android/soongconfig/modules.go - platform/build/soong - Git at Google

 // Copyright 2020 Google Inc. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.

 package soongconfig

 import (
 	"fmt"
 	"io"
 	"reflect"
 	"sort"
 	"strings"

 	"github.com/google/blueprint"
 	"github.com/google/blueprint/parser"
 	"github.com/google/blueprint/proptools"
 )

 var soongConfigProperty = proptools.FieldNameForProperty("soong_config_variables")

 // loadSoongConfigModuleTypeDefinition loads module types from an Android.bp file.  It caches the
 // result so each file is only parsed once.
 func Parse(r io.Reader, from string) (*SoongConfigDefinition, []error) {
 	scope := parser.NewScope(nil)
 	file, errs := parser.ParseAndEval(from, r, scope)

 	if len(errs) > 0 {
 		return nil, errs
 	}

 	mtDef := &SoongConfigDefinition{
 		ModuleTypes: make(map[string]*ModuleType),
 		variables:   make(map[string]soongConfigVariable),
 	}

 	for _, def := range file.Defs {
 		switch def := def.(type) {
 		case *parser.Module:
 			newErrs := processImportModuleDef(mtDef, def)

 			if len(newErrs) > 0 {
 				errs = append(errs, newErrs...)
 			}

 		case *parser.Assignment:
 			// Already handled via Scope object
 		default:
 			panic("unknown definition type")
 		}
 	}

 	if len(errs) > 0 {
 		return nil, errs
 	}

 	for name, moduleType := range mtDef.ModuleTypes {
 		for _, varName := range moduleType.variableNames {
 			if v, ok := mtDef.variables[varName]; ok {
 				moduleType.Variables = append(moduleType.Variables, v)
 			} else {
 				return nil, []error{
 					fmt.Errorf("unknown variable %q in module type %q", varName, name),
 				}
 			}
 		}
 	}

 	return mtDef, nil
 }

 func processImportModuleDef(v *SoongConfigDefinition, def *parser.Module) (errs []error) {
 	switch def.Type {
 	case "soong_config_module_type":
 		return processModuleTypeDef(v, def)
 	case "soong_config_string_variable":
 		return processStringVariableDef(v, def)
 	case "soong_config_bool_variable":
 		return processBoolVariableDef(v, def)
 	default:
 		// Unknown module types will be handled when the file is parsed as a normal
 		// Android.bp file.
 	}

 	return nil
 }

 type ModuleTypeProperties struct {
 	// the name of the new module type.  Unlike most modules, this name does not need to be unique,
 	// although only one module type with any name will be importable into an Android.bp file.
 	Name string

 	// the module type that this module type will extend.
 	Module_type string

 	// the SOONG_CONFIG_NAMESPACE value from a BoardConfig.mk that this module type will read
 	// configuration variables from.
 	Config_namespace string

 	// the list of SOONG_CONFIG variables that this module type will read
 	Variables []string

 	// the list of boolean SOONG_CONFIG variables that this module type will read
 	Bool_variables []string

 	// the list of SOONG_CONFIG variables that this module type will read. The value will be
 	// inserted into the properties with %s substitution.
 	Value_variables []string

 	// the list of properties that this module type will extend.
 	Properties []string
 }

 func processModuleTypeDef(v *SoongConfigDefinition, def *parser.Module) (errs []error) {

 	props := &ModuleTypeProperties{}

 	_, errs = proptools.UnpackProperties(def.Properties, props)
 	if len(errs) > 0 {
 		return errs
 	}

 	if props.Name == "" {
 		errs = append(errs, fmt.Errorf("name property must be set"))
 	}

 	if props.Config_namespace == "" {
 		errs = append(errs, fmt.Errorf("config_namespace property must be set"))
 	}

 	if props.Module_type == "" {
 		errs = append(errs, fmt.Errorf("module_type property must be set"))
 	}

 	if len(errs) > 0 {
 		return errs
 	}

 	mt := &ModuleType{
 		affectableProperties: props.Properties,
 		ConfigNamespace:      props.Config_namespace,
 		BaseModuleType:       props.Module_type,
 		variableNames:        props.Variables,
 	}
 	v.ModuleTypes[props.Name] = mt

 	for _, name := range props.Bool_variables {
 		if name == "" {
 			return []error{fmt.Errorf("bool_variable name must not be blank")}
 		}

