android/override_module.go - LeafOS-Project/android_build_soong - Gitiles

 // Copyright (C) 2019 The Android Open Source Project
 //
 // 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 android

 // This file contains all the foundation components for override modules and their base module
 // types. Override modules are a kind of opposite of default modules in that they override certain
 // properties of an existing base module whereas default modules provide base module data to be
 // overridden. However, unlike default and defaultable module pairs, both override and overridable
 // modules generate and output build actions, and it is up to product make vars to decide which one
 // to actually build and install in the end. In other words, default modules and defaultable modules
 // can be compared to abstract classes and concrete classes in C++ and Java. By the same analogy,
 // both override and overridable modules act like concrete classes.
 //
 // There is one more crucial difference from the logic perspective. Unlike default pairs, most Soong
 // actions happen in the base (overridable) module by creating a local variant for each override
 // module based on it.

 import (
 	"sort"
 	"sync"

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

 // Interface for override module types, e.g. override_android_app, override_apex
 type OverrideModule interface {
 	Module

 	getOverridingProperties() []interface{}
 	setOverridingProperties(properties []interface{})

 	getOverrideModuleProperties() *OverrideModuleProperties

 	// Internal funcs to handle interoperability between override modules and prebuilts.
 	// i.e. cases where an overriding module, too, is overridden by a prebuilt module.
 	setOverriddenByPrebuilt(overridden bool)
 	getOverriddenByPrebuilt() bool

 	// Directory containing the Blueprint definition of the overriding module
 	setModuleDir(string)
 	ModuleDir() string
 }

 // Base module struct for override module types
 type OverrideModuleBase struct {
 	moduleProperties OverrideModuleProperties

 	overridingProperties []interface{}

 	overriddenByPrebuilt bool

 	moduleDir string
 }

 type OverrideModuleProperties struct {
 	// Name of the base module to be overridden
 	Base *string

 	// TODO(jungjw): Add an optional override_name bool flag.
 }

 func (o *OverrideModuleBase) setModuleDir(d string) {
 	o.moduleDir = d
 }

 func (o *OverrideModuleBase) ModuleDir() string {
 	return o.moduleDir
 }

 func (o *OverrideModuleBase) getOverridingProperties() []interface{} {
 	return o.overridingProperties
 }

 func (o *OverrideModuleBase) setOverridingProperties(properties []interface{}) {
 	o.overridingProperties = properties
 }

 func (o *OverrideModuleBase) getOverrideModuleProperties() *OverrideModuleProperties {
 	return &o.moduleProperties
 }

 func (o *OverrideModuleBase) GetOverriddenModuleName() string {
 	return proptools.String(o.moduleProperties.Base)
 }

 func (o *OverrideModuleBase) setOverriddenByPrebuilt(overridden bool) {
 	o.overriddenByPrebuilt = overridden
 }

 func (o *OverrideModuleBase) getOverriddenByPrebuilt() bool {
 	return o.overriddenByPrebuilt
 }

 func InitOverrideModule(m OverrideModule) {
 	m.setOverridingProperties(m.GetProperties())

 	m.AddProperties(m.getOverrideModuleProperties())
 }

 // Interface for overridable module types, e.g. android_app, apex
 type OverridableModule interface {
 	Module
 	moduleBase() *OverridableModuleBase

 	setOverridableProperties(prop []interface{})

 	addOverride(o OverrideModule)
 	getOverrides() []OverrideModule

 	override(ctx BaseModuleContext, m Module, o OverrideModule)
 	GetOverriddenBy() string
 	GetOverriddenByModuleDir() string

 	setOverridesProperty(overridesProperties *[]string)

 	// Due to complications with incoming dependencies, overrides are processed after DepsMutator.
 	// So, overridable properties need to be handled in a separate, dedicated deps mutator.
 	OverridablePropertiesDepsMutator(ctx BottomUpMutatorContext)
 }

 type overridableModuleProperties struct {
 	OverriddenBy          string `blueprint:"mutated"`
 	OverriddenByModuleDir string `blueprint:"mutated"`
 }

