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Add lint on large const arrays
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‎CHANGELOG.md

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Original file line numberDiff line numberDiff line change
@@ -1318,6 +1318,7 @@ Released 2018-09-13
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[`iter_skip_next`]: https://rust-lang.github.io/rust-clippy/master/index.html#iter_skip_next
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[`iterator_step_by_zero`]: https://rust-lang.github.io/rust-clippy/master/index.html#iterator_step_by_zero
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[`just_underscores_and_digits`]: https://rust-lang.github.io/rust-clippy/master/index.html#just_underscores_and_digits
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[`large_const_arrays`]: https://rust-lang.github.io/rust-clippy/master/index.html#large_const_arrays
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[`large_digit_groups`]: https://rust-lang.github.io/rust-clippy/master/index.html#large_digit_groups
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[`large_enum_variant`]: https://rust-lang.github.io/rust-clippy/master/index.html#large_enum_variant
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[`large_stack_arrays`]: https://rust-lang.github.io/rust-clippy/master/index.html#large_stack_arrays

‎README.md

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@@ -5,7 +5,7 @@
55

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A collection of lints to catch common mistakes and improve your [Rust](https://github.com/rust-lang/rust) code.
77

8-
[There are 361 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
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[There are 362 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
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We have a bunch of lint categories to allow you to choose how much Clippy is supposed to ~~annoy~~ help you:
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‎clippy_lints/src/large_const_arrays.rs

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@@ -0,0 +1,85 @@
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use crate::rustc_target::abi::LayoutOf;
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use crate::utils::span_lint_and_then;
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use if_chain::if_chain;
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use rustc::mir::interpret::ConstValue;
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use rustc::ty::{self, ConstKind};
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use rustc_errors::Applicability;
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use rustc_hir::{Item, ItemKind};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::{declare_tool_lint, impl_lint_pass};
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use rustc_span::{BytePos, Pos, Span};
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use rustc_typeck::hir_ty_to_ty;
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declare_clippy_lint! {
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/// **What it does:** Checks for large `const` arrays that should
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/// be defined as `static` instead.
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///
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/// **Why is this bad?** Performance: const variables are inlined upon use.
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/// Static items result in only one instance and has a fixed location in memory.
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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,ignore
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/// // Bad
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/// pub const a = [0u32; 1_000_000];
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///
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/// // Good
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/// pub static a = [0u32; 1_000_000];
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/// ```
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pub LARGE_CONST_ARRAYS,
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perf,
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"large non-scalar const array may cause performance overhead"
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}
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pub struct LargeConstArrays {
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maximum_allowed_size: u64,
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}
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impl LargeConstArrays {
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#[must_use]
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pub fn new(maximum_allowed_size: u64) -> Self {
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Self { maximum_allowed_size }
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}
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}
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impl_lint_pass!(LargeConstArrays => [LARGE_CONST_ARRAYS]);
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LargeConstArrays {
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fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item<'_>) {
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if_chain! {
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if !item.span.from_expansion();
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if let ItemKind::Const(hir_ty, _) = &item.kind;
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let ty = hir_ty_to_ty(cx.tcx, hir_ty);
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if let ty::Array(element_type, cst) = ty.kind;
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if let ConstKind::Value(val) = cst.val;
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if let ConstValue::Scalar(element_count) = val;
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if let Ok(element_count) = element_count.to_machine_usize(&cx.tcx);
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if let Ok(element_size) = cx.layout_of(element_type).map(|l| l.size.bytes());
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if self.maximum_allowed_size < element_count * element_size;
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then {
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let hi_pos = item.ident.span.lo() - BytePos::from_usize(1);
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let sugg_span = Span::new(
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hi_pos - BytePos::from_usize("const".len()),
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hi_pos,
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item.span.ctxt(),
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);
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span_lint_and_then(
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cx,
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LARGE_CONST_ARRAYS,
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item.span,
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"large array defined as const",
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|db| {
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db.span_suggestion(
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sugg_span,
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"make this a static item",
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"static".to_string(),
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Applicability::MachineApplicable,
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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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}

