Merge pull request #1512 from pengowen123/patch-large_enum_variant
Change large_enum_variant to lint against difference in sizes between variants
This commit is contained in:
Oliver Schneider
GitHub
commit
4b29f9a364
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@ -256,7 +256,7 @@ name
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[iter_next_loop](https://github.com/Manishearth/rust-clippy/wiki#iter_next_loop) | warn | for-looping over `_.next()` which is probably not intended
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[iter_nth](https://github.com/Manishearth/rust-clippy/wiki#iter_nth) | warn | using `.iter().nth()` on a standard library type with O(1) element access
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[iter_skip_next](https://github.com/Manishearth/rust-clippy/wiki#iter_skip_next) | warn | using `.skip(x).next()` on an iterator
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[large_enum_variant](https://github.com/Manishearth/rust-clippy/wiki#large_enum_variant) | warn | large variants on an enum
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[large_enum_variant](https://github.com/Manishearth/rust-clippy/wiki#large_enum_variant) | warn | large size difference between variants on an enum
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[len_without_is_empty](https://github.com/Manishearth/rust-clippy/wiki#len_without_is_empty) | warn | traits or impls with a public `len` method but no corresponding `is_empty` method
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[len_zero](https://github.com/Manishearth/rust-clippy/wiki#len_zero) | warn | checking `.len() == 0` or `.len() > 0` (or similar) when `.is_empty()` could be used instead
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[let_and_return](https://github.com/Manishearth/rust-clippy/wiki#let_and_return) | warn | creating a let-binding and then immediately returning it like `let x = expr; x` at the end of a block
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@ -1,4 +1,4 @@
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//! lint when there are large variants on an enum
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//! lint when there is a large size difference between variants on an enum
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use rustc::lint::*;
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use rustc::hir::*;
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@ -7,7 +7,7 @@ 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 large variants on `enum`s.
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/// **What it does:** Checks for large size differences between variants on `enum`s.
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///
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/// **Why is this bad?** Enum size is bounded by the largest variant. Having a large variant
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/// can penalize the memory layout of that enum.
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@ -24,17 +24,17 @@ use rustc::traits::Reveal;
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declare_lint! {
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pub LARGE_ENUM_VARIANT,
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Warn,
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"large variants on an enum"
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"large size difference between variants on an enum"
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}
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#[derive(Copy,Clone)]
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pub struct LargeEnumVariant {
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maximum_variant_size_allowed: u64,
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maximum_size_difference_allowed: u64,
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}
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impl LargeEnumVariant {
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pub fn new(maximum_variant_size_allowed: u64) -> Self {
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LargeEnumVariant { maximum_variant_size_allowed: maximum_variant_size_allowed }
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pub fn new(maximum_size_difference_allowed: u64) -> Self {
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LargeEnumVariant { maximum_size_difference_allowed: maximum_size_difference_allowed }
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}
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}
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@ -50,6 +50,10 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LargeEnumVariant {
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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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let mut smallest_variant: Option<(_, _)> = None;
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let mut largest_variant: Option<(_, _)> = None;
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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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@ -67,32 +71,57 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LargeEnumVariant {
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}
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})
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.sum();
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if size > self.maximum_variant_size_allowed {
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span_lint_and_then(cx,
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LARGE_ENUM_VARIANT,
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def.variants[i].span,
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"large enum variant found",
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|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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let grouped = (size, (i, variant));
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update_if(&mut smallest_variant, grouped, |a, b| b.0 <= a.0);
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update_if(&mut largest_variant, grouped, |a, b| b.0 >= a.0);
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});
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}
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if let (Some(smallest), Some(largest)) = (smallest_variant, largest_variant) {
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let difference = largest.0 - smallest.0;
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if difference > self.maximum_size_difference_allowed {
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let (i, variant) = largest.1;
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span_lint_and_then(cx,
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LARGE_ENUM_VARIANT,
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def.variants[i].span,
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"large size difference between variants",
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|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 the \
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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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fn update_if<T, F>(old: &mut Option<T>, new: T, f: F)
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where F: Fn(&T, &T) -> bool
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{
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if let Some(ref mut val) = *old {
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if f(val, &new) {
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*val = new;
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}
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} else {
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*old = Some(new);
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}
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}
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@ -8,18 +8,17 @@
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enum LargeEnum {
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A(i32),
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B([i32; 8000]),
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}
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enum GenericEnum<T> {
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enum GenericEnumOk<T> {
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A(i32),
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B([T; 8000]),
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}
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enum GenericEnum2<T> {
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A(i32),
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B([i32; 8000]),
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C([T; 8000]),
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D(T, [i32; 8000]),
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C(T, [i32; 8000]),
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}
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trait SomeTrait {
