src/libsyntax_ext/deriving/hash.rs

   1 use crate::deriving::{self, pathvec_std, path_std};
   2 use crate::deriving::generic::*;
   3 use crate::deriving::generic::ty::*;
   4
   5 use syntax::ast::{Expr, MetaItem, Mutability};
   6 use syntax_expand::base::{Annotatable, ExtCtxt};
   7 use syntax::ptr::P;
   8 use syntax::symbol::sym;
   9 use syntax_pos::Span;
  10
  11 pub fn expand_deriving_hash(cx: &mut ExtCtxt<'_>,
  12                             span: Span,
  13                             mitem: &MetaItem,
  14                             item: &Annotatable,
  15                             push: &mut dyn FnMut(Annotatable)) {
  16
  17     let path = Path::new_(pathvec_std!(cx, hash::Hash), None, vec![], PathKind::Std);
  18
  19     let typaram = "__H";
  20
  21     let arg = Path::new_local(typaram);
  22     let hash_trait_def = TraitDef {
  23         span,
  24         attributes: Vec::new(),
  25         path,
  26         additional_bounds: Vec::new(),
  27         generics: LifetimeBounds::empty(),
  28         is_unsafe: false,
  29         supports_unions: false,
  30         methods: vec![MethodDef {
  31                           name: "hash",
  32                           generics: LifetimeBounds {
  33                               lifetimes: Vec::new(),
  34                               bounds: vec![(typaram, vec![path_std!(cx, hash::Hasher)])],
  35                           },
  36                           explicit_self: borrowed_explicit_self(),
  37                           args: vec![(Ptr(Box::new(Literal(arg)),
  38                                          Borrowed(None, Mutability::Mutable)), "state")],
  39                           ret_ty: nil_ty(),
  40                           attributes: vec![],
  41                           is_unsafe: false,
  42                           unify_fieldless_variants: true,
  43                           combine_substructure: combine_substructure(Box::new(|a, b, c| {
  44                               hash_substructure(a, b, c)
  45                           })),
  46                       }],
  47         associated_types: Vec::new(),
  48     };
  49
  50     hash_trait_def.expand(cx, mitem, item, push);
  51 }
  52
  53 fn hash_substructure(cx: &mut ExtCtxt<'_>, trait_span: Span, substr: &Substructure<'_>) -> P<Expr> {
  54     let state_expr = match &substr.nonself_args {
  55         &[o_f] => o_f,
  56         _ => {
  57             cx.span_bug(trait_span,
  58                         "incorrect number of arguments in `derive(Hash)`")
  59         }
  60     };
  61     let call_hash = |span, thing_expr| {
  62         let hash_path = {
  63             let strs = cx.std_path(&[sym::hash, sym::Hash, sym::hash]);
  64
  65             cx.expr_path(cx.path_global(span, strs))
  66         };
  67         let ref_thing = cx.expr_addr_of(span, thing_expr);
  68         let expr = cx.expr_call(span, hash_path, vec![ref_thing, state_expr.clone()]);
  69         cx.stmt_expr(expr)
  70     };
  71     let mut stmts = Vec::new();
  72
  73     let fields = match *substr.fields {
  74         Struct(_, ref fs) | EnumMatching(_, 1, .., ref fs) => fs,
  75         EnumMatching(.., ref fs) => {
  76             let variant_value = deriving::call_intrinsic(cx,
  77                                                          trait_span,
  78                                                          "discriminant_value",
  79                                                          vec![cx.expr_self(trait_span)]);
  80
  81             stmts.push(call_hash(trait_span, variant_value));
  82
  83             fs
  84         }
  85         _ => cx.span_bug(trait_span, "impossible substructure in `derive(Hash)`"),
  86     };
  87
  88     stmts.extend(fields.iter().map(|FieldInfo { ref self_, span, .. }|
  89         call_hash(*span, self_.clone())));
  90
  91     cx.expr_block(cx.block(trait_span, stmts))
  92 }