 		mt.Variables = append(mt.Variables, &boolVariable{
 			baseVariable: baseVariable{
 				variable: name,
 			},
 		})
 	}

 	for _, name := range props.Value_variables {
 		if name == "" {
 			return []error{fmt.Errorf("value_variables entry must not be blank")}
 		}

 		mt.Variables = append(mt.Variables, &valueVariable{
 			baseVariable: baseVariable{
 				variable: name,
 			},
 		})
 	}

 	return nil
 }

 type VariableProperties struct {
 	Name string
 }

 type StringVariableProperties struct {
 	Values []string
 }

 func processStringVariableDef(v *SoongConfigDefinition, def *parser.Module) (errs []error) {
 	stringProps := &StringVariableProperties{}

 	base, errs := processVariableDef(def, stringProps)
 	if len(errs) > 0 {
 		return errs
 	}

 	if len(stringProps.Values) == 0 {
 		return []error{fmt.Errorf("values property must be set")}
 	}

 	v.variables[base.variable] = &stringVariable{
 		baseVariable: base,
 		values:       CanonicalizeToProperties(stringProps.Values),
 	}

 	return nil
 }

 func processBoolVariableDef(v *SoongConfigDefinition, def *parser.Module) (errs []error) {
 	base, errs := processVariableDef(def)
 	if len(errs) > 0 {
 		return errs
 	}

 	v.variables[base.variable] = &boolVariable{
 		baseVariable: base,
 	}

 	return nil
 }

 func processVariableDef(def *parser.Module,
 	extraProps ...interface{}) (cond baseVariable, errs []error) {

 	props := &VariableProperties{}

 	allProps := append([]interface{}{props}, extraProps...)

 	_, errs = proptools.UnpackProperties(def.Properties, allProps...)
 	if len(errs) > 0 {
 		return baseVariable{}, errs
 	}

 	if props.Name == "" {
 		return baseVariable{}, []error{fmt.Errorf("name property must be set")}
 	}

 	return baseVariable{
 		variable: props.Name,
 	}, nil
 }

 type SoongConfigDefinition struct {
 	ModuleTypes map[string]*ModuleType

 	variables map[string]soongConfigVariable
 }

 // CreateProperties returns a reflect.Value of a newly constructed type that contains the desired
 // property layout for the Soong config variables, with each possible value an interface{} that
 // contains a nil pointer to another newly constructed type that contains the affectable properties.
 // The reflect.Value will be cloned for each call to the Soong config module type's factory method.
 //
 // For example, the acme_cc_defaults example above would
 // produce a reflect.Value whose type is:
 // *struct {
 //     Soong_config_variables struct {
 //         Board struct {
 //             Soc_a interface{}
 //             Soc_b interface{}
 //         }
 //     }
 // }
 // And whose value is:
 // &{
 //     Soong_config_variables: {
 //         Board: {
 //             Soc_a: (*struct{ Cflags []string })(nil),
 //             Soc_b: (*struct{ Cflags []string })(nil),
 //         },
 //     },
 // }
 func CreateProperties(factory blueprint.ModuleFactory, moduleType *ModuleType) reflect.Value {
 	var fields []reflect.StructField

 	_, factoryProps := factory()
 	affectablePropertiesType := createAffectablePropertiesType(moduleType.affectableProperties, factoryProps)
 	if affectablePropertiesType == nil {
 		return reflect.Value{}
 	}

 	for _, c := range moduleType.Variables {
 		fields = append(fields, reflect.StructField{
 			Name: proptools.FieldNameForProperty(c.variableProperty()),
 			Type: c.variableValuesType(),
 		})
 	}

 	typ := reflect.StructOf([]reflect.StructField{{
 		Name: soongConfigProperty,
 		Type: reflect.StructOf(fields),
 	}})

 	props := reflect.New(typ)
 	structConditions := props.Elem().FieldByName(soongConfigProperty)

 	for i, c := range moduleType.Variables {
 		c.initializeProperties(structConditions.Field(i), affectablePropertiesType)
 	}

 	return props
 }

 // createAffectablePropertiesType creates a reflect.Type of a struct that has a field for each affectable property
 // that exists in factoryProps.
 func createAffectablePropertiesType(affectableProperties []string, factoryProps []interface{}) reflect.Type {
 	affectableProperties = append([]string(nil), affectableProperties...)
 	sort.Strings(affectableProperties)

