decode.go raw
1 package yaml
2
3 import (
4 "encoding"
5 "encoding/base64"
6 "fmt"
7 "io"
8 "math"
9 "reflect"
10 "strconv"
11 "time"
12 )
13
14 const (
15 documentNode = 1 << iota
16 mappingNode
17 sequenceNode
18 scalarNode
19 aliasNode
20 )
21
22 type node struct {
23 kind int
24 line, column int
25 tag string
26 // For an alias node, alias holds the resolved alias.
27 alias *node
28 value string
29 implicit bool
30 children []*node
31 anchors map[string]*node
32 }
33
34 // ----------------------------------------------------------------------------
35 // Parser, produces a node tree out of a libyaml event stream.
36
37 type parser struct {
38 parser yaml_parser_t
39 event yaml_event_t
40 doc *node
41 doneInit bool
42 }
43
44 func newParser(b []byte) *parser {
45 p := parser{}
46 if !yaml_parser_initialize(&p.parser) {
47 panic("failed to initialize YAML emitter")
48 }
49 if len(b) == 0 {
50 b = []byte{'\n'}
51 }
52 yaml_parser_set_input_string(&p.parser, b)
53 return &p
54 }
55
56 func newParserFromReader(r io.Reader) *parser {
57 p := parser{}
58 if !yaml_parser_initialize(&p.parser) {
59 panic("failed to initialize YAML emitter")
60 }
61 yaml_parser_set_input_reader(&p.parser, r)
62 return &p
63 }
64
65 func (p *parser) init() {
66 if p.doneInit {
67 return
68 }
69 p.expect(yaml_STREAM_START_EVENT)
70 p.doneInit = true
71 }
72
73 func (p *parser) destroy() {
74 if p.event.typ != yaml_NO_EVENT {
75 yaml_event_delete(&p.event)
76 }
77 yaml_parser_delete(&p.parser)
78 }
79
80 // expect consumes an event from the event stream and
81 // checks that it's of the expected type.
82 func (p *parser) expect(e yaml_event_type_t) {
83 if p.event.typ == yaml_NO_EVENT {
84 if !yaml_parser_parse(&p.parser, &p.event) {
85 p.fail()
86 }
87 }
88 if p.event.typ == yaml_STREAM_END_EVENT {
89 failf("attempted to go past the end of stream; corrupted value?")
90 }
91 if p.event.typ != e {
92 p.parser.problem = fmt.Sprintf("expected %s event but got %s", e, p.event.typ)
93 p.fail()
94 }
95 yaml_event_delete(&p.event)
96 p.event.typ = yaml_NO_EVENT
97 }
98
99 // peek peeks at the next event in the event stream,
100 // puts the results into p.event and returns the event type.
101 func (p *parser) peek() yaml_event_type_t {
102 if p.event.typ != yaml_NO_EVENT {
103 return p.event.typ
104 }
105 if !yaml_parser_parse(&p.parser, &p.event) {
106 p.fail()
107 }
108 return p.event.typ
109 }
110
111 func (p *parser) fail() {
112 var where string
113 var line int
114 if p.parser.problem_mark.line != 0 {
115 line = p.parser.problem_mark.line
116 // Scanner errors don't iterate line before returning error
117 if p.parser.error == yaml_SCANNER_ERROR {
118 line++
119 }
120 } else if p.parser.context_mark.line != 0 {
121 line = p.parser.context_mark.line
122 }
123 if line != 0 {
124 where = "line " + strconv.Itoa(line) + ": "
125 }
126 var msg string
127 if len(p.parser.problem) > 0 {
128 msg = p.parser.problem
129 } else {
130 msg = "unknown problem parsing YAML content"
131 }
132 failf("%s%s", where, msg)
133 }
134
135 func (p *parser) anchor(n *node, anchor []byte) {
136 if anchor != nil {
137 p.doc.anchors[string(anchor)] = n
138 }
139 }
140
141 func (p *parser) parse() *node {
142 p.init()
143 switch p.peek() {
144 case yaml_SCALAR_EVENT:
145 return p.scalar()
146 case yaml_ALIAS_EVENT:
147 return p.alias()
148 case yaml_MAPPING_START_EVENT:
149 return p.mapping()
150 case yaml_SEQUENCE_START_EVENT:
151 return p.sequence()
152 case yaml_DOCUMENT_START_EVENT:
153 return p.document()
154 case yaml_STREAM_END_EVENT:
155 // Happens when attempting to decode an empty buffer.
