CSharp: Add support for source groups with out-of-source builds

This also fixes support for multiple sources of the same name in
different directories.  Add a test for both problems.

Issue: #19505

1 files changed, 13 insertions, 0 deletions

diff --git a/Tests/CSharpOnly/nested/lib1.cs b/Tests/CSharpOnly/nested/lib1.cs
new file mode 100644
index 0000000..c2fde4b
--- /dev/null
+++ b/Tests/CSharpOnly/nested/lib1.cs
@@ -0,0 +1,13 @@
+namespace CSharpOnly
+{
+    namespace nested
+    {
+        public class Lib1
+        {
+            public static int getResult()
+            {
+                return 23;
+            }
+        }
+    }
+}