According to the doc -- obtained by TMZ -- The Cranberries singer's cause of death is listed as drowning and alcohol intoxication ... and the conclusion is that it was an accident.

As we reported ... the coroner's report revealed Dolores was found dead in a bathtub in her London hotel in January. Toxicology results show she had a blood alcohol level that was four times the legal limit for driving.

Dolores died in January, a day before she was set to record new music with another band. Despite friends of hers telling us she was very depressed at the time -- implying she may have committed suicide -- she sounded upbeat and happy on a voicemail to a friend just hours before she passed.

Suicide was officially ruled out last month by the coroner, who added ... "There's no evidence that this was anything other than an accident."

O'Riordan's funeral was held in her home country of Ireland, where there was a massive service.

Dolores was 46.