156 return nil
157 default:
158 panic("attempted to parse unknown event: " + p.event.typ.String())
159 }
160 }
161
162 func (p *parser) node(kind int) *node {
163 return &node{
164 kind: kind,
165 line: p.event.start_mark.line,
166 column: p.event.start_mark.column,
167 }
168 }
169
170 func (p *parser) document() *node {
171 n := p.node(documentNode)
172 n.anchors = make(map[string]*node)
173 p.doc = n
174 p.expect(yaml_DOCUMENT_START_EVENT)
175 n.children = append(n.children, p.parse())
176 p.expect(yaml_DOCUMENT_END_EVENT)
177 return n
178 }
179
180 func (p *parser) alias() *node {
181 n := p.node(aliasNode)
182 n.value = string(p.event.anchor)
183 n.alias = p.doc.anchors[n.value]
184 if n.alias == nil {
185 failf("unknown anchor '%s' referenced", n.value)
186 }
187 p.expect(yaml_ALIAS_EVENT)
188 return n
189 }
190
191 func (p *parser) scalar() *node {
192 n := p.node(scalarNode)
193 n.value = string(p.event.value)
194 n.tag = string(p.event.tag)
195 n.implicit = p.event.implicit
196 p.anchor(n, p.event.anchor)
197 p.expect(yaml_SCALAR_EVENT)
198 return n
199 }
200
201 func (p *parser) sequence() *node {
202 n := p.node(sequenceNode)
203 p.anchor(n, p.event.anchor)
204 p.expect(yaml_SEQUENCE_START_EVENT)
205 for p.peek() != yaml_SEQUENCE_END_EVENT {
206 n.children = append(n.children, p.parse())
207 }
208 p.expect(yaml_SEQUENCE_END_EVENT)
209 return n
210 }
211
212 func (p *parser) mapping() *node {
213 n := p.node(mappingNode)
214 p.anchor(n, p.event.anchor)
215 p.expect(yaml_MAPPING_START_EVENT)
216 for p.peek() != yaml_MAPPING_END_EVENT {
217 n.children = append(n.children, p.parse(), p.parse())
218 }
219 p.expect(yaml_MAPPING_END_EVENT)
220 return n
221 }
222
223 // ----------------------------------------------------------------------------
224 // Decoder, unmarshals a node into a provided value.
225
226 type decoder struct {
227 doc *node
228 aliases map[*node]bool
229 mapType reflect.Type
230 terrors []string
231 strict bool
232
233 decodeCount int
234 aliasCount int
235 aliasDepth int
236 }
237
238 var (
239 mapItemType = reflect.TypeOf(MapItem{})
240 durationType = reflect.TypeOf(time.Duration(0))
241 defaultMapType = reflect.TypeOf(map[interface{}]interface{}{})
242 ifaceType = defaultMapType.Elem()
243 timeType = reflect.TypeOf(time.Time{})
244 ptrTimeType = reflect.TypeOf(&time.Time{})
245 )
246
247 func newDecoder(strict bool) *decoder {
248 d := &decoder{mapType: defaultMapType, strict: strict}
249 d.aliases = make(map[*node]bool)
250 return d
251 }
252
253 func (d *decoder) terror(n *node, tag string, out reflect.Value) {
254 if n.tag != "" {
255 tag = n.tag
256 }
257 value := n.value
258 if tag != yaml_SEQ_TAG && tag != yaml_MAP_TAG {
259 if len(value) > 10 {
260 value = " `" + value[:7] + "...`"
261 } else {
262 value = " `" + value + "`"
263 }
264 }
265 d.terrors = append(d.terrors, fmt.Sprintf("line %d: cannot unmarshal %s%s into %s", n.line+1, shortTag(tag), value, out.Type()))
266 }
267
268 func (d *decoder) callUnmarshaler(n *node, u Unmarshaler) (good bool) {
269 terrlen := len(d.terrors)
270 err := u.UnmarshalYAML(func(v interface{}) (err error) {
271 defer handleErr(&err)
272 d.unmarshal(n, reflect.ValueOf(v))
273 if len(d.terrors) > terrlen {
274 issues := d.terrors[terrlen:]
275 d.terrors = d.terrors[:terrlen]
276 return &TypeError{issues}
277 }
278 return nil
279 })
280 if e, ok := err.(*TypeError); ok {
281 d.terrors = append(d.terrors, e.Errors...)
