1 use clippy_utils::diagnostics::span_lint_and_then;
2 use if_chain::if_chain;
3 use rustc_errors::Applicability;
4 use rustc_hir::{Item, ItemKind};
5 use rustc_lint::{LateContext, LateLintPass};
6 use rustc_middle::mir::interpret::ConstValue;
7 use rustc_middle::ty::layout::LayoutOf;
8 use rustc_middle::ty::{self, ConstKind};
9 use rustc_session::{declare_tool_lint, impl_lint_pass};
10 use rustc_span::{BytePos, Pos, Span};
11 use rustc_typeck::hir_ty_to_ty;
13 declare_clippy_lint! {
15 /// Checks for large `const` arrays that should
16 /// be defined as `static` instead.
18 /// ### Why is this bad?
19 /// Performance: const variables are inlined upon use.
20 /// Static items result in only one instance and has a fixed location in memory.
25 /// pub const a = [0u32; 1_000_000];
28 /// pub static a = [0u32; 1_000_000];
30 #[clippy::version = "1.44.0"]
31 pub LARGE_CONST_ARRAYS,
33 "large non-scalar const array may cause performance overhead"
36 pub struct LargeConstArrays {
37 maximum_allowed_size: u64,
40 impl LargeConstArrays {
42 pub fn new(maximum_allowed_size: u64) -> Self {
43 Self { maximum_allowed_size }
47 impl_lint_pass!(LargeConstArrays => [LARGE_CONST_ARRAYS]);
49 impl<'tcx> LateLintPass<'tcx> for LargeConstArrays {
50 fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
52 if !item.span.from_expansion();
53 if let ItemKind::Const(hir_ty, _) = &item.kind;
54 let ty = hir_ty_to_ty(cx.tcx, hir_ty);
55 if let ty::Array(element_type, cst) = ty.kind();
56 if let ConstKind::Value(ConstValue::Scalar(element_count)) = cst.val;
57 if let Ok(element_count) = element_count.to_machine_usize(&cx.tcx);
58 if let Ok(element_size) = cx.layout_of(element_type).map(|l| l.size.bytes());
59 if self.maximum_allowed_size < element_count * element_size;
62 let hi_pos = item.ident.span.lo() - BytePos::from_usize(1);
63 let sugg_span = Span::new(
64 hi_pos - BytePos::from_usize("const".len()),
73 "large array defined as const",
77 "make this a static item",
79 Applicability::MachineApplicable,