 // Base module struct for overridable module types
 type OverridableModuleBase struct {
 	// List of OverrideModules that override this base module
 	overrides []OverrideModule
 	// Used to parallelize registerOverrideMutator executions. Note that only addOverride locks this
 	// mutex. It is because addOverride and getOverride are used in different mutators, and so are
 	// guaranteed to be not mixed. (And, getOverride only reads from overrides, and so don't require
 	// mutex locking.)
 	overridesLock sync.Mutex

 	overridableProperties []interface{}

 	// If an overridable module has a property to list other modules that itself overrides, it should
 	// set this to a pointer to the property through the InitOverridableModule function, so that
 	// override information is propagated and aggregated correctly.
 	overridesProperty *[]string

 	overridableModuleProperties overridableModuleProperties
 }

 func InitOverridableModule(m OverridableModule, overridesProperty *[]string) {
 	m.setOverridableProperties(m.(Module).GetProperties())
 	m.setOverridesProperty(overridesProperty)
 	m.AddProperties(&m.moduleBase().overridableModuleProperties)
 }

 func (o *OverridableModuleBase) moduleBase() *OverridableModuleBase {
 	return o
 }

 func (b *OverridableModuleBase) setOverridableProperties(prop []interface{}) {
 	b.overridableProperties = prop
 }

 func (b *OverridableModuleBase) addOverride(o OverrideModule) {
 	b.overridesLock.Lock()
 	b.overrides = append(b.overrides, o)
 	b.overridesLock.Unlock()
 }

 // Should NOT be used in the same mutator as addOverride.
 func (b *OverridableModuleBase) getOverrides() []OverrideModule {
 	b.overridesLock.Lock()
 	sort.Slice(b.overrides, func(i, j int) bool {
 		return b.overrides[i].Name() < b.overrides[j].Name()
 	})
 	b.overridesLock.Unlock()
 	return b.overrides
 }

 func (b *OverridableModuleBase) setOverridesProperty(overridesProperty *[]string) {
 	b.overridesProperty = overridesProperty
 }

 // Overrides a base module with the given OverrideModule.
 func (b *OverridableModuleBase) override(ctx BaseModuleContext, m Module, o OverrideModule) {

 	for _, p := range b.overridableProperties {
 		for _, op := range o.getOverridingProperties() {
 			if proptools.TypeEqual(p, op) {
 				err := proptools.ExtendProperties(p, op, nil, proptools.OrderReplace)
 				if err != nil {
 					if propertyErr, ok := err.(*proptools.ExtendPropertyError); ok {
 						ctx.PropertyErrorf(propertyErr.Property, "%s", propertyErr.Err.Error())
 					} else {
 						panic(err)
 					}
 				}
 			}
 		}
 	}
 	// Adds the base module to the overrides property, if exists, of the overriding module. See the
 	// comment on OverridableModuleBase.overridesProperty for details.
 	if b.overridesProperty != nil {
 		*b.overridesProperty = append(*b.overridesProperty, ctx.ModuleName())
 	}
 	b.overridableModuleProperties.OverriddenBy = o.Name()
 	b.overridableModuleProperties.OverriddenByModuleDir = o.ModuleDir()

 	if oBazelable, ok := o.base().module.(Bazelable); ok {
 		if bBazelable, ok := m.(Bazelable); ok {
 			oProps := oBazelable.bazelProps()
 			bProps := bBazelable.bazelProps()
 			bProps.Bazel_module.Bp2build_available = oProps.Bazel_module.Bp2build_available
 			bProps.Bazel_module.Label = oProps.Bazel_module.Label
 		} else {
 			ctx.ModuleErrorf("Override type cannot be Bazelable if original module type is not Bazelable %v %v.", o.Name(), m.Name())
 		}
 	}
 }

 // GetOverriddenBy returns the name of the override module that has overridden this module.
 // For example, if an override module foo has its 'base' property set to bar, then another local variant
 // of bar is created and its properties are overriden by foo. This method returns bar when called from
 // the new local variant. It returns "" when called from the original variant of bar.
 func (b *OverridableModuleBase) GetOverriddenBy() string {
 	return b.overridableModuleProperties.OverriddenBy
 }

 func (b *OverridableModuleBase) GetOverriddenByModuleDir() string {
 	return b.overridableModuleProperties.OverriddenByModuleDir
 }

 func (b *OverridableModuleBase) OverridablePropertiesDepsMutator(ctx BottomUpMutatorContext) {
 }

