gccrs: Update SlicePattern typechecking against slice reference parents

gcc/rust/ChangeLog:

	* typecheck/rust-hir-type-check-pattern.cc (TypeCheckPattern::visit(SlicePattern)):
		Add new type check case for SliceType wrapped in ReferenceType.
	* backend/rust-compile-pattern.cc: Adjusted the asserts accordingly for
		CompilePatternCheckExpr(SlicePattern) & CompilePatternBindings(SlicePattern).

Signed-off-by: Yap Zhi Heng <yapzhhg@gmail.com>

Author: Polygonalr

gcc/rust/backend/rust-compile-pattern.cc

@@ -529,7 +529,8 @@ CompilePatternCheckExpr::visit (HIR::SlicePattern &pattern)
   // pattern must either be ArrayType or SliceType, should be already confirmed
   // by type checking
   rust_assert (lookup->get_kind () == TyTy::TypeKind::ARRAY
-	       || lookup->get_kind () == TyTy::TypeKind::SLICE);
+	       || lookup->get_kind () == TyTy::TypeKind::SLICE
+	       || lookup->get_kind () == TyTy::REF);
 
   size_t array_element_index = 0;
   switch (lookup->get_kind ())
@@ -895,7 +896,8 @@ CompilePatternBindings::visit (HIR::SlicePattern &pattern)
   rust_assert (ok);
 
   rust_assert (lookup->get_kind () == TyTy::TypeKind::ARRAY
-	       || lookup->get_kind () == TyTy::TypeKind::SLICE);
+	       || lookup->get_kind () == TyTy::TypeKind::SLICE
+	       || lookup->get_kind () == TyTy::REF);
 
   size_t array_element_index = 0;
   switch (lookup->get_kind ())

gcc/rust/typecheck/rust-hir-type-check-pattern.cc

@@ -675,8 +675,21 @@ TypeCheckPattern::visit (HIR::SlicePattern &pattern)
       }
     case TyTy::SLICE:
       {
-	auto &array_ty_ty = static_cast<TyTy::SliceType &> (*parent);
-	parent_element_ty = array_ty_ty.get_element_type ();
+	auto &slice_ty_ty = static_cast<TyTy::SliceType &> (*parent);
+	parent_element_ty = slice_ty_ty.get_element_type ();
+	break;
+      }
+    case TyTy::REF:
+      {
+	auto &ref_ty_ty = static_cast<TyTy::ReferenceType &> (*parent);
+	const TyTy::SliceType *slice = nullptr;
+	if (!ref_ty_ty.is_dyn_slice_type (&slice))
+	  {
+	    rust_error_at (pattern.get_locus (), "expected %s, found slice",
+			   parent->as_string ().c_str ());
+	    return;
+	  }
+	parent_element_ty = slice->get_element_type ();
 	break;
       }
     default: