Auto merge of #66279 - cjgillot:hashstable, r=Zoxc

Use proc-macro to derive HashStable everywhere

Hello,

A second proc-macro is added to derive HashStable for crates librustc depends on.
This proc-macro `HashStable_Generic` (to bikeshed) allows to decouple code and strip much of librustc's boilerplate.

Still, two implementations `Span` and `TokenKind` require to be placed in librustc.
The latter only depends on the `bug` macro. Advise welcome on how to sever that link.
A trait `StableHasingContextLike` has been introduced at each crate root,
in order to handle those implementations which require librustc's very `StableHashingContext`.

This overall effort allowed to remove the `impl_stable_hash_for` macro.

Each commit passes the `x.py check`.
I still have to double check there was no change in the implementation.

4 files changed, 48 insertions, 10 deletions

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index dc26929100a..5bf12c54c4a 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -33,6 +33,7 @@ use syntax_pos::symbol::{kw, sym, Symbol};
 use syntax_pos::{Span, DUMMY_SP, ExpnId};
 
 use rustc_data_structures::fx::FxHashSet;
+use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::sync::Lrc;
 use rustc_data_structures::thin_vec::ThinVec;
 use rustc_index::vec::Idx;
@@ -54,7 +55,7 @@ mod tests;
 /// ```
 ///
 /// `'outer` is a label.
-#[derive(Clone, RustcEncodable, RustcDecodable, Copy)]
+#[derive(Clone, RustcEncodable, RustcDecodable, Copy, HashStable_Generic)]
 pub struct Label {
     pub ident: Ident,
 }
@@ -112,6 +113,15 @@ impl PartialEq<Symbol> for Path {
     }
 }
 
+impl<CTX> HashStable<CTX> for Path {
+    fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
+        self.segments.len().hash_stable(hcx, hasher);
+        for segment in &self.segments {
+            segment.ident.name.hash_stable(hcx, hasher);
+        }
+    }
+}
+
 impl Path {
     // Convert a span and an identifier to the corresponding
     // one-segment path.
@@ -473,7 +483,7 @@ pub struct Crate {
 /// Possible values inside of compile-time attribute lists.
 ///
 /// E.g., the '..' in `#[name(..)]`.
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, RustcEncodable, RustcDecodable, Debug, HashStable_Generic)]
 pub enum NestedMetaItem {
     /// A full MetaItem, for recursive meta items.
     MetaItem(MetaItem),
@@ -486,7 +496,7 @@ pub enum NestedMetaItem {
 /// A spanned compile-time attribute item.
 ///
 /// E.g., `#[test]`, `#[derive(..)]`, `#[rustfmt::skip]` or `#[feature = "foo"]`.
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, RustcEncodable, RustcDecodable, Debug, HashStable_Generic)]
 pub struct MetaItem {
     pub path: Path,
     pub kind: MetaItemKind,
@@ -496,7 +506,7 @@ pub struct MetaItem {
 /// A compile-time attribute item.
 ///
 /// E.g., `#[test]`, `#[derive(..)]` or `#[feature = "foo"]`.
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, RustcEncodable, RustcDecodable, Debug, HashStable_Generic)]
 pub enum MetaItemKind {
     /// Word meta item.
     ///
@@ -1426,7 +1436,7 @@ pub enum StrStyle {
 }
 
 /// An AST literal.
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, RustcEncodable, RustcDecodable, Debug, HashStable_Generic)]
 pub struct Lit {
     /// The original literal token as written in source code.
     pub token: token::Lit,
@@ -2286,7 +2296,7 @@ impl rustc_serialize::Decodable for AttrId {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, RustcEncodable, RustcDecodable, Debug, HashStable_Generic)]
 pub struct AttrItem {
     pub path: Path,
     pub tokens: TokenStream,
diff --git a/src/libsyntax/lib.rs b/src/libsyntax/lib.rs
index e3eca75dfe7..22b49862f49 100644
--- a/src/libsyntax/lib.rs
+++ b/src/libsyntax/lib.rs
@@ -110,3 +110,8 @@ pub mod print {
 }
 
 pub mod early_buffered_lints;
+
+/// 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 librustc.
+pub trait HashStableContext: syntax_pos::HashStableContext {}
diff --git a/src/libsyntax/token.rs b/src/libsyntax/token.rs
index fd1623384a4..6f45211ac5f 100644
--- a/src/libsyntax/token.rs
+++ b/src/libsyntax/token.rs
@@ -14,10 +14,12 @@ use syntax_pos::{self, Span, DUMMY_SP};
 
 use std::fmt;
 use std::mem;
+use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::sync::Lrc;
 use rustc_macros::HashStable_Generic;
 
