Merge changes from topic "elide_empty_variants" into main

* changes: Convert sdk mutator to TransitionMutator Convert link mutator to TransitionMutator Convert version mutator to TransitionMutator Convert python_version mutator to TransitionMutator Convert rust_libraries and rust_stdlinkage mutators to TransitionMutators
2024-07-18 17:37:38 +00:00
parent e9871abe44 ac57a6c6df
commit ea1b3b78b8
15 changed files with 543 additions and 359 deletions
--- a/androidmk/parser/parser_test.go
+++ b/androidmk/parser/parser_test.go
@@ -86,20 +86,19 @@ endif`,
 	},
 	{
 		name: "Blank line in rule's command",
-		in:   `all:
+		in: `all:
 	echo first line

 	echo second line`,
 		out: []Node{
 			&Rule{
-				Target: SimpleMakeString("all", NoPos),
-				RecipePos: NoPos,
-				Recipe: "echo first line\necho second line",
+				Target:        SimpleMakeString("all", NoPos),
+				RecipePos:     NoPos,
+				Recipe:        "echo first line\necho second line",
 				Prerequisites: SimpleMakeString("", NoPos),
 			},
 		},
 	},
-
 }

 func TestParse(t *testing.T) {
--- a/apex/apex.go
+++ b/apex/apex.go
@@ -703,7 +703,6 @@ func addDependenciesForNativeModules(ctx android.BottomUpMutatorContext, nativeM
 	rustLibVariations := append(
 		target.Variations(), []blueprint.Variation{
 			{Mutator: "rust_libraries", Variation: "dylib"},
-			{Mutator: "link", Variation: ""},
 		}...,
 	)

--- a/cc/cc.go
+++ b/cc/cc.go
@@ -48,10 +48,10 @@ func RegisterCCBuildComponents(ctx android.RegistrationContext) {
 	ctx.RegisterModuleType("cc_defaults", defaultsFactory)

 	ctx.PreDepsMutators(func(ctx android.RegisterMutatorsContext) {
-		ctx.BottomUp("sdk", sdkMutator).Parallel()
+		ctx.Transition("sdk", &sdkTransitionMutator{})
 		ctx.BottomUp("llndk", llndkMutator).Parallel()
-		ctx.BottomUp("link", LinkageMutator).Parallel()
-		ctx.BottomUp("version", versionMutator).Parallel()
+		ctx.Transition("link", &linkageTransitionMutator{})
+		ctx.Transition("version", &versionTransitionMutator{})
 		ctx.BottomUp("begin", BeginMutator).Parallel()
 	})

--- a/cc/library.go
+++ b/cc/library.go
@@ -19,6 +19,7 @@ import (
 	"io"
 	"path/filepath"
 	"regexp"
+	"slices"
 	"strconv"
 	"strings"
 	"sync"
@@ -711,7 +712,7 @@ type versionedInterface interface {
 	setStubsVersion(string)
 	stubsVersion() string

-	stubsVersions(ctx android.BaseMutatorContext) []string
+	stubsVersions(ctx android.BaseModuleContext) []string
 	setAllStubsVersions([]string)
 	allStubsVersions() []string

@@ -1903,7 +1904,7 @@ func (library *libraryDecorator) isStubsImplementationRequired() bool {
 	return BoolDefault(library.Properties.Stubs.Implementation_installable, true)
 }

-func (library *libraryDecorator) stubsVersions(ctx android.BaseMutatorContext) []string {
+func (library *libraryDecorator) stubsVersions(ctx android.BaseModuleContext) []string {
 	if !library.hasStubsVariants() {
 		return nil
 	}
@@ -2064,26 +2065,26 @@ func NewLibrary(hod android.HostOrDeviceSupported) (*Module, *libraryDecorator)

 // connects a shared library to a static library in order to reuse its .o files to avoid
 // compiling source files twice.
-func reuseStaticLibrary(mctx android.BottomUpMutatorContext, static, shared *Module) {
-	if staticCompiler, ok := static.compiler.(*libraryDecorator); ok {
-		sharedCompiler := shared.compiler.(*libraryDecorator)
+func reuseStaticLibrary(ctx android.BottomUpMutatorContext, shared *Module) {
+	if sharedCompiler, ok := shared.compiler.(*libraryDecorator); ok {

