fix(schema): throw error if duplicate index definition using unique in schema path and subsequent .index() call

[vkarpov15]

Fix #15056

Summary

Defining an index using unique in schema path and later calling schema.index() causes 2 indexes to be added, which is likely a user error.

Examples

[hasezoey]

LGTM, though the lint should be fixed.

[tonynelson19]

I think the isDeepStrictEqual check breaks compound indexes that share the same fields, since field order is important in compound indexes.

For example, it's valid to have indexes on both { a: 1, b: 1 } and { b: 1, a: 1 }, but the isDeepStrictEqual check will now throw an error since it does not consider the order of object keys when comparing objects.

[ruizmarc]

I think the isDeepStrictEqual check breaks compound indexes that share the same fields, since field order is important in compound indexes.

For example, it's valid to have indexes on both { a: 1, b: 1 } and { b: 1, a: 1 }, but the isDeepStrictEqual check will now throw an error since it does not consider the order of object keys when comparing objects.

We are just facing this issue after update. We have to compound indexes with same fields, but different order with unique tag. Since the update, mongoose is crashing

[tonynelson19]

I think compound index issues should be fixed with #15112

[mete89]

Named indexes are ignored as well which cause mongoose crashing. Expecting a release with #15112