Improve Eq deriving

src/libcore/cmp.rs

@@ -129,7 +129,7 @@ pub trait PartialEq<Rhs: ?Sized = Self> {
 /// This trait can be used with `#[derive]`. When `derive`d, because `Eq` has
 /// no extra methods, it is only informing the compiler that this is an
 /// equivalence relation rather than a partial equivalence relation. Note that
-/// the `derive` strategy requires all fields are `PartialEq`, which isn't
+/// the `derive` strategy requires all fields are `Eq`, which isn't
 /// always desired.
 ///
 /// ## How can I implement `Eq`?
@@ -165,6 +165,17 @@ pub trait Eq: PartialEq<Self> {
     fn assert_receiver_is_total_eq(&self) {}
 }
 
+// FIXME: this struct is used solely by #[derive] to
+// assert that every component of a type implements Eq.
+//
+// This struct should never appear in user code.
+#[doc(hidden)]
+#[allow(missing_debug_implementations)]
+#[unstable(feature = "derive_eq",
+           reason = "deriving hack, should not be public",
+           issue = "0")]
+pub struct AssertParamIsEq<T: Eq + ?Sized> { _field: ::marker::PhantomData<T> }
+
 /// An `Ordering` is the result of a comparison between two values.
 ///
 /// # Examples

src/libsyntax/ext/build.rs

@@ -97,6 +97,7 @@ pub trait AstBuilder {
                       typ: P<ast::Ty>,
                       ex: P<ast::Expr>)
                       -> P<ast::Stmt>;
+    fn stmt_let_type_only(&self, span: Span, ty: P<ast::Ty>) -> ast::Stmt;
     fn stmt_item(&self, sp: Span, item: P<ast::Item>) -> ast::Stmt;
 
     // blocks
@@ -577,6 +578,23 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         })
     }
 
+    // Generate `let _: Type;`, usually used for type assertions.
+    fn stmt_let_type_only(&self, span: Span, ty: P<ast::Ty>) -> ast::Stmt {
+        let local = P(ast::Local {
+            pat: self.pat_wild(span),
+            ty: Some(ty),
+            init: None,
+            id: ast::DUMMY_NODE_ID,
+            span: span,
+            attrs: ast::ThinVec::new(),
+        });
+        ast::Stmt {
+            id: ast::DUMMY_NODE_ID,
+            node: ast::StmtKind::Local(local),
+            span: span,
+        }
+    }
+
     fn stmt_item(&self, sp: Span, item: P<ast::Item>) -> ast::Stmt {
         ast::Stmt {
             id: ast::DUMMY_NODE_ID,

src/libsyntax_ext/deriving/clone.rs

@@ -115,20 +115,7 @@ fn cs_clone_shallow(name: &str,
         let assert_path = cx.path_all(span, true,
                                         cx.std_path(&["clone", helper_name]),
                                         vec![], vec![ty], vec![]);
-        let local = P(ast::Local {
-            pat: cx.pat_wild(span),
-            ty: Some(cx.ty_path(assert_path)),
-            init: None,
-            id: ast::DUMMY_NODE_ID,
-            span: span,
-            attrs: ast::ThinVec::new(),
-        });
-        let stmt = ast::Stmt {
-            id: ast::DUMMY_NODE_ID,
-            node: ast::StmtKind::Local(local),
-            span: span,
-        };
-        stmts.push(stmt);
+        stmts.push(cx.stmt_let_type_only(span, cx.ty_path(assert_path)));
     }
     fn process_variant(cx: &mut ExtCtxt, stmts: &mut Vec<ast::Stmt>, variant: &VariantData) {
         for field in variant.fields() {

src/libsyntax_ext/deriving/cmp/eq.rs

@@ -11,7 +11,7 @@
 use deriving::generic::*;
 use deriving::generic::ty::*;
 
