src/librustc_builtin_macros/deriving/mod.rs

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