Fix implicit string conversion breaking NativeStrings (#6035)

* Fix implicit string conversion breaking NativeStrings

* Allow string literals to coerce to either string type

* Add test for CPU string passing

---------

Co-authored-by: Yong He <yonghe@outlook.com>

2 files changed, 23 insertions, 0 deletions

diff --git a/tests/cpu-program/string-passing.slang b/tests/cpu-program/string-passing.slang
new file mode 100644
index 000000000..3ae736a57
--- /dev/null
+++ b/tests/cpu-program/string-passing.slang
@@ -0,0 +1,17 @@
+//TEST:EXECUTABLE:
+
+void printer(NativeString string)
+{
+    printf(string);
+}
+
+void indirectPrinter(String string)
+{
+    printer(string);
+}
+
+export __extern_cpp int main()
+{
+    indirectPrinter("success\n");
+    return 0;
+}
diff --git a/tests/cpu-program/string-passing.slang.expected b/tests/cpu-program/string-passing.slang.expected
new file mode 100644
index 000000000..0eb55acbf
--- /dev/null
+++ b/tests/cpu-program/string-passing.slang.expected
@@ -0,0 +1,6 @@
+result code = 0
+standard error = {
+}
+standard output = {
+success
+}