 // Mutators for override/overridable modules. All the fun happens in these functions. It is critical
 // to keep them in this order and not put any order mutators between them.
 func RegisterOverridePostDepsMutators(ctx RegisterMutatorsContext) {
 	ctx.BottomUp("override_deps", overrideModuleDepsMutator).Parallel()
 	ctx.BottomUp("perform_override", performOverrideMutator).Parallel()
 	// overridableModuleDepsMutator calls OverridablePropertiesDepsMutator so that overridable modules can
 	// add deps from overridable properties.
 	ctx.BottomUp("overridable_deps", overridableModuleDepsMutator).Parallel()
 	// Because overridableModuleDepsMutator is run after PrebuiltPostDepsMutator,
 	// prebuilt's ReplaceDependencies doesn't affect to those deps added by overridable properties.
 	// By running PrebuiltPostDepsMutator again after overridableModuleDepsMutator, deps via overridable properties
 	// can be replaced with prebuilts.
 	ctx.BottomUp("replace_deps_on_prebuilts_for_overridable_deps_again", PrebuiltPostDepsMutator).Parallel()
 	ctx.BottomUp("replace_deps_on_override", replaceDepsOnOverridingModuleMutator).Parallel()
 }

 type overrideBaseDependencyTag struct {
 	blueprint.BaseDependencyTag
 }

 var overrideBaseDepTag overrideBaseDependencyTag

 // Adds dependency on the base module to the overriding module so that they can be visited in the
 // next phase.
 func overrideModuleDepsMutator(ctx BottomUpMutatorContext) {
 	if module, ok := ctx.Module().(OverrideModule); ok {
 		base := String(module.getOverrideModuleProperties().Base)
 		if !ctx.OtherModuleExists(base) {
 			ctx.PropertyErrorf("base", "%q is not a valid module name", base)
 			return
 		}
 		// See if there's a prebuilt module that overrides this override module with prefer flag,
 		// in which case we call HideFromMake on the corresponding variant later.
 		ctx.VisitDirectDepsWithTag(PrebuiltDepTag, func(dep Module) {
 			prebuilt := GetEmbeddedPrebuilt(dep)
 			if prebuilt == nil {
 				panic("PrebuiltDepTag leads to a non-prebuilt module " + dep.Name())
 			}
 			if prebuilt.UsePrebuilt() {
 				module.setOverriddenByPrebuilt(true)
 				return
 			}
 		})
 		baseModule := ctx.AddDependency(ctx.Module(), overrideBaseDepTag, *module.getOverrideModuleProperties().Base)[0]
 		if o, ok := baseModule.(OverridableModule); ok {
 			overrideModule := ctx.Module().(OverrideModule)
 			overrideModule.setModuleDir(ctx.ModuleDir())
 			o.addOverride(overrideModule)
 		}
 	}
 }

 // Now, goes through all overridable modules, finds all modules overriding them, creates a local
 // variant for each of them, and performs the actual overriding operation by calling override().
 func performOverrideMutator(ctx BottomUpMutatorContext) {
 	if b, ok := ctx.Module().(OverridableModule); ok {
 		overrides := b.getOverrides()
 		if len(overrides) == 0 {
 			return
 		}
 		variants := make([]string, len(overrides)+1)
 		// The first variant is for the original, non-overridden, base module.
 		variants[0] = ""
 		for i, o := range overrides {
 			variants[i+1] = o.(Module).Name()
 		}
 		mods := ctx.CreateLocalVariations(variants...)
 		// Make the original variation the default one to depend on if no other override module variant
 		// is specified.
 		ctx.AliasVariation(variants[0])
 		for i, o := range overrides {
 			mods[i+1].(OverridableModule).override(ctx, mods[i+1], o)
 			if o.getOverriddenByPrebuilt() {
 				// The overriding module itself, too, is overridden by a prebuilt.
 				// Copy the flag and hide it in make
 				mods[i+1].ReplacedByPrebuilt()
 			}
 		}
 	} else if o, ok := ctx.Module().(OverrideModule); ok {
 		// Create a variant of the overriding module with its own name. This matches the above local
 		// variant name rule for overridden modules, and thus allows ReplaceDependencies to match the
 		// two.
 		ctx.CreateLocalVariations(o.Name())
 		// To allow dependencies to be added without having to know the above variation.
 		ctx.AliasVariation(o.Name())
 	}
 }

