When modeling BulkWriteCommandResult (PHPC-2494), I was relying on mongoc_bulkwritereturn_t.res being non-null to infer whether the write was acknowledged since there is no other indication on mongoc_bulkwritereturn_t.

However, mongoc_bulkwrite_execute has a condition that destroys mongoc_bulkwritereturn_t.res when (!is_acknowledged || !has_successful_results).

I'm not sure if this is intentional, but I wanted to make a note of it in case it was not. I think most users would expect there to be a result object (even empty) for any acknowledged write, although I'm also not sure if that is explicitly discussed in the bulk write spec.

In the meantime, I will revert to explicitly checking a write concern struct (either the explicit option or whatever is inherited by the client).

How to Reproduce

I observed this when constructing a test for bypassDocumentValidation that failed with a single insert. I used the following create command to define a basic validation rule requiring an "x" field:

{
    "create": "coll",
    "validator": {
        "$jsonSchema": {
            "bsonType": "object",
            "required": ["x"]
        }
    }
}

I then constructed a mongoc_bulkwrite_t with bypassDocumentValidation: true and attempted to insert one invalid document without an "x" field.

The resulting mongoc_bulkwritereturn_t struct has a null res field due to a (!is_acknowledged || !has_successful_results) condition near the bottom of mongoc_bulkwrite_execute.

Note: I attempted to produce a single file derived from example-bulkwrite.c, but attempting to compile that locally through my libmongoc submodule was a bit too time consuming given how trivial I expect this will be for a libmongoc engineer to repro on their own.