Auto merge of rust-lang#24270 - pnkfelix:use-disr-val-for-derive-ord, r=brson

Use `discriminant_value` intrinsic for `derive(PartialOrd)`

[breaking-change]

This is a [breaking-change] because it can change the result of comparison operators when enum discriminants have been explicitly assigned.  Notably in a case like:
```rust
#[derive(PartialOrd)]
enum E { A = 2, B = 1}
```

Under the old deriving, `A < B` held, because `A` came before `B` in the order of declaration.  But now we use the ordering according to the provided values, and thus `A > B`.  (However, this change is very unlikely to break much, if any, code, since the orderings themselves should all remain well-defined, total, etc.)

Fix rust-lang#15523

Author: bors

src/libcore/intrinsics.rs

@@ -569,4 +569,10 @@ extern "rust-intrinsic" {
     pub fn overflowing_sub<T>(a: T, b: T) -> T;
     /// Returns (a * b) mod 2^N, where N is the width of N in bits.
     pub fn overflowing_mul<T>(a: T, b: T) -> T;
+
+    /// Returns the value of the discriminant for the variant in 'v',
+    /// cast to a `u64`; if `T` has no discriminant, returns 0.
+    // SNAP 5520801
+    #[cfg(not(stage0))]
+    pub fn discriminant_value<T>(v: &T) -> u64;
 }

src/libcore/lib.rs

@@ -157,6 +157,7 @@ mod tuple;
 
 #[doc(hidden)]
 mod core {
+    pub use intrinsics;
     pub use panicking;
     pub use fmt;
     pub use clone;

src/librustc_trans/trans/intrinsic.rs

@@ -14,6 +14,7 @@ use llvm;
 use llvm::{SequentiallyConsistent, Acquire, Release, AtomicXchg, ValueRef, TypeKind};
 use middle::subst;
 use middle::subst::FnSpace;
+use trans::adt;
 use trans::base::*;
 use trans::build::*;
 use trans::callee;
@@ -683,6 +684,17 @@ pub fn trans_intrinsic_call<'a, 'blk, 'tcx>(mut bcx: Block<'blk, 'tcx>,
             }
         }
 
+        (_, "discriminant_value") => {
+            let val_ty = substs.types.get(FnSpace, 0);
+            match val_ty.sty {
+                ty::ty_enum(..) => {
+                    let repr = adt::represent_type(ccx, *val_ty);
+                    adt::trans_get_discr(bcx, &*repr, llargs[0], Some(llret_ty))
+                }
+                _ => C_null(llret_ty)
+            }
+        }
+
         // This requires that atomic intrinsics follow a specific naming pattern:
         // "atomic_<operation>[_<ordering>]", and no ordering means SeqCst
         (_, name) if name.starts_with("atomic_") => {

src/librustc_typeck/check/mod.rs

@@ -5073,6 +5073,12 @@ pub fn check_intrinsic_type(ccx: &CrateCtxt, it: &ast::ForeignItem) {
 
             "assume" => (0, vec![tcx.types.bool], ty::mk_nil(tcx)),
 
+            "discriminant_value" => (1, vec![
+                    ty::mk_imm_rptr(tcx,
+                                    tcx.mk_region(ty::ReLateBound(ty::DebruijnIndex::new(1),
+                                                                  ty::BrAnon(0))),
+                                    param(ccx, 0))], tcx.types.u64),
+
             ref other => {
                 span_err!(tcx.sess, it.span, E0093,
                     "unrecognized intrinsic function: `{}`", *other);

src/libsyntax/ext/deriving/generic/mod.rs

@@ -201,6 +201,7 @@ use ext::base::ExtCtxt;
 use ext::build::AstBuilder;
 use codemap::{self, DUMMY_SP};
 use codemap::Span;
+use diagnostic::SpanHandler;
 use fold::MoveMap;
 use owned_slice::OwnedSlice;
 use parse::token::InternedString;
@@ -391,6 +392,7 @@ impl<'a> TraitDef<'a> {
             ast::ItemEnum(ref enum_def, ref generics) => {
                 self.expand_enum_def(cx,
                                      enum_def,
+                                     &item.attrs[..],
                                      item.ident,
                                      generics)
             }
@@ -653,6 +655,7 @@ impl<'a> TraitDef<'a> {
     fn expand_enum_def(&self,
                        cx: &mut ExtCtxt,
                        enum_def: &EnumDef,
+                       type_attrs: &[ast::Attribute],
                        type_ident: Ident,
                        generics: &Generics) -> P<ast::Item> {
         let mut field_tys = Vec::new();
@@ -687,6 +690,7 @@ impl<'a> TraitDef<'a> {
                 method_def.expand_enum_method_body(cx,
                                                    self,
                                                    enum_def,
+                                                   type_attrs,
                                                    type_ident,
                                                    self_args,
                                                    &nonself_args[..])
@@ -706,13 +710,30 @@ impl<'a> TraitDef<'a> {
     }
 }
 
