Function analyze_root 

pub fn analyze_root<F>(
    root: WorkspaceFile,
    workspace_root: Option<&Path>,
    preview_features: &PreviewFeatures,
    target: &Target,
    open_text: F,
) -> AnalysisResult
where
    F: FnMut(&Path) -> Option<String>,

Analyze a single root file plus its transitively-@import-reachable closure. Builds the closure (open-buffer text wins over disk), runs the frontend, and returns per-file diagnostics with an optional Snapshot when sema completed.