validateSync middleware cycle

[AbdelrahmanHafez]

Is this intended or a bug?

schema.pre('validate', () => ++pre);
schema.post('validate', () => ++post);

doc.validateSync(); // pre/post stay 0
await doc.validate(); // pre/post run

doc.validateSync() has a middleware: false option added in #15883 , but there's not validateSync middleware cycle at all right now.
I should either remove the option from the docs/TS, or add a validateSync synchronous middleware akin to init.

Thoughts? @vkarpov15 @hasezoey

[vkarpov15]

What do you think about removing validateSync() altogether?

My original rationale for adding validateSync() was primarily validation against a schema in the browser. The secondary concern was more concise syntax (no callbacks) in cases where that was desirable. Both are less of a concern now - doc.validateSync() vs await doc.validate() isn't a big difference complexity-wise; and since we split off the Mongoose browser library into a separate package in Mongoose 9 the npm download numbers tell us that Mongoose usage in the browser is practically 0.

For now, I think doc.validateSync() not running middleware is intentional. We can remove that middleware option for consistency. But I'm starting to think that we should consider deprecating validateSync() precisely because it adds potential confusion for the validation API. For example, users may wonder whether save() uses validate() or validateSync(); or what other tradeoffs there are between validate() and validateSync().

[AbdelrahmanHafez]

Yeah sounds good. I think the plan would be three-fold:

1. Remove the middleware option for consistency for now.
2. Add deprecation warning and marker to the JSDoc in TS types and whatnot.
3. In 10.0 delete it altogether.

WDYT?