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Auto merge of #7677 - surechen:edit_large_enum_variant, r=camsteffen
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fix bug for large_enum_variants

Fix the discussion problem in the issue of #7666 (comment)

About the false positive problem of case:
```rust
enum LargeEnum6 {
    A,
    B([u8;255]),
    C([u8;200]),
}
```
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@bors
bors committed Sep 30, 2021
2 parents ab99eec + 56f0c9a commit cb72a2f
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Showing 3 changed files with 171 additions and 71 deletions.
161 changes: 98 additions & 63 deletions clippy_lints/src/large_enum_variant.rs
View file
Original file line number Diff line number Diff line change
@@ -1,13 +1,14 @@
//! lint when there is a large size difference between variants on an enum
use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::source::snippet_opt;
use clippy_utils::source::snippet_with_applicability;
use rustc_errors::Applicability;
use rustc_hir::{Item, ItemKind, VariantData};
use rustc_hir::{Item, ItemKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::lint::in_external_macro;
use rustc_middle::ty::layout::LayoutOf;
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::source_map::Span;

declare_clippy_lint! {
/// ### What it does
Expand Down Expand Up @@ -58,6 +59,17 @@ impl LargeEnumVariant {
}
}

struct FieldInfo {
ind: usize,
size: u64,
}

struct VariantInfo {
ind: usize,
size: u64,
fields_size: Vec<FieldInfo>,
}

impl_lint_pass!(LargeEnumVariant => [LARGE_ENUM_VARIANT]);

impl<'tcx> LateLintPass<'tcx> for LargeEnumVariant {
Expand All @@ -68,72 +80,95 @@ impl<'tcx> LateLintPass<'tcx> for LargeEnumVariant {
if let ItemKind::Enum(ref def, _) = item.kind {
let ty = cx.tcx.type_of(item.def_id);
let adt = ty.ty_adt_def().expect("already checked whether this is an enum");

let mut largest_variant: Option<(_, _)> = None;
let mut second_variant: Option<(_, _)> = None;

for (i, variant) in adt.variants.iter().enumerate() {
let size: u64 = variant
.fields
.iter()
.filter_map(|f| {
let ty = cx.tcx.type_of(f.did);
// don't count generics by filtering out everything
// that does not have a layout
cx.layout_of(ty).ok().map(|l| l.size.bytes())
})
.sum();

let grouped = (size, (i, variant));

if grouped.0 >= largest_variant.map_or(0, |x| x.0) {
second_variant = largest_variant;
largest_variant = Some(grouped);
}
if adt.variants.len() <= 1 {
return;
}
let mut variants_size: Vec<VariantInfo> = adt
.variants
.iter()
.enumerate()
.map(|(i, variant)| {
let mut fields_size = Vec::new();
let size: u64 = variant
.fields
.iter()
.enumerate()
.filter_map(|(i, f)| {
let ty = cx.tcx.type_of(f.did);
// don't count generics by filtering out everything
// that does not have a layout
cx.layout_of(ty).ok().map(|l| {
let size = l.size.bytes();
fields_size.push(FieldInfo { ind: i, size });
size
})
})
.sum();
VariantInfo {
ind: i,
size,
fields_size,
}
})
.collect();

if let (Some(largest), Some(second)) = (largest_variant, second_variant) {
let difference = largest.0 - second.0;
variants_size.sort_by(|a, b| (b.size.cmp(&a.size)));

if difference > self.maximum_size_difference_allowed {
let (i, variant) = largest.1;
let mut difference = variants_size[0].size - variants_size[1].size;
if difference > self.maximum_size_difference_allowed {
let help_text = "consider boxing the large fields to reduce the total size of the enum";
span_lint_and_then(
cx,
LARGE_ENUM_VARIANT,
def.variants[variants_size[0].ind].span,
"large size difference between variants",
|diag| {
diag.span_label(
def.variants[variants_size[0].ind].span,
&format!("this variant is {} bytes", variants_size[0].size),
);
diag.span_note(
def.variants[variants_size[1].ind].span,
&format!("and the second-largest variant is {} bytes:", variants_size[1].size),
);

let help_text = "consider boxing the large fields to reduce the total size of the enum";
span_lint_and_then(
cx,
LARGE_ENUM_VARIANT,
def.variants[i].span,
"large size difference between variants",
|diag| {
diag.span_label(
def.variants[(largest.1).0].span,
&format!("this variant is {} bytes", largest.0),
);
diag.span_note(
def.variants[(second.1).0].span,
&format!("and the second-largest variant is {} bytes:", second.0),
);
if variant.fields.len() == 1 {
let span = match def.variants[i].data {
VariantData::Struct(fields, ..) | VariantData::Tuple(fields, ..) => {
fields[0].ty.span
},
VariantData::Unit(..) => unreachable!(),
};
if let Some(snip) = snippet_opt(cx, span) {
diag.span_suggestion(
span,
help_text,
format!("Box<{}>", snip),
Applicability::MaybeIncorrect,
);
return;
let fields = def.variants[variants_size[0].ind].data.fields();
variants_size[0].fields_size.sort_by(|a, b| (a.size.cmp(&b.size)));
let mut applicability = Applicability::MaybeIncorrect;
let sugg: Vec<(Span, String)> = variants_size[0]
.fields_size
.iter()
.rev()
.map_while(|val| {
if difference > self.maximum_size_difference_allowed {
difference = difference.saturating_sub(val.size);
Some((
fields[val.ind].ty.span,
format!(
"Box<{}>",
snippet_with_applicability(
cx,
fields[val.ind].ty.span,
"..",
&mut applicability
)
.into_owned()
),
))
} else {
None
}
}
diag.span_help(def.variants[i].span, help_text);
},
);
}
})
.collect();

