Fix literal code emission for containers when empty

trans/transpiler/phases/emit_cpp/expr.py

@@ -183,14 +183,22 @@ class ExpressionVisitor(NodeVisitor):
         yield node.attr
 
     def visit_List(self, node: ast.List) -> Iterable[str]:
-        yield "PyList{"
-        yield from join(", ", map(self.reset().visit, node.elts))
-        yield "}"
+        if node.elts:
+            yield "PyList{"
+            yield from join(", ", map(self.reset().visit, node.elts))
+            yield "}"
+        else:
+            yield from self.visit(node.type)
+            yield "{}"
 
     def visit_Set(self, node: ast.Set) -> Iterable[str]:
-        yield "PySet{"
-        yield from join(", ", map(self.reset().visit, node.elts))
-        yield "}"
+        if node.elts:
+            yield "PySet{"
+            yield from join(", ", map(self.reset().visit, node.elts))
+            yield "}"
+        else:
+            yield from self.visit(node.type)
+            yield "{}"
 
     def visit_Dict(self, node: ast.Dict) -> Iterable[str]:
         def visit_item(key, value):
@@ -200,9 +208,13 @@ class ExpressionVisitor(NodeVisitor):
             yield from self.reset().visit(value)
             yield "}"
 
-        yield "PyDict{"
-        yield from join(", ", map(visit_item, node.keys, node.values))
-        yield "}"
+        if node.keys:
+            yield "PyDict{"
+            yield from join(", ", map(visit_item, node.keys, node.values))
+            yield "}"
+        else:
+            yield from self.visit(node.type)
+            yield "{}"
 
     def visit_Subscript(self, node: ast.Subscript) -> Iterable[str]:
         yield from self.prec("[]").visit(node.value)