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Add lint on large non scalar const
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‎CHANGELOG.md‎

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@@ -1274,6 +1274,7 @@ Released 2018-09-13
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[`new_without_default`]: https://rust-lang.github.io/rust-clippy/master/index.html#new_without_default
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[`no_effect`]: https://rust-lang.github.io/rust-clippy/master/index.html#no_effect
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[`non_ascii_literal`]: https://rust-lang.github.io/rust-clippy/master/index.html#non_ascii_literal
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[`non_scalar_const`]: https://rust-lang.github.io/rust-clippy/master/index.html#non_scalar_const
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[`nonminimal_bool`]: https://rust-lang.github.io/rust-clippy/master/index.html#nonminimal_bool
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[`nonsensical_open_options`]: https://rust-lang.github.io/rust-clippy/master/index.html#nonsensical_open_options
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[`not_unsafe_ptr_arg_deref`]: https://rust-lang.github.io/rust-clippy/master/index.html#not_unsafe_ptr_arg_deref

‎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.
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[There are 360 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
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[There are 361 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/lib.rs‎

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@@ -268,6 +268,7 @@ pub mod new_without_default;
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pub mod no_effect;
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pub mod non_copy_const;
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pub mod non_expressive_names;
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pub mod non_scalar_const;
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pub mod open_options;
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pub mod option_env_unwrap;
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pub mod overflow_check_conditional;
@@ -719,6 +720,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
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&non_expressive_names::JUST_UNDERSCORES_AND_DIGITS,
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&non_expressive_names::MANY_SINGLE_CHAR_NAMES,
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&non_expressive_names::SIMILAR_NAMES,
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&non_scalar_const::NON_SCALAR_CONST,
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&open_options::NONSENSICAL_OPEN_OPTIONS,
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&option_env_unwrap::OPTION_ENV_UNWRAP,
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&overflow_check_conditional::OVERFLOW_CHECK_CONDITIONAL,
@@ -1003,6 +1005,7 @@ 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 non_scalar_const::NonScalarConst::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);
@@ -1300,6 +1303,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
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LintId::of(&non_copy_const::DECLARE_INTERIOR_MUTABLE_CONST),
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LintId::of(&non_expressive_names::JUST_UNDERSCORES_AND_DIGITS),
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LintId::of(&non_expressive_names::MANY_SINGLE_CHAR_NAMES),
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LintId::of(&non_scalar_const::NON_SCALAR_CONST),
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LintId::of(&open_options::NONSENSICAL_OPEN_OPTIONS),
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LintId::of(&option_env_unwrap::OPTION_ENV_UNWRAP),
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LintId::of(&overflow_check_conditional::OVERFLOW_CHECK_CONDITIONAL),
@@ -1639,6 +1643,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
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LintId::of(&methods::SINGLE_CHAR_PATTERN),
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LintId::of(&misc::CMP_OWNED),
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LintId::of(&mutex_atomic::MUTEX_ATOMIC),
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LintId::of(&non_scalar_const::NON_SCALAR_CONST),
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LintId::of(&redundant_clone::REDUNDANT_CLONE),
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LintId::of(&slow_vector_initialization::SLOW_VECTOR_INITIALIZATION),
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LintId::of(&trivially_copy_pass_by_ref::TRIVIALLY_COPY_PASS_BY_REF),

‎clippy_lints/src/non_scalar_const.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` non-scalar types (ie: array) 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 NON_SCALAR_CONST,
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perf,
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"large non-scalar const variable may cause performance overhead"
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}
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pub struct NonScalarConst {
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maximum_allowed_size: u64,
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}
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impl NonScalarConst {
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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!(NonScalarConst => [NON_SCALAR_CONST]);
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NonScalarConst {
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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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NON_SCALAR_CONST,
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sugg_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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item.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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}

‎src/lintlist/mod.rs‎

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@@ -6,7 +6,7 @@ pub use lint::Lint;
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pub use lint::LINT_LEVELS;
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// begin lint list, do not remove this comment, it’s used in `update_lints`
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pub const ALL_LINTS: [Lint; 360] = [
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pub const ALL_LINTS: [Lint; 361] = [
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Lint {
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name: "absurd_extreme_comparisons",
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group: "correctness",
@@ -1463,6 +1463,13 @@ pub const ALL_LINTS: [Lint; 360] = [
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deprecation: None,
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module: "unicode",
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},
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Lint {
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name: "non_scalar_const",
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group: "perf",
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desc: "large non-scalar const variable may cause performance overhead",
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deprecation: None,
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module: "non_scalar_const",
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},
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Lint {
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name: "nonminimal_bool",
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group: "complexity",

‎tests/ui/non_scalar_const.rs‎

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#![warn(clippy::non_scalar_const)]
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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/non_scalar_const.stderr‎

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error: large array defined as const
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--> $DIR/non_scalar_const.rs:9:12
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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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| -----------^^^^^----------------------------------------------------- help: make this a static item: `static`
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|
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= note: `-D clippy::non-scalar-const` implied by `-D warnings`
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error: large array defined as const
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--> $DIR/non_scalar_const.rs:10:5
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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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| ----^^^^^----------------------------------------------- help: make this a static item: `static`
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error: large array defined as const
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--> $DIR/non_scalar_const.rs:11:1
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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/non_scalar_const.rs:20:9
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|
26+
LL | pub const BAR_PUB: [u32; 1_000_000] = [0u32; 1_000_000];
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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/non_scalar_const.rs:21:5
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|
32+
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/non_scalar_const.rs:22:9
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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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| ----^^^^^----------------------------------------------------------- help: make this a static item: `static`
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error: large array defined as const
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--> $DIR/non_scalar_const.rs:23:5
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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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51+
error: large array defined as const
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--> $DIR/non_scalar_const.rs:24:9
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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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| ----^^^^^------------------------------------------------------------- help: make this a static item: `static`
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error: large array defined as const
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--> $DIR/non_scalar_const.rs:25:5
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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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