core: Move StateValueFromInstanceState shim from helper/schema

This one doesn't depend on any helper/schema specific bits and it'll also
be useful for the shims in our mock provider in core.

helper/schema/shims.go

@@ -3,12 +3,11 @@ package schema
 import (
 	"encoding/json"
 
-	"github.com/hashicorp/terraform/config/hcl2shim"
-	"github.com/hashicorp/terraform/configs/configschema"
-	"github.com/hashicorp/terraform/terraform"
 	"github.com/zclconf/go-cty/cty"
-
 	ctyjson "github.com/zclconf/go-cty/cty/json"
+
+	"github.com/hashicorp/terraform/configs/configschema"
+	"github.com/hashicorp/terraform/terraform"
 )
 
 // DiffFromValues takes the current state and desired state as cty.Values and
@@ -79,23 +78,7 @@ func JSONMapToStateValue(m map[string]interface{}, block *configschema.Block) (c
 // cty.Value as described by the provided cty.Type, and maintains the resource
 // ID as the "id" attribute.
 func StateValueFromInstanceState(is *terraform.InstanceState, ty cty.Type) (cty.Value, error) {
-	if is == nil {
-		// if the state is nil, we need to construct a complete cty.Value with
-		// null attributes, rather than a single cty.NullVal(ty)
-		is = &terraform.InstanceState{}
-	}
-
-	// make sure ID is included in the attributes. The InstanceState.ID value
-	// takes precedent.
-	if is.Attributes == nil {
-		is.Attributes = map[string]string{}
-	}
-
-	if is.ID != "" {
-		is.Attributes["id"] = is.ID
-	}
-
-	return hcl2shim.HCL2ValueFromFlatmap(is.Attributes, ty)
+	return is.AttrsAsObjectValue(ty)
 }
 
 // InstanceStateFromStateValue converts a cty.Value to a

terraform/state.go

@@ -1675,6 +1675,35 @@ func NewInstanceStateShimmedFromValue(state cty.Value, schemaVersion int) *Insta
 	}
 }
 
+// AttrsAsObjectValue shims from the legacy InstanceState representation to
+// a new-style cty object value representation of the state attributes, using
+// the given type for guidance.
+//
+// The given type must be the implied type of the schema of the resource type
+// of the object whose state is being converted, or the result is undefined.
+//
+// This is for shimming from old components only and should not be used in
+// new code.
+func (s *InstanceState) AttrsAsObjectValue(ty cty.Type) (cty.Value, error) {
+	if s == nil {
+		// if the state is nil, we need to construct a complete cty.Value with
+		// null attributes, rather than a single cty.NullVal(ty)
+		s = &InstanceState{}
+	}
+
+	if s.Attributes == nil {
+		s.Attributes = map[string]string{}
+	}
+
+	// make sure ID is included in the attributes. The InstanceState.ID value
+	// takes precedence.
+	if s.ID != "" {
+		s.Attributes["id"] = s.ID
+	}
+
+	return hcl2shim.HCL2ValueFromFlatmap(s.Attributes, ty)
+}
+
 // Copy all the Fields from another InstanceState
 func (s *InstanceState) Set(from *InstanceState) {
 	s.Lock()