-use syntax::ast::{Expr, MetaItem};
+use syntax::ast::{self, Expr, MetaItem};
 use syntax::ext::base::{Annotatable, ExtCtxt};
 use syntax::ext::build::AstBuilder;
 use syntax::parse::token::InternedString;
@@ -23,22 +23,6 @@ pub fn expand_deriving_eq(cx: &mut ExtCtxt,
                           mitem: &MetaItem,
                           item: &Annotatable,
                           push: &mut FnMut(Annotatable)) {
-    fn cs_total_eq_assert(cx: &mut ExtCtxt, span: Span, substr: &Substructure) -> P<Expr> {
-        cs_same_method(|cx, span, exprs| {
-            // create `a.<method>(); b.<method>(); c.<method>(); ...`
-            // (where method is `assert_receiver_is_total_eq`)
-            let stmts = exprs.into_iter().map(|e| cx.stmt_expr(e)).collect();
-            let block = cx.block(span, stmts);
-            cx.expr_block(block)
-        },
-                       Box::new(|cx, sp, _, _| {
-                           cx.span_bug(sp, "non matching enums in derive(Eq)?")
-                       }),
-                       cx,
-                       span,
-                       substr)
-    }
-
     let inline = cx.meta_word(span, InternedString::new("inline"));
     let hidden = cx.meta_list_item_word(span, InternedString::new("hidden"));
     let doc = cx.meta_list(span, InternedString::new("doc"), vec![hidden]);
@@ -50,7 +34,7 @@ pub fn expand_deriving_eq(cx: &mut ExtCtxt,
         additional_bounds: Vec::new(),
         generics: LifetimeBounds::empty(),
         is_unsafe: false,
-        supports_unions: false,
+        supports_unions: true,
         methods: vec![MethodDef {
                           name: "assert_receiver_is_total_eq",
                           generics: LifetimeBounds::empty(),
@@ -66,5 +50,38 @@ pub fn expand_deriving_eq(cx: &mut ExtCtxt,
                       }],
         associated_types: Vec::new(),
     };
-    trait_def.expand(cx, mitem, item, push)
+    trait_def.expand_ext(cx, mitem, item, push, true)
+}
+
+fn cs_total_eq_assert(cx: &mut ExtCtxt, trait_span: Span, substr: &Substructure) -> P<Expr> {
+    fn assert_ty_bounds(cx: &mut ExtCtxt, stmts: &mut Vec<ast::Stmt>,
+                        ty: P<ast::Ty>, span: Span, helper_name: &str) {
+        // Generate statement `let _: helper_name<ty>;`,
+        // set the expn ID so we can use the unstable struct.
+        let span = super::allow_unstable(cx, span, "derive(Eq)");
+        let assert_path = cx.path_all(span, true,
+                                        cx.std_path(&["cmp", helper_name]),
+                                        vec![], vec![ty], vec![]);
+        stmts.push(cx.stmt_let_type_only(span, cx.ty_path(assert_path)));
+    }
+    fn process_variant(cx: &mut ExtCtxt, stmts: &mut Vec<ast::Stmt>, variant: &ast::VariantData) {
+        for field in variant.fields() {
+            // let _: AssertParamIsEq<FieldTy>;
+            assert_ty_bounds(cx, stmts, field.ty.clone(), field.span, "AssertParamIsEq");
+        }
+    }
+
+    let mut stmts = Vec::new();
+    match *substr.fields {
+        StaticStruct(vdata, ..) => {
+            process_variant(cx, &mut stmts, vdata);
+        }
+        StaticEnum(enum_def, ..) => {
+            for variant in &enum_def.variants {
+                process_variant(cx, &mut stmts, &variant.node.data);
+            }
+        }
+        _ => cx.span_bug(trait_span, "unexpected substructure in `derive(Eq)`")
+    }
+    cx.expr_block(cx.block(trait_span, stmts))
 }

src/test/compile-fail/union/union-derive-eq.rs

@@ -0,0 +1,30 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(untagged_unions)]
+
+#[derive(Eq)] // OK
+union U1 {
+    a: u8,
+}
+
+impl PartialEq for U1 { fn eq(&self, rhs: &Self) -> bool { true } }
+
+#[derive(PartialEq)]
+struct PartialEqNotEq;
+
+#[derive(Eq)]
+union U2 {
+    a: PartialEqNotEq, //~ ERROR the trait bound `PartialEqNotEq: std::cmp::Eq` is not satisfied
+}
+
+impl PartialEq for U2 { fn eq(&self, rhs: &Self) -> bool { true } }
+
+fn main() {}

src/test/compile-fail/union/union-derive.rs

@@ -14,7 +14,6 @@
 
 #[derive(
     PartialEq, //~ ERROR this trait cannot be derived for unions
-    Eq, //~ ERROR this trait cannot be derived for unions
     PartialOrd, //~ ERROR this trait cannot be derived for unions
     Ord, //~ ERROR this trait cannot be derived for unions
     Hash, //~ ERROR this trait cannot be derived for unions

src/test/run-pass/union/union-derive.rs

@@ -15,22 +15,33 @@
 #[derive(
     Copy,
     Clone,
+    Eq,
 )]
 union U {
     a: u8,
     b: u16,
 }
 
-#[derive(Clone, Copy)]
+impl PartialEq for U { fn eq(&self, rhs: &Self) -> bool { true } }
+
+#[derive(
+    Clone,
+    Copy,
+    Eq
+)]
 union W<T> {
     a: T,
 }
 
+impl<T> PartialEq for W<T> { fn eq(&self, rhs: &Self) -> bool { true } }
+
 fn main() {
     let u = U { b: 0 };
     let u1 = u;
     let u2 = u.clone();
+    assert!(u1 == u2);
 
     let w = W { a: 0 };
     let w1 = w.clone();
+    assert!(w == w1);
 }