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

   1 use rustc_hir::{Expr, ExprKind};
   2 use rustc_lint::{LateContext, LateLintPass};
   3 use rustc_middle::mir::interpret::ConstValue;
   4 use rustc_middle::ty::{self, ConstKind};
   5 use rustc_session::{declare_tool_lint, impl_lint_pass};
   6
   7 use if_chain::if_chain;
   8
   9 use crate::rustc_target::abi::LayoutOf;
  10 use crate::utils::{snippet, span_lint_and_help};
  11
  12 declare_clippy_lint! {
  13     /// **What it does:** Checks for local arrays that may be too large.
  14     ///
  15     /// **Why is this bad?** Large local arrays may cause stack overflow.
  16     ///
  17     /// **Known problems:** None.
  18     ///
  19     /// **Example:**
  20     /// ```rust,ignore
  21     /// let a = [0u32; 1_000_000];
  22     /// ```
  23     pub LARGE_STACK_ARRAYS,
  24     pedantic,
  25     "allocating large arrays on stack may cause stack overflow"
  26 }
  27
  28 pub struct LargeStackArrays {
  29     maximum_allowed_size: u64,
  30 }
  31
  32 impl LargeStackArrays {
  33     #[must_use]
  34     pub fn new(maximum_allowed_size: u64) -> Self {
  35         Self { maximum_allowed_size }
  36     }
  37 }
  38
  39 impl_lint_pass!(LargeStackArrays => [LARGE_STACK_ARRAYS]);
  40
  41 impl<'tcx> LateLintPass<'tcx> for LargeStackArrays {
  42     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
  43         if_chain! {
  44             if let ExprKind::Repeat(_, _) = expr.kind;
  45             if let ty::Array(element_type, cst) = cx.typeck_results().expr_ty(expr).kind();
  46             if let ConstKind::Value(val) = cst.val;
  47             if let ConstValue::Scalar(element_count) = val;
  48             if let Ok(element_count) = element_count.to_machine_usize(&cx.tcx);
  49             if let Ok(element_size) = cx.layout_of(element_type).map(|l| l.size.bytes());
  50             if self.maximum_allowed_size < element_count * element_size;
  51             then {
  52                 span_lint_and_help(
  53                     cx,
  54                     LARGE_STACK_ARRAYS,
  55                     expr.span,
  56                     &format!(
  57                         "allocating a local array larger than {} bytes",
  58                         self.maximum_allowed_size
  59                     ),
  60                     None,
  61                     &format!(
  62                         "consider allocating on the heap with `vec!{}.into_boxed_slice()`",
  63                         snippet(cx, expr.span, "[...]")
  64                     ),
  65                 );
  66             }
  67         }
  68     }
  69 }