Fix '--make-template' for union types (#1760)

cwltool/main.py

@@ -195,13 +195,15 @@ def generate_example_input(
                 else:
                     comment = "optional"
         else:
-            example = CommentedSeq()
-            for index, entry in enumerate(inptype):
+            example, comment = generate_example_input(inptype[0], default)
+            type_names = []
+            for entry in inptype:
                 value, e_comment = generate_example_input(entry, default)
-                example.append(value)
-                example.yaml_add_eol_comment(e_comment, index)
+                if e_comment:
+                    type_names.append(e_comment)
+            comment = "one of " + ", ".join(type_names)
             if optional:
-                comment = "optional"
+                comment = f"{comment} (optional)"
     elif isinstance(inptype, Mapping) and "type" in inptype:
         if inptype["type"] == "array":
             first_item = cast(MutableSequence[CWLObjectType], inptype["items"])[0]

tests/test_make_template.py

@@ -8,3 +8,21 @@
 def test_anonymous_record() -> None:
     inputs = cmap([{"type": "record", "fields": []}])
     assert main.generate_example_input(inputs, None) == ({}, "Anonymous record type.")
+
+
+def test_union() -> None:
+    """Test for --make-template for a union type."""
+    inputs = cmap(["string", "string[]"])
+    assert main.generate_example_input(inputs, None) == (
+        "a_string",
+        'one of type "string", type "string[]"',
+    )
+
+
+def test_optional_union() -> None:
+    """Test for --make-template for an optional union type."""
+    inputs = cmap(["null", "string", "string[]"])
+    assert main.generate_example_input(inputs, None) == (
+        "a_string",
+        'one of type "string", type "string[]" (optional)',
+    )