Struct Failure 

pub struct Failure {
    pub message: String,
    pub offset: Option<u32>,
    pub compiling: bool,
    pub error: Option<DbError>,
}

Why a statement did not produce rows.

Fields

message: String

What went wrong.

offset: Option<u32>

Where in the statement, when the failure knows.

compiling: bool

Whether it failed to compile rather than while running.

error: Option<DbError>

The engine’s own error, kept so a caller can classify it.

The message is not the classification. The command layer has to tell a caller whether a statement was refused because the engine has not built the construct - the driver’s unsupported - or because it was mistyped, and drivers/README.md argues at length for why folding those two together throws the design away. Only the DbError knows: unsupported() is a field on it, and the primary code separates a constraint from a busy file from corruption. Rendering it to a sentence here and matching on the sentence there would be a second, worse classifier beside the driver’s.