 	var recurse func(prefix string, aps []string) ([]string, reflect.Type)
 	recurse = func(prefix string, aps []string) ([]string, reflect.Type) {
 		var fields []reflect.StructField

 		for len(affectableProperties) > 0 {
 			p := affectableProperties[0]
 			if !strings.HasPrefix(affectableProperties[0], prefix) {
 				break
 			}
 			affectableProperties = affectableProperties[1:]

 			nestedProperty := strings.TrimPrefix(p, prefix)
 			if i := strings.IndexRune(nestedProperty, '.'); i >= 0 {
 				var nestedType reflect.Type
 				nestedPrefix := nestedProperty[:i+1]

 				affectableProperties, nestedType = recurse(prefix+nestedPrefix, affectableProperties)

 				if nestedType != nil {
 					nestedFieldName := proptools.FieldNameForProperty(strings.TrimSuffix(nestedPrefix, "."))

 					fields = append(fields, reflect.StructField{
 						Name: nestedFieldName,
 						Type: nestedType,
 					})
 				}
 			} else {
 				typ := typeForPropertyFromPropertyStructs(factoryProps, p)
 				if typ != nil {
 					fields = append(fields, reflect.StructField{
 						Name: proptools.FieldNameForProperty(nestedProperty),
 						Type: typ,
 					})
 				}
 			}
 		}

 		var typ reflect.Type
 		if len(fields) > 0 {
 			typ = reflect.StructOf(fields)
 		}
 		return affectableProperties, typ
 	}

 	affectableProperties, typ := recurse("", affectableProperties)
 	if len(affectableProperties) > 0 {
 		panic(fmt.Errorf("didn't handle all affectable properties"))
 	}

 	if typ != nil {
 		return reflect.PtrTo(typ)
 	}

 	return nil
 }

 func typeForPropertyFromPropertyStructs(psList []interface{}, property string) reflect.Type {
 	for _, ps := range psList {
 		if typ := typeForPropertyFromPropertyStruct(ps, property); typ != nil {
 			return typ
 		}
 	}

 	return nil
 }

 func typeForPropertyFromPropertyStruct(ps interface{}, property string) reflect.Type {
 	v := reflect.ValueOf(ps)
 	for len(property) > 0 {
 		if !v.IsValid() {
 			return nil
 		}

 		if v.Kind() == reflect.Interface {
 			if v.IsNil() {
 				return nil
 			} else {
 				v = v.Elem()
 			}
 		}

 		if v.Kind() == reflect.Ptr {
 			if v.IsNil() {
 				v = reflect.Zero(v.Type().Elem())
 			} else {
 				v = v.Elem()
 			}
 		}

 		if v.Kind() != reflect.Struct {
 			return nil
 		}

 		if index := strings.IndexRune(property, '.'); index >= 0 {
 			prefix := property[:index]
 			property = property[index+1:]

 			v = v.FieldByName(proptools.FieldNameForProperty(prefix))
 		} else {
 			f := v.FieldByName(proptools.FieldNameForProperty(property))
 			if !f.IsValid() {
 				return nil
 			}
 			return f.Type()
 		}
 	}
 	return nil
 }

 // PropertiesToApply returns the applicable properties from a ModuleType that should be applied
 // based on SoongConfig values.
 func PropertiesToApply(moduleType *ModuleType, props reflect.Value, config SoongConfig) ([]interface{}, error) {
 	var ret []interface{}
 	props = props.Elem().FieldByName(soongConfigProperty)
 	for i, c := range moduleType.Variables {
 		if ps, err := c.PropertiesToApply(config, props.Field(i)); err != nil {
 			return nil, err
 		} else if ps != nil {
 			ret = append(ret, ps)
 		}
 	}
 	return ret, nil
 }

 type ModuleType struct {
 	BaseModuleType  string
 	ConfigNamespace string
 	Variables       []soongConfigVariable

 	affectableProperties []string
 	variableNames        []string
 }

 type soongConfigVariable interface {
 	// variableProperty returns the name of the variable.
 	variableProperty() string

 	// conditionalValuesType returns a reflect.Type that contains an interface{} for each possible value.
 	variableValuesType() reflect.Type

 	// initializeProperties is passed a reflect.Value of the reflect.Type returned by conditionalValuesType and a
 	// reflect.Type of the affectable properties, and should initialize each interface{} in the reflect.Value with
 	// the zero value of the affectable properties type.
 	initializeProperties(v reflect.Value, typ reflect.Type)

