[ast] Adds get last statement to ast::Function

This CL adds a function which returns the last statement of a ast::Function

Change-Id: I1dc68b7f4669c17a24a62c03a87dcc95866a428d
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/26720
Reviewed-by: dan sinclair <dsinclair@chromium.org>
Commit-Queue: dan sinclair <dsinclair@chromium.org>

src/ast/function.cc

@@ -156,6 +156,10 @@ void Function::add_ancestor_entry_point(const std::string& ep) {
   ancestor_entry_points_.push_back(ep);
 }
 
+const Statement* Function::get_last_statement() const {
+  return body_->last();
+}
+
 bool Function::IsValid() const {
   for (const auto& param : params_) {
     if (param == nullptr || !param->IsValid())

src/ast/function.h

@@ -121,6 +121,9 @@ class Function : public Node {
   void set_return_type(type::Type* type) { return_type_ = type; }
   /// @returns the function return type.
   type::Type* return_type() const { return return_type_; }
+  /// @returns a pointer to the last statement of the function or nullptr if
+  // function is empty
+  const Statement* get_last_statement() const;
 
   /// Sets the body of the function
   /// @param body the function body

src/ast/function_test.cc

@@ -349,6 +349,30 @@ TEST_F(FunctionTest, TypeName_WithParams) {
   EXPECT_EQ(f.type_name(), "__func__void__i32__f32");
 }
 
+TEST_F(FunctionTest, GetLastStatement) {
+  type::VoidType void_type;
+
+  VariableList params;
+  auto body = std::make_unique<ast::BlockStatement>();
+  auto stmt = std::make_unique<DiscardStatement>();
+  auto* stmt_ptr = stmt.get();
+  body->append(std::move(stmt));
+  Function f("func", std::move(params), &void_type);
+  f.set_body(std::move(body));
+
+  EXPECT_EQ(f.get_last_statement(), stmt_ptr);
+}
+
+TEST_F(FunctionTest, GetLastStatement_nullptr) {
+  type::VoidType void_type;
+
+  VariableList params;
+  auto body = std::make_unique<ast::BlockStatement>();
+  Function f("func", std::move(params), &void_type);
+  f.set_body(std::move(body));
+
+  EXPECT_EQ(f.get_last_statement(), nullptr);
+}
 }  // namespace
 }  // namespace ast
 }  // namespace tint