282 return false
283 }
284 if err != nil {
285 fail(err)
286 }
287 return true
288 }
289
290 // d.prepare initializes and dereferences pointers and calls UnmarshalYAML
291 // if a value is found to implement it.
292 // It returns the initialized and dereferenced out value, whether
293 // unmarshalling was already done by UnmarshalYAML, and if so whether
294 // its types unmarshalled appropriately.
295 //
296 // If n holds a null value, prepare returns before doing anything.
297 func (d *decoder) prepare(n *node, out reflect.Value) (newout reflect.Value, unmarshaled, good bool) {
298 if n.tag == yaml_NULL_TAG || n.kind == scalarNode && n.tag == "" && (n.value == "null" || n.value == "~" || n.value == "" && n.implicit) {
299 return out, false, false
300 }
301 again := true
302 for again {
303 again = false
304 if out.Kind() == reflect.Ptr {
305 if out.IsNil() {
306 out.Set(reflect.New(out.Type().Elem()))
307 }
308 out = out.Elem()
309 again = true
310 }
311 if out.CanAddr() {
312 if u, ok := out.Addr().Interface().(Unmarshaler); ok {
313 good = d.callUnmarshaler(n, u)
314 return out, true, good
315 }
316 }
317 }
318 return out, false, false
319 }
320
321 const (
322 // 400,000 decode operations is ~500kb of dense object declarations, or
323 // ~5kb of dense object declarations with 10000% alias expansion
324 alias_ratio_range_low = 400000
325
326 // 4,000,000 decode operations is ~5MB of dense object declarations, or
327 // ~4.5MB of dense object declarations with 10% alias expansion
328 alias_ratio_range_high = 4000000
329
330 // alias_ratio_range is the range over which we scale allowed alias ratios
331 alias_ratio_range = float64(alias_ratio_range_high - alias_ratio_range_low)
332 )
333
334 func allowedAliasRatio(decodeCount int) float64 {
335 switch {
336 case decodeCount <= alias_ratio_range_low:
337 // allow 99% to come from alias expansion for small-to-medium documents
338 return 0.99
339 case decodeCount >= alias_ratio_range_high:
340 // allow 10% to come from alias expansion for very large documents
341 return 0.10
342 default:
343 // scale smoothly from 99% down to 10% over the range.
344 // this maps to 396,000 - 400,000 allowed alias-driven decodes over the range.
345 // 400,000 decode operations is ~100MB of allocations in worst-case scenarios (single-item maps).
346 return 0.99 - 0.89*(float64(decodeCount-alias_ratio_range_low)/alias_ratio_range)
347 }
348 }
349
350 func (d *decoder) unmarshal(n *node, out reflect.Value) (good bool) {
351 d.decodeCount++
352 if d.aliasDepth > 0 {
353 d.aliasCount++
354 }
355 if d.aliasCount > 100 && d.decodeCount > 1000 && float64(d.aliasCount)/float64(d.decodeCount) > allowedAliasRatio(d.decodeCount) {
356 failf("document contains excessive aliasing")
357 }
358 switch n.kind {
359 case documentNode:
360 return d.document(n, out)
361 case aliasNode:
362 return d.alias(n, out)
363 }
364 out, unmarshaled, good := d.prepare(n, out)
365 if unmarshaled {
366 return good
367 }
368 switch n.kind {
369 case scalarNode:
370 good = d.scalar(n, out)
371 case mappingNode:
372 good = d.mapping(n, out)
373 case sequenceNode:
374 good = d.sequence(n, out)
375 default:
376 panic("internal error: unknown node kind: " + strconv.Itoa(n.kind))
377 }
378 return good
379 }
380
381 func (d *decoder) document(n *node, out reflect.Value) (good bool) {
382 if len(n.children) == 1 {
383 d.doc = n
384 d.unmarshal(n.children[0], out)
385 return true
386 }
387 return false
388 }
389
390 func (d *decoder) alias(n *node, out reflect.Value) (good bool) {
391 if d.aliases[n] {
392 // TODO this could actually be allowed in some circumstances.
