fixes

examples/issue-0004.sx

@@ -0,0 +1,43 @@
+// issue-0004: scalar-to-vector conversion when all optional struct fields are null
+//
+// When a struct has multiple ?f32 fields and ALL are set to null simultaneously,
+// passing that struct to a virtual function call triggers:
+//   "error: scalar-to-vector conversion failed"
+//
+// Setting at least one field to a concrete value works fine.
+
+#import "modules/std.sx";
+
+ProposedSize :: struct {
+    width: ?f32;
+    height: ?f32;
+}
+
+Sizable :: protocol {
+    size :: (proposal: ProposedSize) -> f32;
+}
+
+Widget :: struct {}
+
+impl Sizable for Widget {
+    size :: (self: *Widget, proposal: ProposedSize) -> f32 {
+        w := if pw := proposal.width { pw; } else { 100.0; };
+        h := if ph := proposal.height { ph; } else { 100.0; };
+        w + h;
+    }
+}
+
+main :: () -> void {
+    w := Widget.{};
+    s : Sizable = w;
+
+    // These work:
+    r1 := s.size(ProposedSize.{ width = 50.0, height = null });
+    print("r1 = {}\n", r1);
+    r2 := s.size(ProposedSize.{ width = null, height = 50.0 });
+    print("r2 = {}\n", r2);
+
+    // This fails with "scalar-to-vector conversion failed":
+    r3 := s.size(ProposedSize.{ width = null, height = null });
+    print("r3 = {}\n", r3);
+}