Add details to the generic BulkWriteCommandException message

[GromNaN]

I'm trying to add more context to the exception. When a BulkWriteCommandException is thrown for individual operation error, the message is not helpful. By mentioning "write concern errors" and "write errors", we give a hint for debugging.

[GromNaN]

@alcaeus I don't know how to debug this error.

src/phongo_execute.c:444:158: error: incomplete definition of type 'mongoc_bulkwriteresult_t' (aka 'struct _mongoc_bulkwriteresult_t')
  444 |                         zend_throw_exception(php_phongo_bulkwritecommandexception_ce, "Bulk write failed with %d write concern errors and %d write errors", error.code, bw_ret.res->n_write_concern_errors, bw_ret.res->n_write_errors);
      |                                                                                                                                                                         ~~~~~~~~~~^

[alcaeus]

This is because of how the mongoc_bulkwriteresult_t is defined. While mongoc_bulkwriteresult_t is defined in the .h file (which we include), it points to a struct that is defined in the .c file. This means that you can access members of a variable in the C file, but not outside of it, for example here as the internal _mongoc_bulkwriteresult_t struct doesn't exist. This makes up for the fact that there are no visibilities for structural members in C, and this way libmongoc limits the scope of its external API.

To access struct fields, libmongoc exposes some functions to extract data from a mongoc_bulkwriteresult_t, but notably it doesn't expose the errorscount field. The n_write_concern_errors and n_write_errors field don't exist in the struct at all.

IMO, we should tell people to check the exception object for error details for the time being; we can then discuss whether the C team can add an API to expose the total number of errors.

[GromNaN]

The BulkWriteCommandException class exposes getWriteErrors and getWriteConcernErrors. It should be possible to count this values to inject this counts in the exception message. Or maybe wrap this exception in PHPLIB to improve the message.