compiler/rustc_builtin_macros/src/derive.rs

   1 use crate::cfg_eval::cfg_eval;
   2
   3 use rustc_ast as ast;
   4 use rustc_ast::{token, GenericParamKind, ItemKind, MetaItemKind, NestedMetaItem, StmtKind};
   5 use rustc_errors::{struct_span_err, Applicability};
   6 use rustc_expand::base::{Annotatable, ExpandResult, ExtCtxt, Indeterminate, MultiItemModifier};
   7 use rustc_feature::AttributeTemplate;
   8 use rustc_parse::validate_attr;
   9 use rustc_session::Session;
  10 use rustc_span::symbol::{sym, Ident};
  11 use rustc_span::Span;
  12
  13 pub(crate) struct Expander(pub bool);
  14
  15 impl MultiItemModifier for Expander {
  16     fn expand(
  17         &self,
  18         ecx: &mut ExtCtxt<'_>,
  19         span: Span,
  20         meta_item: &ast::MetaItem,
  21         item: Annotatable,
  22         _: bool,
  23     ) -> ExpandResult<Vec<Annotatable>, Annotatable> {
  24         let sess = ecx.sess;
  25         if report_bad_target(sess, &item, span) {
  26             // We don't want to pass inappropriate targets to derive macros to avoid
  27             // follow up errors, all other errors below are recoverable.
  28             return ExpandResult::Ready(vec![item]);
  29         }
  30
  31         let (sess, features) = (ecx.sess, ecx.ecfg.features);
  32         let result =
  33             ecx.resolver.resolve_derives(ecx.current_expansion.id, ecx.force_mode, &|| {
  34                 let template =
  35                     AttributeTemplate { list: Some("Trait1, Trait2, ..."), ..Default::default() };
  36                 validate_attr::check_builtin_meta_item(
  37                     &sess.parse_sess,
  38                     &meta_item,
  39                     ast::AttrStyle::Outer,
  40                     sym::derive,
  41                     template,
  42                 );
  43
  44                 let mut resolutions = match &meta_item.kind {
  45                     MetaItemKind::List(list) => {
  46                         list.iter()
  47                             .filter_map(|nested_meta| match nested_meta {
  48                                 NestedMetaItem::MetaItem(meta) => Some(meta),
  49                                 NestedMetaItem::Lit(lit) => {
  50                                     // Reject `#[derive("Debug")]`.
  51                                     report_unexpected_meta_item_lit(sess, &lit);
  52                                     None
  53                                 }
  54                             })
  55                             .map(|meta| {
  56                                 // Reject `#[derive(Debug = "value", Debug(abc))]`, but recover the
  57                                 // paths.
  58                                 report_path_args(sess, &meta);
  59                                 meta.path.clone()
  60                             })
  61                             .map(|path| (path, dummy_annotatable(), None, self.0))
  62                             .collect()
  63                     }
  64                     _ => vec![],
  65                 };
  66
  67                 // Do not configure or clone items unless necessary.
  68                 match &mut resolutions[..] {
  69                     [] => {}
  70                     [(_, first_item, ..), others @ ..] => {
  71                         *first_item = cfg_eval(
  72                             sess,
  73                             features,
  74                             item.clone(),
  75                             ecx.current_expansion.lint_node_id,
  76                         );
  77                         for (_, item, _, _) in others {
  78                             *item = first_item.clone();
  79                         }
  80                     }
  81                 }
  82
  83                 resolutions
  84             });
  85
  86         match result {
  87             Ok(()) => ExpandResult::Ready(vec![item]),
  88             Err(Indeterminate) => ExpandResult::Retry(item),
  89         }
  90     }
  91 }
  92
  93 // The cheapest `Annotatable` to construct.
  94 fn dummy_annotatable() -> Annotatable {
  95     Annotatable::GenericParam(ast::GenericParam {
  96         id: ast::DUMMY_NODE_ID,
  97         ident: Ident::empty(),
  98         attrs: Default::default(),
  99         bounds: Default::default(),
 100         is_placeholder: false,
 101         kind: GenericParamKind::Lifetime,
 102         colon_span: None,
 103     })
 104 }
 105
 106 fn report_bad_target(sess: &Session, item: &Annotatable, span: Span) -> bool {
 107     let item_kind = match item {
 108         Annotatable::Item(item) => Some(&item.kind),
 109         Annotatable::Stmt(stmt) => match &stmt.kind {
 110             StmtKind::Item(item) => Some(&item.kind),
 111             _ => None,
 112         },
 113         _ => None,
 114     };
 115
 116     let bad_target =
 117         !matches!(item_kind, Some(ItemKind::Struct(..) | ItemKind::Enum(..) | ItemKind::Union(..)));
 118     if bad_target {
 119         struct_span_err!(
 120             sess,
 121             span,
 122             E0774,
 123             "`derive` may only be applied to `struct`s, `enum`s and `union`s",
 124         )
 125         .span_label(span, "not applicable here")
 126         .span_label(item.span(), "not a `struct`, `enum` or `union`")
 127         .emit();
 128     }
 129     bad_target
 130 }
 131
 132 fn report_unexpected_meta_item_lit(sess: &Session, lit: &ast::MetaItemLit) {
 133     let help_msg = match lit.token_lit.kind {
 134         token::Str if rustc_lexer::is_ident(lit.token_lit.symbol.as_str()) => {
 135             format!("try using `#[derive({})]`", lit.token_lit.symbol)
 136         }
 137         _ => "for example, write `#[derive(Debug)]` for `Debug`".to_string(),
 138     };
 139     struct_span_err!(sess, lit.span, E0777, "expected path to a trait, found literal",)
 140         .span_label(lit.span, "not a trait")
 141         .help(&help_msg)
 142         .emit();
 143 }
 144
 145 fn report_path_args(sess: &Session, meta: &ast::MetaItem) {
 146     let report_error = |title, action| {
 147         let span = meta.span.with_lo(meta.path.span.hi());
 148         sess.struct_span_err(span, title)
 149             .span_suggestion(span, action, "", Applicability::MachineApplicable)
 150             .emit();
 151     };
 152     match meta.kind {
 153         MetaItemKind::Word => {}
 154         MetaItemKind::List(..) => report_error(
 155             "traits in `#[derive(...)]` don't accept arguments",
 156             "remove the arguments",
 157         ),
 158         MetaItemKind::NameValue(..) => {
 159             report_error("traits in `#[derive(...)]` don't accept values", "remove the value")
 160         }
 161     }
 162 }