Function resolve_output 

pub fn resolve_output(
    flag: Option<&Utf8Path>,
    canonical_target: &Path,
) -> Result<(PathBuf, OutputSource), RkError>

Resolve the output directory: --output first, then a target and version directory below RK_STAGE_ROOT, then the same below the private state root.

Errors

Returns a prerequisite-unmet refusal where neither a flag, the variable, nor a state root names a base.