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@ -27,27 +26,32 @@ trait SomeTrait {
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}
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enum LargeEnumGeneric<A: SomeTrait> {
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Var(A::Item), // regression test, this used to ICE
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Var(A::Item),
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}
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enum AnotherLargeEnum {
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enum LargeEnum2 {
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VariantOk(i32, u32),
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ContainingLargeEnum(LargeEnum),
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}
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enum LargeEnum3 {
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ContainingMoreThanOneField(i32, [i32; 8000], [i32; 9500]),
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VoidVariant,
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StructLikeLittle { x: i32, y: i32 },
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}
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enum LargeEnum4 {
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VariantOk(i32, u32),
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StructLikeLarge { x: [i32; 8000], y: i32 },
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StructLikeLarge2 {
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x:
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[i32; 8000]
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},
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}
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fn main() {
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enum LargeEnum5 {
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VariantOk(i32, u32),
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StructLikeLarge2 { x: [i32; 8000] },
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}
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enum LargeEnumOk {
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LargeA([i32; 8000]),
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LargeB([i32; 8001]),
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}
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fn main() {}
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@ -1,4 +1,4 @@
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error: large enum variant found
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error: large size difference between variants
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--> $DIR/large_enum_variant.rs:10:5
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10 | B([i32; 8000]),
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@ -12,73 +12,59 @@ note: lint level defined here
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help: consider boxing the large fields to reduce the total size of the enum
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| B(Box<[i32; 8000]>),
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error: large enum variant found
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--> $DIR/large_enum_variant.rs:17:5
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17 | B([i32; 8000]),
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| ^^^^^^^^^^^^^^
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help: consider boxing the large fields to reduce the total size of the enum
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| B(Box<[i32; 8000]>),
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error: large enum variant found
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error: large size difference between variants
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--> $DIR/large_enum_variant.rs:21:5
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21 | D(T, [i32; 8000]),
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21 | C(T, [i32; 8000]),
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| ^^^^^^^^^^^^^^^^^
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help: consider boxing the large fields to reduce the total size of the enum
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--> $DIR/large_enum_variant.rs:21:5
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21 | D(T, [i32; 8000]),
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21 | C(T, [i32; 8000]),
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| ^^^^^^^^^^^^^^^^^
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error: large enum variant found
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--> $DIR/large_enum_variant.rs:35:5
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error: large size difference between variants
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--> $DIR/large_enum_variant.rs:34:5
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35 | ContainingLargeEnum(LargeEnum),
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34 | ContainingLargeEnum(LargeEnum),
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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help: consider boxing the large fields to reduce the total size of the enum
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| ContainingLargeEnum(Box<LargeEnum>),
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error: large enum variant found
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--> $DIR/large_enum_variant.rs:38:5
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error: large size difference between variants
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--> $DIR/large_enum_variant.rs:37:5
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38 | ContainingMoreThanOneField(i32, [i32; 8000], [i32; 9500]),
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37 | ContainingMoreThanOneField(i32, [i32; 8000], [i32; 9500]),
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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help: consider boxing the large fields to reduce the total size of the enum
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--> $DIR/large_enum_variant.rs:38:5
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--> $DIR/large_enum_variant.rs:37:5
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38 | ContainingMoreThanOneField(i32, [i32; 8000], [i32; 9500]),
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37 | ContainingMoreThanOneField(i32, [i32; 8000], [i32; 9500]),
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: large enum variant found
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--> $DIR/large_enum_variant.rs:42:5
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42 | StructLikeLarge { x: [i32; 8000], y: i32 },
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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help: consider boxing the large fields to reduce the total size of the enum
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--> $DIR/large_enum_variant.rs:42:5
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42 | StructLikeLarge { x: [i32; 8000], y: i32 },
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: large enum variant found
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error: large size difference between variants
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--> $DIR/large_enum_variant.rs:44:5
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44 | StructLikeLarge2 {
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| _____^ starting here...
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45 | | x:
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46 | | [i32; 8000]
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47 | |
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48 | | },
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| |_____^ ...ending here
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44 | StructLikeLarge { x: [i32; 8000], y: i32 },
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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help: consider boxing the large fields to reduce the total size of the enum
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| Box<[i32; 8000]>
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--> $DIR/large_enum_variant.rs:44:5
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44 | StructLikeLarge { x: [i32; 8000], y: i32 },
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: aborting due to 7 previous errors
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error: large size difference between variants
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--> $DIR/large_enum_variant.rs:49:5
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49 | StructLikeLarge2 { x: [i32; 8000] },
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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help: consider boxing the large fields to reduce the total size of the enum
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| StructLikeLarge2 { x: Box<[i32; 8000]> },
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error: aborting due to 6 previous errors
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