393 failf("anchor '%s' value contains itself", n.value)
394 }
395 d.aliases[n] = true
396 d.aliasDepth++
397 good = d.unmarshal(n.alias, out)
398 d.aliasDepth--
399 delete(d.aliases, n)
400 return good
401 }
402
403 var zeroValue reflect.Value
404
405 func resetMap(out reflect.Value) {
406 for _, k := range out.MapKeys() {
407 out.SetMapIndex(k, zeroValue)
408 }
409 }
410
411 func (d *decoder) scalar(n *node, out reflect.Value) bool {
412 var tag string
413 var resolved interface{}
414 if n.tag == "" && !n.implicit {
415 tag = yaml_STR_TAG
416 resolved = n.value
417 } else {
418 tag, resolved = resolve(n.tag, n.value)
419 if tag == yaml_BINARY_TAG {
420 data, err := base64.StdEncoding.DecodeString(resolved.(string))
421 if err != nil {
422 failf("!!binary value contains invalid base64 data")
423 }
424 resolved = string(data)
425 }
426 }
427 if resolved == nil {
428 if out.Kind() == reflect.Map && !out.CanAddr() {
429 resetMap(out)
430 } else {
431 out.Set(reflect.Zero(out.Type()))
432 }
433 return true
434 }
435 if resolvedv := reflect.ValueOf(resolved); out.Type() == resolvedv.Type() {
436 // We've resolved to exactly the type we want, so use that.
437 out.Set(resolvedv)
438 return true
439 }
440 // Perhaps we can use the value as a TextUnmarshaler to
441 // set its value.
442 if out.CanAddr() {
443 u, ok := out.Addr().Interface().(encoding.TextUnmarshaler)
444 if ok {
445 var text []byte
446 if tag == yaml_BINARY_TAG {
447 text = []byte(resolved.(string))
448 } else {
449 // We let any value be unmarshaled into TextUnmarshaler.
450 // That might be more lax than we'd like, but the
451 // TextUnmarshaler itself should bowl out any dubious values.
452 text = []byte(n.value)
453 }
454 err := u.UnmarshalText(text)
455 if err != nil {
456 fail(err)
457 }
458 return true
459 }
460 }
461 switch out.Kind() {
462 case reflect.String:
463 if tag == yaml_BINARY_TAG {
464 out.SetString(resolved.(string))
465 return true
466 }
467 if resolved != nil {
468 out.SetString(n.value)
469 return true
470 }
471 case reflect.Interface:
472 if resolved == nil {
473 out.Set(reflect.Zero(out.Type()))
474 } else if tag == yaml_TIMESTAMP_TAG {
475 // It looks like a timestamp but for backward compatibility
476 // reasons we set it as a string, so that code that unmarshals
477 // timestamp-like values into interface{} will continue to
478 // see a string and not a time.Time.
479 // TODO(v3) Drop this.
480 out.Set(reflect.ValueOf(n.value))
481 } else {
482 out.Set(reflect.ValueOf(resolved))
483 }
484 return true
485 case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
486 switch resolved := resolved.(type) {
487 case int:
488 if !out.OverflowInt(int64(resolved)) {
489 out.SetInt(int64(resolved))
490 return true
491 }
492 case int64:
493 if !out.OverflowInt(resolved) {
494 out.SetInt(resolved)
495 return true
496 }
497 case uint64:
498 if resolved <= math.MaxInt64 && !out.OverflowInt(int64(resolved)) {
499 out.SetInt(int64(resolved))
500 return true
501 }
502 case float64:
503 if resolved <= math.MaxInt64 && !out.OverflowInt(int64(resolved)) {
504 out.SetInt(int64(resolved))
505 return true
506 }
507 case string:
508 if out.Type() == durationType {
509 d, err := time.ParseDuration(resolved)
510 if err == nil {
511 out.SetInt(int64(d))
512 return true
513 }
514 }
515 }
516 case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
517 switch resolved := resolved.(type) {
518 case int:
519 if resolved >= 0 && !out.OverflowUint(uint64(resolved)) {
520 out.SetUint(uint64(resolved))
521 return true
522 }
523 case int64:
524 if resolved >= 0 && !out.OverflowUint(uint64(resolved)) {
525 out.SetUint(uint64(resolved))
526 return true
527 }
528 case uint64:
529 if !out.OverflowUint(uint64(resolved)) {
530 out.SetUint(uint64(resolved))
531 return true
532 }
533 case float64:
534 if resolved <= math.MaxUint64 && !out.OverflowUint(uint64(resolved)) {
535 out.SetUint(uint64(resolved))
536 return true
537 }
538 }
539 case reflect.Bool:
540 switch resolved := resolved.(type) {
541 case bool:
542 out.SetBool(resolved)
543 return true
544 }
545 case reflect.Float32, reflect.Float64:
546 switch resolved := resolved.(type) {
547 case int:
548 out.SetFloat(float64(resolved))
549 return true
550 case int64:
551 out.SetFloat(float64(resolved))
552 return true
553 case uint64:
554 out.SetFloat(float64(resolved))
555 return true
556 case float64:
557 out.SetFloat(resolved)
558 return true
559 }
560 case reflect.Struct:
561 if resolvedv := reflect.ValueOf(resolved); out.Type() == resolvedv.Type() {
562 out.Set(resolvedv)
563 return true
564 }
565 case reflect.Ptr:
566 if out.Type().Elem() == reflect.TypeOf(resolved) {
567 // TODO DOes this make sense? When is out a Ptr except when decoding a nil value?