 	// PropertiesToApply should return one of the interface{} values set by initializeProperties to be applied
 	// to the module.
 	PropertiesToApply(config SoongConfig, values reflect.Value) (interface{}, error)
 }

 type baseVariable struct {
 	variable string
 }

 func (c *baseVariable) variableProperty() string {
 	return CanonicalizeToProperty(c.variable)
 }

 type stringVariable struct {
 	baseVariable
 	values []string
 }

 func (s *stringVariable) variableValuesType() reflect.Type {
 	var fields []reflect.StructField

 	for _, v := range s.values {
 		fields = append(fields, reflect.StructField{
 			Name: proptools.FieldNameForProperty(v),
 			Type: emptyInterfaceType,
 		})
 	}

 	return reflect.StructOf(fields)
 }

 func (s *stringVariable) initializeProperties(v reflect.Value, typ reflect.Type) {
 	for i := range s.values {
 		v.Field(i).Set(reflect.Zero(typ))
 	}
 }

 func (s *stringVariable) PropertiesToApply(config SoongConfig, values reflect.Value) (interface{}, error) {
 	for j, v := range s.values {
 		if config.String(s.variable) == v {
 			return values.Field(j).Interface(), nil
 		}
 	}

 	return nil, nil
 }

 type boolVariable struct {
 	baseVariable
 }

 func (b boolVariable) variableValuesType() reflect.Type {
 	return emptyInterfaceType
 }

 func (b boolVariable) initializeProperties(v reflect.Value, typ reflect.Type) {
 	v.Set(reflect.Zero(typ))
 }

 func (b boolVariable) PropertiesToApply(config SoongConfig, values reflect.Value) (interface{}, error) {
 	if config.Bool(b.variable) {
 		return values.Interface(), nil
 	}

 	return nil, nil
 }

 type valueVariable struct {
 	baseVariable
 }

 func (s *valueVariable) variableValuesType() reflect.Type {
 	return emptyInterfaceType
 }

 func (s *valueVariable) initializeProperties(v reflect.Value, typ reflect.Type) {
 	v.Set(reflect.Zero(typ))
 }

 func (s *valueVariable) PropertiesToApply(config SoongConfig, values reflect.Value) (interface{}, error) {
 	if !config.IsSet(s.variable) {
 		return nil, nil
 	}
 	configValue := config.String(s.variable)

 	propStruct := values.Elem().Elem()
 	for i := 0; i < propStruct.NumField(); i++ {
 		field := propStruct.Field(i)
 		kind := field.Kind()
 		if kind == reflect.Ptr {
 			if field.IsNil() {
 				continue
 			}
 			field = field.Elem()
 		}
 		switch kind {
 		case reflect.String:
 			err := printfIntoProperty(field, configValue)
 			if err != nil {
 				return nil, fmt.Errorf("soong_config_variables.%s.%s: %s", s.variable, propStruct.Type().Field(i).Name, err)
 			}
 		case reflect.Slice:
 			for j := 0; j < field.Len(); j++ {
 				err := printfIntoProperty(field.Index(j), configValue)
 				if err != nil {
 					return nil, fmt.Errorf("soong_config_variables.%s.%s: %s", s.variable, propStruct.Type().Field(i).Name, err)
 				}
 			}
 		case reflect.Bool:
 			// Nothing to do
 		default:
 			return nil, fmt.Errorf("soong_config_variables.%s.%s: unsupported property type %q", s.variable, propStruct.Type().Field(i).Name, kind)
 		}
 	}

 	return values.Interface(), nil
 }

 func printfIntoProperty(propertyValue reflect.Value, configValue string) error {
 	s := propertyValue.String()

 	count := strings.Count(s, "%")
 	if count == 0 {
 		return nil
 	}

 	if count > 1 {
 		return fmt.Errorf("value variable properties only support a single '%%'")
 	}

 	if !strings.Contains(s, "%s") {
 		return fmt.Errorf("unsupported %% in value variable property")
 	}

 	propertyValue.Set(reflect.ValueOf(fmt.Sprintf(s, configValue)))

 	return nil
 }

 func CanonicalizeToProperty(v string) string {
 	return strings.Map(func(r rune) rune {
 		switch {
 		case r >= 'A' && r <= 'Z',
 			r >= 'a' && r <= 'z',
 			r >= '0' && r <= '9',
 			r == '_':
 			return r
 		default:
 			return '_'
 		}
 	}, v)
 }

 func CanonicalizeToProperties(values []string) []string {
 	ret := make([]string, len(values))
 	for i, v := range values {
 		ret[i] = CanonicalizeToProperty(v)
 	}
 	return ret
 }

 type emptyInterfaceStruct struct {
 	i interface{}
 }

 var emptyInterfaceType = reflect.TypeOf(emptyInterfaceStruct{}).Field(0).Type
	// Copyright 2020 Google Inc. All rights reserved.
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// http://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.

