use rustc::lint::*;
use rustc::hir::*;
-use utils::{span_lint_and_then, snippet_opt};
-use rustc::ty::layout::TargetDataLayout;
-use rustc::ty::TypeFoldable;
-use rustc::traits::Reveal;
+use utils::span_lint_and_then;
/// **What it does:** Checks for `enum`s with no variants.
///
/// ```
declare_lint! {
pub EMPTY_ENUM,
- Warn,
+ Allow,
"enum with no variants"
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for EmptyEnum {
fn check_item(&mut self, cx: &LateContext, item: &Item) {
let did = cx.tcx.hir.local_def_id(item.id);
- if let ItemEnum(ref def, _) = item.node {
+ if let ItemEnum(..) = item.node {
let ty = cx.tcx.item_type(did);
let adt = ty.ty_adt_def().expect("already checked whether this is an enum");
- for (i, variant) in adt.variants.iter().enumerate() {
- let data_layout = TargetDataLayout::parse(cx.sess());
- cx.tcx.infer_ctxt((), Reveal::All).enter(|infcx| {
- let size: u64 = variant.fields
- .iter()
- .map(|f| {
- let ty = cx.tcx.item_type(f.did);
- if ty.needs_subst() {
- 0 // we can't reason about generics, so we treat them as zero sized
- } else {
- ty.layout(&infcx)
- .expect("layout should be computable for concrete type")
- .size(&data_layout)
- .bytes()
- }
- })
- .sum();
- if size > 0 {
- span_lint_and_then(cx, EMPTY_ENUM, def.variants[i].span, "large enum variant found", |db| {
- if variant.fields.len() == 1 {
- let span = match def.variants[i].node.data {
- VariantData::Struct(ref fields, _) |
- VariantData::Tuple(ref fields, _) => fields[0].ty.span,
- VariantData::Unit(_) => unreachable!(),
- };
- if let Some(snip) = snippet_opt(cx, span) {
- db.span_suggestion(span,
- "consider boxing the large fields to reduce the total size of \
- the enum",
- format!("Box<{}>", snip));
- return;
- }
- }
- db.span_help(def.variants[i].span,
- "consider boxing the large fields to reduce the total size of the enum");
- });
- }
+ if adt.variants.is_empty() {
+ span_lint_and_then(cx, EMPTY_ENUM, item.span, "enum with no variants", |db| {
+ db.span_help(item.span,
+ "consider using the uninhabited type `!` or a wrapper around it");
});
}
}