Create a derive macro for HashStable

src/librustc/Cargo.toml

@@ -24,6 +24,7 @@ rustc-rayon = "0.1.2"
 rustc-rayon-core = "0.1.2"
 rustc_apfloat = { path = "../librustc_apfloat" }
 rustc_target = { path = "../librustc_target" }
+rustc_macros = { path = "../librustc_macros" }
 rustc_data_structures = { path = "../librustc_data_structures" }
 errors = { path = "../librustc_errors", package = "rustc_errors" }
 serialize = { path = "../libserialize" }

src/librustc/hir/mod.rs

@@ -32,6 +32,7 @@ use crate::ty::query::Providers;
 
 use rustc_data_structures::sync::{ParallelIterator, par_iter, Send, Sync};
 use rustc_data_structures::thin_vec::ThinVec;
+use rustc_macros::HashStable;
 
 use serialize::{self, Encoder, Encodable, Decoder, Decodable};
 use std::collections::{BTreeSet, BTreeMap};
@@ -149,7 +150,7 @@ pub const DUMMY_HIR_ID: HirId = HirId {
 
 pub const DUMMY_ITEM_LOCAL_ID: ItemLocalId = ItemLocalId::MAX;
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Copy)]
+#[derive(Clone, RustcEncodable, RustcDecodable, Copy, HashStable)]
 pub struct Lifetime {
     pub hir_id: HirId,
     pub span: Span,

src/librustc/ich/impls_hir.rs

@@ -157,12 +157,6 @@ impl_stable_hash_for!(struct ast::Label {
     ident
 });
 
-impl_stable_hash_for!(struct hir::Lifetime {
-    hir_id,
-    span,
-    name
-});
-
 impl_stable_hash_for!(struct hir::Path {
     span,
     def,

src/librustc/lib.rs

@@ -148,6 +148,7 @@ pub mod util {
 #[doc(hidden)]
 mod rustc {
     pub use crate::lint;
+    pub use crate::ich;
 }
 
 // FIXME(#27438): right now the unit tests of librustc don't refer to any actual

src/librustc_macros/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "rustc_macros"
+version = "0.1.0"
+authors = ["The Rust Project Developers"]
+
+[lib]
+proc-macro = true
+
+[dependencies]
+synstructure = "0.10.1"
+syn = { version = "0.15.22", features = ["full"] }
+proc-macro2 = "0.4.24"
+quote = "0.6.10"

src/librustc_macros/src/hash_stable.rs

@@ -0,0 +1,31 @@
+use synstructure;
+use syn;
+use proc_macro2;
+
+pub fn hash_stable_derive(mut s: synstructure::Structure) -> proc_macro2::TokenStream {
+    let generic: syn::GenericParam = parse_quote!('__ctx);
+    s.add_bounds(synstructure::AddBounds::Generics);
+    s.add_impl_generic(generic);
+    let body = s.each(|bi| quote!{
+        ::rustc_data_structures::stable_hasher::HashStable::hash_stable(#bi, __hcx, __hasher);
+    });
+
+    let discriminant = match s.ast().data {
+        syn::Data::Enum(_) => quote! {
+            ::std::mem::discriminant(self).hash_stable(__hcx, __hasher);
+        },
+        syn::Data::Struct(_) => quote! {},
+        syn::Data::Union(_) => panic!("cannot derive on union"),
+    };
+
+    s.bound_impl(quote!(::rustc_data_structures::stable_hasher::HashStable
+                        <::rustc::ich::StableHashingContext<'__ctx>>), quote!{
+        fn hash_stable<__W: ::rustc_data_structures::stable_hasher::StableHasherResult>(
+            &self,
+            __hcx: &mut ::rustc::ich::StableHashingContext<'__ctx>,
+            __hasher: &mut ::rustc_data_structures::stable_hasher::StableHasher<__W>) {
+            #discriminant
+            match *self { #body }
+        }
+    })
+}

src/librustc_macros/src/lib.rs

@@ -0,0 +1,14 @@
+#![feature(proc_macro_hygiene)]
+
+#[macro_use]
+extern crate syn;
+#[macro_use]
+extern crate synstructure;
+#[macro_use]
+extern crate quote;
+extern crate proc_macro;
+extern crate proc_macro2;
+
+mod hash_stable;
+
+decl_derive!([HashStable] => hash_stable::hash_stable_derive);

src/tools/tidy/src/deps.rs

@@ -137,6 +137,7 @@ const WHITELIST: &[Crate<'_>] = &[
     Crate("smallvec"),
     Crate("stable_deref_trait"),
     Crate("syn"),
+    Crate("synstructure"),
     Crate("tempfile"),
     Crate("termcolor"),
     Crate("terminon"),