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