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Add lint on large const arrays
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‎CHANGELOG.md

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@@ -1319,6 +1319,7 @@ 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

‎clippy_lints/src/large_const_arrays.rs

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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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@@ -580,6 +580,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
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&int_plus_one::INT_PLUS_ONE,
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&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,
@@ -1024,6 +1025,7 @@ 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);
@@ -1222,6 +1224,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
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LintId::of(&inherent_to_string::INHERENT_TO_STRING_SHADOW_DISPLAY),
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LintId::of(&inline_fn_without_body::INLINE_FN_WITHOUT_BODY),
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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),
@@ -1651,6 +1654,7 @@ 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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@@ -941,6 +941,13 @@ pub static ref ALL_LINTS: Vec<Lint> = vec![
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deprecation: None,
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module: "non_expressive_names",
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},
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Lint {
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name: "large_const_arrays",
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group: "perf",
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desc: "large non-scalar const array may cause performance overhead",
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deprecation: None,
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module: "large_const_arrays",
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},
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Lint {
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name: "large_digit_groups",
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group: "pedantic",

‎tests/ui/large_const_arrays.fixed

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// run-rustfix
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#![warn(clippy::large_const_arrays)]
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#![allow(dead_code)]
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#[derive(Clone, Copy)]
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pub struct S {
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pub data: [u64; 32],
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}
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// 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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// run-rustfix
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#![warn(clippy::large_const_arrays)]
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#![allow(dead_code)]
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#[derive(Clone, Copy)]
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pub struct S {
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pub data: [u64; 32],
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}
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// 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];
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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 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];
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const 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.stderr

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error: large array defined as const
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--> $DIR/large_const_arrays.rs:12:1
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|
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LL | pub(crate) const FOO_PUB_CRATE: [u32; 1_000_000] = [0u32; 1_000_000];
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| ^^^^^^^^^^^-----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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| |
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| help: make this a static item: `static`
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|
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= note: `-D clippy::large-const-arrays` implied by `-D warnings`
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error: large array defined as const
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--> $DIR/large_const_arrays.rs:13:1
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|
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LL | pub const FOO_PUB: [u32; 1_000_000] = [0u32; 1_000_000];
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| ^^^^-----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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| |
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| help: make this a static item: `static`
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error: large array defined as const
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--> $DIR/large_const_arrays.rs:14:1
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|
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LL | const FOO: [u32; 1_000_000] = [0u32; 1_000_000];
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| -----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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| |
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| help: make this a static item: `static`
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error: large array defined as const
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--> $DIR/large_const_arrays.rs:23:5
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|
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LL | pub const BAR_PUB: [u32; 1_000_000] = [0u32; 1_000_000];
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| ^^^^-----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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| |
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| help: make this a static item: `static`
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error: large array defined as const
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--> $DIR/large_const_arrays.rs:24:5
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|
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LL | const BAR: [u32; 1_000_000] = [0u32; 1_000_000];
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| -----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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| |
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| help: make this a static item: `static`
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error: large array defined as const
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--> $DIR/large_const_arrays.rs:25:5
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|
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LL | pub const BAR_STRUCT_PUB: [S; 5_000] = [S { data: [0; 32] }; 5_000];
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| ^^^^-----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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| |
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| help: make this a static item: `static`
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error: large array defined as const
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--> $DIR/large_const_arrays.rs:26:5
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|
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LL | const BAR_STRUCT: [S; 5_000] = [S { data: [0; 32] }; 5_000];
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| -----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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| |
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| help: make this a static item: `static`
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error: large array defined as const
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--> $DIR/large_const_arrays.rs:27:5
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|
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LL | pub const BAR_S_PUB: [Option<&str>; 200_000] = [Some("str"); 200_000];
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| ^^^^-----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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| |
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| help: make this a static item: `static`
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error: large array defined as const
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--> $DIR/large_const_arrays.rs:28:5
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|
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LL | const BAR_S: [Option<&str>; 200_000] = [Some("str"); 200_000];
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| -----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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| |
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| help: make this a static item: `static`
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error: aborting due to 9 previous errors
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