src/tools/clippy/clippy_lints/src/large_stack_arrays.rs

   1 use clippy_utils::diagnostics::span_lint_and_help;
   2 use clippy_utils::source::snippet;
   3 use if_chain::if_chain;
   4 use rustc_hir::{Expr, ExprKind};
   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
  11 declare_clippy_lint! {
  12     /// ### What it does
  13     /// Checks for local arrays that may be too large.
  14     ///
  15     /// ### Why is this bad?
  16     /// Large local arrays may cause stack overflow.
  17     ///
  18     /// ### Example
  19     /// ```rust,ignore
  20     /// let a = [0u32; 1_000_000];
  21     /// ```
  22     pub LARGE_STACK_ARRAYS,
  23     pedantic,
  24     "allocating large arrays on stack may cause stack overflow"
  25 }
  26
  27 pub struct LargeStackArrays {
  28     maximum_allowed_size: u64,
  29 }
  30
  31 impl LargeStackArrays {
  32     #[must_use]
  33     pub fn new(maximum_allowed_size: u64) -> Self {
  34         Self { maximum_allowed_size }
  35     }
  36 }
  37
  38 impl_lint_pass!(LargeStackArrays => [LARGE_STACK_ARRAYS]);
  39
  40 impl<'tcx> LateLintPass<'tcx> for LargeStackArrays {
  41     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
  42         if_chain! {
  43             if let ExprKind::Repeat(_, _) = expr.kind;
  44             if let ty::Array(element_type, cst) = cx.typeck_results().expr_ty(expr).kind();
  45             if let ConstKind::Value(ConstValue::Scalar(element_count)) = cst.val;
  46             if let Ok(element_count) = element_count.to_machine_usize(&cx.tcx);
  47             if let Ok(element_size) = cx.layout_of(element_type).map(|l| l.size.bytes());
  48             if self.maximum_allowed_size < element_count * element_size;
  49             then {
  50                 span_lint_and_help(
  51                     cx,
  52                     LARGE_STACK_ARRAYS,
  53                     expr.span,
  54                     &format!(
  55                         "allocating a local array larger than {} bytes",
  56                         self.maximum_allowed_size
  57                     ),
  58                     None,
  59                     &format!(
  60                         "consider allocating on the heap with `vec!{}.into_boxed_slice()`",
  61                         snippet(cx, expr.span, "[...]")
  62                     ),
  63                 );
  64             }
  65         }
  66     }
  67 }