Defaults to type params are not allowed here

2 files changed, 35 insertions, 0 deletions

diff --git a/gcc/rust/hir/rust-ast-lower-item.h b/gcc/rust/hir/rust-ast-lower-item.h
index 18ead3c..fe0b791 100644
--- a/gcc/rust/hir/rust-ast-lower-item.h
+++ b/gcc/rust/hir/rust-ast-lower-item.h
@@ -349,6 +349,29 @@ public:
       {
 	generic_params
 	  = lower_generic_params (impl_block.get_generic_params ());
+
+	for (auto &generic_param : generic_params)
+	  {
+	    switch (generic_param->get_kind ())
+	      {
+		case HIR::GenericParam::GenericKind::TYPE: {
+		  const HIR::TypeParam &t
+		    = static_cast<const HIR::TypeParam &> (*generic_param);
+
+		  if (t.has_type ())
+		    {
+		      // see https://github.com/rust-lang/rust/issues/36887
+		      rust_error_at (
+			t.get_locus (),
+			"defaults for type parameters are not allowed here");
+		    }
+		}
+		break;
+
+	      default:
+		break;
+	      }
+	  }
       }
 
     HIR::Type *trait_type
diff --git a/gcc/testsuite/rust.test/xfail_compile/generics10.rs b/gcc/testsuite/rust.test/xfail_compile/generics10.rs
new file mode 100644
index 0000000..a734fa8
--- /dev/null
+++ b/gcc/testsuite/rust.test/xfail_compile/generics10.rs
@@ -0,0 +1,12 @@
+struct Foo<A, B>(A, B);
+
+impl<X = i32> Foo<X, f32> { // { dg-error "defaults for type parameters are not allowed here" }
+    fn new(a: X, b: f32) -> Self {
+        Self(a, b)
+    }
+}
+
+fn main() {
+    let a;
+    a = Foo::new(123, 456f32);
+}