-fn variant_to_pat(cx: &mut ExtCtxt, sp: Span, enum_ident: ast::Ident, variant: &ast::Variant)
-                  -> P<ast::Pat> {
-    let path = cx.path(sp, vec![enum_ident, variant.node.name]);
-    cx.pat(sp, match variant.node.kind {
-        ast::TupleVariantKind(..) => ast::PatEnum(path, None),
-        ast::StructVariantKind(..) => ast::PatStruct(path, Vec::new(), true),
-    })
+fn find_repr_type_name(diagnostic: &SpanHandler,
+                       type_attrs: &[ast::Attribute]) -> &'static str {
+    let mut repr_type_name = "i32";
+    for a in type_attrs {
+        for r in &attr::find_repr_attrs(diagnostic, a) {
+            repr_type_name = match *r {
+                attr::ReprAny | attr::ReprPacked => continue,
+                attr::ReprExtern => "i32",
+
+                attr::ReprInt(_, attr::SignedInt(ast::TyIs)) => "isize",
+                attr::ReprInt(_, attr::SignedInt(ast::TyI8)) => "i8",
+                attr::ReprInt(_, attr::SignedInt(ast::TyI16)) => "i16",
+                attr::ReprInt(_, attr::SignedInt(ast::TyI32)) => "i32",
+                attr::ReprInt(_, attr::SignedInt(ast::TyI64)) => "i64",
+
+                attr::ReprInt(_, attr::UnsignedInt(ast::TyUs)) => "usize",
+                attr::ReprInt(_, attr::UnsignedInt(ast::TyU8)) => "u8",
+                attr::ReprInt(_, attr::UnsignedInt(ast::TyU16)) => "u16",
+                attr::ReprInt(_, attr::UnsignedInt(ast::TyU32)) => "u32",
+                attr::ReprInt(_, attr::UnsignedInt(ast::TyU64)) => "u64",
+            }
+        }
+    }
+    repr_type_name
 }
 
 impl<'a> MethodDef<'a> {
@@ -983,12 +1004,13 @@ impl<'a> MethodDef<'a> {
                                cx: &mut ExtCtxt,
                                trait_: &TraitDef,
                                enum_def: &EnumDef,
+                               type_attrs: &[ast::Attribute],
                                type_ident: Ident,
                                self_args: Vec<P<Expr>>,
                                nonself_args: &[P<Expr>])
                                -> P<Expr> {
         self.build_enum_match_tuple(
-            cx, trait_, enum_def, type_ident, self_args, nonself_args)
+            cx, trait_, enum_def, type_attrs, type_ident, self_args, nonself_args)
     }
 
 
@@ -1022,6 +1044,7 @@ impl<'a> MethodDef<'a> {
         cx: &mut ExtCtxt,
         trait_: &TraitDef,
         enum_def: &EnumDef,
+        type_attrs: &[ast::Attribute],
         type_ident: Ident,
         self_args: Vec<P<Expr>>,
         nonself_args: &[P<Expr>]) -> P<Expr> {
@@ -1044,8 +1067,8 @@ impl<'a> MethodDef<'a> {
             .collect::<Vec<ast::Ident>>();
 
         // The `vi_idents` will be bound, solely in the catch-all, to
-        // a series of let statements mapping each self_arg to a usize
-        // corresponding to its variant index.
+        // a series of let statements mapping each self_arg to an int
+        // value corresponding to its discriminant.
         let vi_idents: Vec<ast::Ident> = self_arg_names.iter()
             .map(|name| { let vi_suffix = format!("{}_vi", &name[..]);
                           cx.ident_of(&vi_suffix[..]) })
@@ -1160,33 +1183,44 @@ impl<'a> MethodDef<'a> {
         //   unreachable-pattern error.
         //
         if variants.len() > 1 && self_args.len() > 1 {
-            let arms: Vec<ast::Arm> = variants.iter().enumerate()
-                .map(|(index, variant)| {
-                    let pat = variant_to_pat(cx, sp, type_ident, &**variant);
-                    let lit = ast::LitInt(index as u64, ast::UnsignedIntLit(ast::TyUs));
-                    cx.arm(sp, vec![pat], cx.expr_lit(sp, lit))
-                }).collect();
-
             // Build a series of let statements mapping each self_arg
-            // to a usize corresponding to its variant index.
+            // to its discriminant value. If this is a C-style enum
+            // with a specific repr type, then casts the values to
+            // that type.  Otherwise casts to `i32` (the default repr
+            // type).
+            //
             // i.e. for `enum E<T> { A, B(1), C(T, T) }`, and a deriving
             // with three Self args, builds three statements:
             //
             // ```
-            // let __self0_vi = match   self {
-            //     A => 0, B(..) => 1, C(..) => 2
-            // };
-            // let __self1_vi = match __arg1 {
-            //     A => 0, B(..) => 1, C(..) => 2
-            // };
-            // let __self2_vi = match __arg2 {
-            //     A => 0, B(..) => 1, C(..) => 2
-            // };
+            // let __self0_vi = unsafe {
+            //     std::intrinsics::discriminant_value(&self) } as i32;
+            // let __self1_vi = unsafe {
+            //     std::intrinsics::discriminant_value(&__arg1) } as i32;
+            // let __self2_vi = unsafe {
+            //     std::intrinsics::discriminant_value(&__arg2) } as i32;
             // ```
             let mut index_let_stmts: Vec<P<ast::Stmt>> = Vec::new();
+
+            let target_type_name =
+                find_repr_type_name(&cx.parse_sess.span_diagnostic, type_attrs);
+
             for (&ident, self_arg) in vi_idents.iter().zip(self_args.iter()) {
-                let variant_idx = cx.expr_match(sp, self_arg.clone(), arms.clone());
-                let let_stmt = cx.stmt_let(sp, false, ident, variant_idx);
+                let path = vec![cx.ident_of_std("core"),
+                                cx.ident_of("intrinsics"),
+                                cx.ident_of("discriminant_value")];
+                let call = cx.expr_call_global(
+                    sp, path, vec![cx.expr_addr_of(sp, self_arg.clone())]);
+                let variant_value = cx.expr_block(P(ast::Block {
+                    stmts: vec![],
+                    expr: Some(call),
+                    id: ast::DUMMY_NODE_ID,
+                    rules: ast::UnsafeBlock(ast::CompilerGenerated),
+                    span: sp }));
+
+                let target_ty = cx.ty_ident(sp, cx.ident_of(target_type_name));
+                let variant_disr = cx.expr_cast(sp, variant_value, target_ty);
+                let let_stmt = cx.stmt_let(sp, false, ident, variant_disr);
                 index_let_stmts.push(let_stmt);
             }
 

