Function run 

pub fn run(
    schema_path: &str,
    supergraph_path: Option<&str>,
    json: bool,
) -> Result<CommandResult>

Run federation check command.

Validates the federation metadata in a compiled schema for correctness. If supergraph_path is provided, also validates composition against it. When json is true, the result is serialized and written to stdout before returning.

Errors

Returns an error if the schema file cannot be read or parsed.