 func overridableModuleDepsMutator(ctx BottomUpMutatorContext) {
 	if b, ok := ctx.Module().(OverridableModule); ok && b.Enabled() {
 		b.OverridablePropertiesDepsMutator(ctx)
 	}
 }

 func replaceDepsOnOverridingModuleMutator(ctx BottomUpMutatorContext) {
 	if b, ok := ctx.Module().(OverridableModule); ok {
 		if o := b.GetOverriddenBy(); o != "" {
 			// Redirect dependencies on the overriding module to this overridden module. Overriding
 			// modules are basically pseudo modules, and all build actions are associated to overridden
 			// modules. Therefore, dependencies on overriding modules need to be forwarded there as well.
 			ctx.ReplaceDependencies(o)
 		}
 	}
 }

 // ModuleNameWithPossibleOverride returns the name of the OverrideModule that overrides the current
 // variant of this OverridableModule, or ctx.ModuleName() if this module is not an OverridableModule
 // or if this variant is not overridden.
 func ModuleNameWithPossibleOverride(ctx BazelConversionContext) string {
 	return moduleNameWithPossibleOverride(ctx, ctx.Module())
 }

 func moduleNameWithPossibleOverride(ctx bazelOtherModuleContext, module blueprint.Module) string {
 	if overridable, ok := module.(OverridableModule); ok {
 		if o := overridable.GetOverriddenBy(); o != "" {
 			return o
 		}
 	}
 	return ctx.OtherModuleName(module)
 }

 // moduleDirWithPossibleOverride returns the dir of the OverrideModule that overrides the current
 // variant of the given OverridableModule, or ctx.OtherModuleName() if the module is not an
 // OverridableModule or if the variant is not overridden.
 func moduleDirWithPossibleOverride(ctx bazelOtherModuleContext, module blueprint.Module) string {
 	if overridable, ok := module.(OverridableModule); ok {
 		if o := overridable.GetOverriddenByModuleDir(); o != "" {
 			return o
 		}
 	}
 	return ctx.OtherModuleDir(module)
 }
	// Copyright (C) 2019 The Android Open Source Project
	//
	// 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 android

	// This file contains all the foundation components for override modules and their base module
	// types. Override modules are a kind of opposite of default modules in that they override certain
	// properties of an existing base module whereas default modules provide base module data to be
	// overridden. However, unlike default and defaultable module pairs, both override and overridable
	// modules generate and output build actions, and it is up to product make vars to decide which one
	// to actually build and install in the end. In other words, default modules and defaultable modules
	// can be compared to abstract classes and concrete classes in C++ and Java. By the same analogy,
	// both override and overridable modules act like concrete classes.
	//
	// There is one more crucial difference from the logic perspective. Unlike default pairs, most Soong
	// actions happen in the base (overridable) module by creating a local variant for each override
	// module based on it.

	import (
	"sort"
	"sync"

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

	// Interface for override module types, e.g. override_android_app, override_apex
	type OverrideModule interface {
	Module

	getOverridingProperties() []interface{}
	setOverridingProperties(properties []interface{})

	getOverrideModuleProperties() *OverrideModuleProperties

	// Internal funcs to handle interoperability between override modules and prebuilts.
	// i.e. cases where an overriding module, too, is overridden by a prebuilt module.
	setOverriddenByPrebuilt(overridden bool)
	getOverriddenByPrebuilt() bool

	// Directory containing the Blueprint definition of the overriding module
	setModuleDir(string)
	ModuleDir() string
	}

	// Base module struct for override module types
	type OverrideModuleBase struct {
	moduleProperties OverrideModuleProperties

	overridingProperties []interface{}

	overriddenByPrebuilt bool

	moduleDir string
	}

	type OverrideModuleProperties struct {
	// Name of the base module to be overridden
	Base *string

