| 1 | package culpa |
| 2 | |
| 3 | import "reflect" |
| 4 | |
| 5 | // MergeStrategy defines how duplicate detail types are resolved |
| 6 | // when the same type appears in multiple layers of the error chain. |
| 7 | type MergeStrategy int |
| 8 | |
| 9 | const ( |
| 10 | // MergeOverwrite — outermost (latest) value wins. Default. |
| 11 | MergeOverwrite MergeStrategy = iota |
| 12 | // MergeCombine — values from all layers are collected into a slice. |
| 13 | MergeCombine |
| 14 | ) |
| 15 | |
| 16 | // MergeStrategyProvider is implemented by detail types that declare |
| 17 | // a non-default merge strategy. |
| 18 | type MergeStrategyProvider interface { |
| 19 | MergeStrategy() MergeStrategy |
| 20 | } |
| 21 | |
| 22 | // detailsWrap is an error wrapper that carries attached details. |
| 23 | // It has no message of its own — it is transparent in the message chain. |
| 24 | type detailsWrap struct { |
| 25 | cause error |
| 26 | details []any |
| 27 | } |
| 28 | |
| 29 | // Error delegates to the cause. |
| 30 | func (d *detailsWrap) Error() string { |
| 31 | if d.cause == nil { |
| 32 | return "" |
| 33 | } |
| 34 | return d.cause.Error() |
| 35 | } |
| 36 | |
| 37 | // Unwrap returns the wrapped cause. |
| 38 | func (d *detailsWrap) Unwrap() error { |
| 39 | return d.cause |
| 40 | } |
| 41 | |
| 42 | // WithDetail attaches a single detail to the error. |
| 43 | // Returns nil if err is nil. |
| 44 | func WithDetail(err error, detail any) error { |
| 45 | if err == nil { |
| 46 | return nil |
| 47 | } |
| 48 | return &detailsWrap{cause: err, details: []any{detail}} |
| 49 | } |
| 50 | |
| 51 | // WithDetails attaches multiple details to the error in a single layer. |
| 52 | // Returns nil if err is nil. |
| 53 | func WithDetails(err error, details ...any) error { |
| 54 | if err == nil { |
| 55 | return nil |
| 56 | } |
| 57 | if len(details) == 0 { |
| 58 | return err |
| 59 | } |
| 60 | return &detailsWrap{cause: err, details: details} |
| 61 | } |
| 62 | |
| 63 | // FindDetail finds the first detail of type T in the error tree |
| 64 | // (pre-order, depth-first) and writes it into dst. dst must be a non-nil |
| 65 | // pointer. Returns true if found. |
| 66 | func FindDetail(err error, dst any) bool { |
| 67 | dstVal := reflect.ValueOf(dst) |
| 68 | if dstVal.Kind() != reflect.Pointer || dstVal.IsNil() { |
| 69 | return false |
| 70 | } |
| 71 | target := dstVal.Elem().Type() |
| 72 | |
| 73 | var found bool |
| 74 | walkTree(err, func(e error) bool { |
| 75 | if dw, ok := e.(*detailsWrap); ok { |
| 76 | for _, d := range dw.details { |
| 77 | if reflect.TypeOf(d) == target { |
| 78 | dstVal.Elem().Set(reflect.ValueOf(d)) |
| 79 | found = true |
| 80 | return false |
| 81 | } |
| 82 | } |
| 83 | } |
| 84 | return true |
| 85 | }) |
| 86 | return found |
| 87 | } |
| 88 | |
| 89 | // FindDetails finds all details of type T in the error tree. |
| 90 | func FindDetails[T any](err error) []T { |
| 91 | var result []T |
| 92 | walkTree(err, func(e error) bool { |
| 93 | if dw, ok := e.(*detailsWrap); ok { |
| 94 | for _, d := range dw.details { |
| 95 | if v, ok := d.(T); ok { |
| 96 | result = append(result, v) |
| 97 | } |
| 98 | } |
| 99 | } |
| 100 | return true |
| 101 | }) |
| 102 | return result |
| 103 | } |
| 104 | |
| 105 | // AllDetails returns all details from the error tree as a flat list. |
| 106 | func AllDetails(err error) []any { |
| 107 | var result []any |
| 108 | walkTree(err, func(e error) bool { |
| 109 | if dw, ok := e.(*detailsWrap); ok { |
| 110 | result = append(result, dw.details...) |
| 111 | } |
| 112 | return true |
| 113 | }) |
| 114 | return result |
| 115 | } |
| 116 | |
| 117 | // walkTree performs a pre-order, depth-first traversal of the error tree. |
| 118 | // It handles both single-unwrap (Unwrap() error) and multi-unwrap |
| 119 | // (Unwrap() []error) errors. Stops early if fn returns false. |
| 120 | func walkTree(err error, fn func(error) bool) { |
| 121 | if err == nil { |
| 122 | return |
| 123 | } |
| 124 | stack := []error{err} |
| 125 | for len(stack) > 0 { |
| 126 | e := stack[len(stack)-1] |
| 127 | stack = stack[:len(stack)-1] |
| 128 | if !fn(e) { |
| 129 | return |
| 130 | } |
| 131 | switch u := e.(type) { |
| 132 | case interface{ Unwrap() error }: |
| 133 | if next := u.Unwrap(); next != nil { |
| 134 | stack = append(stack, next) |
| 135 | } |
| 136 | case interface{ Unwrap() []error }: |
| 137 | errs := u.Unwrap() |
| 138 | // Push in reverse order so the first child is visited first. |
| 139 | for i := len(errs) - 1; i >= 0; i-- { |
| 140 | if errs[i] != nil { |
| 141 | stack = append(stack, errs[i]) |
| 142 | } |
| 143 | } |
| 144 | } |
| 145 | } |
| 146 | } |
| 147 | |