src/test/run-pass/discriminant_value.rs

@@ -0,0 +1,77 @@
+// Copyright 2014 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(core)]
+
+extern crate core;
+use core::intrinsics::discriminant_value;
+
+enum CLike1 {
+    A,
+    B,
+    C,
+    D
+}
+
+enum CLike2 {
+    A = 5,
+    B = 2,
+    C = 19,
+    D
+}
+
+#[repr(i8)]
+enum CLike3 {
+    A = 5,
+    B,
+    C = -1,
+    D
+}
+
+enum ADT {
+    First(u32, u32),
+    Second(u64)
+}
+
+enum NullablePointer {
+    Something(&'static u32),
+    Nothing
+}
+
+static CONST : u32 = 0xBEEF;
+
+pub fn main() {
+    unsafe {
+
+        assert_eq!(discriminant_value(&CLike1::A), 0);
+        assert_eq!(discriminant_value(&CLike1::B), 1);
+        assert_eq!(discriminant_value(&CLike1::C), 2);
+        assert_eq!(discriminant_value(&CLike1::D), 3);
+
+        assert_eq!(discriminant_value(&CLike2::A), 5);
+        assert_eq!(discriminant_value(&CLike2::B), 2);
+        assert_eq!(discriminant_value(&CLike2::C), 19);
+        assert_eq!(discriminant_value(&CLike2::D), 20);
+
+        assert_eq!(discriminant_value(&CLike3::A), 5);
+        assert_eq!(discriminant_value(&CLike3::B), 6);
+        assert_eq!(discriminant_value(&CLike3::C), -1_i8 as u64);
+        assert_eq!(discriminant_value(&CLike3::D), 0);
+
+        assert_eq!(discriminant_value(&ADT::First(0,0)), 0);
+        assert_eq!(discriminant_value(&ADT::Second(5)), 1);
+
+        assert_eq!(discriminant_value(&NullablePointer::Nothing), 1);
+        assert_eq!(discriminant_value(&NullablePointer::Something(&CONST)), 0);
+
+        assert_eq!(discriminant_value(&10), 0);
+        assert_eq!(discriminant_value(&"test"), 0);
+    }
+}

src/test/run-pass/issue-15523-big.rs

@@ -0,0 +1,48 @@
+// Copyright 2015 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.
+
+// Issue 15523: derive(PartialOrd) should use the provided
+// discriminant values for the derived ordering.
+//
+// This test is checking corner cases that arise when you have
+// 64-bit values in the variants.
+
+#[derive(PartialEq, PartialOrd)]
+#[repr(u64)]
+enum Eu64 {
+    Pos2 = 2,
+    PosMax = !0,
+    Pos1 = 1,
+}
+
+#[derive(PartialEq, PartialOrd)]
+#[repr(i64)]
+enum Ei64 {
+    Pos2 = 2,
+    Neg1 = -1,
+    NegMin = 1 << 63,
+    PosMax = !(1 << 63),
+    Pos1 = 1,
+}
+
+fn main() {
+    assert!(Eu64::Pos2 > Eu64::Pos1);
+    assert!(Eu64::Pos2 < Eu64::PosMax);
+    assert!(Eu64::Pos1 < Eu64::PosMax);
+
+
+    assert!(Ei64::Pos2 > Ei64::Pos1);
+    assert!(Ei64::Pos2 > Ei64::Neg1);
+    assert!(Ei64::Pos1 > Ei64::Neg1);
+    assert!(Ei64::Pos2 > Ei64::NegMin);
+    assert!(Ei64::Pos1 > Ei64::NegMin);
+    assert!(Ei64::Pos2 < Ei64::PosMax);
+    assert!(Ei64::Pos1 < Ei64::PosMax);
+}