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

Author: J-ZhengLi

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)
 }

tests/ui/auxiliary/proc_macros.rs

@@ -9,6 +9,7 @@ use proc_macro::token_stream::IntoIter;
 use proc_macro::Delimiter::{self, Brace, Parenthesis};
 use proc_macro::Spacing::{self, Alone, Joint};
 use proc_macro::{Group, Ident, Literal, Punct, Span, TokenStream, TokenTree as TT};
+use syn::spanned::Spanned;
 
 type Result<T> = core::result::Result<T, TokenStream>;
 
@@ -124,6 +125,22 @@ fn write_with_span(s: Span, mut input: IntoIter, out: &mut TokenStream) -> Resul
     Ok(())
 }
 
+/// Takes an array repeat expression such as `[0_u32; 2]`, and return the tokens with 10 times the
+/// original size, which turns to `[0_u32; 20]`.
+#[proc_macro]
+pub fn make_it_big(input: TokenStream) -> TokenStream {
+    let mut expr_repeat = syn::parse_macro_input!(input as syn::ExprRepeat);
+    let len_span = expr_repeat.len.span();
+    if let syn::Expr::Lit(expr_lit) = &mut *expr_repeat.len {
+        if let syn::Lit::Int(lit_int) = &expr_lit.lit {
+            let orig_val = lit_int.base10_parse::<usize>().expect("not a valid length parameter");
+            let new_val = orig_val.saturating_mul(10);
+            expr_lit.lit = syn::parse_quote_spanned!( len_span => #new_val);
+        }
+    }
+    quote::quote!(#expr_repeat).into()
+}
+
 /// Within the item this attribute is attached to, an `inline!` macro is available which expands the
 /// contained tokens as though they came from a macro expansion.
 ///

tests/ui/large_stack_arrays.rs

@@ -1,6 +1,9 @@
+//@aux-build:proc_macros.rs
 #![warn(clippy::large_stack_arrays)]
 #![allow(clippy::large_enum_variant)]
 
+extern crate proc_macros;
+
 #[derive(Clone, Copy)]
 struct S {
     pub data: [u64; 32],
@@ -79,7 +82,6 @@ fn issue_12586() {
     let y = vec![x, x, x, x, x];
     let y = vec![dummy![x, x, x, x, x]];
     let y = vec![dummy![[x, x, x, x, x]]];
-    //~^ ERROR: allocating a local array larger than 512000 bytes
     let y = dummy![x, x, x, x, x];
     let y = [x, x, dummy!(x), x, x];
     //~^ ERROR: allocating a local array larger than 512000 bytes
@@ -88,4 +90,8 @@ fn issue_12586() {
     let y = dummy!(vec![dummy![x, x, x, x, x]]);
     let y = dummy![[x, x, x, x, x]];
     //~^ ERROR: allocating a local array larger than 512000 bytes
+
+    let y = proc_macros::make_it_big!([x; 1]);
+    //~^ ERROR: allocating a local array larger than 512000 bytes
+    let y = vec![proc_macros::make_it_big!([x; 10])];
 }

tests/ui/large_stack_arrays.stderr

@@ -1,5 +1,5 @@
 error: allocating a local array larger than 512000 bytes
-  --> tests/ui/large_stack_arrays.rs:29:14
+  --> tests/ui/large_stack_arrays.rs:32:14
    |
 LL |     let _x = [build(); 3];
    |              ^^^^^^^^^^^^
@@ -9,71 +9,63 @@ LL |     let _x = [build(); 3];
    = help: to override `-D warnings` add `#[allow(clippy::large_stack_arrays)]`
 
 error: allocating a local array larger than 512000 bytes
-  --> tests/ui/large_stack_arrays.rs:32:14
+  --> tests/ui/large_stack_arrays.rs:35:14
    |
 LL |     let _y = [build(), build(), build()];
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: consider allocating on the heap with `vec![build(), build(), build()].into_boxed_slice()`
 
 error: allocating a local array larger than 512000 bytes
-  --> tests/ui/large_stack_arrays.rs:38:9
+  --> tests/ui/large_stack_arrays.rs:41:9
    |
 LL |         [0u32; 20_000_000],
    |         ^^^^^^^^^^^^^^^^^^
    |
    = help: consider allocating on the heap with `vec![0u32; 20_000_000].into_boxed_slice()`
 
 error: allocating a local array larger than 512000 bytes
-  --> tests/ui/large_stack_arrays.rs:40:9
+  --> tests/ui/large_stack_arrays.rs:43:9
    |
 LL |         [S { data: [0; 32] }; 5000],
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: consider allocating on the heap with `vec![S { data: [0; 32] }; 5000].into_boxed_slice()`
 
 error: allocating a local array larger than 512000 bytes
-  --> tests/ui/large_stack_arrays.rs:42:9
+  --> tests/ui/large_stack_arrays.rs:45:9
    |
 LL |         [Some(""); 20_000_000],
    |         ^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: consider allocating on the heap with `vec![Some(""); 20_000_000].into_boxed_slice()`
 
 error: allocating a local array larger than 512000 bytes
-  --> tests/ui/large_stack_arrays.rs:44:9
+  --> tests/ui/large_stack_arrays.rs:47:9
    |
 LL |         [E::T(0); 5000],
    |         ^^^^^^^^^^^^^^^
    |
    = help: consider allocating on the heap with `vec![E::T(0); 5000].into_boxed_slice()`
 
 error: allocating a local array larger than 512000 bytes
-  --> tests/ui/large_stack_arrays.rs:46:9
+  --> tests/ui/large_stack_arrays.rs:49:9
    |
 LL |         [0u8; usize::MAX],
    |         ^^^^^^^^^^^^^^^^^
    |
    = help: consider allocating on the heap with `vec![0u8; usize::MAX].into_boxed_slice()`
 
 error: allocating a local array larger than 512000 bytes
-  --> tests/ui/large_stack_arrays.rs:81:25
-   |
-LL |     let y = vec![dummy![[x, x, x, x, x]]];
-   |                         ^^^^^^^^^^^^^^^
-   |
-   = help: consider allocating on the heap with `vec![x, x, x, x, x].into_boxed_slice()`
-
-error: allocating a local array larger than 512000 bytes
-  --> tests/ui/large_stack_arrays.rs:84:13
+  --> tests/ui/large_stack_arrays.rs:86:13
    |
 LL |     let y = [x, x, dummy!(x), x, x];
    |             ^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: consider allocating on the heap with `vec![x, x, dummy!(x), x, x].into_boxed_slice()`
 
 error: allocating a local array larger than 512000 bytes
-  --> tests/ui/large_stack_arrays.rs:67:13
+  --> tests/ui/large_stack_arrays.rs:70:13
    |
 LL |             [$a, $b, $a, $b]
    |             ^^^^^^^^^^^^^^^^
@@ -84,12 +76,18 @@ LL |     let y = dummy![x => x];
    = note: this error originates in the macro `dummy` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: allocating a local array larger than 512000 bytes
-  --> tests/ui/large_stack_arrays.rs:89:20
+  --> tests/ui/large_stack_arrays.rs:91:20
    |
 LL |     let y = dummy![[x, x, x, x, x]];
    |                    ^^^^^^^^^^^^^^^
    |
    = help: consider allocating on the heap with `vec![x, x, x, x, x].into_boxed_slice()`
 
+error: allocating a local array larger than 512000 bytes
+  --> tests/ui/large_stack_arrays.rs:94:39
+   |
+LL |     let y = proc_macros::make_it_big!([x; 1]);
+   |                                       ^^^^^^
+
 error: aborting due to 11 previous errors