As it’s fairly common, recommended by Gould, and—depending on house style for longer measures—sometimes necessary to have single measure MMRs marked with a “1” in orchestral parts, it should be documented how this can be achieved:
\set restNumberThreshold = 0
The default seems to be “unset” but in multi-measure-rest-engraver.cc it is hardcoded to 1; you won’t find this value in engraver-init.ly.
commit c7bf27ada348587be6028a0fc48d367b4dbffec9
Author: Malte Meyn lilypond@maltemeyn.de
Date: Fri Dec 28 11:55:37 2018 +0100
commit 349fb5690375b28e6fe3df3013997f7bd8394b51
Author: Malte Meyn lilypond@maltemeyn.de
Date: Wed Dec 26 13:31:28 2018 +0100
commit 253b2489859c49c6b116acf9e18cc380351a3719
Author: Malte Meyn lilypond@maltemeyn.de
Date: Mon Dec 24 13:08:57 2018 +0100