src/librustc_middle/dep_graph/dep_node.rs - third_party/rust - Git at Google

 //! This module defines the `DepNode` type which the compiler uses to represent
 //! nodes in the dependency graph. A `DepNode` consists of a `DepKind` (which
 //! specifies the kind of thing it represents, like a piece of HIR, MIR, etc)
 //! and a `Fingerprint`, a 128 bit hash value the exact meaning of which
 //! depends on the node's `DepKind`. Together, the kind and the fingerprint
 //! fully identify a dependency node, even across multiple compilation sessions.
 //! In other words, the value of the fingerprint does not depend on anything
 //! that is specific to a given compilation session, like an unpredictable
 //! interning key (e.g., NodeId, DefId, Symbol) or the numeric value of a
 //! pointer. The concept behind this could be compared to how git commit hashes
 //! uniquely identify a given commit and has a few advantages:
 //!
 //! * A `DepNode` can simply be serialized to disk and loaded in another session
 //!   without the need to do any "rebasing (like we have to do for Spans and
 //!   NodeIds) or "retracing" like we had to do for `DefId` in earlier
 //!   implementations of the dependency graph.
 //! * A `Fingerprint` is just a bunch of bits, which allows `DepNode` to
 //!   implement `Copy`, `Sync`, `Send`, `Freeze`, etc.
 //! * Since we just have a bit pattern, `DepNode` can be mapped from disk into
 //!   memory without any post-processing (e.g., "abomination-style" pointer
 //!   reconstruction).
 //! * Because a `DepNode` is self-contained, we can instantiate `DepNodes` that
 //!   refer to things that do not exist anymore. In previous implementations
 //!   `DepNode` contained a `DefId`. A `DepNode` referring to something that
 //!   had been removed between the previous and the current compilation session
 //!   could not be instantiated because the current compilation session
 //!   contained no `DefId` for thing that had been removed.
 //!
 //! `DepNode` definition happens in the `define_dep_nodes!()` macro. This macro
 //! defines the `DepKind` enum and a corresponding `DepConstructor` enum. The
 //! `DepConstructor` enum links a `DepKind` to the parameters that are needed at
 //! runtime in order to construct a valid `DepNode` fingerprint.
 //!
 //! Because the macro sees what parameters a given `DepKind` requires, it can
 //! "infer" some properties for each kind of `DepNode`:
 //!
 //! * Whether a `DepNode` of a given kind has any parameters at all. Some
 //!   `DepNode`s could represent global concepts with only one value.
 //! * Whether it is possible, in principle, to reconstruct a query key from a
 //!   given `DepNode`. Many `DepKind`s only require a single `DefId` parameter,
 //!   in which case it is possible to map the node's fingerprint back to the
 //!   `DefId` it was computed from. In other cases, too much information gets
 //!   lost during fingerprint computation.
 //!
 //! The `DepConstructor` enum, together with `DepNode::new()` ensures that only
 //! valid `DepNode` instances can be constructed. For example, the API does not
 //! allow for constructing parameterless `DepNode`s with anything other
 //! than a zeroed out fingerprint. More generally speaking, it relieves the
 //! user of the `DepNode` API of having to know how to compute the expected
 //! fingerprint for a given set of node parameters.

 use crate::mir::interpret::{GlobalId, LitToConstInput};
 use crate::traits;
 use crate::traits::query::{
     CanonicalPredicateGoal, CanonicalProjectionGoal, CanonicalTyGoal,
     CanonicalTypeOpAscribeUserTypeGoal, CanonicalTypeOpEqGoal, CanonicalTypeOpNormalizeGoal,
     CanonicalTypeOpProvePredicateGoal, CanonicalTypeOpSubtypeGoal,
 };
 use crate::ty::subst::{GenericArg, SubstsRef};
 use crate::ty::{self, ParamEnvAnd, Ty, TyCtxt};

