Add HashStable_NoContext to simplify HashStable implementations in rustc_type_ir

compiler/rustc_ast/src/lib.rs

@@ -59,9 +59,7 @@ use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 /// Requirements for a `StableHashingContext` to be used in this crate.
 /// This is a hack to allow using the `HashStable_Generic` derive macro
 /// instead of implementing everything in `rustc_middle`.
-pub trait HashStableContext:
-    rustc_type_ir::HashStableContext + rustc_span::HashStableContext
-{
+pub trait HashStableContext: rustc_span::HashStableContext {
     fn hash_attr(&mut self, _: &ast::Attribute, hasher: &mut StableHasher);
 }
 

compiler/rustc_macros/src/hash_stable.rs

@@ -38,51 +38,80 @@ fn parse_attributes(field: &syn::Field) -> Attributes {
     attrs
 }
 
+pub(crate) fn hash_stable_derive(s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
+    hash_stable_derive_with_mode(s, HashStableMode::Normal)
+}
+
 pub(crate) fn hash_stable_generic_derive(
-    mut s: synstructure::Structure<'_>,
+    s: synstructure::Structure<'_>,
 ) -> proc_macro2::TokenStream {
-    let generic: syn::GenericParam = parse_quote!(__CTX);
-    s.add_bounds(synstructure::AddBounds::Generics);
-    s.add_impl_generic(generic);
-    s.add_where_predicate(parse_quote! { __CTX: crate::HashStableContext });
+    hash_stable_derive_with_mode(s, HashStableMode::Generic)
+}
 
-    let discriminant = hash_stable_discriminant(&mut s);
-    let body = hash_stable_body(&mut s);
+pub(crate) fn hash_stable_no_context_derive(
+    s: synstructure::Structure<'_>,
+) -> proc_macro2::TokenStream {
+    hash_stable_derive_with_mode(s, HashStableMode::NoContext)
+}
 
-    s.bound_impl(
-        quote!(::rustc_data_structures::stable_hasher::HashStable<__CTX>),
-        quote! {
-            #[inline]
-            fn hash_stable(
-                &self,
-                __hcx: &mut __CTX,
-                __hasher: &mut ::rustc_data_structures::stable_hasher::StableHasher) {
-                #discriminant
-                match *self { #body }
-            }
-        },
-    )
+enum HashStableMode {
+    // Use the query-system aware stable hashing context.
+    Normal,
+    // Emit a generic implementation that uses a crate-local `StableHashingContext`
+    // trait, when the crate is upstream of `rustc_middle`.
+    Generic,
+    // Emit a hash-stable implementation that takes no context,
+    // and emits per-field where clauses for (almost-)perfect derives.
+    NoContext,
 }
 
-pub(crate) fn hash_stable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
-    let generic: syn::GenericParam = parse_quote!('__ctx);
-    s.add_bounds(synstructure::AddBounds::Generics);
+fn hash_stable_derive_with_mode(
+    mut s: synstructure::Structure<'_>,
+    mode: HashStableMode,
+) -> proc_macro2::TokenStream {
+    let generic: syn::GenericParam = match mode {
+        HashStableMode::Normal => parse_quote!('__ctx),
+        HashStableMode::Generic | HashStableMode::NoContext => parse_quote!(__CTX),
+    };
+
+    // no_context impl is able to derive by-field, which is closer to a perfect derive.
+    s.add_bounds(match mode {
+        HashStableMode::Normal | HashStableMode::Generic => synstructure::AddBounds::Generics,
+        HashStableMode::NoContext => synstructure::AddBounds::Fields,
+    });
+
+    // For generic impl, add `where __CTX: HashStableContext`.
+    match mode {
+        HashStableMode::Normal => {}
+        HashStableMode::Generic => {
+            s.add_where_predicate(parse_quote! { __CTX: crate::HashStableContext });
+        }
+        HashStableMode::NoContext => {}
+    }
+
     s.add_impl_generic(generic);
 
     let discriminant = hash_stable_discriminant(&mut s);
     let body = hash_stable_body(&mut s);
 