568 elem := reflect.New(out.Type().Elem())
569 elem.Elem().Set(reflect.ValueOf(resolved))
570 out.Set(elem)
571 return true
572 }
573 }
574 d.terror(n, tag, out)
575 return false
576 }
577
578 func settableValueOf(i interface{}) reflect.Value {
579 v := reflect.ValueOf(i)
580 sv := reflect.New(v.Type()).Elem()
581 sv.Set(v)
582 return sv
583 }
584
585 func (d *decoder) sequence(n *node, out reflect.Value) (good bool) {
586 l := len(n.children)
587
588 var iface reflect.Value
589 switch out.Kind() {
590 case reflect.Slice:
591 out.Set(reflect.MakeSlice(out.Type(), l, l))
592 case reflect.Array:
593 if l != out.Len() {
594 failf("invalid array: want %d elements but got %d", out.Len(), l)
595 }
596 case reflect.Interface:
597 // No type hints. Will have to use a generic sequence.
598 iface = out
599 out = settableValueOf(make([]interface{}, l))
600 default:
601 d.terror(n, yaml_SEQ_TAG, out)
602 return false
603 }
604 et := out.Type().Elem()
605
606 j := 0
607 for i := 0; i < l; i++ {
608 e := reflect.New(et).Elem()
609 if ok := d.unmarshal(n.children[i], e); ok {
610 out.Index(j).Set(e)
611 j++
612 }
613 }
614 if out.Kind() != reflect.Array {
615 out.Set(out.Slice(0, j))
616 }
617 if iface.IsValid() {
618 iface.Set(out)
619 }
620 return true
621 }
622
623 func (d *decoder) mapping(n *node, out reflect.Value) (good bool) {
624 switch out.Kind() {
625 case reflect.Struct:
626 return d.mappingStruct(n, out)
627 case reflect.Slice:
628 return d.mappingSlice(n, out)
629 case reflect.Map:
630 // okay
631 case reflect.Interface:
632 if d.mapType.Kind() == reflect.Map {
633 iface := out
634 out = reflect.MakeMap(d.mapType)
635 iface.Set(out)
636 } else {
637 slicev := reflect.New(d.mapType).Elem()
638 if !d.mappingSlice(n, slicev) {
639 return false
640 }
641 out.Set(slicev)
642 return true
643 }
644 default:
645 d.terror(n, yaml_MAP_TAG, out)
646 return false
647 }
648 outt := out.Type()
649 kt := outt.Key()
650 et := outt.Elem()
651
652 mapType := d.mapType
653 if outt.Key() == ifaceType && outt.Elem() == ifaceType {
654 d.mapType = outt
655 }
656
657 if out.IsNil() {
658 out.Set(reflect.MakeMap(outt))
659 }
660 l := len(n.children)
661 for i := 0; i < l; i += 2 {
662 if isMerge(n.children[i]) {
663 d.merge(n.children[i+1], out)
664 continue
665 }
666 k := reflect.New(kt).Elem()
667 if d.unmarshal(n.children[i], k) {
668 kkind := k.Kind()
669 if kkind == reflect.Interface {
670 kkind = k.Elem().Kind()
671 }
672 if kkind == reflect.Map || kkind == reflect.Slice {
673 failf("invalid map key: %#v", k.Interface())
674 }
675 e := reflect.New(et).Elem()
676 if d.unmarshal(n.children[i+1], e) {
677 d.setMapIndex(n.children[i+1], out, k, e)
678 }
679 }
680 }
681 d.mapType = mapType
682 return true
683 }
684
685 func (d *decoder) setMapIndex(n *node, out, k, v reflect.Value) {
686 if d.strict && out.MapIndex(k) != zeroValue {
687 d.terrors = append(d.terrors, fmt.Sprintf("line %d: key %#v already set in map", n.line+1, k.Interface()))
688 return
689 }
690 out.SetMapIndex(k, v)
691 }
692
693 func (d *decoder) mappingSlice(n *node, out reflect.Value) (good bool) {
694 outt := out.Type()
695 if outt.Elem() != mapItemType {
