core: Move some of the helper/schema shims so provider mock can use them

The old names are now wrappers around these new functions.

helper/schema/shims.go

@@ -2,9 +2,7 @@ package schema
 
 import (
 	"encoding/json"
-	"fmt"
 
-	"github.com/hashicorp/terraform/config"
 	"github.com/hashicorp/terraform/config/hcl2shim"
 	"github.com/hashicorp/terraform/configs/configschema"
 	"github.com/hashicorp/terraform/terraform"
@@ -40,57 +38,7 @@ func diffFromValues(prior, planned cty.Value, res *Resource, cust CustomizeDiffF
 // the legacy provider Diff method to the state required for the new
 // PlanResourceChange method.
 func ApplyDiff(state cty.Value, d *terraform.InstanceDiff, schemaBlock *configschema.Block) (cty.Value, error) {
-	// No diff means the state is unchanged.
-	if d.Empty() {
-		return state, nil
-	}
-
-	// Create an InstanceState attributes from our existing state.
-	// We can use this to more easily apply the diff changes.
-	attrs := hcl2shim.FlatmapValueFromHCL2(state)
-	if attrs == nil {
-		attrs = map[string]string{}
-	}
-
-	if d.Destroy || d.DestroyDeposed || d.DestroyTainted {
-		// to mark a destroy, we remove all attributes
-		attrs = map[string]string{}
-	} else if attrs["id"] == "" || d.RequiresNew() {
-		// Since "id" is always computed, make sure it always has a value. Set
-		// it as unknown to generate the correct cty.Value
-		attrs["id"] = config.UnknownVariableValue
-	}
-
-	for attr, diff := range d.Attributes {
-		old, exists := attrs[attr]
-
-		if exists &&
-			old != diff.Old &&
-			// if new or old is unknown, then there's no mismatch
-			old != config.UnknownVariableValue &&
-			diff.Old != config.UnknownVariableValue {
-			return state, fmt.Errorf("mismatched diff: %q != %q", old, diff.Old)
-		}
-
-		if diff.NewComputed {
-			attrs[attr] = config.UnknownVariableValue
-			continue
-		}
-
-		if diff.NewRemoved {
-			delete(attrs, attr)
-			continue
-		}
-
-		attrs[attr] = diff.New
-	}
-
-	val, err := hcl2shim.HCL2ValueFromFlatmap(attrs, schemaBlock.ImpliedType())
-	if err != nil {
-		return val, err
-	}
-
-	return schemaBlock.CoerceValue(val)
+	return d.ApplyToValue(state, schemaBlock)
 }
 
 // StateValueToJSONMap converts a cty.Value to generic JSON map via the cty JSON
@@ -155,12 +103,5 @@ func StateValueFromInstanceState(is *terraform.InstanceState, ty cty.Type) (cty.
 // the provider, because the legacy providers used the private Meta data in the
 // InstanceState to store the schema version.
 func InstanceStateFromStateValue(state cty.Value, schemaVersion int) *terraform.InstanceState {
-	attrs := hcl2shim.FlatmapValueFromHCL2(state)
-	return &terraform.InstanceState{
-		ID:         attrs["id"],
-		Attributes: attrs,
-		Meta: map[string]interface{}{
-			"schema_version": schemaVersion,
-		},
-	}
+	return terraform.NewInstanceStateShimmedFromValue(state, schemaVersion)
 }

terraform/diff.go

@@ -11,6 +11,10 @@ import (
 	"sync"
 
 	"github.com/hashicorp/terraform/addrs"
+	"github.com/hashicorp/terraform/config"
+	"github.com/hashicorp/terraform/config/hcl2shim"
+	"github.com/hashicorp/terraform/configs/configschema"
+	"github.com/zclconf/go-cty/cty"
 
 	"github.com/mitchellh/copystructure"
 )
@@ -404,6 +408,66 @@ type InstanceDiff struct {
 func (d *InstanceDiff) Lock()   { d.mu.Lock() }
 func (d *InstanceDiff) Unlock() { d.mu.Unlock() }
 