‎clippy_lints/src/lib.rs

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@@ -229,6 +229,7 @@ pub mod inline_fn_without_body;
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pub mod int_plus_one;
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pub mod integer_division;
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pub mod items_after_statements;
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pub mod large_const_arrays;
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pub mod large_enum_variant;
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pub mod large_stack_arrays;
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pub mod len_zero;
@@ -573,6 +574,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
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&int_plus_one::INT_PLUS_ONE,
574575
&integer_division::INTEGER_DIVISION,
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&items_after_statements::ITEMS_AFTER_STATEMENTS,
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&large_const_arrays::LARGE_CONST_ARRAYS,
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&large_enum_variant::LARGE_ENUM_VARIANT,
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&large_stack_arrays::LARGE_STACK_ARRAYS,
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&len_zero::LEN_WITHOUT_IS_EMPTY,
@@ -1008,6 +1010,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
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store.register_late_pass(|| box to_digit_is_some::ToDigitIsSome);
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let array_size_threshold = conf.array_size_threshold;
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store.register_late_pass(move || box large_stack_arrays::LargeStackArrays::new(array_size_threshold));
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store.register_late_pass(move || box large_const_arrays::LargeConstArrays::new(array_size_threshold));
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store.register_late_pass(move || box floating_point_arithmetic::FloatingPointArithmetic);
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store.register_early_pass(|| box as_conversions::AsConversions);
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store.register_early_pass(|| box utils::internal_lints::ProduceIce);
@@ -1198,6 +1201,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
11981201
LintId::of(&inherent_to_string::INHERENT_TO_STRING_SHADOW_DISPLAY),
11991202
LintId::of(&inline_fn_without_body::INLINE_FN_WITHOUT_BODY),
12001203
LintId::of(&int_plus_one::INT_PLUS_ONE),
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LintId::of(&large_const_arrays::LARGE_CONST_ARRAYS),
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LintId::of(&large_enum_variant::LARGE_ENUM_VARIANT),
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LintId::of(&len_zero::LEN_WITHOUT_IS_EMPTY),
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LintId::of(&len_zero::LEN_ZERO),
@@ -1637,6 +1641,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
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LintId::of(&bytecount::NAIVE_BYTECOUNT),
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LintId::of(&entry::MAP_ENTRY),
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LintId::of(&escape::BOXED_LOCAL),
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LintId::of(&large_const_arrays::LARGE_CONST_ARRAYS),
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LintId::of(&large_enum_variant::LARGE_ENUM_VARIANT),
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LintId::of(&loops::MANUAL_MEMCPY),
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LintId::of(&loops::NEEDLESS_COLLECT),

‎src/lintlist/mod.rs

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@@ -6,7 +6,7 @@ pub use lint::Lint;
66
pub use lint::LINT_LEVELS;
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88
// begin lint list, do not remove this comment, it’s used in `update_lints`
9-
pub const ALL_LINTS: [Lint; 361] = [
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pub const ALL_LINTS: [Lint; 362] = [
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Lint {
1111
name: "absurd_extreme_comparisons",
1212
group: "correctness",
@@ -931,6 +931,13 @@ pub const ALL_LINTS: [Lint; 361] = [
931931
deprecation: None,
932932
module: "non_expressive_names",
933933
},
934+
Lint {
935+
name: "large_const_arrays",
936+
group: "perf",
937+
desc: "large non-scalar const array may cause performance overhead",
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deprecation: None,
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module: "large_const_arrays",
940+
},
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Lint {
935942
name: "large_digit_groups",
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group: "pedantic",

‎tests/ui/large_const_arrays.fixed

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1+
// run-rustfix
2+
3+
#![warn(clippy::large_const_arrays)]
4+
#![allow(dead_code)]
5+
6+
#[derive(Clone, Copy)]
7+
pub struct S {
8+
pub data: [u64; 32],
9+
}
10+
11+
// Should lint
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pub(crate) static FOO_PUB_CRATE: [u32; 1_000_000] = [0u32; 1_000_000];
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pub static FOO_PUB: [u32; 1_000_000] = [0u32; 1_000_000];
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static FOO: [u32; 1_000_000] = [0u32; 1_000_000];
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// Good
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pub(crate) const G_FOO_PUB_CRATE: [u32; 1_000] = [0u32; 1_000];
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pub const G_FOO_PUB: [u32; 1_000] = [0u32; 1_000];
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const G_FOO: [u32; 1_000] = [0u32; 1_000];
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fn main() {
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// Should lint
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pub static BAR_PUB: [u32; 1_000_000] = [0u32; 1_000_000];
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static BAR: [u32; 1_000_000] = [0u32; 1_000_000];
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pub static BAR_STRUCT_PUB: [S; 5_000] = [S { data: [0; 32] }; 5_000];
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static BAR_STRUCT: [S; 5_000] = [S { data: [0; 32] }; 5_000];
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pub static BAR_S_PUB: [Option<&str>; 200_000] = [Some("str"); 200_000];
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static BAR_S: [Option<&str>; 200_000] = [Some("str"); 200_000];
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// Good
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pub const G_BAR_PUB: [u32; 1_000] = [0u32; 1_000];
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const G_BAR: [u32; 1_000] = [0u32; 1_000];
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pub const G_BAR_STRUCT_PUB: [S; 500] = [S { data: [0; 32] }; 500];
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const G_BAR_STRUCT: [S; 500] = [S { data: [0; 32] }; 500];
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pub const G_BAR_S_PUB: [Option<&str>; 200] = [Some("str"); 200];
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const G_BAR_S: [Option<&str>; 200] = [Some("str"); 200];
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}