 		// Check libraries in addition to cflags, since libraries may be exporting different
 		// include directories.
-		if len(staticCompiler.StaticProperties.Static.Cflags.GetOrDefault(mctx, nil)) == 0 &&
-			len(sharedCompiler.SharedProperties.Shared.Cflags.GetOrDefault(mctx, nil)) == 0 &&
-			len(staticCompiler.StaticProperties.Static.Whole_static_libs) == 0 &&
+		if len(sharedCompiler.StaticProperties.Static.Cflags.GetOrDefault(ctx, nil)) == 0 &&
+			len(sharedCompiler.SharedProperties.Shared.Cflags.GetOrDefault(ctx, nil)) == 0 &&
+			len(sharedCompiler.StaticProperties.Static.Whole_static_libs) == 0 &&
 			len(sharedCompiler.SharedProperties.Shared.Whole_static_libs) == 0 &&
-			len(staticCompiler.StaticProperties.Static.Static_libs) == 0 &&
+			len(sharedCompiler.StaticProperties.Static.Static_libs) == 0 &&
 			len(sharedCompiler.SharedProperties.Shared.Static_libs) == 0 &&
-			len(staticCompiler.StaticProperties.Static.Shared_libs) == 0 &&
+			len(sharedCompiler.StaticProperties.Static.Shared_libs) == 0 &&
 			len(sharedCompiler.SharedProperties.Shared.Shared_libs) == 0 &&
 			// Compare System_shared_libs properties with nil because empty lists are
 			// semantically significant for them.
-			staticCompiler.StaticProperties.Static.System_shared_libs == nil &&
+			sharedCompiler.StaticProperties.Static.System_shared_libs == nil &&
 			sharedCompiler.SharedProperties.Shared.System_shared_libs == nil {

-			mctx.AddInterVariantDependency(reuseObjTag, shared, static)
+			// TODO: namespaces?
+			ctx.AddVariationDependencies([]blueprint.Variation{{"link", "static"}}, reuseObjTag, ctx.ModuleName())
 			sharedCompiler.baseCompiler.Properties.OriginalSrcs =
 				sharedCompiler.baseCompiler.Properties.Srcs
 			sharedCompiler.baseCompiler.Properties.Srcs = nil
@@ -2091,19 +2092,21 @@ func reuseStaticLibrary(mctx android.BottomUpMutatorContext, static, shared *Mod
 		}

 		// This dep is just to reference static variant from shared variant
-		mctx.AddInterVariantDependency(staticVariantTag, shared, static)
+		ctx.AddVariationDependencies([]blueprint.Variation{{"link", "static"}}, staticVariantTag, ctx.ModuleName())
 	}
 }

-// LinkageMutator adds "static" or "shared" variants for modules depending
+// linkageTransitionMutator adds "static" or "shared" variants for modules depending
 // on whether the module can be built as a static library or a shared library.
-func LinkageMutator(mctx android.BottomUpMutatorContext) {
+type linkageTransitionMutator struct{}
+
+func (linkageTransitionMutator) Split(ctx android.BaseModuleContext) []string {
 	ccPrebuilt := false
-	if m, ok := mctx.Module().(*Module); ok && m.linker != nil {
+	if m, ok := ctx.Module().(*Module); ok && m.linker != nil {
 		_, ccPrebuilt = m.linker.(prebuiltLibraryInterface)
 	}
 	if ccPrebuilt {
-		library := mctx.Module().(*Module).linker.(prebuiltLibraryInterface)
+		library := ctx.Module().(*Module).linker.(prebuiltLibraryInterface)

