Grouped reductions break ICU collation

[davisp]

ICU Collation of Grouped Reductions is broken

Description

This was encountered as an issue by @nevans on CouchDB Slack. It turns out that we're not properly using UCA sorting when dealing with grouped reduce rows due to the use of an erlang dict for storing rows.

Steps to Reproduce

#!/usr/bin/env python

import json

import requests


s = requests.session()
s.auth = ("adm", "pass")
s.headers["Content-Type"] = "application/json"

DB_URL = "https://127.0.0.1:15984/test"

s.delete(DB_URL)
r = s.put(DB_URL)
# q=1&n=1 "fixes" the issue because fabric only
# ends up with a single group
#r = s.put(DB_URL, params={"q": "1", "n": "1"})
r.raise_for_status()


ddoc = {
    "_id": "_design/bar",
    "views": {
        "uca": {
            "map": "function(doc) {emit(doc.value, null);}",
            "reduce": "_count"
        }
    }
}
r = s.put(DB_URL + "/_design/bar", data=json.dumps(ddoc))
r.raise_for_status()

values = [u"\u2708\ufe0f New Arrivals", u"\u2708 New Arrivals"]

for i in range(10):
    for v in values:
        doc = {"value": v}
        r = s.post(DB_URL, data=json.dumps(doc))
        r.raise_for_status()

print "View Rows"
r = s.get(DB_URL + "/_design/bar/_view/uca", params={"reduce": "false"})
r.raise_for_status()
print json.dumps(r.json(), indent=4, sort_keys=True)
print

print "Total Reudce"
r = s.get(DB_URL + "/_design/bar/_view/uca")
r.raise_for_status()
print json.dumps(r.json(), indent=4, sort_keys=True)
print

print "Grouped Reduce"
r = s.get(DB_URL + "/_design/bar/_view/uca", params={"group": "true"})
r.raise_for_status()
print json.dumps(r.json(), indent=4, sort_keys=True)

Expected Behaviour

The above script returns two grouped rows that have keys that sort equal using UCA.

Your Environment

Unimportant

Additional context

There's previous work to address this issue for map views which are similar but not quite the same issue. A fix for this issue will look somewhat like the changes in this commit:

1be5506

[kocolosk]

Rediscovered in #3773 and fixed by #3783

[nevans]

Fixed? 🎉 🥳 🎉

[kocolosk]

Better late than never!