src/libsyntax_ext/deriving/default.rs

   1 // Copyright 2012-2013 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 deriving::path_std;
  12 use deriving::generic::*;
  13 use deriving::generic::ty::*;
  14
  15 use syntax::ast::{Expr, MetaItem};
  16 use syntax::ext::base::{Annotatable, ExtCtxt};
  17 use syntax::ext::build::AstBuilder;
  18 use syntax::ptr::P;
  19 use syntax::symbol::Symbol;
  20 use syntax_pos::Span;
  21
  22 pub fn expand_deriving_default(cx: &mut ExtCtxt,
  23                                span: Span,
  24                                mitem: &MetaItem,
  25                                item: &Annotatable,
  26                                push: &mut dyn FnMut(Annotatable)) {
  27     let inline = cx.meta_word(span, Symbol::intern("inline"));
  28     let attrs = vec![cx.attribute(span, inline)];
  29     let trait_def = TraitDef {
  30         span,
  31         attributes: Vec::new(),
  32         path: path_std!(cx, default::Default),
  33         additional_bounds: Vec::new(),
  34         generics: LifetimeBounds::empty(),
  35         is_unsafe: false,
  36         supports_unions: false,
  37         methods: vec![MethodDef {
  38                           name: "default",
  39                           generics: LifetimeBounds::empty(),
  40                           explicit_self: None,
  41                           args: Vec::new(),
  42                           ret_ty: Self_,
  43                           attributes: attrs,
  44                           is_unsafe: false,
  45                           unify_fieldless_variants: false,
  46                           combine_substructure: combine_substructure(Box::new(|a, b, c| {
  47                               default_substructure(a, b, c)
  48                           })),
  49                       }],
  50         associated_types: Vec::new(),
  51     };
  52     trait_def.expand(cx, mitem, item, push)
  53 }
  54
  55 fn default_substructure(cx: &mut ExtCtxt, trait_span: Span, substr: &Substructure) -> P<Expr> {
  56     let default_ident = cx.std_path(&["default", "Default", "default"]);
  57     let default_call = |span| cx.expr_call_global(span, default_ident.clone(), Vec::new());
  58
  59     return match *substr.fields {
  60         StaticStruct(_, ref summary) => {
  61             match *summary {
  62                 Unnamed(ref fields, is_tuple) => {
  63                     if !is_tuple {
  64                         cx.expr_ident(trait_span, substr.type_ident)
  65                     } else {
  66                         let exprs = fields.iter().map(|sp| default_call(*sp)).collect();
  67                         cx.expr_call_ident(trait_span, substr.type_ident, exprs)
  68                     }
  69                 }
  70                 Named(ref fields) => {
  71                     let default_fields = fields.iter()
  72                         .map(|&(ident, span)| cx.field_imm(span, ident, default_call(span)))
  73                         .collect();
  74                     cx.expr_struct_ident(trait_span, substr.type_ident, default_fields)
  75                 }
  76             }
  77         }
  78         StaticEnum(..) => {
  79             span_err_if_not_stage0!(cx, trait_span, E0665,
  80                                     "`Default` cannot be derived for enums, only structs");
  81             // let compilation continue
  82             cx.expr_usize(trait_span, 0)
  83         }
  84         _ => cx.span_bug(trait_span, "Non-static method in `derive(Default)`"),
  85     };
  86 }