The tee verb passed the same record pointer both to its file-output
handler (which writes asynchronously on another goroutine, and whose
buffering formats like pprint/json can hold records until close) and
downstream in the verb chain, where subsequent verbs mutate records in
place. Downstream mutations could therefore leak into the tee'd output:
mlr tee -p cat then cat -n then nothing <<EOF
a=1,b=2
a=3,b=4
a=5,b=6
EOF
emitted "n=3,a=5,b=6" for the last tee'd record, and with pprint/json
tee formats every record picked up downstream fields.
Fix: give the file-writer its own deep copy of the record. Same fix
applied to the split verb when -v (emit downstream) is used, which
shared records with downstream the same way.
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