 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, CRATE_DEF_INDEX};
 use rustc_hir::definitions::DefPathHash;
 use rustc_hir::HirId;
 use rustc_span::symbol::Symbol;
 use std::hash::Hash;

 pub use rustc_query_system::dep_graph::{DepContext, DepNodeParams};

 // erase!() just makes tokens go away. It's used to specify which macro argument
 // is repeated (i.e., which sub-expression of the macro we are in) but don't need
 // to actually use any of the arguments.
 macro_rules! erase {
     ($x:tt) => {{}};
 }

 macro_rules! is_anon_attr {
     (anon) => {
         true
     };
     ($attr:ident) => {
         false
     };
 }

 macro_rules! is_eval_always_attr {
     (eval_always) => {
         true
     };
     ($attr:ident) => {
         false
     };
 }

 macro_rules! contains_anon_attr {
     ($($attr:ident $(($($attr_args:tt)*))* ),*) => ({$(is_anon_attr!($attr) | )* false});
 }

 macro_rules! contains_eval_always_attr {
     ($($attr:ident $(($($attr_args:tt)*))* ),*) => ({$(is_eval_always_attr!($attr) | )* false});
 }

 macro_rules! define_dep_nodes {
     (<$tcx:tt>
     $(
         [$($attrs:tt)*]
         $variant:ident $(( $tuple_arg_ty:ty $(,)? ))*
       ,)*
     ) => (
         #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash,
                  RustcEncodable, RustcDecodable)]
         #[allow(non_camel_case_types)]
         pub enum DepKind {
             $($variant),*
         }

         impl DepKind {
             #[allow(unreachable_code)]
             pub fn can_reconstruct_query_key<$tcx>(&self) -> bool {
                 match *self {
                     $(
                         DepKind :: $variant => {
                             if contains_anon_attr!($($attrs)*) {
                                 return false;
                             }

                             // tuple args
                             $({
                                 return <$tuple_arg_ty as DepNodeParams<TyCtxt<'_>>>
                                     ::can_reconstruct_query_key();
                             })*

                             true
                         }
                     )*
                 }
             }

             pub fn is_anon(&self) -> bool {
                 match *self {
                     $(
                         DepKind :: $variant => { contains_anon_attr!($($attrs)*) }
                     )*
                 }
             }

             pub fn is_eval_always(&self) -> bool {
                 match *self {
                     $(
                         DepKind :: $variant => { contains_eval_always_attr!($($attrs)*) }
                     )*
                 }
             }

             #[allow(unreachable_code)]
             pub fn has_params(&self) -> bool {
                 match *self {
                     $(
                         DepKind :: $variant => {
                             // tuple args
                             $({
                                 erase!($tuple_arg_ty);
                                 return true;
                             })*

                             false
                         }
                     )*
                 }
             }
         }

         pub struct DepConstructor;

         #[allow(non_camel_case_types)]
         impl DepConstructor {
             $(
                 #[inline(always)]
                 #[allow(unreachable_code, non_snake_case)]
                 pub fn $variant(_tcx: TyCtxt<'_>, $(arg: $tuple_arg_ty)*) -> DepNode {
                     // tuple args
                     $({
                         erase!($tuple_arg_ty);
                         return DepNode::construct(_tcx, DepKind::$variant, &arg)
                     })*

                     return DepNode::construct(_tcx, DepKind::$variant, &())
                 }
             )*
         }

         pub type DepNode = rustc_query_system::dep_graph::DepNode<DepKind>;

         pub trait DepNodeExt: Sized {
             /// Construct a DepNode from the given DepKind and DefPathHash. This
             /// method will assert that the given DepKind actually requires a
             /// single DefId/DefPathHash parameter.
             fn from_def_path_hash(def_path_hash: DefPathHash, kind: DepKind) -> Self;

