Original discovery reported at https://phabricator.wikimedia.org/T102578#1584302.
This is yet another bug that is causing all file module cache to be invalidated whenever we deploy a new branch.
@@ -1,5 +1,5 @@ > return $wgVersion; -1.26wmf19 +1.26wmf20 > return $m->getModuleContent( $c ); array(3) { ["scripts"]=> @@ -82,15 +82,13 @@ bool(false) } ["fileHashes"]=> - array(2) { + array(1) { [0]=> string(40) "2c8553784d9e0e8b565d6c4cd525556ce87fbdd0" - [1]=> - string(40) "2c8553784d9e0e8b565d6c4cd525556ce87fbdd0" } ["msgBlobMtime"]=> int(1) } } > return $m->getVersionHash( $c ); -f1Ifa+cB +eqAznAKY
The funny thing is that when switching it's alternating inconsistently. One when I switched testwiki from wmf19 to wmf20 the entry was added. Another time the entry was removed. It doesn't seem deterministic (e.g. not a bug in wmf20, but something we've had for a while).
The same happened when wikis switched to wmf21 earlier this week.