83 lines
3.2 KiB
Rust
83 lines
3.2 KiB
Rust
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//! lint when there is an enum with no variants
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use rustc::lint::*;
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use rustc::hir::*;
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use utils::{span_lint_and_then, snippet_opt};
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use rustc::ty::layout::TargetDataLayout;
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use rustc::ty::TypeFoldable;
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use rustc::traits::Reveal;
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/// **What it does:** Checks for `enum`s with no variants.
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///
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/// **Why is this bad?** Enum's with no variants should be replaced with `!`.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// enum Test {}
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/// ```
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declare_lint! {
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pub EMPTY_ENUM,
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Warn,
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"enum with no variants"
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}
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#[derive(Copy,Clone)]
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pub struct EmptyEnum;
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impl LintPass for EmptyEnum {
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fn get_lints(&self) -> LintArray {
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lint_array!(EMPTY_ENUM)
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for EmptyEnum {
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fn check_item(&mut self, cx: &LateContext, item: &Item) {
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let did = cx.tcx.hir.local_def_id(item.id);
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if let ItemEnum(ref def, _) = item.node {
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let ty = cx.tcx.item_type(did);
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let adt = ty.ty_adt_def().expect("already checked whether this is an enum");
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for (i, variant) in adt.variants.iter().enumerate() {
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let data_layout = TargetDataLayout::parse(cx.sess());
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cx.tcx.infer_ctxt((), Reveal::All).enter(|infcx| {
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let size: u64 = variant.fields
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.iter()
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.map(|f| {
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let ty = cx.tcx.item_type(f.did);
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if ty.needs_subst() {
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0 // we can't reason about generics, so we treat them as zero sized
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} else {
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ty.layout(&infcx)
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.expect("layout should be computable for concrete type")
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.size(&data_layout)
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.bytes()
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}
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})
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.sum();
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if size > 0 {
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span_lint_and_then(cx, EMPTY_ENUM, def.variants[i].span, "large enum variant found", |db| {
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if variant.fields.len() == 1 {
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let span = match def.variants[i].node.data {
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VariantData::Struct(ref fields, _) |
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VariantData::Tuple(ref fields, _) => fields[0].ty.span,
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VariantData::Unit(_) => unreachable!(),
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};
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if let Some(snip) = snippet_opt(cx, span) {
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db.span_suggestion(span,
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"consider boxing the large fields to reduce the total size of \
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the enum",
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format!("Box<{}>", snip));
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return;
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}
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}
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db.span_help(def.variants[i].span,
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"consider boxing the large fields to reduce the total size of the enum");
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});
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}
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});
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}
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}
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}
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}
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