+    let context: syn::Type = match mode {
+        HashStableMode::Normal => {
+            parse_quote!(::rustc_query_system::ich::StableHashingContext<'__ctx>)
+        }
+        HashStableMode::Generic | HashStableMode::NoContext => parse_quote!(__CTX),
+    };
+
     s.bound_impl(
         quote!(
             ::rustc_data_structures::stable_hasher::HashStable<
-                ::rustc_query_system::ich::StableHashingContext<'__ctx>,
+                #context
             >
         ),
         quote! {
             #[inline]
             fn hash_stable(
                 &self,
-                __hcx: &mut ::rustc_query_system::ich::StableHashingContext<'__ctx>,
+                __hcx: &mut #context,
                 __hasher: &mut ::rustc_data_structures::stable_hasher::StableHasher) {
                 #discriminant
                 match *self { #body }

compiler/rustc_macros/src/lib.rs

@@ -48,6 +48,13 @@ decl_derive!(
     [HashStable_Generic, attributes(stable_hasher)] =>
     hash_stable::hash_stable_generic_derive
 );
+decl_derive!(
+    [HashStable_NoContext] =>
+    /// `HashStable` implementation that has no `HashStableContext` bound and
+    /// which adds `where` bounds for `HashStable` based off of fields and not
+    /// generics. This is suitable for use in crates like `rustc_type_ir`.
+    hash_stable::hash_stable_no_context_derive
+);
 
 decl_derive!([Decodable] => serialize::decodable_derive);
 decl_derive!([Encodable] => serialize::encodable_derive);

compiler/rustc_query_system/src/ich/impls_syntax.rs

@@ -123,5 +123,3 @@ impl<'tcx> HashStable<StableHashingContext<'tcx>> for rustc_feature::Features {
         });
     }
 }
-
-impl<'ctx> rustc_type_ir::HashStableContext for StableHashingContext<'ctx> {}

compiler/rustc_type_ir/src/canonical.rs

@@ -2,9 +2,6 @@ use std::fmt;
 use std::hash::Hash;
 use std::ops::ControlFlow;
 
-#[cfg(feature = "nightly")]
-use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
-
 use crate::fold::{FallibleTypeFolder, TypeFoldable};
 use crate::visit::{TypeVisitable, TypeVisitor};
 use crate::{Interner, UniverseIndex};
@@ -14,7 +11,7 @@ use crate::{Interner, UniverseIndex};
 /// numbered starting from 0 in order of first appearance.
 #[derive(derivative::Derivative)]
 #[derivative(Clone(bound = "V: Clone"), Hash(bound = "V: Hash"))]
-#[cfg_attr(feature = "nightly", derive(TyEncodable, TyDecodable))]
+#[cfg_attr(feature = "nightly", derive(TyEncodable, TyDecodable, HashStable_NoContext))]
 pub struct Canonical<I: Interner, V> {
     pub value: V,
     pub max_universe: UniverseIndex,
@@ -61,19 +58,6 @@ impl<I: Interner, V> Canonical<I, V> {
     }
 }
 
-#[cfg(feature = "nightly")]
-impl<CTX: crate::HashStableContext, I: Interner, V: HashStable<CTX>> HashStable<CTX>
-    for Canonical<I, V>
-where
-    I::CanonicalVars: HashStable<CTX>,
-{
-    fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
-        self.value.hash_stable(hcx, hasher);
-        self.max_universe.hash_stable(hcx, hasher);
-        self.variables.hash_stable(hcx, hasher);
-    }
-}
-
 impl<I: Interner, V: Eq> Eq for Canonical<I, V> {}
 
 impl<I: Interner, V: PartialEq> PartialEq for Canonical<I, V> {

compiler/rustc_type_ir/src/const_kind.rs

@@ -16,7 +16,7 @@ use self::ConstKind::*;
     Ord = "feature_allow_slow_enum",
     Hash(bound = "")
 )]
-#[cfg_attr(feature = "nightly", derive(TyEncodable, TyDecodable))]
+#[cfg_attr(feature = "nightly", derive(TyEncodable, TyDecodable, HashStable_NoContext))]
 pub enum ConstKind<I: Interner> {
     /// A const generic parameter.
     Param(I::ParamConst),
@@ -47,49 +47,6 @@ pub enum ConstKind<I: Interner> {
     Expr(I::ExprConst),
 }
 
