src/libsyntax/ext/deriving/hash.rs

   1 // Copyright 2014 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 use ast::{MetaItem, Item, Expr, MutMutable};
  12 use codemap::Span;
  13 use ext::base::ExtCtxt;
  14 use ext::build::AstBuilder;
  15 use ext::deriving::generic::*;
  16 use parse::token::InternedString;
  17
  18 pub fn expand_deriving_hash(cx: &mut ExtCtxt,
  19                             span: Span,
  20                             mitem: @MetaItem,
  21                             item: @Item,
  22                             push: |@Item|) {
  23
  24     let allow_default_type_param_usage = cx.attribute(
  25         span,
  26         cx.meta_list(
  27             span,
  28             InternedString::new("allow"),
  29             ~[cx.meta_word(span, InternedString::new("default_type_param_usage"))]));
  30
  31     let hash_trait_def = TraitDef {
  32         span: span,
  33         attributes: ~[allow_default_type_param_usage],
  34         path: Path::new_(~["std", "hash", "Hash"], None,
  35                          ~[~Literal(Path::new_local("__H"))], true),
  36         additional_bounds: ~[],
  37         generics: LifetimeBounds {
  38             lifetimes: ~[],
  39             bounds: ~[("__H", ~[Path::new(~["std", "io", "Writer"])])],
  40         },
  41         methods: ~[
  42             MethodDef {
  43                 name: "hash",
  44                 generics: LifetimeBounds::empty(),
  45                 explicit_self: borrowed_explicit_self(),
  46                 args: ~[Ptr(~Literal(Path::new_local("__H")),
  47                             Borrowed(None, MutMutable))],
  48                 ret_ty: nil_ty(),
  49                 inline: true,
  50                 const_nonmatching: false,
  51                 combine_substructure: hash_substructure
  52             }
  53         ]
  54     };
  55
  56     hash_trait_def.expand(cx, mitem, item, push);
  57 }
  58
  59 fn hash_substructure(cx: &mut ExtCtxt, trait_span: Span, substr: &Substructure) -> @Expr {
  60     let state_expr = match substr.nonself_args {
  61         [state_expr] => state_expr,
  62         _ => cx.span_bug(trait_span, "incorrect number of arguments in `deriving(Hash)`")
  63     };
  64     let hash_ident = substr.method_ident;
  65     let call_hash = |span, thing_expr| {
  66         let expr = cx.expr_method_call(span, thing_expr, hash_ident, ~[state_expr]);
  67         cx.stmt_expr(expr)
  68     };
  69     let mut stmts = ~[];
  70
  71     let fields = match *substr.fields {
  72         Struct(ref fs) => fs,
  73         EnumMatching(index, variant, ref fs) => {
  74             // Determine the discriminant. We will feed this value to the byte
  75             // iteration function.
  76             let discriminant = match variant.node.disr_expr {
  77                 Some(d) => d,
  78                 None => cx.expr_uint(trait_span, index)
  79             };
  80
  81             stmts.push(call_hash(trait_span, discriminant));
  82
  83             fs
  84         }
  85         _ => cx.span_bug(trait_span, "impossible substructure in `deriving(Hash)`")
  86     };
  87
  88     for &FieldInfo { self_, span, .. } in fields.iter() {
  89         stmts.push(call_hash(span, self_));
  90     }
  91
  92     if stmts.len() == 0 {
  93         cx.span_bug(trait_span, "#[deriving(Hash)] needs at least one field");
  94     }
  95
  96     cx.expr_block(cx.block(trait_span, stmts, None))
  97 }