partial_ord.rs

// Copyright 2013 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.

pub use self::OrderingOp::*;

use deriving::generic::*;
use deriving::generic::ty::*;

use syntax::ast::{self, BinOpKind, Expr, MetaItem};
use syntax::ext::base::{Annotatable, ExtCtxt};
use syntax::ext::build::AstBuilder;
use syntax::parse::token::InternedString;
use syntax::ptr::P;
use syntax_pos::Span;

pub fn expand_deriving_partial_ord(cx: &mut ExtCtxt,
                                   span: Span,
                                   mitem: &MetaItem,
                                   item: &Annotatable,
                                   push: &mut FnMut(Annotatable)) {
    macro_rules! md {
        ($name:expr, $op:expr, $equal:expr) => { {
            let inline = cx.meta_word(span, InternedString::new("inline"));
            let attrs = vec!(cx.attribute(span, inline));
            MethodDef {
                name: $name,
                generics: LifetimeBounds::empty(),
                explicit_self: borrowed_explicit_self(),
                args: vec!(borrowed_self()),
                ret_ty: Literal(path_local!(bool)),
                attributes: attrs,
                is_unsafe: false,
                unify_fieldless_variants: true,
                combine_substructure: combine_substructure(Box::new(|cx, span, substr| {
                    cs_op($op, $equal, cx, span, substr)
                }))
            }
        } }
    }

    let ordering_ty = Literal(path_std!(cx, core::cmp::Ordering));
    let ret_ty = Literal(Path::new_(pathvec_std!(cx, core::option::Option),
                                    None,
                                    vec![Box::new(ordering_ty)],
                                    true));

    let inline = cx.meta_word(span, InternedString::new("inline"));
    let attrs = vec![cx.attribute(span, inline)];

    let partial_cmp_def = MethodDef {
        name: "partial_cmp",
        generics: LifetimeBounds::empty(),
        explicit_self: borrowed_explicit_self(),
        args: vec![borrowed_self()],
        ret_ty: ret_ty,
        attributes: attrs,
        is_unsafe: false,
        unify_fieldless_variants: true,
        combine_substructure: combine_substructure(Box::new(|cx, span, substr| {
            cs_partial_cmp(cx, span, substr)
        })),
    };

    // avoid defining extra methods if we can
    // c-like enums, enums without any fields and structs without fields
    // can safely define only `partial_cmp`.
    let methods = if is_type_without_fields(item) {
        vec![partial_cmp_def]
    } else {
        vec![partial_cmp_def,
             md!("lt", true, false),
             md!("le", true, true),
             md!("gt", false, false),
             md!("ge", false, true)]
    };

    let trait_def = TraitDef {
        span: span,
        attributes: vec![],
        path: path_std!(cx, core::cmp::PartialOrd),
        additional_bounds: vec![],
        generics: LifetimeBounds::empty(),
        is_unsafe: false,
        methods: methods,
        associated_types: Vec::new(),
    };
    trait_def.expand(cx, mitem, item, push)
}

#[derive(Copy, Clone)]
pub enum OrderingOp {
    PartialCmpOp,
    LtOp,
    LeOp,
    GtOp,
    GeOp,
}

pub fn some_ordering_collapsed(cx: &mut ExtCtxt,
                               span: Span,
                               op: OrderingOp,
                               self_arg_tags: &[ast::Ident])
                               -> P<ast::Expr> {
    let lft = cx.expr_ident(span, self_arg_tags[0]);
    let rgt = cx.expr_addr_of(span, cx.expr_ident(span, self_arg_tags[1]));
    let op_str = match op {
        PartialCmpOp => "partial_cmp",
        LtOp => "lt",
        LeOp => "le",
        GtOp => "gt",
        GeOp => "ge",
    };
    cx.expr_method_call(span, lft, cx.ident_of(op_str), vec![rgt])
}

pub fn cs_partial_cmp(cx: &mut ExtCtxt, span: Span, substr: &Substructure) -> P<Expr> {
    let test_id = cx.ident_of("__cmp");
    let ordering = cx.path_global(span, cx.std_path(&["cmp", "Ordering", "Equal"]));
    let ordering_expr = cx.expr_path(ordering.clone());
    let equals_expr = cx.expr_some(span, ordering_expr);

    let partial_cmp_path = cx.std_path(&["cmp", "PartialOrd", "partial_cmp"]);