-#[cfg(feature = "nightly")]
-const fn const_kind_discriminant<I: Interner>(value: &ConstKind<I>) -> usize {
-    match value {
-        Param(_) => 0,
-        Infer(_) => 1,
-        Bound(_, _) => 2,
-        Placeholder(_) => 3,
-        Unevaluated(_) => 4,
-        Value(_) => 5,
-        Error(_) => 6,
-        Expr(_) => 7,
-    }
-}
-
-#[cfg(feature = "nightly")]
-impl<CTX: crate::HashStableContext, I: Interner> HashStable<CTX> for ConstKind<I>
-where
-    I::ParamConst: HashStable<CTX>,
-    I::BoundConst: HashStable<CTX>,
-    I::PlaceholderConst: HashStable<CTX>,
-    I::AliasConst: HashStable<CTX>,
-    I::ValueConst: HashStable<CTX>,
-    I::ErrorGuaranteed: HashStable<CTX>,
-    I::ExprConst: HashStable<CTX>,
-{
-    fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
-        const_kind_discriminant(self).hash_stable(hcx, hasher);
-        match self {
-            Param(p) => p.hash_stable(hcx, hasher),
-            Infer(i) => i.hash_stable(hcx, hasher),
-            Bound(d, b) => {
-                d.hash_stable(hcx, hasher);
-                b.hash_stable(hcx, hasher);
-            }
-            Placeholder(p) => p.hash_stable(hcx, hasher),
-            Unevaluated(u) => u.hash_stable(hcx, hasher),
-            Value(v) => v.hash_stable(hcx, hasher),
-            Error(e) => e.hash_stable(hcx, hasher),
-            Expr(e) => e.hash_stable(hcx, hasher),
-        }
-    }
-}
-
 impl<I: Interner> PartialEq for ConstKind<I> {
     fn eq(&self, other: &Self) -> bool {
         match (self, other) {

compiler/rustc_type_ir/src/lib.rs

@@ -51,9 +51,6 @@ pub use region_kind::*;
 pub use ty_info::*;
 pub use ty_kind::*;
 
-/// Needed so we can use #[derive(HashStable_Generic)]
-pub trait HashStableContext {}
-
 rustc_index::newtype_index! {
     /// A [De Bruijn index][dbi] is a standard means of representing
     /// regions (and perhaps later types) in a higher-ranked setting. In
@@ -94,7 +91,7 @@ rustc_index::newtype_index! {
     /// is the outer fn.
     ///
     /// [dbi]: https://en.wikipedia.org/wiki/De_Bruijn_index
-    #[cfg_attr(feature = "nightly", derive(HashStable_Generic))]
+    #[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
     #[debug_format = "DebruijnIndex({})"]
     #[gate_rustc_only]
     pub struct DebruijnIndex {
@@ -179,7 +176,7 @@ pub fn debug_bound_var<T: std::fmt::Write>(
 }
 
 #[derive(Copy, Clone, PartialEq, Eq)]
-#[cfg_attr(feature = "nightly", derive(Decodable, Encodable, Hash, HashStable_Generic))]
+#[cfg_attr(feature = "nightly", derive(Decodable, Encodable, Hash, HashStable_NoContext))]
 #[cfg_attr(feature = "nightly", rustc_pass_by_value)]
 pub enum Variance {
     Covariant,     // T<A> <: T<B> iff A <: B -- e.g., function return type
@@ -295,7 +292,7 @@ rustc_index::newtype_index! {
     /// declared, but a type name in a non-zero universe is a placeholder
     /// type -- an idealized representative of "types in general" that we
     /// use for checking generic functions.
-    #[cfg_attr(feature = "nightly", derive(HashStable_Generic))]
+    #[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
     #[debug_format = "U{}"]
     #[gate_rustc_only]
     pub struct UniverseIndex {}