 		// Differentiate between header only and building an actual static/shared library
 		buildStatic := library.buildStatic()
@@ -2112,75 +2115,118 @@ func LinkageMutator(mctx android.BottomUpMutatorContext) {
 			// Always create both the static and shared variants for prebuilt libraries, and then disable the one
 			// that is not being used.  This allows them to share the name of a cc_library module, which requires that
 			// all the variants of the cc_library also exist on the prebuilt.
-			modules := mctx.CreateLocalVariations("static", "shared")
-			static := modules[0].(*Module)
-			shared := modules[1].(*Module)
-
-			static.linker.(prebuiltLibraryInterface).setStatic()
-			shared.linker.(prebuiltLibraryInterface).setShared()
-
-			if buildShared {
-				mctx.AliasVariation("shared")
-			} else if buildStatic {
-				mctx.AliasVariation("static")
-			}
-
-			if !buildStatic {
-				static.linker.(prebuiltLibraryInterface).disablePrebuilt()
-			}
-			if !buildShared {
-				shared.linker.(prebuiltLibraryInterface).disablePrebuilt()
-			}
+			return []string{"static", "shared"}
 		} else {
 			// Header only
 		}
-
-	} else if library, ok := mctx.Module().(LinkableInterface); ok && (library.CcLibraryInterface() || library.RustLibraryInterface()) {
+	} else if library, ok := ctx.Module().(LinkableInterface); ok && (library.CcLibraryInterface() || library.RustLibraryInterface()) {
 		// Non-cc.Modules may need an empty variant for their mutators.
 		variations := []string{}
 		if library.NonCcVariants() {
 			variations = append(variations, "")
 		}
 		isLLNDK := false
-		if m, ok := mctx.Module().(*Module); ok {
+		if m, ok := ctx.Module().(*Module); ok {
 			isLLNDK = m.IsLlndk()
 		}
 		buildStatic := library.BuildStaticVariant() && !isLLNDK
 		buildShared := library.BuildSharedVariant()
 		if buildStatic && buildShared {
-			variations := append([]string{"static", "shared"}, variations...)
-
-			modules := mctx.CreateLocalVariations(variations...)
-			static := modules[0].(LinkableInterface)
-			shared := modules[1].(LinkableInterface)
-			static.SetStatic()
-			shared.SetShared()
-
-			if _, ok := library.(*Module); ok {
-				reuseStaticLibrary(mctx, static.(*Module), shared.(*Module))
-			}
-			mctx.AliasVariation("shared")
+			variations = append([]string{"static", "shared"}, variations...)
+			return variations
 		} else if buildStatic {
-			variations := append([]string{"static"}, variations...)
-
-			modules := mctx.CreateLocalVariations(variations...)
-			modules[0].(LinkableInterface).SetStatic()
-			mctx.AliasVariation("static")
+			variations = append([]string{"static"}, variations...)
 		} else if buildShared {
-			variations := append([]string{"shared"}, variations...)
-
-			modules := mctx.CreateLocalVariations(variations...)
-			modules[0].(LinkableInterface).SetShared()
-			mctx.AliasVariation("shared")
-		} else if len(variations) > 0 {
-			mctx.CreateLocalVariations(variations...)
-			mctx.AliasVariation(variations[0])
+			variations = append([]string{"shared"}, variations...)
 		}
-		if library.BuildRlibVariant() && library.IsRustFFI() && !buildStatic {
+
+		if len(variations) > 0 {
+			return variations
+		}
+	}
+	return []string{""}
+}
+
+func (linkageTransitionMutator) OutgoingTransition(ctx android.OutgoingTransitionContext, sourceVariation string) string {
+	return ""
+}
+
+func (linkageTransitionMutator) IncomingTransition(ctx android.IncomingTransitionContext, incomingVariation string) string {
+	ccPrebuilt := false
+	if m, ok := ctx.Module().(*Module); ok && m.linker != nil {
+		_, ccPrebuilt = m.linker.(prebuiltLibraryInterface)
+	}
+	if ccPrebuilt {
+		if incomingVariation != "" {
+			return incomingVariation
+		}
+		library := ctx.Module().(*Module).linker.(prebuiltLibraryInterface)
+		if library.buildShared() {
+			return "shared"
+		} else if library.buildStatic() {
+			return "static"
+		}
+		return ""
+	} else if library, ok := ctx.Module().(LinkableInterface); ok && library.CcLibraryInterface() {
+		isLLNDK := false
+		if m, ok := ctx.Module().(*Module); ok {
+			isLLNDK = m.IsLlndk()
+		}
+		buildStatic := library.BuildStaticVariant() && !isLLNDK
+		buildShared := library.BuildSharedVariant()
+		if library.BuildRlibVariant() && library.IsRustFFI() && !buildStatic && (incomingVariation == "static" || incomingVariation == "") {
 			// Rust modules do not build static libs, but rlibs are used as if they
 			// were via `static_libs`. Thus we need to alias the BuildRlibVariant
 			// to "static" for Rust FFI libraries.
-			mctx.CreateAliasVariation("static", "")
+			return ""
+		}
+		if incomingVariation != "" {
+			return incomingVariation
+		}
+		if buildShared {
+			return "shared"
+		} else if buildStatic {
+			return "static"
+		}
+		return ""
+	}
+	return ""
+}
+
+func (linkageTransitionMutator) Mutate(ctx android.BottomUpMutatorContext, variation string) {
+	ccPrebuilt := false
+	if m, ok := ctx.Module().(*Module); ok && m.linker != nil {
+		_, ccPrebuilt = m.linker.(prebuiltLibraryInterface)
+	}
+	if ccPrebuilt {
+		library := ctx.Module().(*Module).linker.(prebuiltLibraryInterface)
+		if variation == "static" {
+			library.setStatic()
+			if !library.buildStatic() {
+				library.disablePrebuilt()
+			}
+		} else if variation == "shared" {
+			library.setShared()
+			if !library.buildShared() {
+				library.disablePrebuilt()
+			}
+		}
+	} else if library, ok := ctx.Module().(LinkableInterface); ok && library.CcLibraryInterface() {
+		if variation == "static" {
+			library.SetStatic()
+		} else if variation == "shared" {
+			library.SetShared()
+			var isLLNDK bool
+			if m, ok := ctx.Module().(*Module); ok {
+				isLLNDK = m.IsLlndk()
+			}
+			buildStatic := library.BuildStaticVariant() && !isLLNDK
+			buildShared := library.BuildSharedVariant()
+			if buildStatic && buildShared {
+				if _, ok := library.(*Module); ok {
+					reuseStaticLibrary(ctx, library.(*Module))
+				}
+			}
 		}
 	}
 }
@@ -2204,64 +2250,14 @@ func normalizeVersions(ctx android.BaseModuleContext, versions []string) {
 	}
 }

