rust/hgcli/build.rs

upgrade: speed up when we have only nodemap to downgrade

Similar to what we do on upgrade, if we have only persistent-nodemap to
downgrade we will just delete the nodemap files and update repository
requirements instead of processing all the revlogs.

After downgrade, we are left with unrequired docket and transaction files which
seems fine but can work on deleting them if someone feels we should.

Differential Revision: https://phab.mercurial-scm.org/D9992

// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at https://mozilla.org/MPL/2.0/.

/*! Build script to integrate PyOxidizer. */

fn main() {
    if let Ok(config_rs) =
        std::env::var("DEP_PYTHONXY_DEFAULT_PYTHON_CONFIG_RS")
    {
        println!(
            "cargo:rustc-env=PYOXIDIZER_DEFAULT_PYTHON_CONFIG_RS={}",
            config_rs
        );
    } else {
        panic!("unable to find build artifacts generated by pyembed crate");
    }
}