unsafe: Add checks for union field accesses

Co-authored-by: philberty <philip.herron@embecosm.com>

2 files changed, 27 insertions, 3 deletions

diff --git a/gcc/rust/checks/errors/rust-unsafe-checker.cc b/gcc/rust/checks/errors/rust-unsafe-checker.cc
index def3cc1..99f59ac 100644
--- a/gcc/rust/checks/errors/rust-unsafe-checker.cc
+++ b/gcc/rust/checks/errors/rust-unsafe-checker.cc
@@ -262,10 +262,24 @@ UnsafeChecker::visit (MethodCallExpr &expr)
 void
 UnsafeChecker::visit (FieldAccessExpr &expr)
 {
-  // FIXME: If the receiver is an union, we need to be in an unsafe context to
-  // access it. Make sure to check.
-
   expr.get_receiver_expr ()->accept_vis (*this);
+
+  if (is_unsafe_context ())
+    return;
+
+  TyTy::BaseType *receiver_ty;
+  auto ok = context.lookup_type (
+    expr.get_receiver_expr ()->get_mappings ().get_hirid (), &receiver_ty);
+  rust_assert (ok);
+
+  if (receiver_ty->get_kind () == TyTy::TypeKind::ADT)
+    {
+      auto maybe_union = static_cast<TyTy::ADTType *> (receiver_ty);
+      if (maybe_union->is_union ())
+	rust_error_at (
+	  expr.get_locus (),
+	  "access to union field requires unsafe function or block");
+    }
 }
 
 void
diff --git a/gcc/testsuite/rust/compile/unsafe9.rs b/gcc/testsuite/rust/compile/unsafe9.rs
new file mode 100644
index 0000000..fb46c8f
--- /dev/null
+++ b/gcc/testsuite/rust/compile/unsafe9.rs
@@ -0,0 +1,10 @@
+union U {
+    a: i32,
+    b: f32,
+    c: u8,
+}
+
+fn main() {
+    let u = U { a: 14 };
+    let _ = u.a; // { dg-error "access to union" }
+}