	package soongconfig

	import (
	"fmt"
	"io"
	"reflect"
	"sort"
	"strings"

	"github.com/google/blueprint"
	"github.com/google/blueprint/parser"
	"github.com/google/blueprint/proptools"
	)

	var soongConfigProperty = proptools.FieldNameForProperty("soong_config_variables")

	// loadSoongConfigModuleTypeDefinition loads module types from an Android.bp file. It caches the
	// result so each file is only parsed once.
	func Parse(r io.Reader, from string) (*SoongConfigDefinition, []error) {
	scope := parser.NewScope(nil)
	file, errs := parser.ParseAndEval(from, r, scope)

	if len(errs) > 0 {
	return nil, errs
	}

	mtDef := &SoongConfigDefinition{
	ModuleTypes: make(map[string]*ModuleType),
	variables: make(map[string]soongConfigVariable),
	}

	for _, def := range file.Defs {
	switch def := def.(type) {
	case *parser.Module:
	newErrs := processImportModuleDef(mtDef, def)

	if len(newErrs) > 0 {
	errs = append(errs, newErrs...)
	}

	case *parser.Assignment:
	// Already handled via Scope object
	default:
	panic("unknown definition type")
	}
	}

	if len(errs) > 0 {
	return nil, errs
	}

	for name, moduleType := range mtDef.ModuleTypes {
	for _, varName := range moduleType.variableNames {
	if v, ok := mtDef.variables[varName]; ok {
	moduleType.Variables = append(moduleType.Variables, v)
	} else {
	return nil, []error{
	fmt.Errorf("unknown variable %q in module type %q", varName, name),
	}
	}
	}
	}

	return mtDef, nil
	}

	func processImportModuleDef(v SoongConfigDefinition, def parser.Module) (errs []error) {
	switch def.Type {
	case "soong_config_module_type":
	return processModuleTypeDef(v, def)
	case "soong_config_string_variable":
	return processStringVariableDef(v, def)
	case "soong_config_bool_variable":
	return processBoolVariableDef(v, def)
	default:
	// Unknown module types will be handled when the file is parsed as a normal
	// Android.bp file.
	}

	return nil
	}

	type ModuleTypeProperties struct {
	// the name of the new module type. Unlike most modules, this name does not need to be unique,
	// although only one module type with any name will be importable into an Android.bp file.
	Name string

	// the module type that this module type will extend.
	Module_type string

	// the SOONG_CONFIG_NAMESPACE value from a BoardConfig.mk that this module type will read
	// configuration variables from.
	Config_namespace string

	// the list of SOONG_CONFIG variables that this module type will read
	Variables []string

	// the list of boolean SOONG_CONFIG variables that this module type will read
	Bool_variables []string

	// the list of SOONG_CONFIG variables that this module type will read. The value will be
	// inserted into the properties with %s substitution.
	Value_variables []string

	// the list of properties that this module type will extend.
	Properties []string
	}

	func processModuleTypeDef(v SoongConfigDefinition, def parser.Module) (errs []error) {

	props := &ModuleTypeProperties{}

	_, errs = proptools.UnpackProperties(def.Properties, props)
	if len(errs) > 0 {
	return errs
	}

	if props.Name == "" {
	errs = append(errs, fmt.Errorf("name property must be set"))
	}

	if props.Config_namespace == "" {
	errs = append(errs, fmt.Errorf("config_namespace property must be set"))
	}

	if props.Module_type == "" {
	errs = append(errs, fmt.Errorf("module_type property must be set"))
	}

	if len(errs) > 0 {
	return errs
	}

	mt := &ModuleType{
	affectableProperties: props.Properties,
	ConfigNamespace: props.Config_namespace,
	BaseModuleType: props.Module_type,
	variableNames: props.Variables,
	}
	v.ModuleTypes[props.Name] = mt

