/**
 * Tests that sparse indexes are disallowed for $exists:false queries.
 */
(function() {
"use strict";

const coll = db.jstests_existsa;
coll.drop();

assert.commandWorked(coll.insert({}));
assert.commandWorked(coll.insert({a: 1}));
assert.commandWorked(coll.insert({a: {x: 1}, b: 1}));

let indexKeySpec = {};
let indexKeyField = '';

/** Configure testing of an index { <indexKeyField>:1 }. */
function setIndex(_indexKeyField) {
    indexKeyField = _indexKeyField;
    indexKeySpec = {};
    indexKeySpec[indexKeyField] = 1;
    coll.ensureIndex(indexKeySpec, {sparse: true});
}
setIndex('a');

/** @return count when hinting the index to use. */
function hintedCount(query) {
    return coll.find(query).hint(indexKeySpec).itcount();
}

/** The query field does not exist and the sparse index is not used without a hint. */
function assertMissing(query, expectedMissing = 1, expectedIndexedMissing = 0) {
    assert.eq(expectedMissing, coll.count(query));
    // We also shouldn't get a different count depending on whether
    // an index is used or not.
    assert.eq(expectedIndexedMissing, hintedCount(query));
}

/** The query field exists and the sparse index is used without a hint. */
function assertExists(query, expectedExists = 2) {
    assert.eq(expectedExists, coll.count(query));
    // An $exists:true predicate generates no index filters. Add another predicate on the index
    // key to trigger use of the index.
    let andClause = {};
    andClause[indexKeyField] = {$ne: null};
    Object.extend(query, {$and: [andClause]});
    assert.eq(expectedExists, coll.count(query));
    assert.eq(expectedExists, hintedCount(query));
}

/** The query field exists and the sparse index is not used without a hint. */
function assertExistsUnindexed(query, expectedExists = 2) {
    assert.eq(expectedExists, coll.count(query));
    // Even with another predicate on the index key, the sparse index is disallowed.
    let andClause = {};
    andClause[indexKeyField] = {$ne: null};
    Object.extend(query, {$and: [andClause]});
    assert.eq(expectedExists, coll.count(query));
    assert.eq(expectedExists, hintedCount(query));
}

// $exists:false queries match the proper number of documents and disallow the sparse index.
assertMissing({a: {$exists: false}});
assertMissing({a: {$not: {$exists: true}}});
assertMissing({$and: [{a: {$exists: false}}]});
assertMissing({$or: [{a: {$exists: false}}]});
assertMissing({$nor: [{a: {$exists: true}}]});
assertMissing({'a.x': {$exists: false}}, 2, 1);

// Currently a sparse index is disallowed even if the $exists:false query is on a different
// field.
assertMissing({b: {$exists: false}}, 2, 1);
assertMissing({b: {$exists: false}, a: {$ne: 6}}, 2, 1);
assertMissing({b: {$not: {$exists: true}}}, 2, 1);

// Top level $exists:true queries match the proper number of documents
// and use the sparse index on { a : 1 }.
assertExists({a: {$exists: true}});

// Nested $exists queries match the proper number of documents and disallow the sparse index.
assertExistsUnindexed({$nor: [{a: {$exists: false}}]});
assertExistsUnindexed({$nor: [{'a.x': {$exists: false}}]}, 1);
assertExistsUnindexed({a: {$not: {$exists: false}}});

// Nested $exists queries disallow the sparse index in some cases where it is not strictly
// necessary to do so.  (Descriptive tests.)
assertExistsUnindexed({$nor: [{b: {$exists: false}}]}, 1);  // Unindexed field.
assertExists({$or: [{a: {$exists: true}}]});                // $exists:true not $exists:false.

// Behavior is similar with $elemMatch.
coll.drop();
assert.commandWorked(coll.insert({a: [{}]}));
assert.commandWorked(coll.insert({a: [{b: 1}]}));
assert.commandWorked(coll.insert({a: [{b: [1]}]}));
setIndex('a.b');

assertMissing({a: {$elemMatch: {b: {$exists: false}}}});

// A $elemMatch predicate is treated as nested, and the index should be used for $exists:true.
assertExists({a: {$elemMatch: {b: {$exists: true}}}});

// A $not within $elemMatch should not attempt to use a sparse index for $exists:false.
assertExistsUnindexed({'a.b': {$elemMatch: {$not: {$exists: false}}}}, 1);
assertExistsUnindexed({'a.b': {$elemMatch: {$gt: 0, $not: {$exists: false}}}}, 1);

// A non sparse index will not be disallowed.
coll.drop();
assert.commandWorked(coll.insert({}));
coll.ensureIndex({a: 1});
assert.eq(1, coll.find({a: {$exists: false}}).itcount());
})();