	// TODO(jungjw): Add an optional override_name bool flag.
	}

	func (o *OverrideModuleBase) setModuleDir(d string) {
	o.moduleDir = d
	}

	func (o *OverrideModuleBase) ModuleDir() string {
	return o.moduleDir
	}

	func (o *OverrideModuleBase) getOverridingProperties() []interface{} {
	return o.overridingProperties
	}

	func (o *OverrideModuleBase) setOverridingProperties(properties []interface{}) {
	o.overridingProperties = properties
	}

	func (o OverrideModuleBase) getOverrideModuleProperties() OverrideModuleProperties {
	return &o.moduleProperties
	}

	func (o *OverrideModuleBase) GetOverriddenModuleName() string {
	return proptools.String(o.moduleProperties.Base)
	}

	func (o *OverrideModuleBase) setOverriddenByPrebuilt(overridden bool) {
	o.overriddenByPrebuilt = overridden
	}

	func (o *OverrideModuleBase) getOverriddenByPrebuilt() bool {
	return o.overriddenByPrebuilt
	}

	func InitOverrideModule(m OverrideModule) {
	m.setOverridingProperties(m.GetProperties())

	m.AddProperties(m.getOverrideModuleProperties())
	}

	// Interface for overridable module types, e.g. android_app, apex
	type OverridableModule interface {
	Module
	moduleBase() *OverridableModuleBase

	setOverridableProperties(prop []interface{})

	addOverride(o OverrideModule)
	getOverrides() []OverrideModule

	override(ctx BaseModuleContext, m Module, o OverrideModule)
	GetOverriddenBy() string
	GetOverriddenByModuleDir() string

	setOverridesProperty(overridesProperties *[]string)

	// Due to complications with incoming dependencies, overrides are processed after DepsMutator.
	// So, overridable properties need to be handled in a separate, dedicated deps mutator.
	OverridablePropertiesDepsMutator(ctx BottomUpMutatorContext)
	}

	type overridableModuleProperties struct {
	OverriddenBy string `blueprint:"mutated"`
	OverriddenByModuleDir string `blueprint:"mutated"`
	}

	// Base module struct for overridable module types
	type OverridableModuleBase struct {
	// List of OverrideModules that override this base module
	overrides []OverrideModule
	// Used to parallelize registerOverrideMutator executions. Note that only addOverride locks this
	// mutex. It is because addOverride and getOverride are used in different mutators, and so are
	// guaranteed to be not mixed. (And, getOverride only reads from overrides, and so don't require
	// mutex locking.)
	overridesLock sync.Mutex

	overridableProperties []interface{}

	// If an overridable module has a property to list other modules that itself overrides, it should
	// set this to a pointer to the property through the InitOverridableModule function, so that
	// override information is propagated and aggregated correctly.
	overridesProperty *[]string

	overridableModuleProperties overridableModuleProperties
	}

	func InitOverridableModule(m OverridableModule, overridesProperty *[]string) {
	m.setOverridableProperties(m.(Module).GetProperties())
	m.setOverridesProperty(overridesProperty)
	m.AddProperties(&m.moduleBase().overridableModuleProperties)
	}

	func (o OverridableModuleBase) moduleBase() OverridableModuleBase {
	return o
	}

	func (b *OverridableModuleBase) setOverridableProperties(prop []interface{}) {
	b.overridableProperties = prop
	}

	func (b *OverridableModuleBase) addOverride(o OverrideModule) {
	b.overridesLock.Lock()
	b.overrides = append(b.overrides, o)
	b.overridesLock.Unlock()
	}

	// Should NOT be used in the same mutator as addOverride.
	func (b *OverridableModuleBase) getOverrides() []OverrideModule {
	b.overridesLock.Lock()
	sort.Slice(b.overrides, func(i, j int) bool {
	return b.overrides[i].Name() < b.overrides[j].Name()
	})
	b.overridesLock.Unlock()
	return b.overrides
	}

	func (b OverridableModuleBase) setOverridesProperty(overridesProperty []string) {
	b.overridesProperty = overridesProperty
	}

