Function refuse_retired_calls 

pub fn refuse_retired_calls(
    stmts: &[Stmt<'_>],
    interner: &Interner,
) -> Result<(), String>

The first call, in source order, to a builtin the language no longer has (crate::semantics::builtins::retired_builtin), refused in that builtin’s own sentence. A name the program defines or binds is its own and is called. Every tier’s front end runs this before the program runs, so each refuses the call in the same words, whether or not the call is ever reached.