Decouple PLS from MGS.

service/datastore/pls_impl.go

Index: service/datastore/pls_impl.go
diff --git a/service/datastore/pls_impl.go b/service/datastore/pls_impl.go
index 535b8d524b1acb868bb3889f1111e45ccf259c11..0900f9106c51f032a5a15a2953e9953262f17d27 100644
--- a/service/datastore/pls_impl.go
+++ b/service/datastore/pls_impl.go
@@ -35,7 +35,6 @@ type structCodec struct {
 	byName   map[string]int
 	byIndex  []structTag
 	hasSlice bool
-	mgs      bool
 	problem  error
 }
 
@@ -44,13 +43,6 @@ type structPLS struct {
 	c *structCodec
 }
 
-func (p *structPLS) getMGS() MetaGetterSetter {
-	if !p.c.mgs {
-		return nil
-	}
-	return p.o.Addr().Interface().(MetaGetterSetter)
-}
-
 var _ PropertyLoadSaver = (*structPLS)(nil)
 
 // typeMismatchReason returns a string explaining why the property p could not
@@ -226,6 +218,9 @@ func (p *structPLS) Save(withMeta bool) (PropertyMap, error) {
 }
 
 func (p *structPLS) getDefaultKind() string {
+	if !p.o.IsValid() {
+		return ""
+	}
 	return p.o.Type().Name()
 }
 
@@ -302,14 +297,6 @@ func (p *structPLS) GetMeta(key string) (interface{}, error) {
 		return p.getMetaFor(idx), nil
 	}
 
-	if p.c.mgs {
-		ret, err := p.getMGS().GetMeta(key)
-		if err == nil {
-			return ret, err
-		} else if err != ErrMetaFieldUnset {
-			return nil, err
-		}
-	}
 	if key == "kind" {
 		return p.getDefaultKind(), nil
 	}
@@ -332,15 +319,8 @@ func (p *structPLS) getMetaFor(idx int) interface{} {
 }
 
 func (p *structPLS) GetAllMeta() PropertyMap {
-	ret := PropertyMap(nil)
 	needKind := true
-	if p.c.mgs {
-		ret = p.getMGS().GetAllMeta()
-		_, haveKind := ret["$kind"]
-		needKind = !haveKind
-	} else {
-		ret = make(PropertyMap, len(p.c.byMeta)+1)
-	}
+	ret := make(PropertyMap, len(p.c.byMeta)+1)
 	for k, idx := range p.c.byMeta {
 		val := p.getMetaFor(idx)
 		p := Property{}
@@ -367,9 +347,6 @@ func (p *structPLS) SetMeta(key string, val interface{}) (err error) {
 	}
 	idx, ok := p.c.byMeta[key]
 	if !ok {
-		if p.c.mgs {
-			return p.getMGS().SetMeta(key, val)
-		}
 		return ErrMetaFieldUnset
 	}
 	if !p.c.byIndex[idx].canSet {
@@ -448,7 +425,6 @@ func getStructCodecLocked(t reflect.Type) (c *structCodec) {
 		byName:  make(map[string]int, t.NumField()),
 		byMeta:  make(map[string]int, t.NumField()),
 		problem: errRecursiveStruct, // we'll clear this later if it's not recursive
-		mgs:     reflect.PtrTo(t).Implements(typeOfMGS),
 	}
 	defer func() {
 		// If the codec has a problem, free up the indexes