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Implement empty_enum lint and add a test

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Owen Sanchez 2017-02-04 21:52:44 -07:00
parent e88e637b67
commit 49238ad1d2
2 changed files with 17 additions and 43 deletions
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50
clippy_lints/src/empty_enum.rs
View file

@ -2,10 +2,7 @@
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.
///
@ -19,7 +16,7 @@ use rustc::traits::Reveal;
/// ```
declare_lint! {
pub EMPTY_ENUM,
Warn,
Allow,
"enum with no variants"
}
@ -35,46 +32,13 @@ impl LintPass for EmptyEnum {
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");
});
}
}

10
tests/compile-fail/empty_enum.rs Normal file
View file

@ -0,0 +1,10 @@
#![feature(plugin)]
#![plugin(clippy)]
#![deny(empty_enum)]
enum Empty {} //~ ERROR enum with no variants
//~^ HELP consider using the uninhabited type `!` or a wrapper around it
fn main() {
}