             /// Extracts the DefId corresponding to this DepNode. This will work
             /// if two conditions are met:
             ///
             /// 1. The Fingerprint of the DepNode actually is a DefPathHash, and
             /// 2. the item that the DefPath refers to exists in the current tcx.
             ///
             /// Condition (1) is determined by the DepKind variant of the
             /// DepNode. Condition (2) might not be fulfilled if a DepNode
             /// refers to something from the previous compilation session that
             /// has been removed.
             fn extract_def_id(&self, tcx: TyCtxt<'_>) -> Option<DefId>;

             /// Used in testing
             fn from_label_string(label: &str, def_path_hash: DefPathHash)
                 -> Result<Self, ()>;

             /// Used in testing
             fn has_label_string(label: &str) -> bool;
         }

         impl DepNodeExt for DepNode {
             /// Construct a DepNode from the given DepKind and DefPathHash. This
             /// method will assert that the given DepKind actually requires a
             /// single DefId/DefPathHash parameter.
             fn from_def_path_hash(def_path_hash: DefPathHash, kind: DepKind) -> DepNode {
                 debug_assert!(kind.can_reconstruct_query_key() && kind.has_params());
                 DepNode {
                     kind,
                     hash: def_path_hash.0,
                 }
             }

             /// Extracts the DefId corresponding to this DepNode. This will work
             /// if two conditions are met:
             ///
             /// 1. The Fingerprint of the DepNode actually is a DefPathHash, and
             /// 2. the item that the DefPath refers to exists in the current tcx.
             ///
             /// Condition (1) is determined by the DepKind variant of the
             /// DepNode. Condition (2) might not be fulfilled if a DepNode
             /// refers to something from the previous compilation session that
             /// has been removed.
             fn extract_def_id(&self, tcx: TyCtxt<'tcx>) -> Option<DefId> {
                 if self.kind.can_reconstruct_query_key() {
                     let def_path_hash = DefPathHash(self.hash);
                     tcx.def_path_hash_to_def_id.as_ref()?.get(&def_path_hash).cloned()
                 } else {
                     None
                 }
             }

             /// Used in testing
             fn from_label_string(label: &str, def_path_hash: DefPathHash) -> Result<DepNode, ()> {
                 let kind = match label {
                     $(
                         stringify!($variant) => DepKind::$variant,
                     )*
                     _ => return Err(()),
                 };

                 if !kind.can_reconstruct_query_key() {
                     return Err(());
                 }

                 if kind.has_params() {
                     Ok(DepNode::from_def_path_hash(def_path_hash, kind))
                 } else {
                     Ok(DepNode::new_no_params(kind))
                 }
             }

             /// Used in testing
             fn has_label_string(label: &str) -> bool {
                 match label {
                     $(
                         stringify!($variant) => true,
                     )*
                     _ => false,
                 }
             }
         }

         /// Contains variant => str representations for constructing
         /// DepNode groups for tests.
         #[allow(dead_code, non_upper_case_globals)]
         pub mod label_strs {
            $(
                 pub const $variant: &str = stringify!($variant);
             )*
         }
     );
 }

 rustc_dep_node_append!([define_dep_nodes!][ <'tcx>
     // We use this for most things when incr. comp. is turned off.
     [] Null,

     // Represents metadata from an extern crate.
     [eval_always] CrateMetadata(CrateNum),

     [anon] TraitSelect,

     [] CompileCodegenUnit(Symbol),
 ]);

 impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for DefId {
     #[inline]
     fn can_reconstruct_query_key() -> bool {
         true
     }

     fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
         tcx.def_path_hash(*self).0
     }

     fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
         tcx.def_path_str(*self)
     }

     fn recover(tcx: TyCtxt<'tcx>, dep_node: &DepNode) -> Option<Self> {
         dep_node.extract_def_id(tcx)
     }
 }

 impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for LocalDefId {
     #[inline]
     fn can_reconstruct_query_key() -> bool {
         true
     }

     fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
         self.to_def_id().to_fingerprint(tcx)
     }

     fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
         self.to_def_id().to_debug_str(tcx)
     }

     fn recover(tcx: TyCtxt<'tcx>, dep_node: &DepNode) -> Option<Self> {
         dep_node.extract_def_id(tcx).map(|id| id.expect_local())
     }
 }

 impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for CrateNum {
     #[inline]
     fn can_reconstruct_query_key() -> bool {
         true
     }

     fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
         let def_id = DefId { krate: *self, index: CRATE_DEF_INDEX };
         tcx.def_path_hash(def_id).0
     }

     fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
         tcx.crate_name(*self).to_string()
     }

     fn recover(tcx: TyCtxt<'tcx>, dep_node: &DepNode) -> Option<Self> {
         dep_node.extract_def_id(tcx).map(|id| id.krate)
     }
 }

 impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for (DefId, DefId) {
     #[inline]
     fn can_reconstruct_query_key() -> bool {
         false
     }

     // We actually would not need to specialize the implementation of this
     // method but it's faster to combine the hashes than to instantiate a full
     // hashing context and stable-hashing state.
     fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
         let (def_id_0, def_id_1) = *self;

         let def_path_hash_0 = tcx.def_path_hash(def_id_0);
         let def_path_hash_1 = tcx.def_path_hash(def_id_1);

         def_path_hash_0.0.combine(def_path_hash_1.0)
     }

     fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
         let (def_id_0, def_id_1) = *self;

         format!("({}, {})", tcx.def_path_debug_str(def_id_0), tcx.def_path_debug_str(def_id_1))
     }
 }

 impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for HirId {
     #[inline]
     fn can_reconstruct_query_key() -> bool {
         false
     }

     // We actually would not need to specialize the implementation of this
     // method but it's faster to combine the hashes than to instantiate a full
     // hashing context and stable-hashing state.
     fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
         let HirId { owner, local_id } = *self;

         let def_path_hash = tcx.def_path_hash(owner.to_def_id());
         let local_id = Fingerprint::from_smaller_hash(local_id.as_u32().into());

         def_path_hash.0.combine(local_id)
     }
 }
	//! This module defines the `DepNode` type which the compiler uses to represent
	//! nodes in the dependency graph. A `DepNode` consists of a `DepKind` (which
	//! specifies the kind of thing it represents, like a piece of HIR, MIR, etc)
	//! and a `Fingerprint`, a 128 bit hash value the exact meaning of which
	//! depends on the node's `DepKind`. Together, the kind and the fingerprint
	//! fully identify a dependency node, even across multiple compilation sessions.
	//! In other words, the value of the fingerprint does not depend on anything
	//! that is specific to a given compilation session, like an unpredictable
	//! interning key (e.g., NodeId, DefId, Symbol) or the numeric value of a
	//! pointer. The concept behind this could be compared to how git commit hashes
	//! uniquely identify a given commit and has a few advantages:
	//!
	//! * A `DepNode` can simply be serialized to disk and loaded in another session
	//! without the need to do any "rebasing (like we have to do for Spans and
	//! NodeIds) or "retracing" like we had to do for `DefId` in earlier
	//! implementations of the dependency graph.
	//! * A `Fingerprint` is just a bunch of bits, which allows `DepNode` to
	//! implement `Copy`, `Sync`, `Send`, `Freeze`, etc.
	//! * Since we just have a bit pattern, `DepNode` can be mapped from disk into
	//! memory without any post-processing (e.g., "abomination-style" pointer
	//! reconstruction).
	//! * Because a `DepNode` is self-contained, we can instantiate `DepNodes` that
	//! refer to things that do not exist anymore. In previous implementations
	//! `DepNode` contained a `DefId`. A `DepNode` referring to something that
	//! had been removed between the previous and the current compilation session
	//! could not be instantiated because the current compilation session
	//! contained no `DefId` for thing that had been removed.
	//!
	//! `DepNode` definition happens in the `define_dep_nodes!()` macro. This macro
	//! defines the `DepKind` enum and a corresponding `DepConstructor` enum. The
	//! `DepConstructor` enum links a `DepKind` to the parameters that are needed at
	//! runtime in order to construct a valid `DepNode` fingerprint.
	//!
	//! Because the macro sees what parameters a given `DepKind` requires, it can
	//! "infer" some properties for each kind of `DepNode`:
	//!
	//! * Whether a `DepNode` of a given kind has any parameters at all. Some
	//! `DepNode`s could represent global concepts with only one value.
	//! * Whether it is possible, in principle, to reconstruct a query key from a
	//! given `DepNode`. Many `DepKind`s only require a single `DefId` parameter,
	//! in which case it is possible to map the node's fingerprint back to the
	//! `DefId` it was computed from. In other cases, too much information gets
	//! lost during fingerprint computation.
	//!
	//! The `DepConstructor` enum, together with `DepNode::new()` ensures that only
	//! valid `DepNode` instances can be constructed. For example, the API does not
	//! allow for constructing parameterless `DepNode`s with anything other
	//! than a zeroed out fingerprint. More generally speaking, it relieves the
	//! user of the `DepNode` API of having to know how to compute the expected
	//! fingerprint for a given set of node parameters.