	// Overrides a base module with the given OverrideModule.
	func (b *OverridableModuleBase) override(ctx BaseModuleContext, m Module, o OverrideModule) {

	for _, p := range b.overridableProperties {
	for _, op := range o.getOverridingProperties() {
	if proptools.TypeEqual(p, op) {
	err := proptools.ExtendProperties(p, op, nil, proptools.OrderReplace)
	if err != nil {
	if propertyErr, ok := err.(*proptools.ExtendPropertyError); ok {
	ctx.PropertyErrorf(propertyErr.Property, "%s", propertyErr.Err.Error())
	} else {
	panic(err)
	}
	}
	}
	}
	}
	// Adds the base module to the overrides property, if exists, of the overriding module. See the
	// comment on OverridableModuleBase.overridesProperty for details.
	if b.overridesProperty != nil {
	b.overridesProperty = append(b.overridesProperty, ctx.ModuleName())
	}
	b.overridableModuleProperties.OverriddenBy = o.Name()
	b.overridableModuleProperties.OverriddenByModuleDir = o.ModuleDir()

	if oBazelable, ok := o.base().module.(Bazelable); ok {
	if bBazelable, ok := m.(Bazelable); ok {
	oProps := oBazelable.bazelProps()
	bProps := bBazelable.bazelProps()
	bProps.Bazel_module.Bp2build_available = oProps.Bazel_module.Bp2build_available
	bProps.Bazel_module.Label = oProps.Bazel_module.Label
	} else {
	ctx.ModuleErrorf("Override type cannot be Bazelable if original module type is not Bazelable %v %v.", o.Name(), m.Name())
	}
	}
	}

	// GetOverriddenBy returns the name of the override module that has overridden this module.
	// For example, if an override module foo has its 'base' property set to bar, then another local variant
	// of bar is created and its properties are overriden by foo. This method returns bar when called from
	// the new local variant. It returns "" when called from the original variant of bar.
	func (b *OverridableModuleBase) GetOverriddenBy() string {
	return b.overridableModuleProperties.OverriddenBy
	}

	func (b *OverridableModuleBase) GetOverriddenByModuleDir() string {
	return b.overridableModuleProperties.OverriddenByModuleDir
	}

	func (b *OverridableModuleBase) OverridablePropertiesDepsMutator(ctx BottomUpMutatorContext) {
	}

	// Mutators for override/overridable modules. All the fun happens in these functions. It is critical
	// to keep them in this order and not put any order mutators between them.
	func RegisterOverridePostDepsMutators(ctx RegisterMutatorsContext) {
	ctx.BottomUp("override_deps", overrideModuleDepsMutator).Parallel()
	ctx.BottomUp("perform_override", performOverrideMutator).Parallel()
	// overridableModuleDepsMutator calls OverridablePropertiesDepsMutator so that overridable modules can
	// add deps from overridable properties.
	ctx.BottomUp("overridable_deps", overridableModuleDepsMutator).Parallel()
	// Because overridableModuleDepsMutator is run after PrebuiltPostDepsMutator,
	// prebuilt's ReplaceDependencies doesn't affect to those deps added by overridable properties.
	// By running PrebuiltPostDepsMutator again after overridableModuleDepsMutator, deps via overridable properties
	// can be replaced with prebuilts.
	ctx.BottomUp("replace_deps_on_prebuilts_for_overridable_deps_again", PrebuiltPostDepsMutator).Parallel()
	ctx.BottomUp("replace_deps_on_override", replaceDepsOnOverridingModuleMutator).Parallel()
	}

