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use crate::cfg_eval::cfg_eval;
use rustc_ast as ast;
use rustc_ast::{attr, token, GenericParamKind, ItemKind, MetaItemKind, NestedMetaItem, StmtKind};
use rustc_errors::{struct_span_err, Applicability};
use rustc_expand::base::{Annotatable, ExpandResult, ExtCtxt, Indeterminate, MultiItemModifier};
use rustc_feature::AttributeTemplate;
use rustc_parse::validate_attr;
use rustc_session::Session;
use rustc_span::symbol::{sym, Ident};
use rustc_span::Span;
pub(crate) struct Expander;
impl MultiItemModifier for Expander {
fn expand(
&self,
ecx: &mut ExtCtxt<'_>,
span: Span,
meta_item: &ast::MetaItem,
item: Annotatable,
) -> ExpandResult<Vec<Annotatable>, Annotatable> {
let sess = ecx.sess;
if report_bad_target(sess, &item, span) {
// We don't want to pass inappropriate targets to derive macros to avoid
// follow up errors, all other errors below are recoverable.
return ExpandResult::Ready(vec![item]);
}
let (sess, features) = (ecx.sess, ecx.ecfg.features);
let result =
ecx.resolver.resolve_derives(ecx.current_expansion.id, ecx.force_mode, &|| {
let template =
AttributeTemplate { list: Some("Trait1, Trait2, ..."), ..Default::default() };
let attr = attr::mk_attr_outer(meta_item.clone());
validate_attr::check_builtin_attribute(
&sess.parse_sess,
&attr,
sym::derive,
template,
);
let mut resolutions: Vec<_> = attr
.meta_item_list()
.unwrap_or_default()
.into_iter()
.filter_map(|nested_meta| match nested_meta {
NestedMetaItem::MetaItem(meta) => Some(meta),
NestedMetaItem::Literal(lit) => {
// Reject `#[derive("Debug")]`.
report_unexpected_literal(sess, &lit);
None
}
})
.map(|meta| {
// Reject `#[derive(Debug = "value", Debug(abc))]`, but recover the paths.
report_path_args(sess, &meta);
meta.path
})
.map(|path| (path, dummy_annotatable(), None))
.collect();
// Do not configure or clone items unless necessary.
match &mut resolutions[..] {
[] => {}
[(_, first_item, _), others @ ..] => {
*first_item = cfg_eval(
sess,
features,
item.clone(),
ecx.current_expansion.lint_node_id,
);
for (_, item, _) in others {
*item = first_item.clone();
}
}
}
resolutions
});
match result {
Ok(()) => ExpandResult::Ready(vec![item]),
Err(Indeterminate) => ExpandResult::Retry(item),
}
}
}
// The cheapest `Annotatable` to construct.
fn dummy_annotatable() -> Annotatable {
Annotatable::GenericParam(ast::GenericParam {
id: ast::DUMMY_NODE_ID,
ident: Ident::empty(),
attrs: Default::default(),
bounds: Default::default(),
is_placeholder: false,
kind: GenericParamKind::Lifetime,
colon_span: None,
})
}
fn report_bad_target(sess: &Session, item: &Annotatable, span: Span) -> bool {
let item_kind = match item {
Annotatable::Item(item) => Some(&item.kind),
Annotatable::Stmt(stmt) => match &stmt.kind {
StmtKind::Item(item) => Some(&item.kind),
_ => None,
},
_ => None,
};
let bad_target =
!matches!(item_kind, Some(ItemKind::Struct(..) | ItemKind::Enum(..) | ItemKind::Union(..)));
if bad_target {
struct_span_err!(
sess,
span,
E0774,
"`derive` may only be applied to `struct`s, `enum`s and `union`s",
)
.span_label(span, "not applicable here")
.span_label(item.span(), "not a `struct`, `enum` or `union`")
.emit();
}
bad_target
}
fn report_unexpected_literal(sess: &Session, lit: &ast::Lit) {
let help_msg = match lit.token.kind {
token::Str if rustc_lexer::is_ident(lit.token.symbol.as_str()) => {
format!("try using `#[derive({})]`", lit.token.symbol)
}
_ => "for example, write `#[derive(Debug)]` for `Debug`".to_string(),
};
struct_span_err!(sess, lit.span, E0777, "expected path to a trait, found literal",)
.span_label(lit.span, "not a trait")
.help(&help_msg)
.emit();
}
fn report_path_args(sess: &Session, meta: &ast::MetaItem) {
let report_error = |title, action| {
let span = meta.span.with_lo(meta.path.span.hi());
sess.struct_span_err(span, title)
.span_suggestion(span, action, "", Applicability::MachineApplicable)
.emit();
};
match meta.kind {
MetaItemKind::Word => {}
MetaItemKind::List(..) => report_error(
"traits in `#[derive(...)]` don't accept arguments",
"remove the arguments",
),
MetaItemKind::NameValue(..) => {
report_error("traits in `#[derive(...)]` don't accept values", "remove the value")
}
}
}
|
