pub type $name<$tcx> = $V;)*
+        }
+
         $(impl<$tcx> QueryConfig<TyCtxt<$tcx>> for queries::$name<$tcx> {
             type Key = $($K)*;
             type Value = $V;