	use crate::mir::interpret::{GlobalId, LitToConstInput};
	use crate::traits;
	use crate::traits::query::{
	CanonicalPredicateGoal, CanonicalProjectionGoal, CanonicalTyGoal,
	CanonicalTypeOpAscribeUserTypeGoal, CanonicalTypeOpEqGoal, CanonicalTypeOpNormalizeGoal,
	CanonicalTypeOpProvePredicateGoal, CanonicalTypeOpSubtypeGoal,
	};
	use crate::ty::subst::{GenericArg, SubstsRef};
	use crate::ty::{self, ParamEnvAnd, Ty, TyCtxt};

	use rustc_data_structures::fingerprint::Fingerprint;
	use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, CRATE_DEF_INDEX};
	use rustc_hir::definitions::DefPathHash;
	use rustc_hir::HirId;
	use rustc_span::symbol::Symbol;
	use std::hash::Hash;

	pub use rustc_query_system::dep_graph::{DepContext, DepNodeParams};

	// erase!() just makes tokens go away. It's used to specify which macro argument
	// is repeated (i.e., which sub-expression of the macro we are in) but don't need
	// to actually use any of the arguments.
	macro_rules! erase {
	($x:tt) => {{}};
	}

	macro_rules! is_anon_attr {
	(anon) => {
	true
	};
	($attr:ident) => {
	false
	};
	}

	macro_rules! is_eval_always_attr {
	(eval_always) => {
	true
	};
	($attr:ident) => {
	false
	};
	}

	macro_rules! contains_anon_attr {
	($($attr:ident $(($($attr_args:tt))) ),) => ({$(is_anon_attr!($attr) \| ) false});
	}

	macro_rules! contains_eval_always_attr {
	($($attr:ident $(($($attr_args:tt))) ),) => ({$(is_eval_always_attr!($attr) \| ) false});
	}

	macro_rules! define_dep_nodes {
	(<$tcx:tt>
	$(
	[$($attrs:tt)*]
	$variant:ident $(( $tuple_arg_ty:ty $(,)? ))*
	,)*
	) => (
	#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash,
	RustcEncodable, RustcDecodable)]
	#[allow(non_camel_case_types)]
	pub enum DepKind {
	$($variant),*
	}

	impl DepKind {
	#[allow(unreachable_code)]
	pub fn can_reconstruct_query_key<$tcx>(&self) -> bool {
	match *self {
	$(
	DepKind :: $variant => {
	if contains_anon_attr!($($attrs)*) {
	return false;
	}

