Sharded timeseries collection can uassert on valid $group queries with $count

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      import {ShardingTest} from "jstests/libs/shardingtest.js";

// Using chunkSize=1 is not necessary to repro the issue, but makes it easier since we need less documents to get data on both shards.
const st = new ShardingTest({shards: 2, other: {chunkSize: 1}});
const sDB = st.s.getDB('test');
assert(sDB.coll.drop());
assert.commandWorked(sDB.adminCommand({enableSharding: 'test', primaryShard: st.shard0.shardName}));
assert.commandWorked(sDB.adminCommand({
    shardCollection: `test.coll`,
    key: {m: 1},
    timeseries: {timeField: 't', metaField: 'm'}
}));

const coll = sDB.coll;
st.startBalancer();

// Insert some docs
const alphabet = 'abcdefghijklmnop';
const docs = [];
for(let i = 0; i < 100; i++){
    docs.push({t: new Date(i * 1000), m: i % 100, otherField: alphabet.repeat(1000)});
}
assert.commandWorked(coll.insert(docs));
// Let the balancer move documents so we have data on both shards
st.awaitBalancerRound();

coll.aggregate([{$group: {_id: null, document_count: {$count: {}}, max_time: {$max: '$t'}}}]).toArray()
// uassert 9961600: Unexpected type on the merging pass of the $sum. This likely happened due to a malformed query.

st.stop();
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      import {ShardingTest} from "jstests/libs/shardingtest.js" ; // Using chunkSize=1 is not necessary to repro the issue, but makes it easier since we need less documents to get data on both shards. const st = new ShardingTest({shards: 2, other: {chunkSize: 1}}); const sDB = st.s.getDB( 'test' ); assert (sDB.coll.drop()); assert .commandWorked(sDB.adminCommand({enableSharding: 'test' , primaryShard: st.shard0.shardName})); assert .commandWorked(sDB.adminCommand({ shardCollection: `test.coll`, key: {m: 1}, timeseries: {timeField: 't' , metaField: 'm' } })); const coll = sDB.coll; st.startBalancer(); // Insert some docs const alphabet = 'abcdefghijklmnop' ; const docs = []; for (let i = 0; i < 100; i++){ docs.push({t: new Date(i * 1000), m: i % 100, otherField: alphabet.repeat(1000)}); } assert .commandWorked(coll.insert(docs)); // Let the balancer move documents so we have data on both shards st.awaitBalancerRound(); coll.aggregate([{$group: {_id: null , document_count: {$count: {}}, max_time: {$max: '$t' }}}]).toArray() // uassert 9961600: Unexpected type on the merging pass of the $sum. This likely happened due to a malformed query. st.stop();
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      The repro below shows that a time-series collection sharded on the meta field can assert on valid $group queries.

      The error seems specific to $count, from here. The sum accumulator (translated from the $count) expects an array when merging, but receives a number.

            Assignee:
            Lee Maguire
            Reporter:
            Matt Boros
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              Created:
              Updated: