typecheck: diagnose conditional-only returns

tests/test_validate_typecheck_diagnostics.py

@@ -47,6 +47,9 @@ class ValidateTypecheckDiagnosticsTests(unittest.TestCase):
     def test_includes_missing_function_return_fixture(self):
         self.assertIn("tests/typecheck_function_missing_return_bad.claro", MODULE.EXPECTED)
 
+    def test_includes_branch_missing_function_return_fixture(self):
+        self.assertIn("tests/typecheck_function_branch_missing_return_bad.claro", MODULE.EXPECTED)
+
     def test_includes_empty_function_return_fixture(self):
         self.assertIn("tests/typecheck_function_empty_return_bad.claro", MODULE.EXPECTED)
 

tests/typecheck_function_branch_missing_return_bad.claro

@@ -0,0 +1,5 @@
+TEACH choose flag RETURNS NUMBER
+    IF flag
+        RETURN 1
+    END
+END