Speed-up of downloads from binary caches. The number of parallel downloads (also known as substitutions) has been separated from the
--max-jobssetting. The new setting is called
max-substitution-jobs. The number of parallel downloads is now set to 16 by default (previously, the default was 1 due to the coupling to build jobs).
builtins.replaceStringsis now lazy in the value of its second argument
to. That is,
tois only evaluated when its corresponding pattern in
fromis matched in the string