src/libsyntax_ext/deriving/mod.rs

   1 //! The compiler code necessary to implement the `#[derive]` extensions.
   2
   3 use syntax::ast::{self, ItemKind, MetaItem};
   4 use syntax_expand::base::{Annotatable, ExtCtxt, MultiItemModifier};
   5 use syntax::ptr::P;
   6 use syntax::symbol::{Symbol, sym};
   7 use syntax_pos::Span;
   8
   9 macro path_local($x:ident) {
  10     generic::ty::Path::new_local(stringify!($x))
  11 }
  12
  13 macro pathvec_std($cx:expr, $($rest:ident)::+) {{
  14     vec![ $( stringify!($rest) ),+ ]
  15 }}
  16
  17 macro path_std($($x:tt)*) {
  18     generic::ty::Path::new( pathvec_std!( $($x)* ) )
  19 }
  20
  21 pub mod bounds;
  22 pub mod clone;
  23 pub mod encodable;
  24 pub mod decodable;
  25 pub mod hash;
  26 pub mod debug;
  27 pub mod default;
  28
  29 #[path="cmp/partial_eq.rs"]
  30 pub mod partial_eq;
  31 #[path="cmp/eq.rs"]
  32 pub mod eq;
  33 #[path="cmp/partial_ord.rs"]
  34 pub mod partial_ord;
  35 #[path="cmp/ord.rs"]
  36 pub mod ord;
  37
  38 pub mod generic;
  39
  40 crate struct BuiltinDerive(
  41     crate fn(&mut ExtCtxt<'_>, Span, &MetaItem, &Annotatable, &mut dyn FnMut(Annotatable))
  42 );
  43
  44 impl MultiItemModifier for BuiltinDerive {
  45     fn expand(&self,
  46               ecx: &mut ExtCtxt<'_>,
  47               span: Span,
  48               meta_item: &MetaItem,
  49               item: Annotatable)
  50               -> Vec<Annotatable> {
  51         // FIXME: Built-in derives often forget to give spans contexts,
  52         // so we are doing it here in a centralized way.
  53         let span = ecx.with_def_site_ctxt(span);
  54         let mut items = Vec::new();
  55         (self.0)(ecx, span, meta_item, &item, &mut |a| items.push(a));
  56         items
  57     }
  58 }
  59
  60 /// Constructs an expression that calls an intrinsic
  61 fn call_intrinsic(cx: &ExtCtxt<'_>,
  62                   span: Span,
  63                   intrinsic: &str,
  64                   args: Vec<P<ast::Expr>>)
  65                   -> P<ast::Expr> {
  66     let span = cx.with_def_site_ctxt(span);
  67     let path = cx.std_path(&[sym::intrinsics, Symbol::intern(intrinsic)]);
  68     let call = cx.expr_call_global(span, path, args);
  69
  70     cx.expr_block(P(ast::Block {
  71         stmts: vec![cx.stmt_expr(call)],
  72         id: ast::DUMMY_NODE_ID,
  73         rules: ast::BlockCheckMode::Unsafe(ast::CompilerGenerated),
  74         span,
  75     }))
  76 }
  77
  78
  79 // Injects `impl<...> Structural for ItemType<...> { }`. In particular,
  80 // does *not* add `where T: Structural` for parameters `T` in `...`.
  81 // (That's the main reason we cannot use TraitDef here.)
  82 fn inject_impl_of_structural_trait(cx: &mut ExtCtxt<'_>,
  83                                    span: Span,
  84                                    item: &Annotatable,
  85                                    structural_path: generic::ty::Path<'_>,
  86                                    push: &mut dyn FnMut(Annotatable)) {
  87     let item = match *item {
  88         Annotatable::Item(ref item) => item,
  89         _ => {
  90             // Non-Item derive is an error, but it should have been
  91             // set earlier; see
  92             // libsyntax/ext/expand.rs:MacroExpander::expand()
  93             return;
  94         }
  95     };
  96
  97     let generics = match item.kind {
  98         ItemKind::Struct(_, ref generics) |
  99         ItemKind::Enum(_, ref generics) => generics,
 100         // Do not inject `impl Structural for Union`. (`PartialEq` does not
 101         // support unions, so we will see error downstream.)
 102         ItemKind::Union(..) => return,
 103         _ => unreachable!(),
 104     };
 105
 106     // Create generics param list for where clauses and impl headers
 107     let mut generics = generics.clone();
 108
 109     // Create the type of `self`.
 110     //
 111     // in addition, remove defaults from type params (impls cannot have them).
 112     let self_params: Vec<_> = generics.params.iter_mut().map(|param| match &mut param.kind {
 113         ast::GenericParamKind::Lifetime => {
 114             ast::GenericArg::Lifetime(cx.lifetime(span, param.ident))
 115         }
 116         ast::GenericParamKind::Type { default } => {
 117             *default = None;
 118             ast::GenericArg::Type(cx.ty_ident(span, param.ident))
 119         }
 120         ast::GenericParamKind::Const { ty: _ } => {
 121             ast::GenericArg::Const(cx.const_ident(span, param.ident))
 122         }
 123     }).collect();
 124
 125     let type_ident = item.ident;
 126
 127     let trait_ref = cx.trait_ref(structural_path.to_path(cx, span, type_ident, &generics));
 128     let self_type = cx.ty_path(cx.path_all(span, false, vec![type_ident], self_params));
 129
 130     // It would be nice to also encode constraint `where Self: Eq` (by adding it
 131     // onto `generics` cloned above). Unfortunately, that strategy runs afoul of
 132     // rust-lang/rust#48214. So we perform that additional check in the compiler
 133     // itself, instead of encoding it here.
 134
 135     // Keep the lint and stability attributes of the original item, to control
 136     // how the generated implementation is linted.
 137     let mut attrs = Vec::new();
 138     attrs.extend(item.attrs
 139                  .iter()
 140                  .filter(|a| {
 141                      [sym::allow, sym::warn, sym::deny, sym::forbid, sym::stable, sym::unstable]
 142                          .contains(&a.name_or_empty())
 143                  })
 144                  .cloned());
 145
 146     let newitem = cx.item(span,
 147                           ast::Ident::invalid(),
 148                           attrs,
 149                           ItemKind::Impl(ast::Unsafety::Normal,
 150                                          ast::ImplPolarity::Positive,
 151                                          ast::Defaultness::Final,
 152                                          generics,
 153                                          Some(trait_ref),
 154                                          self_type,
 155                                          Vec::new()));
 156
 157     push(Annotatable::Item(newitem));
 158 }