/**
 * F002: inside an object $elemMatch, SBE checks path arrayness for the child's
 * element-relative path ("b") against the root document. A non-multikey root
 * index on "b" marks "b" non-array, so SBE skips traversal of arr.$.b and
 * misses array elements whose "b" is an array.
 *
 * @tags: [
 *   requires_fcv_90,
 *   requires_sbe
 * ]
 */

// Default settings except the plan cache: toggled knobs do not clear cached plans.
const conn = MongoRunner.runMongod({setParameter: {internalQueryDisablePlanCache: true}});
const db = conn.getDB(jsTestName());
const coll = db.c;

assert.commandWorked(coll.insert({_id: 0, b: 1, arr: [{b: [1, 2]}]}));
// The root index on "b" is what marks "b" as non-array; without it the bug is gone.
assert.commandWorked(coll.createIndex({b: 1}));

// $group lets the $match run in SBE under the default trySbeRestricted.
const pipeline = [{$match: {arr: {$elemMatch: {b: 2}}}}, {$group: {_id: "$_id"}}];
const expected = [{_id: 0}];

function run(label) {
    const results = coll.aggregate(pipeline).toArray();
    const usedSbe = tojson(coll.explain().aggregate(pipeline)).includes("slotBasedPlan");
    const findResults = coll.find({arr: {$elemMatch: {b: 2}}}).toArray();
    jsTest.log.info("F002 run", {label, usedSbe, results, findResults});
    return {results, usedSbe};
}

const withIndex = run("default, root b index");
assert.commandWorked(db.adminCommand({setParameter: 1, internalEnablePathArrayness: false}));
const arraynessOff = run("internalEnablePathArrayness=false");
assert.commandWorked(db.adminCommand({setParameter: 1, internalEnablePathArrayness: true}));
assert.commandWorked(coll.dropIndex({b: 1}));
const noIndex = run("default, no root b index");

// Every run must take the SBE path, or the comparison proves nothing.
assert(withIndex.usedSbe && arraynessOff.usedSbe && noIndex.usedSbe, "SBE was not used");

assert.sameMembers(arraynessOff.results, expected, "path arrayness off");
assert.sameMembers(noIndex.results, expected, "no root b index");
// Fails at 2e6f9b7f8e7: returns [] because traverseF is elided for arr.$.b.
assert.sameMembers(withIndex.results, expected, "default, root b index");

MongoRunner.stopMongod(conn);