LegacyResourceSchema to remove 0.12 features

This allows us to call CoreConfigSchema and return something that looks
like the original schema.

helper/schema/shims.go

@@ -88,3 +88,46 @@ func JSONMapToStateValue(m map[string]interface{}, block *configschema.Block) (c
 func StateValueFromInstanceState(is *terraform.InstanceState, ty cty.Type) (cty.Value, error) {
 	return is.AttrsAsObjectValue(ty)
 }
+
+// LegacyResourceSchema takes a *Resource and returns a deep copy with 0.12 specific
+// features removed. This is used by the shims to get a configschema that
+// directly matches the structure of the schema.Resource.
+func LegacyResourceSchema(r *Resource) *Resource {
+	if r == nil {
+		return nil
+	}
+	// start with a shallow copy
+	newResource := new(Resource)
+	*newResource = *r
+	newResource.Schema = map[string]*Schema{}
+
+	for k, s := range r.Schema {
+		newResource.Schema[k] = LegacySchema(s)
+	}
+
+	return newResource
+}
+
+// LegacySchema takes a *Schema and returns a deep copy with 0.12 specific
+// features removed. This is used by the shims to get a configschema that
+// directly matches the structure of the schema.Resource.
+func LegacySchema(s *Schema) *Schema {
+	if s == nil {
+		return nil
+	}
+	// start with a shallow copy
+	newSchema := new(Schema)
+	*newSchema = *s
+	newSchema.ConfigMode = SchemaConfigModeAuto
+	newSchema.PromoteSingle = false
+	newSchema.SkipCoreTypeCheck = false
+
+	switch e := newSchema.Elem.(type) {
+	case *Schema:
+		newSchema.Elem = LegacySchema(e)
+	case *Resource:
+		newSchema.Elem = LegacyResourceSchema(e)
+	}
+
+	return newSchema
+}