85 lines
2.8 KiB
Rust
85 lines
2.8 KiB
Rust
use crate::rustc_target::abi::LayoutOf;
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use clippy_utils::diagnostics::span_lint_and_then;
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use if_chain::if_chain;
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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_middle::mir::interpret::ConstValue;
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use rustc_middle::ty::{self, ConstKind};
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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
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/// 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?
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/// 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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/// ### 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<'tcx> LateLintPass<'tcx> for LargeConstArrays {
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fn check_item(&mut self, cx: &LateContext<'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(ConstValue::Scalar(element_count)) = cst.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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|diag| {
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diag.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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}
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