5 files changed, 72 insertions, 11 deletions
diff --git a/compiler/rustc_middle/src/hooks/mod.rs b/compiler/rustc_middle/src/hooks/mod.rs
new file mode 100644
index 00000000000..cb84a5936b3
--- /dev/null
+++ b/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>>;
+}
diff --git a/compiler/rustc_middle/src/lib.rs b/compiler/rustc_middle/src/lib.rs
index 50b69181d67..fe4fc3761b3 100644
--- a/compiler/rustc_middle/src/lib.rs
+++ b/compiler/rustc_middle/src/lib.rs
@@ -89,6 +89,7 @@ mod macros;
 pub mod arena;
 pub mod error;
 pub mod hir;
+pub mod hooks;
 pub mod infer;
 pub mod lint;
 pub mod metadata;
diff --git a/compiler/rustc_middle/src/mir/pretty.rs b/compiler/rustc_middle/src/mir/pretty.rs
index cc2a5aa62c8..8488367189f 100644
--- a/compiler/rustc_middle/src/mir/pretty.rs
+++ b/compiler/rustc_middle/src/mir/pretty.rs
@@ -1691,7 +1691,7 @@ fn pretty_print_const_value_tcx<'tcx>(
         (_, ty::Array(..) | ty::Tuple(..) | ty::Adt(..)) if !ty.has_non_region_param() => {
             let ct = tcx.lift(ct).unwrap();
             let ty = tcx.lift(ty).unwrap();
-            if let Some(contents) = tcx.try_destructure_mir_constant_for_diagnostics((ct, ty)) {
+            if let Some(contents) = tcx.try_destructure_mir_constant_for_diagnostics(ct, ty) {
                 let fields: Vec<(ConstValue<'_>, Ty<'_>)> = contents.fields.to_vec();
                 match *ty.kind() {
                     ty::Array(..) => {
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index d888a2c0fb6..6928f59c3fd 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -1100,16 +1100,6 @@ rustc_queries! {
         desc { "destructuring type level constant"}
     }
 
-    /// 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.
-    query try_destructure_mir_constant_for_diagnostics(
-        key: (mir::ConstValue<'tcx>, Ty<'tcx>)
-    ) -> Option<mir::DestructuredConstant<'tcx>> {
-        desc { "destructuring MIR constant"}
-        no_hash
-        eval_always
-    }
-
     query const_caller_location(key: (rustc_span::Symbol, u32, u32)) -> mir::ConstValue<'tcx> {
         desc { "getting a &core::panic::Location referring to a span" }
     }
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index 9ff4b64f48b..25eafce0d9e 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -554,6 +554,10 @@ pub struct GlobalCtxt<'tcx> {
     /// Common consts, pre-interned for your convenience.
     pub consts: CommonConsts<'tcx>,
 
+    /// Hooks to be able to register functions in other crates that can then still
+    /// be called from rustc_middle.
+    pub(crate) hooks: crate::hooks::Providers,
+
     untracked: Untracked,
 
     pub query_system: QuerySystem<'tcx>,
@@ -703,6 +707,7 @@ impl<'tcx> TyCtxt<'tcx> {
         dep_graph: DepGraph,
         query_kinds: &'tcx [DepKindStruct<'tcx>],
         query_system: QuerySystem<'tcx>,
+        hooks: crate::hooks::Providers,
     ) -> GlobalCtxt<'tcx> {
         let data_layout = s.target.parse_data_layout().unwrap_or_else(|err| {
             s.emit_fatal(err);
@@ -721,6 +726,7 @@ impl<'tcx> TyCtxt<'tcx> {
             hir_arena,
             interners,
             dep_graph,
+            hooks,
             prof: s.prof.clone(),
             types: common_types,
             lifetimes: common_lifetimes,