-func createVersionVariations(mctx android.BottomUpMutatorContext, versions []string) {
-	// "" is for the non-stubs (implementation) variant for system modules, or the LLNDK variant
-	// for LLNDK modules.
-	variants := append(android.CopyOf(versions), "")
-
-	m := mctx.Module().(*Module)
-	isLLNDK := m.IsLlndk()
-	isVendorPublicLibrary := m.IsVendorPublicLibrary()
-	isImportedApiLibrary := m.isImportedApiLibrary()
-
-	modules := mctx.CreateLocalVariations(variants...)
-	for i, m := range modules {
-
-		if variants[i] != "" || isLLNDK || isVendorPublicLibrary || isImportedApiLibrary {
-			// A stubs or LLNDK stubs variant.
-			c := m.(*Module)
-			if c.sanitize != nil {
-				c.sanitize.Properties.ForceDisable = true
-			}
-			if c.stl != nil {
-				c.stl.Properties.Stl = StringPtr("none")
-			}
-			c.Properties.PreventInstall = true
-			lib := moduleLibraryInterface(m)
-			isLatest := i == (len(versions) - 1)
-			lib.setBuildStubs(isLatest)
-
-			if variants[i] != "" {
-				// A non-LLNDK stubs module is hidden from make and has a dependency from the
-				// implementation module to the stubs module.
-				c.Properties.HideFromMake = true
-				lib.setStubsVersion(variants[i])
-				mctx.AddInterVariantDependency(stubImplDepTag, modules[len(modules)-1], modules[i])
-			}
-		}
-	}
-	mctx.AliasVariation("")
-	latestVersion := ""
-	if len(versions) > 0 {
-		latestVersion = versions[len(versions)-1]
-	}
-	mctx.CreateAliasVariation("latest", latestVersion)
-}
-
-func createPerApiVersionVariations(mctx android.BottomUpMutatorContext, minSdkVersion string) {
+func perApiVersionVariations(mctx android.BaseModuleContext, minSdkVersion string) []string {
 	from, err := nativeApiLevelFromUser(mctx, minSdkVersion)
 	if err != nil {
 		mctx.PropertyErrorf("min_sdk_version", err.Error())
-		return
+		return []string{""}
 	}

