helper/schema: Remove PromoteSingle from Schema

helper/schema/field_reader_config.go

@@ -82,19 +82,6 @@ func (r *ConfigFieldReader) readField(
 	k := strings.Join(address, ".")
 	schema := schemaList[len(schemaList)-1]
 
-	// If we're getting the single element of a promoted list, then
-	// check to see if we have a single element we need to promote.
-	if address[len(address)-1] == "0" && len(schemaList) > 1 {
-		lastSchema := schemaList[len(schemaList)-2]
-		if lastSchema.Type == TypeList && lastSchema.PromoteSingle {
-			k := strings.Join(address[:len(address)-1], ".")
-			result, err := r.readPrimitive(k, schema)
-			if err == nil {
-				return result, nil
-			}
-		}
-	}
-
 	if protoVersion5 {
 		switch schema.Type {
 		case TypeList, TypeSet, TypeMap, typeObject:
@@ -115,17 +102,6 @@ func (r *ConfigFieldReader) readField(
 	case TypeBool, TypeFloat, TypeInt, TypeString:
 		return r.readPrimitive(k, schema)
 	case TypeList:
-		// If we support promotion then we first check if we have a lone
-		// value that we must promote.
-		// a value that is alone.
-		if schema.PromoteSingle {
-			result, err := r.readPrimitive(k, schema.Elem.(*Schema))
-			if err == nil && result.Exists {
-				result.Value = []interface{}{result.Value}
-				return result, nil
-			}
-		}
-
 		return readListField(&nestedConfigFieldReader{r}, address, schema)
 	case TypeMap:
 		return r.readMap(k, schema)

helper/schema/schema.go

@@ -189,14 +189,6 @@ type Schema struct {
 	MaxItems int
 	MinItems int
 
-	// PromoteSingle originally allowed for a single element to be assigned
-	// where a primitive list was expected, but this no longer works from
-	// Terraform v0.12 onwards (Terraform Core will require a list to be set
-	// regardless of what this is set to) and so only applies to Terraform v0.11
-	// and earlier, and so should be used only to retain this functionality
-	// for those still using v0.11 with a provider that formerly used this.
-	PromoteSingle bool
-
 	// The following fields are only valid for a TypeSet type.
 	//
 	// Set defines a function to determine the unique ID of an item so that
@@ -1497,13 +1489,6 @@ func (m schemaMap) validateList(
 	// case to []interface{} unless the slice is exactly that type.
 	rawV := reflect.ValueOf(raw)
 
-	// If we support promotion and the raw value isn't a slice, wrap
-	// it in []interface{} and check again.
-	if schema.PromoteSingle && rawV.Kind() != reflect.Slice {
-		raw = []interface{}{raw}
-		rawV = reflect.ValueOf(raw)
-	}
-
 	if rawV.Kind() != reflect.Slice {
 		return nil, []error{fmt.Errorf(
 			"%s: should be a list", k)}

helper/schema/schema_test.go

@@ -543,72 +543,6 @@ func TestSchemaMap_Diff(t *testing.T) {
 			Err: false,
 		},
 
-		{
-			Name: "List decode with promotion",
-			Schema: map[string]*Schema{
-				"ports": &Schema{
-					Type:          TypeList,
-					Required:      true,
-					Elem:          &Schema{Type: TypeInt},
-					PromoteSingle: true,
-				},
-			},
-
-			State: nil,
-
-			Config: map[string]interface{}{
-				"ports": "5",
-			},
-
-			Diff: &terraform.InstanceDiff{
-				Attributes: map[string]*terraform.ResourceAttrDiff{
-					"ports.#": &terraform.ResourceAttrDiff{
-						Old: "0",
-						New: "1",
-					},
-					"ports.0": &terraform.ResourceAttrDiff{
-						Old: "",
-						New: "5",
-					},
-				},
-			},
-
-			Err: false,
-		},
-
-		{
-			Name: "List decode with promotion with list",
-			Schema: map[string]*Schema{
-				"ports": &Schema{
-					Type:          TypeList,
-					Required:      true,
-					Elem:          &Schema{Type: TypeInt},
-					PromoteSingle: true,
-				},
-			},
-
-			State: nil,
-
-			Config: map[string]interface{}{
-				"ports": []interface{}{"5"},
-			},
-
-			Diff: &terraform.InstanceDiff{
-				Attributes: map[string]*terraform.ResourceAttrDiff{
-					"ports.#": &terraform.ResourceAttrDiff{
-						Old: "0",
-						New: "1",
-					},
-					"ports.0": &terraform.ResourceAttrDiff{
-						Old: "",
-						New: "5",
-					},
-				},
-			},
-
-			Err: false,
-		},
-
 		{
 			Schema: map[string]*Schema{
 				"ports": &Schema{
@@ -3992,40 +3926,6 @@ func TestSchemaMap_Validate(t *testing.T) {
 			Err: true,
 		},
 
-		"List with promotion": {
-			Schema: map[string]*Schema{
-				"ingress": &Schema{
-					Type:          TypeList,
-					Elem:          &Schema{Type: TypeInt},
-					PromoteSingle: true,
-					Optional:      true,
-				},
-			},
-
-			Config: map[string]interface{}{
-				"ingress": "5",
-			},
-
-			Err: false,
-		},
-
-		"List with promotion set as list": {
-			Schema: map[string]*Schema{
-				"ingress": &Schema{
-					Type:          TypeList,
-					Elem:          &Schema{Type: TypeInt},
-					PromoteSingle: true,
-					Optional:      true,
-				},
-			},
-
-			Config: map[string]interface{}{
-				"ingress": []interface{}{"5"},
-			},
-
-			Err: false,
-		},
-
 		"Optional sub-resource": {
 			Schema: map[string]*Schema{
 				"ingress": &Schema{

helper/schema/shims_test.go

@@ -913,39 +913,6 @@ func TestShimSchemaMap_Diff(t *testing.T) {
 			Err: false,
 		},
 
-		{
-			Name: "List decode with promotion with list",
-			Schema: map[string]*Schema{
-				"ports": &Schema{
-					Type:          TypeList,
-					Required:      true,
-					Elem:          &Schema{Type: TypeInt},
-					PromoteSingle: true,
-				},
-			},
-
-			State: nil,
-
-			Config: map[string]interface{}{
-				"ports": []interface{}{"5"},
-			},
-
-			Diff: &terraform.InstanceDiff{
-				Attributes: map[string]*terraform.ResourceAttrDiff{
-					"ports.#": &terraform.ResourceAttrDiff{
-						Old: "0",
-						New: "1",
-					},
-					"ports.0": &terraform.ResourceAttrDiff{
-						Old: "",
-						New: "5",
-					},
-				},
-			},
-
-			Err: false,
-		},
-
 		{
 			Schema: map[string]*Schema{
 				"ports": &Schema{