lib.warn: Use or behave like builtins.warn

    version

    versionSuffix

    warn;

  inherit (lib)

    isString

    ;

in {

  ## Simple (higher order) functions

    ```

  */

  warn =

    if lib.elem (builtins.getEnv "NIX_ABORT_ON_WARN") ["1" "true" "yes"]

    then msg: builtins.trace "warning: ${msg}" (abort "NIX_ABORT_ON_WARN=true; warnings are treated as unrecoverable errors.")

    else msg: builtins.trace "warning: ${msg}";

    # Since https://github.com/NixOS/nix/pull/10592

    builtins.warn or (

      let mustAbort = lib.elem (builtins.getEnv "NIX_ABORT_ON_WARN") ["1" "true" "yes"];

      in

        # Do not eta reduce v, so that we have the same strictness as `builtins.warn`.

        msg: v:

          # `builtins.warn` requires a string message, so we enforce that in our implementation, so that callers aren't accidentally incompatible with newer Nix versions.

          assert isString msg;

          if mustAbort

          then builtins.trace "warning: ${msg}" (abort "NIX_ABORT_ON_WARN=true; warnings are treated as unrecoverable errors.")

          else builtins.trace "warning: ${msg}" v

    );

  /**

    Like warn, but only warn when the first argument is `true`.