Plain "sort" in branches of parallel "from" causes a parse error

[philrz]

Repro is with Zed commit 30299b5.

The join tutorial shows this example that runs ok.

$ zq -version
Version: v1.2.0-28-g30299b5a

$ cat embed-opposite.zed 
from (
  file fruit.ndjson => sort flavor
  file people.ndjson => sort likes
) | inner join on flavor=likes eaterinfo:=this

$ zq -z -I embed-opposite.zed
...

However, if I drop the explicit field names on sort, now it's a parse error.

$ cat embed-opposite-plain-sort.zed
from (
  file fruit.ndjson => sort
  file people.ndjson => sort
) | inner join on flavor=likes eaterinfo:=this

$ zq -z -I embed-opposite-plain-sort.zed 
zq: error parsing Zed in embed-opposite-plain-sort.zed at line 3, column 8:
  file people.ndjson => sort
   === ^ ===