Error handling

A single Load reports every missing or malformed variable at once (joined via errors.Join), not one at a time — so you fix your config in one pass.

if err := oneenv.Load(&cfg); err != nil {
    var pe *oneenv.ParseError
    if errors.As(err, &pe) {
        fmt.Printf("syntax error at %s:%d — %s\n", pe.File, pe.Line, pe.Msg)
    }

    var fe *oneenv.FieldError
    if errors.As(err, &fe) {
        fmt.Printf("field %s (env %q) failed: %v\n", fe.Field, fe.Key, fe.Err)
    }
}

Sentinel errors

Match the cause with errors.Is:

Sentinel	Returned when
ErrNotAStruct	The target isn’t a non-nil pointer to a struct.
ErrRequired	A required field has no value from any source.
ErrEmpty	A notEmpty field is present but empty.
ErrSecretFile	A file field names a path that can’t be read.
ErrUnsupportedType	A field has a type oneenv can’t decode.

Error types

• *ParseError — a syntax error in a source, with File, Line and Msg.
• *FieldError — a decode failure, with the struct Field path (e.g. DB.Port), the env Key, and the underlying Err (Unwrap-able).