	for _, name := range props.Bool_variables {
	if name == "" {
	return []error{fmt.Errorf("bool_variable name must not be blank")}
	}

	mt.Variables = append(mt.Variables, &boolVariable{
	baseVariable: baseVariable{
	variable: name,
	},
	})
	}

	for _, name := range props.Value_variables {
	if name == "" {
	return []error{fmt.Errorf("value_variables entry must not be blank")}
	}

	mt.Variables = append(mt.Variables, &valueVariable{
	baseVariable: baseVariable{
	variable: name,
	},
	})
	}

	return nil
	}

	type VariableProperties struct {
	Name string
	}

	type StringVariableProperties struct {
	Values []string
	}

	func processStringVariableDef(v SoongConfigDefinition, def parser.Module) (errs []error) {
	stringProps := &StringVariableProperties{}

	base, errs := processVariableDef(def, stringProps)
	if len(errs) > 0 {
	return errs
	}

	if len(stringProps.Values) == 0 {
	return []error{fmt.Errorf("values property must be set")}
	}

	v.variables[base.variable] = &stringVariable{
	baseVariable: base,
	values: CanonicalizeToProperties(stringProps.Values),
	}

	return nil
	}

	func processBoolVariableDef(v SoongConfigDefinition, def parser.Module) (errs []error) {
	base, errs := processVariableDef(def)
	if len(errs) > 0 {
	return errs
	}

	v.variables[base.variable] = &boolVariable{
	baseVariable: base,
	}

	return nil
	}

	func processVariableDef(def *parser.Module,
	extraProps ...interface{}) (cond baseVariable, errs []error) {

	props := &VariableProperties{}

	allProps := append([]interface{}{props}, extraProps...)

	_, errs = proptools.UnpackProperties(def.Properties, allProps...)
	if len(errs) > 0 {
	return baseVariable{}, errs
	}

	if props.Name == "" {
	return baseVariable{}, []error{fmt.Errorf("name property must be set")}
	}

	return baseVariable{
	variable: props.Name,
	}, nil
	}

	type SoongConfigDefinition struct {
	ModuleTypes map[string]*ModuleType

	variables map[string]soongConfigVariable
	}

	// CreateProperties returns a reflect.Value of a newly constructed type that contains the desired
	// property layout for the Soong config variables, with each possible value an interface{} that
	// contains a nil pointer to another newly constructed type that contains the affectable properties.
	// The reflect.Value will be cloned for each call to the Soong config module type's factory method.
	//
	// For example, the acme_cc_defaults example above would
	// produce a reflect.Value whose type is:
	// *struct {
	// Soong_config_variables struct {
	// Board struct {
	// Soc_a interface{}
	// Soc_b interface{}
	// }
	// }
	// }
	// And whose value is:
	// &{
	// Soong_config_variables: {
	// Board: {
	// Soc_a: (*struct{ Cflags []string })(nil),
	// Soc_b: (*struct{ Cflags []string })(nil),
	// },
	// },
	// }
	func CreateProperties(factory blueprint.ModuleFactory, moduleType *ModuleType) reflect.Value {
	var fields []reflect.StructField

	_, factoryProps := factory()
	affectablePropertiesType := createAffectablePropertiesType(moduleType.affectableProperties, factoryProps)
	if affectablePropertiesType == nil {
	return reflect.Value{}
	}

	for _, c := range moduleType.Variables {
	fields = append(fields, reflect.StructField{
	Name: proptools.FieldNameForProperty(c.variableProperty()),
	Type: c.variableValuesType(),
	})
	}

	typ := reflect.StructOf([]reflect.StructField{{
	Name: soongConfigProperty,
	Type: reflect.StructOf(fields),
	}})

	props := reflect.New(typ)
	structConditions := props.Elem().FieldByName(soongConfigProperty)

	for i, c := range moduleType.Variables {
	c.initializeProperties(structConditions.Field(i), affectablePropertiesType)
	}

	return props
	}

	// createAffectablePropertiesType creates a reflect.Type of a struct that has a field for each affectable property
	// that exists in factoryProps.
	func createAffectablePropertiesType(affectableProperties []string, factoryProps []interface{}) reflect.Type {
	affectableProperties = append([]string(nil), affectableProperties...)
	sort.Strings(affectableProperties)

