Function single_file_asset_errors 

pub fn single_file_asset_errors(
    items: &[CommonsItem],
    build: bool,
) -> Vec<CompileError>

The single-file compile’s asset diagnostics, in declaration order: each asset’s path check and name rule (name_error, against the file’s own functions, types and earlier assets), and, when build is set, its refusal (needs_project_error). Placement needs no check here: a single file is always a commons (an adapter is a parse error).