// SERVER-8141 Avoid treating arrays as literals in aggregation pipeline.
let coll = db.exprs_in_arrays;
coll.drop();

assert.commandWorked(coll.insert({_id: 0, a: ["foo", "bar", "baz"], b: "bar", c: "Baz"}));

// An array of constants should still evaluate to an array of constants.
let pipeline = [{$project: {_id: 0, d: ["constant", 1]}}];
assert.eq(coll.aggregate(pipeline).toArray(), [{d: ["constant", 1]}]);

// A field name inside an array should take on the value of that field.
pipeline = [{$project: {_id: 0, d: ["$b"]}}];
assert.eq(coll.aggregate(pipeline).toArray(), [{d: ["bar"]}]);

// An expression inside an array should be evaluated.
pipeline = [{$project: {_id: 0, d: [{$toLower: "FoO"}]}}];
assert.eq(coll.aggregate(pipeline).toArray(), [{d: ["foo"]}]);

// Both an expression and a field name inside an array should be evaluated.
pipeline = [{$project: {_id: 0, d: ["$b", {$toLower: "FoO"}]}}];
assert.eq(coll.aggregate(pipeline).toArray(), [{d: ["bar", "foo"]}]);

// A nested array should still be evaluated.
pipeline = [{$project: {_id: 0, d: ["$b", "constant", [1, {$toLower: "FoO"}]]}}];
assert.eq(coll.aggregate(pipeline).toArray(), [{d: ["bar", "constant", [1, "foo"]]}]);

// Should still evaluate array elements inside arguments to an expression.
pipeline = [{$project: {_id: 0, d: {$setIntersection: ["$a", ["$b"]]}}}];
assert.eq(coll.aggregate(pipeline).toArray(), [{d: ["bar"]}]);

pipeline = [{$project: {_id: 0, d: {$setIntersection: ["$a", [{$toLower: "FoO"}]]}}}];
assert.eq(coll.aggregate(pipeline).toArray(), [{d: ["foo"]}]);

// Nested arrays.
pipeline = [
    {
        $project: {_id: 0, d: {$setIntersection: [[[1, "foo", "bar"]], [[1, {$toLower: "FoO"}, "$b"]]]}},
    },
];
assert.eq(coll.aggregate(pipeline).toArray(), [{d: [[1, "foo", "bar"]]}]);

coll.drop();

// Should replace missing values with NULL to preserve indices.
assert.commandWorked(coll.insert({_id: 1, x: 1, z: 2}));

pipeline = [{$project: {_id: 0, coordinate: ["$x", "$y", "$z"]}}];
assert.eq(coll.aggregate(pipeline).toArray(), [{coordinate: [1, null, 2]}]);