Function check_binders 

fn check_binders(
    psess: &ParseSess,
    node_id: NodeId,
    lhs: &TokenTree,
    macros: &Stack<'_, MacroState<'_>>,
    binders: &mut FxHashMap<MacroRulesNormalizedIdent, BinderInfo>,
    ops: &Stack<'_, KleeneToken>,
    guar: &mut Option<ErrorGuaranteed>,
)

Checks lhs as part of the LHS of a macro definition.

Arguments:

• psess is used to emit diagnostics and lints
• node_id is used to emit lints
• lhs is checked as part of a LHS
• macros is the stack of possible outer macros
• binders contains the binders of the LHS
• ops is the stack of Kleene operators from the LHS
• guar is set in case of errors