Function reveal_actual_level 

pub fn reveal_actual_level(
    level: Option<(Level, Option<LintExpectationId>)>,
    src: &mut LintLevelSource,
    sess: &Session,
    lint: LintId,
    probe_for_lint_level: impl FnOnce(LintId) -> (Option<(Level, Option<LintExpectationId>)>, LintLevelSource),
) -> (Level, Option<LintExpectationId>)

From an initial level and source, verify the effect of special annotations: warnings lint level and lint caps.

The return of this function is suitable for diagnostics.