Add a way to decouple the implementation and the declaration of a TyCtxt method.

compiler/rustc_middle/src/hooks/mod.rs

@@ -0,0 +1,64 @@
+use crate::mir;
+use crate::query::TyCtxtAt;
+use crate::ty::{Ty, TyCtxt};
+use rustc_span::DUMMY_SP;
+
+macro_rules! declare_hooks {
+    ($($(#[$attr:meta])*hook $name:ident($($arg:ident: $K:ty),*) -> $V:ty;)*) => {
+
+        impl<'tcx> TyCtxt<'tcx> {
+            $(
+            $(#[$attr])*
+            #[inline(always)]
+            #[must_use]
+            pub fn $name(self, $($arg: $K,)*) -> $V
+            {
+                self.at(DUMMY_SP).$name($($arg,)*)
+            }
+            )*
+        }
+
+        impl<'tcx> TyCtxtAt<'tcx> {
+            $(
+            $(#[$attr])*
+            #[inline(always)]
+            #[must_use]
+            pub fn $name(self, $($arg: $K,)*) -> $V
+            {
+                (self.tcx.hooks.$name)(self, $($arg,)*)
+            }
+            )*
+        }
+
+        pub struct Providers {
+            $(pub $name: for<'tcx> fn(
+                TyCtxtAt<'tcx>,
+                $($arg: $K,)*
+            ) -> $V,)*
+        }
+
+        impl Default for Providers {
+            fn default() -> Self {
+                Providers {
+                    $($name: |_, $($arg,)*| bug!(
+                        "`tcx.{}{:?}` cannot be called as `{}` was never assigned to a provider function.\n",
+                        stringify!($name),
+                        ($($arg,)*),
+                        stringify!($name),
+                    ),)*
+                }
+            }
+        }
+
+        impl Copy for Providers {}
+        impl Clone for Providers {
+            fn clone(&self) -> Self { *self }
+        }
+    };
+}
+
+declare_hooks! {
+    /// Tries to destructure an `mir::Const` ADT or array into its variant index
+    /// and its field values. This should only be used for pretty printing.
+    hook try_destructure_mir_constant_for_diagnostics(val: mir::ConstValue<'tcx>, ty: Ty<'tcx>) -> Option<mir::DestructuredConstant<'tcx>>;
+}