	// tuple args
	$({
	return <$tuple_arg_ty as DepNodeParams<TyCtxt<'_>>>
	::can_reconstruct_query_key();
	})*

	true
	}
	)*
	}
	}

	pub fn is_anon(&self) -> bool {
	match *self {
	$(
	DepKind :: $variant => { contains_anon_attr!($($attrs)*) }
	)*
	}
	}

	pub fn is_eval_always(&self) -> bool {
	match *self {
	$(
	DepKind :: $variant => { contains_eval_always_attr!($($attrs)*) }
	)*
	}
	}

	#[allow(unreachable_code)]
	pub fn has_params(&self) -> bool {
	match *self {
	$(
	DepKind :: $variant => {
	// tuple args
	$({
	erase!($tuple_arg_ty);
	return true;
	})*

	false
	}
	)*
	}
	}
	}

	pub struct DepConstructor;

	#[allow(non_camel_case_types)]
	impl DepConstructor {
	$(
	#[inline(always)]
	#[allow(unreachable_code, non_snake_case)]
	pub fn $variant(_tcx: TyCtxt<'_>, $(arg: $tuple_arg_ty)*) -> DepNode {
	// tuple args
	$({
	erase!($tuple_arg_ty);
	return DepNode::construct(_tcx, DepKind::$variant, &arg)
	})*

	return DepNode::construct(_tcx, DepKind::$variant, &())
	}
	)*
	}

	pub type DepNode = rustc_query_system::dep_graph::DepNode<DepKind>;

	pub trait DepNodeExt: Sized {
	/// Construct a DepNode from the given DepKind and DefPathHash. This
	/// method will assert that the given DepKind actually requires a
	/// single DefId/DefPathHash parameter.
	fn from_def_path_hash(def_path_hash: DefPathHash, kind: DepKind) -> Self;

	/// Extracts the DefId corresponding to this DepNode. This will work
	/// if two conditions are met:
	///
	/// 1. The Fingerprint of the DepNode actually is a DefPathHash, and
	/// 2. the item that the DefPath refers to exists in the current tcx.
	///
	/// Condition (1) is determined by the DepKind variant of the
	/// DepNode. Condition (2) might not be fulfilled if a DepNode
	/// refers to something from the previous compilation session that
	/// has been removed.
	fn extract_def_id(&self, tcx: TyCtxt<'_>) -> Option<DefId>;

	/// Used in testing
	fn from_label_string(label: &str, def_path_hash: DefPathHash)
	-> Result<Self, ()>;

	/// Used in testing
	fn has_label_string(label: &str) -> bool;
	}

	impl DepNodeExt for DepNode {
	/// Construct a DepNode from the given DepKind and DefPathHash. This
	/// method will assert that the given DepKind actually requires a
	/// single DefId/DefPathHash parameter.
	fn from_def_path_hash(def_path_hash: DefPathHash, kind: DepKind) -> DepNode {
	debug_assert!(kind.can_reconstruct_query_key() && kind.has_params());
	DepNode {
	kind,
	hash: def_path_hash.0,
	}
	}

	/// Extracts the DefId corresponding to this DepNode. This will work
	/// if two conditions are met:
	///
	/// 1. The Fingerprint of the DepNode actually is a DefPathHash, and
	/// 2. the item that the DefPath refers to exists in the current tcx.
	///
	/// Condition (1) is determined by the DepKind variant of the
	/// DepNode. Condition (2) might not be fulfilled if a DepNode
	/// refers to something from the previous compilation session that
	/// has been removed.
	fn extract_def_id(&self, tcx: TyCtxt<'tcx>) -> Option<DefId> {
	if self.kind.can_reconstruct_query_key() {
	let def_path_hash = DefPathHash(self.hash);
	tcx.def_path_hash_to_def_id.as_ref()?.get(&def_path_hash).cloned()
	} else {
	None
	}
	}

