I think it's too late to change now, but just wanted to mention.

Sincetokio_postgres::Errorduplicates itscause in Display:

if let Some(ref cause) = self.0.cause {    write!(fmt, ": {}", cause)?;}

... this means that things likeanyhow::Error (with:#) that walk the cause chain and concatenate the description will duplicate the message, e.g.:

db error: ERROR: syntax error at or near "SELECTa": ERROR: syntax error at or near "SELECTa"

Ideally, it would either

• includecause and only print things relevant to itself in the description, or
• not include cause, and include it in its own description, or
• support both modes likeanyhow::Error (concatenate only in alternate mode).