pkgs.traceDrvLicenses

The following is the current implementation of this function.

traceDrvLicenses =
    stdenv:
    stdenv.override (old: {
      mkDerivationFromStdenv = overrideMkDerivationResult (
        pkg:
        let
          printDrvPath =
            val:
            let
              drvPath = builtins.unsafeDiscardStringContext pkg.drvPath;
              license = pkg.meta.license or null;
            in
            builtins.trace "@:drv:${toString drvPath}:${builtins.toString license}:@" val;
        in
        pkg
        // {
          outPath = printDrvPath pkg.outPath;
          drvPath = printDrvPath pkg.drvPath;
        }
      );
    });