1 files changed, 80 insertions, 0 deletions
diff --git a/compiler/rustc_builtin_macros/src/deriving/hash.rs b/compiler/rustc_builtin_macros/src/deriving/hash.rs
new file mode 100644
index 000000000..32ae3d344
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/deriving/hash.rs
@@ -0,0 +1,80 @@
+use crate::deriving::generic::ty::*;
+use crate::deriving::generic::*;
+use crate::deriving::{path_std, pathvec_std};
+
+use rustc_ast::{MetaItem, Mutability};
+use rustc_expand::base::{Annotatable, ExtCtxt};
+use rustc_span::symbol::sym;
+use rustc_span::Span;
+
+pub fn expand_deriving_hash(
+    cx: &mut ExtCtxt<'_>,
+    span: Span,
+    mitem: &MetaItem,
+    item: &Annotatable,
+    push: &mut dyn FnMut(Annotatable),
+) {
+    let path = Path::new_(pathvec_std!(hash::Hash), vec![], PathKind::Std);
+
+    let typaram = sym::__H;
+
+    let arg = Path::new_local(typaram);
+    let hash_trait_def = TraitDef {
+        span,
+        attributes: Vec::new(),
+        path,
+        additional_bounds: Vec::new(),
+        generics: Bounds::empty(),
+        supports_unions: false,
+        methods: vec![MethodDef {
+            name: sym::hash,
+            generics: Bounds { bounds: vec![(typaram, vec![path_std!(hash::Hasher)])] },
+            explicit_self: true,
+            nonself_args: vec![(Ref(Box::new(Path(arg)), Mutability::Mut), sym::state)],
+            ret_ty: Unit,
+            attributes: vec![],
+            unify_fieldless_variants: true,
+            combine_substructure: combine_substructure(Box::new(|a, b, c| {
+                hash_substructure(a, b, c)
+            })),
+        }],
+        associated_types: Vec::new(),
+    };
+
+    hash_trait_def.expand(cx, mitem, item, push);
+}
+
+fn hash_substructure(
+    cx: &mut ExtCtxt<'_>,
+    trait_span: Span,
+    substr: &Substructure<'_>,
+) -> BlockOrExpr {
+    let [state_expr] = substr.nonselflike_args else {
+        cx.span_bug(trait_span, "incorrect number of arguments in `derive(Hash)`");
+    };
+    let call_hash = |span, expr| {
+        let hash_path = {
+            let strs = cx.std_path(&[sym::hash, sym::Hash, sym::hash]);
+
+            cx.expr_path(cx.path_global(span, strs))
+        };
+        let expr = cx.expr_call(span, hash_path, vec![expr, state_expr.clone()]);
+        cx.stmt_expr(expr)
+    };
+
+    let (stmts, match_expr) = match substr.fields {
+        Struct(_, fields) | EnumMatching(.., fields) => {
+            let stmts =
+                fields.iter().map(|field| call_hash(field.span, field.self_expr.clone())).collect();
+            (stmts, None)
+        }
+        EnumTag(tag_field, match_expr) => {
+            assert!(tag_field.other_selflike_exprs.is_empty());
+            let stmts = vec![call_hash(tag_field.span, tag_field.self_expr.clone())];
+            (stmts, match_expr.clone())
+        }
+        _ => cx.span_bug(trait_span, "impossible substructure in `derive(Hash)`"),
+    };
+
+    BlockOrExpr::new_mixed(stmts, match_expr)
+}