Function complete 

pub fn complete(
    line_prefix: &str,
    doc_text: &str,
    files: Option<&HashMap<PathBuf, String>>,
) -> Vec<Completion>

Produce completions for the cursor, given the text of the line up to the cursor, the current document text, and the project source root (if any). Without a project root, a project’s dependencies are found from the manifest in files (crate::packages::DependencyView::from_files); the language server calls complete_in with the root it knows.