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
::ty
::layout
::LayoutOf
;
7 use rustc_middle
::ty
::{self, ConstKind}
;
8 use rustc_session
::{declare_tool_lint, impl_lint_pass}
;
9 use rustc_span
::{BytePos, Pos, Span}
;
10 use rustc_typeck
::hir_ty_to_ty
;
12 declare_clippy_lint
! {
14 /// Checks for large `const` arrays that should
15 /// be defined as `static` instead.
17 /// ### Why is this bad?
18 /// Performance: const variables are inlined upon use.
19 /// Static items result in only one instance and has a fixed location in memory.
23 /// 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(ty
::ValTree
::Leaf(element_count
)) = cst
.kind();
57 if let Ok(element_count
) = element_count
.try_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
,