Add new lint: large stack array

added documentation

minor style fix

change as to ::from

add ignore to doc

include threshold in lint message/make suggestion more apparent/use Scalar api instead of matching

style fix

shange snippet_opt to snippet

clippy_lints/src/large_stack_arrays.rs

@@ -0,0 +1,67 @@
+use rustc::hir::*;
+use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
+use rustc::mir::interpret::ConstValue;
+use rustc::ty;
+use rustc::{declare_tool_lint, impl_lint_pass};
+
+use if_chain::if_chain;
+
+use crate::rustc_target::abi::LayoutOf;
+use crate::utils::{snippet, span_help_and_lint};
+
+declare_clippy_lint! {
+    /// **What it does:** Checks for local arrays that may be too large.
+    ///
+    /// **Why is this bad?** Large local arrays may cause stack overflow.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// ```rust,ignore
+    /// let a = [0u32; 1_000_000];
+    /// ```
+    pub LARGE_STACK_ARRAYS,
+    pedantic,
+    "allocating large arrays on stack may cause stack overflow"
+}
+
+pub struct LargeStackArrays {
+    maximum_allowed_size: u64,
+}
+
+impl LargeStackArrays {
+    #[must_use]
+    pub fn new(maximum_allowed_size: u64) -> Self {
+        Self { maximum_allowed_size }
+    }
+}
+
+impl_lint_pass!(LargeStackArrays => [LARGE_STACK_ARRAYS]);
+
+impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LargeStackArrays {
+    fn check_expr(&mut self, cx: &LateContext<'_, '_>, expr: &Expr) {
+        if_chain! {
+            if let ExprKind::Repeat(_, _) = expr.kind;
+            if let ty::Array(element_type, cst) = cx.tables.expr_ty(expr).kind;
+            if let ConstValue::Scalar(element_count) = cst.val;
+            if let Ok(element_count) = element_count.to_machine_usize(&cx.tcx);
+            if let Ok(element_size) = cx.layout_of(element_type).map(|l| l.size.bytes());
+            if self.maximum_allowed_size < element_count * element_size;
+            then {
+                span_help_and_lint(
+                    cx,
+                    LARGE_STACK_ARRAYS,
+                    expr.span,
+                    &format!(
+                        "allocating a local array larger than {} bytes",
+                        self.maximum_allowed_size
+                    ),
+                    &format!(
+                        "consider allocating on the heap with vec!{}.into_boxed_slice()",
+                        snippet(cx, expr.span, "[...]")
+                    ),
+                );
+            }
+        }
+    }
+}

clippy_lints/src/lib.rs

@@ -211,6 +211,7 @@ pub mod int_plus_one;
 pub mod integer_division;
 pub mod items_after_statements;
 pub mod large_enum_variant;
+pub mod large_stack_arrays;
 pub mod len_zero;
 pub mod let_if_seq;
 pub mod lifetimes;
@@ -537,6 +538,7 @@ pub fn register_plugins(store: &mut lint::LintStore, sess: &Session, conf: &Conf
         &integer_division::INTEGER_DIVISION,
         &items_after_statements::ITEMS_AFTER_STATEMENTS,
         &large_enum_variant::LARGE_ENUM_VARIANT,
+        &large_stack_arrays::LARGE_STACK_ARRAYS,
         &len_zero::LEN_WITHOUT_IS_EMPTY,
         &len_zero::LEN_ZERO,
         &let_if_seq::USELESS_LET_IF_SEQ,
@@ -949,6 +951,8 @@ pub fn register_plugins(store: &mut lint::LintStore, sess: &Session, conf: &Conf
     store.register_late_pass(|| box mutable_debug_assertion::DebugAssertWithMutCall);
     store.register_late_pass(|| box exit::Exit);
     store.register_late_pass(|| box to_digit_is_some::ToDigitIsSome);
+    let array_size_threshold = conf.array_size_threshold;
+    store.register_late_pass(move || box large_stack_arrays::LargeStackArrays::new(array_size_threshold));
 
     store.register_group(true, "clippy::restriction", Some("clippy_restriction"), vec![
         LintId::of(&arithmetic::FLOAT_ARITHMETIC),
@@ -1002,6 +1006,7 @@ pub fn register_plugins(store: &mut lint::LintStore, sess: &Session, conf: &Conf
         LintId::of(&if_not_else::IF_NOT_ELSE),
         LintId::of(&infinite_iter::MAYBE_INFINITE_ITER),
         LintId::of(&items_after_statements::ITEMS_AFTER_STATEMENTS),
+        LintId::of(&large_stack_arrays::LARGE_STACK_ARRAYS),
         LintId::of(&literal_representation::LARGE_DIGIT_GROUPS),
         LintId::of(&loops::EXPLICIT_INTO_ITER_LOOP),
         LintId::of(&loops::EXPLICIT_ITER_LOOP),

clippy_lints/src/utils/conf.rs

@@ -151,6 +151,8 @@ define_Conf! {
     (trivial_copy_size_limit, "trivial_copy_size_limit", None => Option<u64>),
     /// Lint: TOO_MANY_LINES. The maximum number of lines a function or method can have
     (too_many_lines_threshold, "too_many_lines_threshold", 100 => u64),
+    /// Lint: LARGE_STACK_ARRAYS. The maximum allowed size for arrays on the stack
+    (array_size_threshold, "array_size_threshold", 512_000 => u64),
 }
 
 impl Default for Conf {