	var recurse func(prefix string, aps []string) ([]string, reflect.Type)
	recurse = func(prefix string, aps []string) ([]string, reflect.Type) {
	var fields []reflect.StructField

	for len(affectableProperties) > 0 {
	p := affectableProperties[0]
	if !strings.HasPrefix(affectableProperties[0], prefix) {
	break
	}
	affectableProperties = affectableProperties[1:]

	nestedProperty := strings.TrimPrefix(p, prefix)
	if i := strings.IndexRune(nestedProperty, '.'); i >= 0 {
	var nestedType reflect.Type
	nestedPrefix := nestedProperty[:i+1]

	affectableProperties, nestedType = recurse(prefix+nestedPrefix, affectableProperties)

	if nestedType != nil {
	nestedFieldName := proptools.FieldNameForProperty(strings.TrimSuffix(nestedPrefix, "."))

	fields = append(fields, reflect.StructField{
	Name: nestedFieldName,
	Type: nestedType,
	})
	}
	} else {
	typ := typeForPropertyFromPropertyStructs(factoryProps, p)
	if typ != nil {
	fields = append(fields, reflect.StructField{
	Name: proptools.FieldNameForProperty(nestedProperty),
	Type: typ,
	})
	}
	}
	}

	var typ reflect.Type
	if len(fields) > 0 {
	typ = reflect.StructOf(fields)
	}
	return affectableProperties, typ
	}

	affectableProperties, typ := recurse("", affectableProperties)
	if len(affectableProperties) > 0 {
	panic(fmt.Errorf("didn't handle all affectable properties"))
	}

	if typ != nil {
	return reflect.PtrTo(typ)
	}

	return nil
	}

	func typeForPropertyFromPropertyStructs(psList []interface{}, property string) reflect.Type {
	for _, ps := range psList {
	if typ := typeForPropertyFromPropertyStruct(ps, property); typ != nil {
	return typ
	}
	}

	return nil
	}

	func typeForPropertyFromPropertyStruct(ps interface{}, property string) reflect.Type {
	v := reflect.ValueOf(ps)
	for len(property) > 0 {
	if !v.IsValid() {
	return nil
	}

	if v.Kind() == reflect.Interface {
	if v.IsNil() {
	return nil
	} else {
	v = v.Elem()
	}
	}

	if v.Kind() == reflect.Ptr {
	if v.IsNil() {
	v = reflect.Zero(v.Type().Elem())
	} else {
	v = v.Elem()
	}
	}

	if v.Kind() != reflect.Struct {
	return nil
	}

	if index := strings.IndexRune(property, '.'); index >= 0 {
	prefix := property[:index]
	property = property[index+1:]

	v = v.FieldByName(proptools.FieldNameForProperty(prefix))
	} else {
	f := v.FieldByName(proptools.FieldNameForProperty(property))
	if !f.IsValid() {
	return nil
	}
	return f.Type()
	}
	}
	return nil
	}

	// PropertiesToApply returns the applicable properties from a ModuleType that should be applied
	// based on SoongConfig values.
	func PropertiesToApply(moduleType *ModuleType, props reflect.Value, config SoongConfig) ([]interface{}, error) {
	var ret []interface{}
	props = props.Elem().FieldByName(soongConfigProperty)
	for i, c := range moduleType.Variables {
	if ps, err := c.PropertiesToApply(config, props.Field(i)); err != nil {
	return nil, err
	} else if ps != nil {
	ret = append(ret, ps)
	}
	}
	return ret, nil
	}

	type ModuleType struct {
	BaseModuleType string
	ConfigNamespace string
	Variables []soongConfigVariable

	affectableProperties []string
	variableNames []string
	}

	type soongConfigVariable interface {
	// variableProperty returns the name of the variable.
	variableProperty() string

	// conditionalValuesType returns a reflect.Type that contains an interface{} for each possible value.
	variableValuesType() reflect.Type

	// initializeProperties is passed a reflect.Value of the reflect.Type returned by conditionalValuesType and a
	// reflect.Type of the affectable properties, and should initialize each interface{} in the reflect.Value with
	// the zero value of the affectable properties type.
	initializeProperties(v reflect.Value, typ reflect.Type)