    // Builds:
    //
    // match ::std::cmp::PartialOrd::partial_cmp(&self_field1, &other_field1) {
    // ::std::option::Option::Some(::std::cmp::Ordering::Equal) =>
    // match ::std::cmp::PartialOrd::partial_cmp(&self_field2, &other_field2) {
    // ::std::option::Option::Some(::std::cmp::Ordering::Equal) => {
    // ...
    // }
    // __cmp => __cmp
    // },
    // __cmp => __cmp
    // }
    //
    cs_fold(// foldr nests the if-elses correctly, leaving the first field
            // as the outermost one, and the last as the innermost.
            false,
            |cx, span, old, self_f, other_fs| {
        // match new {
        //     Some(::std::cmp::Ordering::Equal) => old,
        //     __cmp => __cmp
        // }

        let new = {
            let other_f = match (other_fs.len(), other_fs.get(0)) {
                (1, Some(o_f)) => o_f,
                _ => cx.span_bug(span, "not exactly 2 arguments in `derive(PartialOrd)`"),
            };

            let args = vec![
                    cx.expr_addr_of(span, self_f),
                    cx.expr_addr_of(span, other_f.clone()),
                ];

            cx.expr_call_global(span, partial_cmp_path.clone(), args)
        };

        let eq_arm = cx.arm(span,
                            vec![cx.pat_some(span, cx.pat_path(span, ordering.clone()))],
                            old);
        let neq_arm = cx.arm(span,
                             vec![cx.pat_ident(span, test_id)],
                             cx.expr_ident(span, test_id));

        cx.expr_match(span, new, vec![eq_arm, neq_arm])
    },
            equals_expr.clone(),
            Box::new(|cx, span, (self_args, tag_tuple), _non_self_args| {
        if self_args.len() != 2 {
            cx.span_bug(span, "not exactly 2 arguments in `derive(PartialOrd)`")
        } else {
            some_ordering_collapsed(cx, span, PartialCmpOp, tag_tuple)
        }
    }),
            cx,
            span,
            substr)
}

/// Strict inequality.
fn cs_op(less: bool, equal: bool, cx: &mut ExtCtxt, span: Span, substr: &Substructure) -> P<Expr> {
    let op = if less { BinOpKind::Lt } else { BinOpKind::Gt };
    cs_fold(false, // need foldr,
            |cx, span, subexpr, self_f, other_fs| {
        // build up a series of chain ||'s and &&'s from the inside
        // out (hence foldr) to get lexical ordering, i.e. for op ==
        // `ast::lt`
        //
        // ```
        // self.f1 < other.f1 || (!(other.f1 < self.f1) &&
        // (self.f2 < other.f2 || (!(other.f2 < self.f2) &&
        // (false)
        // ))
        // )
        // ```
        //
        // The optimiser should remove the redundancy. We explicitly
        // get use the binops to avoid auto-deref dereferencing too many
        // layers of pointers, if the type includes pointers.
        //
        let other_f = match (other_fs.len(), other_fs.get(0)) {
            (1, Some(o_f)) => o_f,
            _ => cx.span_bug(span, "not exactly 2 arguments in `derive(PartialOrd)`"),
        };

        let cmp = cx.expr_binary(span, op, self_f.clone(), other_f.clone());

        let not_cmp = cx.expr_unary(span,
                                    ast::UnOp::Not,
                                    cx.expr_binary(span, op, other_f.clone(), self_f));

        let and = cx.expr_binary(span, BinOpKind::And, not_cmp, subexpr);
        cx.expr_binary(span, BinOpKind::Or, cmp, and)
    },
            cx.expr_bool(span, equal),
            Box::new(|cx, span, (self_args, tag_tuple), _non_self_args| {
        if self_args.len() != 2 {
            cx.span_bug(span, "not exactly 2 arguments in `derive(PartialOrd)`")
        } else {
            let op = match (less, equal) {
                (true, true) => LeOp,
                (true, false) => LtOp,
                (false, true) => GeOp,
                (false, false) => GtOp,
            };
            some_ordering_collapsed(cx, span, op, tag_tuple)
        }
    }),
            cx,
            span,
            substr)
}