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 ext::deriving::generic::ty::*;
  17 use parse::token::InternedString;
  18 use ptr::P;
  19
  20 pub fn expand_deriving_hash<F>(cx: &mut ExtCtxt,
  21                                span: Span,
  22                                mitem: &MetaItem,
  23                                item: &Item,
  24                                push: F) where
  25     F: FnOnce(P<Item>),
  26 {
  27
  28     let path = Path::new_(vec!("std", "hash", "Hash"), None,
  29                           vec!(box Literal(Path::new_local("__S"))), true);
  30     let generics = LifetimeBounds {
  31         lifetimes: Vec::new(),
  32         bounds: vec!(("__S",
  33                       vec!(Path::new(vec!("std", "hash", "Writer")),
  34                            Path::new(vec!("std", "hash", "Hasher"))))),
  35     };
  36     let args = Path::new_local("__S");
  37     let inline = cx.meta_word(span, InternedString::new("inline"));
  38     let attrs = vec!(cx.attribute(span, inline));
  39     let hash_trait_def = TraitDef {
  40         span: span,
  41         attributes: Vec::new(),
  42         path: path,
  43         additional_bounds: Vec::new(),
  44         generics: generics,
  45         methods: vec!(
  46             MethodDef {
  47                 name: "hash",
  48                 generics: LifetimeBounds::empty(),
  49                 explicit_self: borrowed_explicit_self(),
  50                 args: vec!(Ptr(box Literal(args), Borrowed(None, MutMutable))),
  51                 ret_ty: nil_ty(),
  52                 attributes: attrs,
  53                 combine_substructure: combine_substructure(box |a, b, c| {
  54                     hash_substructure(a, b, c)
  55                 })
  56             }
  57         )
  58     };
  59
  60     hash_trait_def.expand(cx, mitem, item, push);
  61 }
  62
  63 fn hash_substructure(cx: &mut ExtCtxt, trait_span: Span, substr: &Substructure) -> P<Expr> {
  64     let state_expr = match substr.nonself_args {
  65         [ref state_expr] => state_expr,
  66         _ => cx.span_bug(trait_span, "incorrect number of arguments in `deriving(Hash)`")
  67     };
  68     let hash_ident = substr.method_ident;
  69     let call_hash = |&: span, thing_expr| {
  70         let expr = cx.expr_method_call(span, thing_expr, hash_ident, vec!(state_expr.clone()));
  71         cx.stmt_expr(expr)
  72     };
  73     let mut stmts = Vec::new();
  74
  75     let fields = match *substr.fields {
  76         Struct(ref fs) => fs,
  77         EnumMatching(index, variant, ref fs) => {
  78             // Determine the discriminant. We will feed this value to the byte
  79             // iteration function.
  80             let discriminant = match variant.node.disr_expr {
  81                 Some(ref d) => d.clone(),
  82                 None => cx.expr_uint(trait_span, index)
  83             };
  84
  85             stmts.push(call_hash(trait_span, discriminant));
  86
  87             fs
  88         }
  89         _ => cx.span_bug(trait_span, "impossible substructure in `deriving(Hash)`")
  90     };
  91
  92     for &FieldInfo { ref self_, span, .. } in fields.iter() {
  93         stmts.push(call_hash(span, self_.clone()));
  94     }
  95
  96     if stmts.len() == 0 {
  97         cx.span_bug(trait_span, "#[derive(Hash)] needs at least one field");
  98     }
  99
 100     cx.expr_block(cx.block(trait_span, stmts, None))
 101 }