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;
  12 use ast::{MetaItem, Item, Expr, MutMutable};
  13 use codemap::Span;
  14 use ext::base::ExtCtxt;
  15 use ext::build::AstBuilder;
  16 use ext::deriving::generic::*;
  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 (path, generics, args) = if cx.ecfg.deriving_hash_type_parameter {
  25         (Path::new_(vec!("std", "hash", "Hash"), None,
  26                     vec!(~Literal(Path::new_local("__S"))), true),
  27          LifetimeBounds {
  28              lifetimes: Vec::new(),
  29              bounds: vec!(("__S", ast::StaticSize, vec!(Path::new(vec!("std", "io", "Writer"))))),
  30          },
  31          Path::new_local("__S"))
  32     } else {
  33         (Path::new(vec!("std", "hash", "Hash")),
  34          LifetimeBounds::empty(),
  35          Path::new(vec!("std", "hash", "sip", "SipState")))
  36     };
  37     let hash_trait_def = TraitDef {
  38         span: span,
  39         attributes: Vec::new(),
  40         path: path,
  41         additional_bounds: Vec::new(),
  42         generics: generics,
  43         methods: vec!(
  44             MethodDef {
  45                 name: "hash",
  46                 generics: LifetimeBounds::empty(),
  47                 explicit_self: borrowed_explicit_self(),
  48                 args: vec!(Ptr(~Literal(args), Borrowed(None, MutMutable))),
  49                 ret_ty: nil_ty(),
  50                 inline: true,
  51                 const_nonmatching: false,
  52                 combine_substructure: combine_substructure(|a, b, c| {
  53                     hash_substructure(a, b, c)
  54                 })
  55             }
  56         )
  57     };
  58
  59     hash_trait_def.expand(cx, mitem, item, push);
  60 }
  61
  62 fn hash_substructure(cx: &mut ExtCtxt, trait_span: Span, substr: &Substructure) -> @Expr {
  63     let state_expr = match substr.nonself_args {
  64         [state_expr] => state_expr,
  65         _ => cx.span_bug(trait_span, "incorrect number of arguments in `deriving(Hash)`")
  66     };
  67     let hash_ident = substr.method_ident;
  68     let call_hash = |span, thing_expr| {
  69         let expr = cx.expr_method_call(span, thing_expr, hash_ident, vec!(state_expr));
  70         cx.stmt_expr(expr)
  71     };
  72     let mut stmts = Vec::new();
  73
  74     let fields = match *substr.fields {
  75         Struct(ref fs) => fs,
  76         EnumMatching(index, variant, ref fs) => {
  77             // Determine the discriminant. We will feed this value to the byte
  78             // iteration function.
  79             let discriminant = match variant.node.disr_expr {
  80                 Some(d) => d,
  81                 None => cx.expr_uint(trait_span, index)
  82             };
  83
  84             stmts.push(call_hash(trait_span, discriminant));
  85
  86             fs
  87         }
  88         _ => cx.span_bug(trait_span, "impossible substructure in `deriving(Hash)`")
  89     };
  90
  91     for &FieldInfo { self_, span, .. } in fields.iter() {
  92         stmts.push(call_hash(span, self_));
  93     }
  94
  95     if stmts.len() == 0 {
  96         cx.span_bug(trait_span, "#[deriving(Hash)] needs at least one field");
  97     }
  98
  99     cx.expr_block(cx.block(trait_span, stmts, None))
 100 }