Support IdString parameters in stringf

tests/unit/kernel/ioTest.cc

@@ -1,6 +1,7 @@
 #include <gtest/gtest.h>
 
 #include "kernel/io.h"
+#include "kernel/rtlil.h"
 
 YOSYS_NAMESPACE_BEGIN
 
@@ -44,6 +45,12 @@ TEST(KernelStringfTest, stringViewParam)
         EXPECT_EQ(stringf("%s", std::string_view("hello")), "hello");
 }
 
+TEST(KernelStringfTest, idStringParam)
+{
+        RTLIL::IdString id("$hello");
+        EXPECT_EQ(stringf("%s", id), "$hello");
+}
+
 TEST(KernelStringfTest, escapePercent)
 {
 	EXPECT_EQ(stringf("%%"), "%");