The first field configuration_format_version encodes a versioning number internal to R8/D8 in the form of an unsigned integer. It allows R8/D8 to know if the file given is supported. Non-backward compatible changes to the desugared library increase the version number, and such library cannot be compiled without upgrading R8/D8 to the latest version.
The second field version holds the version of the content for the configuration. This number must be updated each time the configuration is changed.
The third field required_compilation_api_level encodes the minimal Android API level required for the desugared library to be compiled correctly. If the API of library used for compilation of the library or a program using the library is lower than this level, one has to upgrade the SDK version used to be able to use desugared libraries.
The fourth and fifth fields are library_flags and program_flags. They include the set of flags required for respectively the library and the program using the desugared library compilation. The sets of flags are different depending on the min API level used. The flags are in a list, where each list entry specifies up to which min API level the set of flags should be applied. During compilation, R8/D8 adds up all the required flags for the min API level specified at compilation.
For example, let's say the program_flags have entries for api_level_below_or_equal 20, 24 and 26. If compiling the program for min API 24, R8/D8 will use both the set of flags for API 24 and 26 (24 <= 24, 24 <= 26 but !(24 <= 20)).
The last field is extra_keep_rules, it includes keep rules that are appended by L8 when shrinking the desugared library. It includes keep rules related to reflection inside the desugared library, related to enum to have EnumSet working and to keep the j$ prefix.
Copyright (c) 2019, the R8 project authors. Please see the AUTHORS file for details. All rights reserved. Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.