Support visibility control and default to `internal`. (#3380)

* Support visibility control and default to `internal`.

* Fix wip.

* Fixes.

* Fix.

* Fix test.

* Add legacy language detection and compatibility for existing code.

* Add doc.

---------

Co-authored-by: Yong He <yhe@nvidia.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/tests/diagnostics/internal-visibility/that-module-impl.slang b/tests/diagnostics/internal-visibility/that-module-impl.slang
new file mode 100644
index 000000000..893510afe
--- /dev/null
+++ b/tests/diagnostics/internal-visibility/that-module-impl.slang
@@ -0,0 +1,17 @@
+implementing "that-module";
+
+
+public void publicFunc2() { }
+
+internal void internalFunc1() {}
+
+public struct PublicStruct
+{
+    int x;
+    public int y;
+}
+
+public namespace Namespace
+{
+    public static int publicVar2;
+}