test [large_stack_arrays] with proc-macro and make sure not to offer false help messages if in one.

clippy_lints/src/large_stack_arrays.rs

@@ -1,7 +1,8 @@
 use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::is_from_proc_macro;
 use clippy_utils::macros::macro_backtrace;
 use clippy_utils::source::snippet;
-use rustc_hir::{Expr, ExprKind, Item, ItemKind, Node};
+use rustc_hir::{ArrayLen, Expr, ExprKind, Item, ItemKind, Node};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty::layout::LayoutOf;
 use rustc_middle::ty::{self, ConstKind};
@@ -27,21 +28,41 @@ declare_clippy_lint! {
 
 pub struct LargeStackArrays {
     maximum_allowed_size: u128,
+    prev_vec_macro_callsite: Option<Span>,
 }
 
 impl LargeStackArrays {
     #[must_use]
     pub fn new(maximum_allowed_size: u128) -> Self {
-        Self { maximum_allowed_size }
+        Self {
+            maximum_allowed_size,
+            prev_vec_macro_callsite: None,
+        }
+    }
+
+    /// Check if the given span of an expr is already in a `vec!` call.
+    fn is_from_vec_macro(&mut self, cx: &LateContext<'_>, span: Span) -> bool {
+        // First, we check if this is span is within the last encountered `vec!` macro's root callsite.
+        self.prev_vec_macro_callsite
+            .is_some_and(|vec_mac| vec_mac.contains(span))
+            || {
+                // Then, we try backtracking the macro expansions, to see if there's a `vec!` macro,
+                // and update the `prev_vec_macro_callsite`.
+                let res = macro_backtrace(span).any(|mac| cx.tcx.is_diagnostic_item(sym::vec_macro, mac.def_id));
+                if res {
+                    self.prev_vec_macro_callsite = Some(span.source_callsite());
+                }
+                res
+            }
     }
 }
 
 impl_lint_pass!(LargeStackArrays => [LARGE_STACK_ARRAYS]);
 
 impl<'tcx> LateLintPass<'tcx> for LargeStackArrays {
-    fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
         if let ExprKind::Repeat(_, _) | ExprKind::Array(_) = expr.kind
-            && !is_from_vec_macro(cx, expr.span)
+            && !self.is_from_vec_macro(cx, expr.span)
             && let ty::Array(element_type, cst) = cx.typeck_results().expr_ty(expr).kind()
             && let ConstKind::Value(ty::ValTree::Leaf(element_count)) = cst.kind()
             && let Ok(element_count) = element_count.try_to_target_usize(cx.tcx)
@@ -66,7 +87,7 @@ impl<'tcx> LateLintPass<'tcx> for LargeStackArrays {
                     self.maximum_allowed_size
                 ),
                 |diag| {
-                    if !expr.span.from_expansion() {
+                    if !might_be_expanded(cx, expr) {
                         diag.help(format!(
                             "consider allocating on the heap with `vec!{}.into_boxed_slice()`",
                             snippet(cx, expr.span, "[...]")
@@ -78,7 +99,20 @@ impl<'tcx> LateLintPass<'tcx> for LargeStackArrays {
     }
 }
 
-/// We shouldn't lint messages if the expr is already in a `vec!` call
-fn is_from_vec_macro(cx: &LateContext<'_>, expr_span: Span) -> bool {
-    macro_backtrace(expr_span).any(|mac| cx.tcx.is_diagnostic_item(sym::vec_macro, mac.def_id))
+/// Only giving help messages if the expr does not contains macro expanded codes.
+fn might_be_expanded<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) -> bool {
+    /// Check if the span of `ArrayLen` of a repeat expression is within the expr's span,
+    /// if not, meaning this repeat expr is definitely from some proc-macro.
+    ///
+    /// This is a fail-safe to a case where even the `is_from_proc_macro` is unable to determain the
+    /// correct result.
+    fn repeat_expr_might_be_expanded<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) -> bool {
+        let ExprKind::Repeat(_, ArrayLen::Body(anon_const)) = expr.kind else {
+            return false;
+        };
+        let len_span = cx.tcx.def_span(anon_const.def_id);
+        !expr.span.contains(len_span)
+    }
+
+    expr.span.from_expansion() || is_from_proc_macro(cx, expr) || repeat_expr_might_be_expanded(cx, expr)
 }