if !sugg.is_empty() {
diag.multipart_suggestion(help_text, sugg, Applicability::MaybeIncorrect);
return;
}

diag.span_help(def.variants[variants_size[0].ind].span, help_text);
},
);
}
}
}
Expand Down
18 changes: 18 additions & 0 deletions tests/ui/large_enum_variant.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,7 @@ enum LargeEnum2 {
VariantOk(i32, u32),
ContainingLargeEnum(LargeEnum),
}

enum LargeEnum3 {
ContainingMoreThanOneField(i32, [i32; 8000], [i32; 9500]),
VoidVariant,
Expand All @@ -56,6 +57,23 @@ enum LargeEnumOk {
LargeB([i32; 8001]),
}

enum LargeEnum6 {
A,
B([u8; 255]),
C([u8; 200]),
}

enum LargeEnum7 {
A,
B([u8; 1255]),
C([u8; 200]),
}

enum LargeEnum8 {
VariantOk(i32, u32),
ContainingMoreThanOneField([i32; 8000], [i32; 2], [i32; 9500], [i32; 30]),
}

fn main() {
large_enum_variant!();
}
63 changes: 55 additions & 8 deletions tests/ui/large_enum_variant.stderr
View file
Original file line number Diff line number Diff line change
Expand Up @@ -32,30 +32,45 @@ LL | ContainingLargeEnum(Box<LargeEnum>),
| ~~~~~~~~~~~~~~

error: large size difference between variants
--> $DIR/large_enum_variant.rs:46:5
--> $DIR/large_enum_variant.rs:40:5
|
LL | ContainingMoreThanOneField(i32, [i32; 8000], [i32; 9500]),
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ this variant is 70004 bytes
|
note: and the second-largest variant is 8 bytes:
--> $DIR/large_enum_variant.rs:42:5
|
LL | StructLikeLittle { x: i32, y: i32 },
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: consider boxing the large fields to reduce the total size of the enum
|
LL | ContainingMoreThanOneField(i32, Box<[i32; 8000]>, Box<[i32; 9500]>),
| ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~

error: large size difference between variants
--> $DIR/large_enum_variant.rs:47:5
|
LL | StructLikeLarge { x: [i32; 8000], y: i32 },
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ this variant is 32004 bytes
|
note: and the second-largest variant is 8 bytes:
--> $DIR/large_enum_variant.rs:45:5
--> $DIR/large_enum_variant.rs:46:5
|
LL | VariantOk(i32, u32),
| ^^^^^^^^^^^^^^^^^^^
help: consider boxing the large fields to reduce the total size of the enum
--> $DIR/large_enum_variant.rs:46:5
|
LL | StructLikeLarge { x: [i32; 8000], y: i32 },
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
LL | StructLikeLarge { x: Box<[i32; 8000]>, y: i32 },
| ~~~~~~~~~~~~~~~~

error: large size difference between variants
--> $DIR/large_enum_variant.rs:51:5
--> $DIR/large_enum_variant.rs:52:5
|
LL | StructLikeLarge2 { x: [i32; 8000] },
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ this variant is 32000 bytes
|
note: and the second-largest variant is 8 bytes:
--> $DIR/large_enum_variant.rs:50:5
--> $DIR/large_enum_variant.rs:51:5
|
LL | VariantOk(i32, u32),
| ^^^^^^^^^^^^^^^^^^^
Expand All @@ -64,5 +79,37 @@ help: consider boxing the large fields to reduce the total size of the enum
LL | StructLikeLarge2 { x: Box<[i32; 8000]> },
| ~~~~~~~~~~~~~~~~

error: aborting due to 4 previous errors
error: large size difference between variants
--> $DIR/large_enum_variant.rs:68:5
|
LL | B([u8; 1255]),
| ^^^^^^^^^^^^^ this variant is 1255 bytes
|
note: and the second-largest variant is 200 bytes:
--> $DIR/large_enum_variant.rs:69:5
|
LL | C([u8; 200]),
| ^^^^^^^^^^^^
help: consider boxing the large fields to reduce the total size of the enum
|
LL | B(Box<[u8; 1255]>),
| ~~~~~~~~~~~~~~~

error: large size difference between variants
--> $DIR/large_enum_variant.rs:74:5
|
LL | ContainingMoreThanOneField([i32; 8000], [i32; 2], [i32; 9500], [i32; 30]),
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ this variant is 70128 bytes
|
note: and the second-largest variant is 8 bytes:
--> $DIR/large_enum_variant.rs:73:5
|
LL | VariantOk(i32, u32),
| ^^^^^^^^^^^^^^^^^^^
help: consider boxing the large fields to reduce the total size of the enum
|
LL | ContainingMoreThanOneField(Box<[i32; 8000]>, [i32; 2], Box<[i32; 9500]>, [i32; 30]),
| ~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~

error: aborting due to 7 previous errors

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