	/// Used in testing
	fn from_label_string(label: &str, def_path_hash: DefPathHash) -> Result<DepNode, ()> {
	let kind = match label {
	$(
	stringify!($variant) => DepKind::$variant,
	)*
	_ => return Err(()),
	};

	if !kind.can_reconstruct_query_key() {
	return Err(());
	}

	if kind.has_params() {
	Ok(DepNode::from_def_path_hash(def_path_hash, kind))
	} else {
	Ok(DepNode::new_no_params(kind))
	}
	}

	/// Used in testing
	fn has_label_string(label: &str) -> bool {
	match label {
	$(
	stringify!($variant) => true,
	)*
	_ => false,
	}
	}
	}

	/// Contains variant => str representations for constructing
	/// DepNode groups for tests.
	#[allow(dead_code, non_upper_case_globals)]
	pub mod label_strs {
	$(
	pub const $variant: &str = stringify!($variant);
	)*
	}
	);
	}

	rustc_dep_node_append!([define_dep_nodes!][ <'tcx>
	// We use this for most things when incr. comp. is turned off.
	[] Null,

	// Represents metadata from an extern crate.
	[eval_always] CrateMetadata(CrateNum),

	[anon] TraitSelect,

	[] CompileCodegenUnit(Symbol),
	]);

	impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for DefId {
	#[inline]
	fn can_reconstruct_query_key() -> bool {
	true
	}

	fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
	tcx.def_path_hash(*self).0
	}

	fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
	tcx.def_path_str(*self)
	}

	fn recover(tcx: TyCtxt<'tcx>, dep_node: &DepNode) -> Option<Self> {
	dep_node.extract_def_id(tcx)
	}
	}

	impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for LocalDefId {
	#[inline]
	fn can_reconstruct_query_key() -> bool {
	true
	}

	fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
	self.to_def_id().to_fingerprint(tcx)
	}

	fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
	self.to_def_id().to_debug_str(tcx)
	}

	fn recover(tcx: TyCtxt<'tcx>, dep_node: &DepNode) -> Option<Self> {
	dep_node.extract_def_id(tcx).map(\|id\| id.expect_local())
	}
	}

	impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for CrateNum {
	#[inline]
	fn can_reconstruct_query_key() -> bool {
	true
	}

	fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
	let def_id = DefId { krate: *self, index: CRATE_DEF_INDEX };
	tcx.def_path_hash(def_id).0
	}

	fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
	tcx.crate_name(*self).to_string()
	}

	fn recover(tcx: TyCtxt<'tcx>, dep_node: &DepNode) -> Option<Self> {
	dep_node.extract_def_id(tcx).map(\|id\| id.krate)
	}
	}

	impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for (DefId, DefId) {
	#[inline]
	fn can_reconstruct_query_key() -> bool {
	false
	}

	// We actually would not need to specialize the implementation of this
	// method but it's faster to combine the hashes than to instantiate a full
	// hashing context and stable-hashing state.
	fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
	let (def_id_0, def_id_1) = *self;

	let def_path_hash_0 = tcx.def_path_hash(def_id_0);
	let def_path_hash_1 = tcx.def_path_hash(def_id_1);

	def_path_hash_0.0.combine(def_path_hash_1.0)
	}

	fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
	let (def_id_0, def_id_1) = *self;

	format!("({}, {})", tcx.def_path_debug_str(def_id_0), tcx.def_path_debug_str(def_id_1))
	}
	}

	impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for HirId {
	#[inline]
	fn can_reconstruct_query_key() -> bool {
	false
	}

	// We actually would not need to specialize the implementation of this
	// method but it's faster to combine the hashes than to instantiate a full
	// hashing context and stable-hashing state.
	fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
	let HirId { owner, local_id } = *self;

	let def_path_hash = tcx.def_path_hash(owner.to_def_id());
	let local_id = Fingerprint::from_smaller_hash(local_id.as_u32().into());

	def_path_hash.0.combine(local_id)
	}
	}