‎tests/ui/large_const_arrays.rs

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@@ -0,0 +1,37 @@
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// run-rustfix
2+
3+
#![warn(clippy::large_const_arrays)]
4+
#![allow(dead_code)]
5+
6+
#[derive(Clone, Copy)]
7+
pub struct S {
8+
pub data: [u64; 32],
9+
}
10+
11+
// Should lint
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pub(crate) const FOO_PUB_CRATE: [u32; 1_000_000] = [0u32; 1_000_000];
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pub const FOO_PUB: [u32; 1_000_000] = [0u32; 1_000_000];
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const FOO: [u32; 1_000_000] = [0u32; 1_000_000];
15+
16+
// Good
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pub(crate) const G_FOO_PUB_CRATE: [u32; 1_000] = [0u32; 1_000];
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pub const G_FOO_PUB: [u32; 1_000] = [0u32; 1_000];
19+
const G_FOO: [u32; 1_000] = [0u32; 1_000];
20+
21+
fn main() {
22+
// Should lint
23+
pub const BAR_PUB: [u32; 1_000_000] = [0u32; 1_000_000];
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const BAR: [u32; 1_000_000] = [0u32; 1_000_000];
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pub const BAR_STRUCT_PUB: [S; 5_000] = [S { data: [0; 32] }; 5_000];
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const BAR_STRUCT: [S; 5_000] = [S { data: [0; 32] }; 5_000];
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pub const BAR_S_PUB: [Option<&str>; 200_000] = [Some("str"); 200_000];
28+
const BAR_S: [Option<&str>; 200_000] = [Some("str"); 200_000];
29+
30+
// Good
31+
pub const G_BAR_PUB: [u32; 1_000] = [0u32; 1_000];
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const G_BAR: [u32; 1_000] = [0u32; 1_000];
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pub const G_BAR_STRUCT_PUB: [S; 500] = [S { data: [0; 32] }; 500];
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const G_BAR_STRUCT: [S; 500] = [S { data: [0; 32] }; 500];
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pub const G_BAR_S_PUB: [Option<&str>; 200] = [Some("str"); 200];
36+
const G_BAR_S: [Option<&str>; 200] = [Some("str"); 200];
37+
}

‎tests/ui/large_const_arrays.stderr

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1+
error: large array defined as const
2+
--> $DIR/large_const_arrays.rs:12:1
3+
|
4+
LL | pub(crate) const FOO_PUB_CRATE: [u32; 1_000_000] = [0u32; 1_000_000];
5+
| ^^^^^^^^^^^-----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6+
| |
7+
| help: make this a static item: `static`
8+
|
9+
= note: `-D clippy::large-const-arrays` implied by `-D warnings`
10+
11+
error: large array defined as const
12+
--> $DIR/large_const_arrays.rs:13:1
13+
|
14+
LL | pub const FOO_PUB: [u32; 1_000_000] = [0u32; 1_000_000];
15+
| ^^^^-----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
16+
| |
17+
| help: make this a static item: `static`
18+
19+
error: large array defined as const
20+
--> $DIR/large_const_arrays.rs:14:1
21+
|
22+
LL | const FOO: [u32; 1_000_000] = [0u32; 1_000_000];
23+
| -----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
24+
| |
25+
| help: make this a static item: `static`
26+
27+
error: large array defined as const
28+
--> $DIR/large_const_arrays.rs:23:5
29+
|
30+
LL | pub const BAR_PUB: [u32; 1_000_000] = [0u32; 1_000_000];
31+
| ^^^^-----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
32+
| |
33+
| help: make this a static item: `static`
34+
35+
error: large array defined as const
36+
--> $DIR/large_const_arrays.rs:24:5
37+
|
38+
LL | const BAR: [u32; 1_000_000] = [0u32; 1_000_000];
39+
| -----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
40+
| |
41+
| help: make this a static item: `static`
42+
43+
error: large array defined as const
44+
--> $DIR/large_const_arrays.rs:25:5
45+
|
46+
LL | pub const BAR_STRUCT_PUB: [S; 5_000] = [S { data: [0; 32] }; 5_000];
47+
| ^^^^-----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
48+
| |
49+
| help: make this a static item: `static`
50+
51+
error: large array defined as const
52+
--> $DIR/large_const_arrays.rs:26:5
53+
|
54+
LL | const BAR_STRUCT: [S; 5_000] = [S { data: [0; 32] }; 5_000];
55+
| -----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
56+
| |
57+
| help: make this a static item: `static`
58+
59+
error: large array defined as const
60+
--> $DIR/large_const_arrays.rs:27:5
61+
|
62+
LL | pub const BAR_S_PUB: [Option<&str>; 200_000] = [Some("str"); 200_000];
63+
| ^^^^-----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
64+
| |
65+
| help: make this a static item: `static`
66+
67+
error: large array defined as const
68+
--> $DIR/large_const_arrays.rs:28:5
69+
|
70+
LL | const BAR_S: [Option<&str>; 200_000] = [Some("str"); 200_000];
71+
| -----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
72+
| |
73+
| help: make this a static item: `static`
74+
75+
error: aborting due to 9 previous errors
76+

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