ygot related enhancements and fixes (sonic-net#34)

Enhanced the unmarshaling method to update the existing list entries instead of replacing it, and by providing this as one more option in the method.
Optimized the EmitJson method to improve the performance of the Marshaling of object into json data
Fixed the issue in finding the type, if the type is defined as typedf which got included as part of Include statement.
Added the support to synchronize the access of the pathToSchema, ChildSchema, regexp maps
Fixed the issue in MergeStruct method by comparing with src. object and updating the content of the dest. object properly
Added the lint:ignore statment to avoid static check on the methods getNodeName, getObjectFieldName
Fixed the issue to only skip the validation for sonic yang model, since the validation is handled in the CVL.

patches/goyang/goyang.patch

@@ -412,45 +412,54 @@ index 0000000..286a29c
 +}
 +
 diff --git a/pkg/yang/entry.go b/pkg/yang/entry.go
-index ef658d6..cd3b046 100644
+index dfd4525..cdf6eb1 100644
 --- a/pkg/yang/entry.go
 +++ b/pkg/yang/entry.go
-@@ -80,6 +80,7 @@ type Entry struct {
+@@ -29,6 +29,7 @@ import (
+ 	"sort"
+ 	"strconv"
+ 	"strings"
++	"sync"
+
+ 	"github.com/openconfig/goyang/pkg/indent"
+ )
+@@ -80,6 +81,7 @@ type Entry struct {
 
  	// Fields associated with directory nodes
  	Dir map[string]*Entry `json:",omitempty"`
 +	DirOKeys    []string  // Ordered Keys list in Dir
  	Key string            `json:",omitempty"` // Optional key name for lists (i.e., maps)
 
  	// Fields associated with leaf nodes
-@@ -115,6 +116,10 @@ type Entry struct {
+@@ -115,6 +117,11 @@ type Entry struct {
  	// the augmenting entity per RFC6020 Section 7.15.2. The namespace
  	// of the Entry should be accessed using the Namespace function.
  	namespace *Value
 +
 +	ChildSchemaCache map[reflect.StructTag]*Entry `json:"-"`
-+
++	ChildSchemaMutex sync.RWMutex `json:"-"`
++	
 +	IsSchemaValidated bool `json:"-"`
  }
 
  // An RPCEntry contains information related to an RPC Node.
-@@ -264,6 +269,7 @@ func newDirectory(n Node) *Entry {
+@@ -264,6 +271,7 @@ func newDirectory(n Node) *Entry {
  	return &Entry{
  		Kind:  DirectoryEntry,
  		Dir:   make(map[string]*Entry),
 +		DirOKeys: make([]string, 0),
  		Node:  n,
  		Name:  n.NName(),
  		Extra: map[string][]interface{}{},
-@@ -366,6 +372,7 @@ func (e *Entry) add(key string, value *Entry) *Entry {
+@@ -360,6 +368,7 @@ func (e *Entry) add(key string, value *Entry) *Entry {
  		return e
  	}
  	e.Dir[key] = value
 +	e.DirOKeys = append(e.DirOKeys, key)
  	return e
  }
 
-@@ -1007,7 +1014,7 @@ func (e *Entry) ApplyDeviate() []error {
+@@ -999,7 +1008,7 @@ func (e *Entry) ApplyDeviate() []error {
  					}
 
  					if devSpec.Default != "" {
@@ -459,15 +468,15 @@ index ef658d6..cd3b046 100644
  					}
 
  					if devSpec.Mandatory != TSUnset {
-@@ -1090,6 +1097,7 @@ func (e *Entry) FixChoice() {
+@@ -1082,6 +1091,7 @@ func (e *Entry) FixChoice() {
  				}
  				ce.Parent = ne
  				e.Dir[k] = ne
 +				e.DirOKeys = append(e.DirOKeys, k)
  			}
  		}
  	}
-@@ -1260,6 +1268,14 @@ func (e *Entry) shallowDup() *Entry {
+@@ -1252,6 +1262,14 @@ func (e *Entry) shallowDup() *Entry {
  	// copied we will have to explicitly uncopy them.
  	ne := *e
 
@@ -482,7 +491,7 @@ index ef658d6..cd3b046 100644
  	// Now only copy direct children, clear their Dir, and fix up
  	// Parent pointers.
  	if e.Dir != nil {
-@@ -1283,6 +1299,14 @@ func (e *Entry) dup() *Entry {
+@@ -1275,6 +1293,14 @@ func (e *Entry) dup() *Entry {
  	// to do that.
  	ne := *e
 
@@ -497,15 +506,15 @@ index ef658d6..cd3b046 100644
  	// Now recurse down to all of our children, fixing up Parent
  	// pointers as we go.
  	if e.Dir != nil {
-@@ -1317,6 +1341,7 @@ func (e *Entry) merge(prefix *Value, namespace *Value, oe *Entry) {
- 		} else {
+@@ -1310,6 +1336,7 @@ func (e *Entry) merge(prefix *Value, namespace *Value, oe *Entry) {
  			v.Parent = e
+ 			v.Exts = append(v.Exts, oe.Exts...)
  			e.Dir[k] = v
 +			e.DirOKeys = append(e.DirOKeys, k)
  		}
  	}
  }
-@@ -1378,8 +1403,8 @@ func (s sortedErrors) Less(i, j int) bool {
+@@ -1371,8 +1398,8 @@ func (s sortedErrors) Less(i, j int) bool {
  		}
  		return nless(fi[x], fj[x])
  	}
@@ -516,6 +525,33 @@ index ef658d6..cd3b046 100644
  		case -1:
  			return true
  		case 1:
+diff --git a/pkg/yang/types.go b/pkg/yang/types.go
+index 307610a..ffb59a6 100644
+--- a/pkg/yang/types.go
++++ b/pkg/yang/types.go
+@@ -12,6 +12,9 @@
+ // See the License for the specific language governing permissions and
+ // limitations under the License.
+
++// This file is changed by Broadcom.
++// Modifications - Copyright 2019 Broadcom. The term Broadcom refers to Broadcom Inc. and/or its subsidiaries.
++
+ package yang
+
+ // This file implements the functions relating to types and typedefs.
+@@ -69,6 +72,12 @@ func (d *typeDictionary) findExternal(n Node, prefix, name string) (*Typedef, er
+ 	}
+ 	if td := d.find(root, name); td != nil {
+ 		return td, nil
++	} else {
++		for _, in := range root.Include {
++			if td := typeDict.find(in.Module, name); td != nil {
++				return td, nil
++			}
++		}
+ 	}
+ 	if prefix != "" {
+ 		name = prefix + ":" + name
 diff --git a/yang.go b/yang.go
 index 2480a4e..515d1b3 100644
 --- a/yang.go