error: 'caller' is not a valid name for a macro
 --> <source attribute>:1:2
       "- macro caller() -%}{%- endmacro -%}"
 --> tests/ui/macro-caller.rs:4:21
  |
4 | #[template(source = "{%- macro caller() -%}{%- endmacro -%}", ext = "html")]
  |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^