src/librustc_builtin_macros/deriving/mod.rs

   1 //! The compiler code necessary to implement the `#[derive]` extensions.
   2
   3 use rustc_ast as ast;
   4 use rustc_ast::ptr::P;
   5 use rustc_ast::{ItemKind, MetaItem};
   6 use rustc_expand::base::{Annotatable, ExpandResult, ExtCtxt, MultiItemModifier};
   7 use rustc_span::symbol::{sym, Ident, Symbol};
   8 use rustc_span::Span;
   9
  10 macro path_local($x:ident) {
  11     generic::ty::Path::new_local(sym::$x)
  12 }
  13
  14 macro pathvec_std($($rest:ident)::+) {{
  15     vec![ $( sym::$rest ),+ ]
  16 }}
  17
  18 macro path_std($($x:tt)*) {
  19     generic::ty::Path::new( pathvec_std!( $($x)* ) )
  20 }
  21
  22 pub mod bounds;
  23 pub mod clone;
  24 pub mod debug;
  25 pub mod decodable;
  26 pub mod default;
  27 pub mod encodable;
  28 pub mod hash;
  29
  30 #[path = "cmp/eq.rs"]
  31 pub mod eq;
  32 #[path = "cmp/ord.rs"]
  33 pub mod ord;
  34 #[path = "cmp/partial_eq.rs"]
  35 pub mod partial_eq;
  36 #[path = "cmp/partial_ord.rs"]
  37 pub mod partial_ord;
  38
  39 pub mod generic;
  40
  41 crate struct BuiltinDerive(
  42     crate fn(&mut ExtCtxt<'_>, Span, &MetaItem, &Annotatable, &mut dyn FnMut(Annotatable)),
  43 );
  44
  45 impl MultiItemModifier for BuiltinDerive {
  46     fn expand(
  47         &self,
  48         ecx: &mut ExtCtxt<'_>,
  49         span: Span,
  50         meta_item: &MetaItem,
  51         item: Annotatable,
  52     ) -> ExpandResult<Vec<Annotatable>, Annotatable> {
  53         // FIXME: Built-in derives often forget to give spans contexts,
  54         // so we are doing it here in a centralized way.
  55         let span = ecx.with_def_site_ctxt(span);
  56         let mut items = Vec::new();
  57         (self.0)(ecx, span, meta_item, &item, &mut |a| items.push(a));
  58         ExpandResult::Ready(items)
  59     }
  60 }
  61
  62 /// Constructs an expression that calls an intrinsic
  63 fn call_intrinsic(
  64     cx: &ExtCtxt<'_>,
  65     span: Span,
  66     intrinsic: Symbol,
  67     args: Vec<P<ast::Expr>>,
  68 ) -> P<ast::Expr> {
  69     let span = cx.with_def_site_ctxt(span);
  70     let path = cx.std_path(&[sym::intrinsics, intrinsic]);
  71     let call = cx.expr_call_global(span, path, args);
  72
  73     cx.expr_block(P(ast::Block {
  74         stmts: vec![cx.stmt_expr(call)],
  75         id: ast::DUMMY_NODE_ID,
  76         rules: ast::BlockCheckMode::Unsafe(ast::CompilerGenerated),
  77         span,
  78     }))
  79 }
  80
  81 // Injects `impl<...> Structural for ItemType<...> { }`. In particular,
  82 // does *not* add `where T: Structural` for parameters `T` in `...`.
  83 // (That's the main reason we cannot use TraitDef here.)
  84 fn inject_impl_of_structural_trait(
  85     cx: &mut ExtCtxt<'_>,
  86     span: Span,
  87     item: &Annotatable,
  88     structural_path: generic::ty::Path,
  89     push: &mut dyn FnMut(Annotatable),
  90 ) {
  91     let item = match *item {
  92         Annotatable::Item(ref item) => item,
  93         _ => {
  94             // Non-Item derive is an error, but it should have been
  95             // set earlier; see
  96             // librustc_expand/expand.rs:MacroExpander::fully_expand_fragment()
  97             // librustc_expand/base.rs:Annotatable::derive_allowed()
  98             return;
  99         }
 100     };
 101
 102     let generics = match item.kind {
 103         ItemKind::Struct(_, ref generics) | ItemKind::Enum(_, ref generics) => generics,
 104         // Do not inject `impl Structural for Union`. (`PartialEq` does not
 105         // support unions, so we will see error downstream.)
 106         ItemKind::Union(..) => return,
 107         _ => unreachable!(),
 108     };
 109
 110     // Create generics param list for where clauses and impl headers
 111     let mut generics = generics.clone();
 112
 113     // Create the type of `self`.
 114     //
 115     // in addition, remove defaults from type params (impls cannot have them).
 116     let self_params: Vec<_> = generics
 117         .params
 118         .iter_mut()
 119         .map(|param| match &mut param.kind {
 120             ast::GenericParamKind::Lifetime => {
 121                 ast::GenericArg::Lifetime(cx.lifetime(span, param.ident))
 122             }
 123             ast::GenericParamKind::Type { default } => {
 124                 *default = None;
 125                 ast::GenericArg::Type(cx.ty_ident(span, param.ident))
 126             }
 127             ast::GenericParamKind::Const { ty: _, kw_span: _ } => {
 128                 ast::GenericArg::Const(cx.const_ident(span, param.ident))
 129             }
 130         })
 131         .collect();
 132
 133     let type_ident = item.ident;
 134
 135     let trait_ref = cx.trait_ref(structural_path.to_path(cx, span, type_ident, &generics));
 136     let self_type = cx.ty_path(cx.path_all(span, false, vec![type_ident], self_params));
 137
 138     // It would be nice to also encode constraint `where Self: Eq` (by adding it
 139     // onto `generics` cloned above). Unfortunately, that strategy runs afoul of
 140     // rust-lang/rust#48214. So we perform that additional check in the compiler
 141     // itself, instead of encoding it here.
 142
 143     // Keep the lint and stability attributes of the original item, to control
 144     // how the generated implementation is linted.
 145     let mut attrs = Vec::new();
 146     attrs.extend(
 147         item.attrs
 148             .iter()
 149             .filter(|a| {
 150                 [sym::allow, sym::warn, sym::deny, sym::forbid, sym::stable, sym::unstable]
 151                     .contains(&a.name_or_empty())
 152             })
 153             .cloned(),
 154     );
 155
 156     let newitem = cx.item(
 157         span,
 158         Ident::invalid(),
 159         attrs,
 160         ItemKind::Impl {
 161             unsafety: ast::Unsafe::No,
 162             polarity: ast::ImplPolarity::Positive,
 163             defaultness: ast::Defaultness::Final,
 164             constness: ast::Const::No,
 165             generics,
 166             of_trait: Some(trait_ref),
 167             self_ty: self_type,
 168             items: Vec::new(),
 169         },
 170     );
 171
 172     push(Annotatable::Item(newitem));
 173 }