+// ApplyToValue merges the receiver into the given base value, returning a
+// new value that incorporates the planned changes. The given value must
+// conform to the given schema, or this method will panic.
+//
+// This method is intended for shimming old subsystems that still use this
+// legacy diff type to work with the new-style types.
+func (d *InstanceDiff) ApplyToValue(base cty.Value, schema *configschema.Block) (cty.Value, error) {
+	// No diff means the state is unchanged.
+	if d.Empty() {
+		return base, nil
+	}
+
+	// Create an InstanceState attributes from our existing state.
+	// We can use this to more easily apply the diff changes.
+	attrs := hcl2shim.FlatmapValueFromHCL2(base)
+	if attrs == nil {
+		attrs = map[string]string{}
+	}
+
+	if d.Destroy || d.DestroyDeposed || d.DestroyTainted {
+		// to mark a destroy, we remove all attributes
+		attrs = map[string]string{}
+	} else if attrs["id"] == "" || d.RequiresNew() {
+		// Since "id" is always computed, make sure it always has a value. Set
+		// it as unknown to generate the correct cty.Value
+		attrs["id"] = config.UnknownVariableValue
+	}
+
+	for attr, diff := range d.Attributes {
+		old, exists := attrs[attr]
+
+		if exists &&
+			old != diff.Old &&
+			// if new or old is unknown, then there's no mismatch
+			old != config.UnknownVariableValue &&
+			diff.Old != config.UnknownVariableValue {
+			return base, fmt.Errorf("mismatched diff: %q != %q", old, diff.Old)
+		}
+
+		if diff.NewComputed {
+			attrs[attr] = config.UnknownVariableValue
+			continue
+		}
+
+		if diff.NewRemoved {
+			delete(attrs, attr)
+			continue
+		}
+
+		attrs[attr] = diff.New
+	}
+
+	val, err := hcl2shim.HCL2ValueFromFlatmap(attrs, schema.ImpliedType())
+	if err != nil {
+		return val, err
+	}
+
+	return schema.CoerceValue(val)
+}
+
 // ResourceAttrDiff is the diff of a single attribute of a resource.
 type ResourceAttrDiff struct {
 	Old         string      // Old Value

terraform/state.go

@@ -17,22 +17,23 @@ import (
 	"sync"
 
 	"github.com/hashicorp/errwrap"
-	"github.com/hashicorp/terraform/plans"
-
 	"github.com/hashicorp/go-multierror"
 	"github.com/hashicorp/go-uuid"
 	"github.com/hashicorp/go-version"
 	"github.com/hashicorp/hcl2/hcl"
 	"github.com/hashicorp/hcl2/hcl/hclsyntax"
+	"github.com/mitchellh/copystructure"
+	"github.com/zclconf/go-cty/cty"
+	ctyjson "github.com/zclconf/go-cty/cty/json"
+
 	"github.com/hashicorp/terraform/addrs"
 	"github.com/hashicorp/terraform/config"
+	"github.com/hashicorp/terraform/config/hcl2shim"
 	"github.com/hashicorp/terraform/configs"
 	"github.com/hashicorp/terraform/configs/configschema"
+	"github.com/hashicorp/terraform/plans"
 	"github.com/hashicorp/terraform/tfdiags"
 	tfversion "github.com/hashicorp/terraform/version"
-	"github.com/mitchellh/copystructure"
-	"github.com/zclconf/go-cty/cty"
-	ctyjson "github.com/zclconf/go-cty/cty/json"
 )
 
 const (
@@ -1658,6 +1659,22 @@ func (s *InstanceState) init() {
 	s.Ephemeral.init()
 }
 
+// NewInstanceStateShimmedFromValue is a shim method to lower a new-style
+// object value representing the attributes of an instance object into the
+// legacy InstanceState representation.
+//
+// This is for shimming to old components only and should not be used in new code.
+func NewInstanceStateShimmedFromValue(state cty.Value, schemaVersion int) *InstanceState {
+	attrs := hcl2shim.FlatmapValueFromHCL2(state)
+	return &InstanceState{
+		ID:         attrs["id"],
+		Attributes: attrs,
+		Meta: map[string]interface{}{
+			"schema_version": schemaVersion,
+		},
+	}
+}
+
 // Copy all the Fields from another InstanceState
 func (s *InstanceState) Set(from *InstanceState) {
 	s.Lock()