src/libsyntax_ext/deriving/cmp/partial_ord.rs

   1 // Copyright 2013 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 pub use self::OrderingOp::*;
  12
  13 use deriving::generic::*;
  14 use deriving::generic::ty::*;
  15
  16 use syntax::ast::{self, BinOpKind, Expr, MetaItem};
  17 use syntax::ext::base::{Annotatable, ExtCtxt};
  18 use syntax::ext::build::AstBuilder;
  19 use syntax::parse::token::InternedString;
  20 use syntax::ptr::P;
  21 use syntax_pos::Span;
  22
  23 pub fn expand_deriving_partial_ord(cx: &mut ExtCtxt,
  24                                    span: Span,
  25                                    mitem: &MetaItem,
  26                                    item: &Annotatable,
  27                                    push: &mut FnMut(Annotatable)) {
  28     macro_rules! md {
  29         ($name:expr, $op:expr, $equal:expr) => { {
  30             let inline = cx.meta_word(span, InternedString::new("inline"));
  31             let attrs = vec!(cx.attribute(span, inline));
  32             MethodDef {
  33                 name: $name,
  34                 generics: LifetimeBounds::empty(),
  35                 explicit_self: borrowed_explicit_self(),
  36                 args: vec!(borrowed_self()),
  37                 ret_ty: Literal(path_local!(bool)),
  38                 attributes: attrs,
  39                 is_unsafe: false,
  40                 unify_fieldless_variants: true,
  41                 combine_substructure: combine_substructure(Box::new(|cx, span, substr| {
  42                     cs_op($op, $equal, cx, span, substr)
  43                 }))
  44             }
  45         } }
  46     }
  47
  48     let ordering_ty = Literal(path_std!(cx, core::cmp::Ordering));
  49     let ret_ty = Literal(Path::new_(pathvec_std!(cx, core::option::Option),
  50                                     None,
  51                                     vec![Box::new(ordering_ty)],
  52                                     true));
  53
  54     let inline = cx.meta_word(span, InternedString::new("inline"));
  55     let attrs = vec![cx.attribute(span, inline)];
  56
  57     let partial_cmp_def = MethodDef {
  58         name: "partial_cmp",
  59         generics: LifetimeBounds::empty(),
  60         explicit_self: borrowed_explicit_self(),
  61         args: vec![borrowed_self()],
  62         ret_ty: ret_ty,
  63         attributes: attrs,
  64         is_unsafe: false,
  65         unify_fieldless_variants: true,
  66         combine_substructure: combine_substructure(Box::new(|cx, span, substr| {
  67             cs_partial_cmp(cx, span, substr)
  68         })),
  69     };
  70
  71     // avoid defining extra methods if we can
  72     // c-like enums, enums without any fields and structs without fields
  73     // can safely define only `partial_cmp`.
  74     let methods = if is_type_without_fields(item) {
  75         vec![partial_cmp_def]
  76     } else {
  77         vec![partial_cmp_def,
  78              md!("lt", true, false),
  79              md!("le", true, true),
  80              md!("gt", false, false),
  81              md!("ge", false, true)]
  82     };
  83
  84     let trait_def = TraitDef {
  85         span: span,
  86         attributes: vec![],
  87         path: path_std!(cx, core::cmp::PartialOrd),
  88         additional_bounds: vec![],
  89         generics: LifetimeBounds::empty(),
  90         is_unsafe: false,
  91         supports_unions: false,
  92         methods: methods,
  93         associated_types: Vec::new(),
  94     };
  95     trait_def.expand(cx, mitem, item, push)
  96 }
  97
  98 #[derive(Copy, Clone)]
  99 pub enum OrderingOp {
 100     PartialCmpOp,
 101     LtOp,
 102     LeOp,
 103     GtOp,
 104     GeOp,
 105 }
 106
 107 pub fn some_ordering_collapsed(cx: &mut ExtCtxt,
 108                                span: Span,
 109                                op: OrderingOp,
 110                                self_arg_tags: &[ast::Ident])
 111                                -> P<ast::Expr> {
 112     let lft = cx.expr_ident(span, self_arg_tags[0]);
 113     let rgt = cx.expr_addr_of(span, cx.expr_ident(span, self_arg_tags[1]));
 114     let op_str = match op {
 115         PartialCmpOp => "partial_cmp",
 116         LtOp => "lt",
 117         LeOp => "le",
 118         GtOp => "gt",
 119         GeOp => "ge",
 120     };
 121     cx.expr_method_call(span, lft, cx.ident_of(op_str), vec![rgt])
 122 }
 123
 124 pub fn cs_partial_cmp(cx: &mut ExtCtxt, span: Span, substr: &Substructure) -> P<Expr> {
 125     let test_id = cx.ident_of("__cmp");
 126     let ordering = cx.path_global(span, cx.std_path(&["cmp", "Ordering", "Equal"]));
 127     let ordering_expr = cx.expr_path(ordering.clone());
 128     let equals_expr = cx.expr_some(span, ordering_expr);
 129
 130     let partial_cmp_path = cx.std_path(&["cmp", "PartialOrd", "partial_cmp"]);
 131
 132     // Builds:
 133     //
 134     // match ::std::cmp::PartialOrd::partial_cmp(&self_field1, &other_field1) {
 135     // ::std::option::Option::Some(::std::cmp::Ordering::Equal) =>
 136     // match ::std::cmp::PartialOrd::partial_cmp(&self_field2, &other_field2) {
 137     // ::std::option::Option::Some(::std::cmp::Ordering::Equal) => {
 138     // ...
