Auto merge of #6133 - JPTIZ:no-box-for-c-ffi, r=ebroto

clippy_lints: Do not warn against Box parameter in C FFI

changelog: [`boxed_local`]: don't lint in `extern fn` arguments

Fixes #5542.

When using C FFI, to handle pointers in parameters it is needed to
declare them as `Box` in its Rust-side signature. However, the current
linter warns against the usage of Box stating that "local variable
doesn't need to be boxed here".

This commit fixes it by ignoring functions whose Abi is C.

2 files changed, 16 insertions, 1 deletions

diff --git a/clippy_lints/src/escape.rs b/clippy_lints/src/escape.rs
index 82549c12d0a..8b022912573 100644
--- a/clippy_lints/src/escape.rs
+++ b/clippy_lints/src/escape.rs
@@ -6,6 +6,7 @@ use rustc_middle::ty::{self, Ty};
 use rustc_session::{declare_tool_lint, impl_lint_pass};
 use rustc_span::source_map::Span;
 use rustc_target::abi::LayoutOf;
+use rustc_target::spec::abi::Abi;
 use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, PlaceBase, PlaceWithHirId};
 
 use crate::utils::span_lint;
@@ -60,12 +61,18 @@ impl<'tcx> LateLintPass<'tcx> for BoxedLocal {
     fn check_fn(
         &mut self,
         cx: &LateContext<'tcx>,
-        _: intravisit::FnKind<'tcx>,
+        fn_kind: intravisit::FnKind<'tcx>,
         _: &'tcx FnDecl<'_>,
         body: &'tcx Body<'_>,
         _: Span,
         hir_id: HirId,
     ) {
+        if let Some(header) = fn_kind.header() {
+            if header.abi != Abi::Rust {
+                return;
+            }
+        }
+
         // If the method is an impl for a trait, don't warn.
         let parent_id = cx.tcx.hir().get_parent_item(hir_id);
         let parent_node = cx.tcx.hir().find(parent_id);
diff --git a/tests/ui/escape_analysis.rs b/tests/ui/escape_analysis.rs
index c0a52d832c0..07004489610 100644
--- a/tests/ui/escape_analysis.rs
+++ b/tests/ui/escape_analysis.rs
@@ -174,3 +174,11 @@ mod issue_3739 {
         };
     }
 }
+
+/// Issue #5542
+///
+/// This shouldn't warn for `boxed_local` as it is intended to called from non-Rust code.
+pub extern "C" fn do_not_warn_me(_c_pointer: Box<String>) -> () {}
+
+#[rustfmt::skip] // Forces rustfmt to not add ABI
+pub extern fn do_not_warn_me_no_abi(_c_pointer: Box<String>) -> () {}