	type overrideBaseDependencyTag struct {
	blueprint.BaseDependencyTag
	}

	var overrideBaseDepTag overrideBaseDependencyTag

	// Adds dependency on the base module to the overriding module so that they can be visited in the
	// next phase.
	func overrideModuleDepsMutator(ctx BottomUpMutatorContext) {
	if module, ok := ctx.Module().(OverrideModule); ok {
	base := String(module.getOverrideModuleProperties().Base)
	if !ctx.OtherModuleExists(base) {
	ctx.PropertyErrorf("base", "%q is not a valid module name", base)
	return
	}
	// See if there's a prebuilt module that overrides this override module with prefer flag,
	// in which case we call HideFromMake on the corresponding variant later.
	ctx.VisitDirectDepsWithTag(PrebuiltDepTag, func(dep Module) {
	prebuilt := GetEmbeddedPrebuilt(dep)
	if prebuilt == nil {
	panic("PrebuiltDepTag leads to a non-prebuilt module " + dep.Name())
	}
	if prebuilt.UsePrebuilt() {
	module.setOverriddenByPrebuilt(true)
	return
	}
	})
	baseModule := ctx.AddDependency(ctx.Module(), overrideBaseDepTag, *module.getOverrideModuleProperties().Base)[0]
	if o, ok := baseModule.(OverridableModule); ok {
	overrideModule := ctx.Module().(OverrideModule)
	overrideModule.setModuleDir(ctx.ModuleDir())
	o.addOverride(overrideModule)
	}
	}
	}

	// Now, goes through all overridable modules, finds all modules overriding them, creates a local
	// variant for each of them, and performs the actual overriding operation by calling override().
	func performOverrideMutator(ctx BottomUpMutatorContext) {
	if b, ok := ctx.Module().(OverridableModule); ok {
	overrides := b.getOverrides()
	if len(overrides) == 0 {
	return
	}
	variants := make([]string, len(overrides)+1)
	// The first variant is for the original, non-overridden, base module.
	variants[0] = ""
	for i, o := range overrides {
	variants[i+1] = o.(Module).Name()
	}
	mods := ctx.CreateLocalVariations(variants...)
	// Make the original variation the default one to depend on if no other override module variant
	// is specified.
	ctx.AliasVariation(variants[0])
	for i, o := range overrides {
	mods[i+1].(OverridableModule).override(ctx, mods[i+1], o)
	if o.getOverriddenByPrebuilt() {
	// The overriding module itself, too, is overridden by a prebuilt.
	// Copy the flag and hide it in make
	mods[i+1].ReplacedByPrebuilt()
	}
	}
	} else if o, ok := ctx.Module().(OverrideModule); ok {
	// Create a variant of the overriding module with its own name. This matches the above local
	// variant name rule for overridden modules, and thus allows ReplaceDependencies to match the
	// two.
	ctx.CreateLocalVariations(o.Name())
	// To allow dependencies to be added without having to know the above variation.
	ctx.AliasVariation(o.Name())
	}
	}

	func overridableModuleDepsMutator(ctx BottomUpMutatorContext) {
	if b, ok := ctx.Module().(OverridableModule); ok && b.Enabled() {
	b.OverridablePropertiesDepsMutator(ctx)
	}
	}

	func replaceDepsOnOverridingModuleMutator(ctx BottomUpMutatorContext) {
	if b, ok := ctx.Module().(OverridableModule); ok {
	if o := b.GetOverriddenBy(); o != "" {
	// Redirect dependencies on the overriding module to this overridden module. Overriding
	// modules are basically pseudo modules, and all build actions are associated to overridden
	// modules. Therefore, dependencies on overriding modules need to be forwarded there as well.
	ctx.ReplaceDependencies(o)
	}
	}
	}

	// ModuleNameWithPossibleOverride returns the name of the OverrideModule that overrides the current
	// variant of this OverridableModule, or ctx.ModuleName() if this module is not an OverridableModule
	// or if this variant is not overridden.
	func ModuleNameWithPossibleOverride(ctx BazelConversionContext) string {
	return moduleNameWithPossibleOverride(ctx, ctx.Module())
	}

	func moduleNameWithPossibleOverride(ctx bazelOtherModuleContext, module blueprint.Module) string {
	if overridable, ok := module.(OverridableModule); ok {
	if o := overridable.GetOverriddenBy(); o != "" {
	return o
	}
	}
	return ctx.OtherModuleName(module)
	}

	// moduleDirWithPossibleOverride returns the dir of the OverrideModule that overrides the current
	// variant of the given OverridableModule, or ctx.OtherModuleName() if the module is not an
	// OverridableModule or if the variant is not overridden.
	func moduleDirWithPossibleOverride(ctx bazelOtherModuleContext, module blueprint.Module) string {
	if overridable, ok := module.(OverridableModule); ok {
	if o := overridable.GetOverriddenByModuleDir(); o != "" {
	return o
	}
	}
	return ctx.OtherModuleDir(module)
	}