fn parse_top_level_assignment(line: &str) -> Option<(&str, &str)>Expand description
Parse a bare top-level assignment, returning its name and trimmed RHS.
Ignore indented closures and targets containing $, [[ or ::, or a
call such as S7::method(...). Backtick-quoted names are returned without
the quotes, with escapes kept as emitted. Find the closing backtick before
the arrow so replacement names such as `[<-.Foo` parse correctly.