These two contiguous builds used the cache, and there were no changes to anything but JS files, so basically everything should come from cache:

https://evergreen.mongodb.com/task/mongodb_mongo_master_enterprise_rhel_62_64_bit_compile_a2698593ede55dd3aaaedc882beec5aa30ff056e_18_03_16_15_15_24

https://evergreen.mongodb.com/task/mongodb_mongo_master_enterprise_rhel_62_64_bit_compile_fafb34dda41840937f062ab0a48fd784d63b8803_18_03_16_15_52_22

They don't share generated files though, because the venv paths differ:

https://evergreen.mongodb.com/task_log_raw/mongodb_mongo_master_enterprise_rhel_62_64_bit_compile_a2698593ede55dd3aaaedc882beec5aa30ff056e_18_03_16_15_15_24/0?type=T#L424

https://evergreen.mongodb.com/task_log_raw/mongodb_mongo_master_enterprise_rhel_62_64_bit_compile_fafb34dda41840937f062ab0a48fd784d63b8803_18_03_16_15_52_22/0?type=T#L425

It isn't too harmful, because the files they actually generate are identical, and SCons does notice this, but it would be even nicer if they didn't need to be regenerated and could come from the cache.