696 d.terror(n, yaml_MAP_TAG, out)
697 return false
698 }
699
700 mapType := d.mapType
701 d.mapType = outt
702
703 var slice []MapItem
704 var l = len(n.children)
705 for i := 0; i < l; i += 2 {
706 if isMerge(n.children[i]) {
707 d.merge(n.children[i+1], out)
708 continue
709 }
710 item := MapItem{}
711 k := reflect.ValueOf(&item.Key).Elem()
712 if d.unmarshal(n.children[i], k) {
713 v := reflect.ValueOf(&item.Value).Elem()
714 if d.unmarshal(n.children[i+1], v) {
715 slice = append(slice, item)
716 }
717 }
718 }
719 out.Set(reflect.ValueOf(slice))
720 d.mapType = mapType
721 return true
722 }
723
724 func (d *decoder) mappingStruct(n *node, out reflect.Value) (good bool) {
725 sinfo, err := getStructInfo(out.Type())
726 if err != nil {
727 panic(err)
728 }
729 name := settableValueOf("")
730 l := len(n.children)
731
732 var inlineMap reflect.Value
733 var elemType reflect.Type
734 if sinfo.InlineMap != -1 {
735 inlineMap = out.Field(sinfo.InlineMap)
736 inlineMap.Set(reflect.New(inlineMap.Type()).Elem())
737 elemType = inlineMap.Type().Elem()
738 }
739
740 var doneFields []bool
741 if d.strict {
742 doneFields = make([]bool, len(sinfo.FieldsList))
743 }
744 for i := 0; i < l; i += 2 {
745 ni := n.children[i]
746 if isMerge(ni) {
747 d.merge(n.children[i+1], out)
748 continue
749 }
750 if !d.unmarshal(ni, name) {
751 continue
752 }
753 if info, ok := sinfo.FieldsMap[name.String()]; ok {
754 if d.strict {
755 if doneFields[info.Id] {
756 d.terrors = append(d.terrors, fmt.Sprintf("line %d: field %s already set in type %s", ni.line+1, name.String(), out.Type()))
757 continue
758 }
759 doneFields[info.Id] = true
760 }
761 var field reflect.Value
762 if info.Inline == nil {
763 field = out.Field(info.Num)
764 } else {
765 field = out.FieldByIndex(info.Inline)
766 }
767 d.unmarshal(n.children[i+1], field)
768 } else if sinfo.InlineMap != -1 {
769 if inlineMap.IsNil() {
770 inlineMap.Set(reflect.MakeMap(inlineMap.Type()))
771 }
772 value := reflect.New(elemType).Elem()
773 d.unmarshal(n.children[i+1], value)
774 d.setMapIndex(n.children[i+1], inlineMap, name, value)
775 } else if d.strict {
776 d.terrors = append(d.terrors, fmt.Sprintf("line %d: field %s not found in type %s", ni.line+1, name.String(), out.Type()))
777 }
778 }
779 return true
780 }
781
782 func failWantMap() {
783 failf("map merge requires map or sequence of maps as the value")
784 }
785
786 func (d *decoder) merge(n *node, out reflect.Value) {
787 switch n.kind {
788 case mappingNode:
789 d.unmarshal(n, out)
790 case aliasNode:
791 if n.alias != nil && n.alias.kind != mappingNode {
792 failWantMap()
793 }
794 d.unmarshal(n, out)
795 case sequenceNode:
796 // Step backwards as earlier nodes take precedence.
797 for i := len(n.children) - 1; i >= 0; i-- {
798 ni := n.children[i]
799 if ni.kind == aliasNode {
800 if ni.alias != nil && ni.alias.kind != mappingNode {
801 failWantMap()
802 }
803 } else if ni.kind != mappingNode {
804 failWantMap()
805 }
806 d.unmarshal(ni, out)
807 }
808 default:
809 failWantMap()
810 }
811 }
812
813 func isMerge(n *node) bool {
814 return n.kind == scalarNode && n.value == "<<" && (n.implicit == true || n.tag == yaml_MERGE_TAG)
815 }
816