 139     // }
 140     // __cmp => __cmp
 141     // },
 142     // __cmp => __cmp
 143     // }
 144     //
 145     cs_fold(// foldr nests the if-elses correctly, leaving the first field
 146             // as the outermost one, and the last as the innermost.
 147             false,
 148             |cx, span, old, self_f, other_fs| {
 149         // match new {
 150         //     Some(::std::cmp::Ordering::Equal) => old,
 151         //     __cmp => __cmp
 152         // }
 153
 154         let new = {
 155             let other_f = match (other_fs.len(), other_fs.get(0)) {
 156                 (1, Some(o_f)) => o_f,
 157                 _ => cx.span_bug(span, "not exactly 2 arguments in `derive(PartialOrd)`"),
 158             };
 159
 160             let args = vec![
 161                     cx.expr_addr_of(span, self_f),
 162                     cx.expr_addr_of(span, other_f.clone()),
 163                 ];
 164
 165             cx.expr_call_global(span, partial_cmp_path.clone(), args)
 166         };
 167
 168         let eq_arm = cx.arm(span,
 169                             vec![cx.pat_some(span, cx.pat_path(span, ordering.clone()))],
 170                             old);
 171         let neq_arm = cx.arm(span,
 172                              vec![cx.pat_ident(span, test_id)],
 173                              cx.expr_ident(span, test_id));
 174
 175         cx.expr_match(span, new, vec![eq_arm, neq_arm])
 176     },
 177             equals_expr.clone(),
 178             Box::new(|cx, span, (self_args, tag_tuple), _non_self_args| {
 179         if self_args.len() != 2 {
 180             cx.span_bug(span, "not exactly 2 arguments in `derive(PartialOrd)`")
 181         } else {
 182             some_ordering_collapsed(cx, span, PartialCmpOp, tag_tuple)
 183         }
 184     }),
 185             cx,
 186             span,
 187             substr)
 188 }
 189
 190 /// Strict inequality.
 191 fn cs_op(less: bool, equal: bool, cx: &mut ExtCtxt, span: Span, substr: &Substructure) -> P<Expr> {
 192     let op = if less { BinOpKind::Lt } else { BinOpKind::Gt };
 193     cs_fold(false, // need foldr,
 194             |cx, span, subexpr, self_f, other_fs| {
 195         // build up a series of chain ||'s and &&'s from the inside
 196         // out (hence foldr) to get lexical ordering, i.e. for op ==
 197         // `ast::lt`
 198         //
 199         // ```
 200         // self.f1 < other.f1 || (!(other.f1 < self.f1) &&
 201         // (self.f2 < other.f2 || (!(other.f2 < self.f2) &&
 202         // (false)
 203         // ))
 204         // )
 205         // ```
 206         //
 207         // The optimiser should remove the redundancy. We explicitly
 208         // get use the binops to avoid auto-deref dereferencing too many
 209         // layers of pointers, if the type includes pointers.
 210         //
 211         let other_f = match (other_fs.len(), other_fs.get(0)) {
 212             (1, Some(o_f)) => o_f,
 213             _ => cx.span_bug(span, "not exactly 2 arguments in `derive(PartialOrd)`"),
 214         };
 215
 216         let cmp = cx.expr_binary(span, op, self_f.clone(), other_f.clone());
 217
 218         let not_cmp = cx.expr_unary(span,
 219                                     ast::UnOp::Not,
 220                                     cx.expr_binary(span, op, other_f.clone(), self_f));
 221
 222         let and = cx.expr_binary(span, BinOpKind::And, not_cmp, subexpr);
 223         cx.expr_binary(span, BinOpKind::Or, cmp, and)
 224     },
 225             cx.expr_bool(span, equal),
 226             Box::new(|cx, span, (self_args, tag_tuple), _non_self_args| {
 227         if self_args.len() != 2 {
 228             cx.span_bug(span, "not exactly 2 arguments in `derive(PartialOrd)`")
 229         } else {
 230             let op = match (less, equal) {
 231                 (true, true) => LeOp,
 232                 (true, false) => LtOp,
 233                 (false, true) => GeOp,
 234                 (false, false) => GtOp,
 235             };
 236             some_ordering_collapsed(cx, span, op, tag_tuple)
 237         }
 238     }),
 239             cx,
 240             span,
 241             substr)
 242 }