 #[derive(Clone, PartialEq, RustcEncodable, RustcDecodable, Hash, Debug, Copy)]
+#[derive(HashStable_Generic)]
 pub enum BinOpToken {
     Plus,
     Minus,
@@ -33,6 +35,7 @@ pub enum BinOpToken {
 
 /// A delimiter token.
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug, Copy)]
+#[derive(HashStable_Generic)]
 pub enum DelimToken {
     /// A round parenthesis (i.e., `(` or `)`).
     Paren,
@@ -190,7 +193,7 @@ fn ident_can_begin_type(name: ast::Name, span: Span, is_raw: bool) -> bool {
     ].contains(&name)
 }
 
-#[derive(Clone, PartialEq, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, PartialEq, RustcEncodable, RustcDecodable, Debug, HashStable_Generic)]
 pub enum TokenKind {
     /* Expression-operator symbols. */
     Eq,
@@ -262,7 +265,7 @@ pub enum TokenKind {
 #[cfg(target_arch = "x86_64")]
 rustc_data_structures::static_assert_size!(TokenKind, 16);
 
-#[derive(Clone, PartialEq, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, PartialEq, RustcEncodable, RustcDecodable, Debug, HashStable_Generic)]
 pub struct Token {
     pub kind: TokenKind,
     pub span: Span,
@@ -725,3 +728,11 @@ impl fmt::Debug for Nonterminal {
         }
     }
 }
+
+impl<CTX> HashStable<CTX> for Nonterminal
+    where CTX: crate::HashStableContext
+{
+    fn hash_stable(&self, _hcx: &mut CTX, _hasher: &mut StableHasher) {
+        panic!("interpolated tokens should not be present in the HIR")
+    }
+}
diff --git a/src/libsyntax/tokenstream.rs b/src/libsyntax/tokenstream.rs
index 2201f1ed6ca..6a0523dd655 100644
--- a/src/libsyntax/tokenstream.rs
+++ b/src/libsyntax/tokenstream.rs
@@ -16,6 +16,8 @@
 use crate::token::{self, DelimToken, Token, TokenKind};
 
 use syntax_pos::{Span, DUMMY_SP};
+use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+use rustc_macros::HashStable_Generic;
 use rustc_data_structures::sync::Lrc;
 use smallvec::{SmallVec, smallvec};
 
@@ -33,7 +35,7 @@ use std::{iter, mem};
 ///
 /// The RHS of an MBE macro is the only place `SubstNt`s are substituted.
 /// Nothing special happens to misnamed or misplaced `SubstNt`s.
-#[derive(Debug, Clone, PartialEq, RustcEncodable, RustcDecodable)]
+#[derive(Debug, Clone, PartialEq, RustcEncodable, RustcDecodable, HashStable_Generic)]
 pub enum TokenTree {
     /// A single token
     Token(Token),
@@ -115,6 +117,16 @@ impl TokenTree {
     }
 }
 
+impl<CTX> HashStable<CTX> for TokenStream
+    where CTX: crate::HashStableContext
+{
+    fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
+        for sub_tt in self.trees() {
+            sub_tt.hash_stable(hcx, hasher);
+        }
+    }
+}
+
 /// A `TokenStream` is an abstract sequence of tokens, organized into `TokenTree`s.
 ///
 /// The goal is for procedural macros to work with `TokenStream`s and `TokenTree`s
@@ -444,7 +456,7 @@ impl Cursor {
     }
 }
 
-#[derive(Debug, Copy, Clone, PartialEq, RustcEncodable, RustcDecodable)]
+#[derive(Debug, Copy, Clone, PartialEq, RustcEncodable, RustcDecodable, HashStable_Generic)]
 pub struct DelimSpan {
     pub open: Span,
     pub close: Span,