https://github.com/rust-lang/rust/blob/ba4081a5a8573875fed17545846f6f6902c8ba8d/src/librustc/driver/driver.rs#L64

gistfile1.rs

    // We need nested scopes here, because the intermediate results can keep
    // large chunks of memory alive and we want to free them as soon as
    // possible to keep the peak memory usage low
    let (outputs, trans, sess) = {
        let (outputs, expanded_crate, id) = {
            let krate = phase_1_parse_input(&sess, cfg, input);
            if stop_after_phase_1(&sess) { return; }
            let outputs = build_output_filenames(input,
                                                 outdir,
                                                 output,
                                                 krate.attrs.as_slice(),
                                                 &sess);
            let id = link::find_crate_name(Some(&sess), krate.attrs.as_slice(),
                                           input);
            let expanded_crate
                = match phase_2_configure_and_expand(&sess, krate, id.as_slice(),
                                                     addl_plugins) {
                    None => return,
                    Some(k) => k
                };
    
            (outputs, expanded_crate, id)
        };
        
        // blah...
    }