Context

It was identified in SERVER-136132 that a BSON validation `ErrorCodes::NonConformantBSON` error was swallowed and the code continued to operate on the `BSONObj`. The assumption seemed to be that BSON that fails validation with `ErrorCodes::NonConformantBSON` would still be structurally valid BSON. That assumption is incorrect.

Proposal

We should consider any of the following:

• BSON validation continues to validate until structurally invalid BSON is detected (aka `ErrorCodes::InvalidBSON` is hit).
  • We can preserve other error codes hit until validation finishes.

• It's more clearly stated that `validateBSON` fails on the first error hit.

Error codes explained

The relevant BSON validate error codes in this ticket:

• InvalidBSON - indicates validation failed due to structurally invalid BSON, buffer is not safe to parse.
• NonConformantBSON - breaks certain BSON rules, but doesn't affect parsing (e.g. duplicate field names)