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