	// PropertiesToApply should return one of the interface{} values set by initializeProperties to be applied
	// to the module.
	PropertiesToApply(config SoongConfig, values reflect.Value) (interface{}, error)
	}

	type baseVariable struct {
	variable string
	}

	func (c *baseVariable) variableProperty() string {
	return CanonicalizeToProperty(c.variable)
	}

	type stringVariable struct {
	baseVariable
	values []string
	}

	func (s *stringVariable) variableValuesType() reflect.Type {
	var fields []reflect.StructField

	for _, v := range s.values {
	fields = append(fields, reflect.StructField{
	Name: proptools.FieldNameForProperty(v),
	Type: emptyInterfaceType,
	})
	}

	return reflect.StructOf(fields)
	}

	func (s *stringVariable) initializeProperties(v reflect.Value, typ reflect.Type) {
	for i := range s.values {
	v.Field(i).Set(reflect.Zero(typ))
	}
	}

	func (s *stringVariable) PropertiesToApply(config SoongConfig, values reflect.Value) (interface{}, error) {
	for j, v := range s.values {
	if config.String(s.variable) == v {
	return values.Field(j).Interface(), nil
	}
	}

	return nil, nil
	}

	type boolVariable struct {
	baseVariable
	}

	func (b boolVariable) variableValuesType() reflect.Type {
	return emptyInterfaceType
	}

	func (b boolVariable) initializeProperties(v reflect.Value, typ reflect.Type) {
	v.Set(reflect.Zero(typ))
	}

	func (b boolVariable) PropertiesToApply(config SoongConfig, values reflect.Value) (interface{}, error) {
	if config.Bool(b.variable) {
	return values.Interface(), nil
	}

	return nil, nil
	}

	type valueVariable struct {
	baseVariable
	}

	func (s *valueVariable) variableValuesType() reflect.Type {
	return emptyInterfaceType
	}

	func (s *valueVariable) initializeProperties(v reflect.Value, typ reflect.Type) {
	v.Set(reflect.Zero(typ))
	}

	func (s *valueVariable) PropertiesToApply(config SoongConfig, values reflect.Value) (interface{}, error) {
	if !config.IsSet(s.variable) {
	return nil, nil
	}
	configValue := config.String(s.variable)

	propStruct := values.Elem().Elem()
	for i := 0; i < propStruct.NumField(); i++ {
	field := propStruct.Field(i)
	kind := field.Kind()
	if kind == reflect.Ptr {
	if field.IsNil() {
	continue
	}
	field = field.Elem()
	}
	switch kind {
	case reflect.String:
	err := printfIntoProperty(field, configValue)
	if err != nil {
	return nil, fmt.Errorf("soong_config_variables.%s.%s: %s", s.variable, propStruct.Type().Field(i).Name, err)
	}
	case reflect.Slice:
	for j := 0; j < field.Len(); j++ {
	err := printfIntoProperty(field.Index(j), configValue)
	if err != nil {
	return nil, fmt.Errorf("soong_config_variables.%s.%s: %s", s.variable, propStruct.Type().Field(i).Name, err)
	}
	}
	case reflect.Bool:
	// Nothing to do
	default:
	return nil, fmt.Errorf("soong_config_variables.%s.%s: unsupported property type %q", s.variable, propStruct.Type().Field(i).Name, kind)
	}
	}

	return values.Interface(), nil
	}

	func printfIntoProperty(propertyValue reflect.Value, configValue string) error {
	s := propertyValue.String()

	count := strings.Count(s, "%")
	if count == 0 {
	return nil
	}

	if count > 1 {
	return fmt.Errorf("value variable properties only support a single '%%'")
	}

	if !strings.Contains(s, "%s") {
	return fmt.Errorf("unsupported %% in value variable property")
	}

	propertyValue.Set(reflect.ValueOf(fmt.Sprintf(s, configValue)))

	return nil
	}

	func CanonicalizeToProperty(v string) string {
	return strings.Map(func(r rune) rune {
	switch {
	case r >= 'A' && r <= 'Z',
	r >= 'a' && r <= 'z',
	r >= '0' && r <= '9',
	r == '_':
	return r
	default:
	return '_'
	}
	}, v)
	}

	func CanonicalizeToProperties(values []string) []string {
	ret := make([]string, len(values))
	for i, v := range values {
	ret[i] = CanonicalizeToProperty(v)
	}
	return ret
	}

	type emptyInterfaceStruct struct {
	i interface{}
	}

	var emptyInterfaceType = reflect.TypeOf(emptyInterfaceStruct{}).Field(0).Type