-	versionStrs := ndkLibraryVersions(mctx, from)
-	modules := mctx.CreateLocalVariations(versionStrs...)
-
-	for i, module := range modules {
-		module.(*Module).Properties.Sdk_version = StringPtr(versionStrs[i])
-		module.(*Module).Properties.Min_sdk_version = StringPtr(versionStrs[i])
-	}
+	return ndkLibraryVersions(mctx, from)
 }

 func canBeOrLinkAgainstVersionVariants(module interface {
@@ -2291,7 +2287,7 @@ func moduleLibraryInterface(module blueprint.Module) libraryInterface {
 }

 // setStubsVersions normalizes the versions in the Stubs.Versions property into MutatedProperties.AllStubsVersions.
-func setStubsVersions(mctx android.BottomUpMutatorContext, library libraryInterface, module *Module) {
+func setStubsVersions(mctx android.BaseModuleContext, library libraryInterface, module *Module) {
 	if !library.buildShared() || !canBeVersionVariant(module) {
 		return
 	}
@@ -2304,25 +2300,98 @@ func setStubsVersions(mctx android.BottomUpMutatorContext, library libraryInterf
 	library.setAllStubsVersions(versions)
 }

-// versionMutator splits a module into the mandatory non-stubs variant
+// versionTransitionMutator splits a module into the mandatory non-stubs variant
 // (which is unnamed) and zero or more stubs variants.
-func versionMutator(mctx android.BottomUpMutatorContext) {
-	if mctx.Os() != android.Android {
-		return
+type versionTransitionMutator struct{}
+
+func (versionTransitionMutator) Split(ctx android.BaseModuleContext) []string {
+	if ctx.Os() != android.Android {
+		return []string{""}
 	}

-	m, ok := mctx.Module().(*Module)
-	if library := moduleLibraryInterface(mctx.Module()); library != nil && canBeVersionVariant(m) {
-		setStubsVersions(mctx, library, m)
+	m, ok := ctx.Module().(*Module)
+	if library := moduleLibraryInterface(ctx.Module()); library != nil && canBeVersionVariant(m) {
+		setStubsVersions(ctx, library, m)

-		createVersionVariations(mctx, library.allStubsVersions())
-		return
+		return append(slices.Clone(library.allStubsVersions()), "")
+	} else if ok && m.SplitPerApiLevel() && m.IsSdkVariant() {
+		return perApiVersionVariations(ctx, m.MinSdkVersion())
 	}

-	if ok {
-		if m.SplitPerApiLevel() && m.IsSdkVariant() {
-			createPerApiVersionVariations(mctx, m.MinSdkVersion())
+	return []string{""}
+}
+
+func (versionTransitionMutator) OutgoingTransition(ctx android.OutgoingTransitionContext, sourceVariation string) string {
+	return ""
+}
+
+func (versionTransitionMutator) IncomingTransition(ctx android.IncomingTransitionContext, incomingVariation string) string {
+	if ctx.Os() != android.Android {
+		return ""
+	}
+	m, ok := ctx.Module().(*Module)
+	if library := moduleLibraryInterface(ctx.Module()); library != nil && canBeVersionVariant(m) {
+		if incomingVariation == "latest" {
+			latestVersion := ""
+			versions := library.allStubsVersions()
+			if len(versions) > 0 {
+				latestVersion = versions[len(versions)-1]
+			}
+			return latestVersion
 		}
+		return incomingVariation
+	} else if ok && m.SplitPerApiLevel() && m.IsSdkVariant() {
+		// If this module only has variants with versions and the incoming dependency doesn't specify which one
+		// is needed then assume the latest version.
+		if incomingVariation == "" {
+			return android.FutureApiLevel.String()
+		}
+		return incomingVariation
+	}
+
+	return ""
+}
+
+func (versionTransitionMutator) Mutate(ctx android.BottomUpMutatorContext, variation string) {
+	// Optimization: return early if this module can't be affected.
+	if ctx.Os() != android.Android {
+		return
+	}
+
+	m, ok := ctx.Module().(*Module)
+	if library := moduleLibraryInterface(ctx.Module()); library != nil && canBeVersionVariant(m) {
+		isLLNDK := m.IsLlndk()
+		isVendorPublicLibrary := m.IsVendorPublicLibrary()
+		isImportedApiLibrary := m.isImportedApiLibrary()
+
+		if variation != "" || isLLNDK || isVendorPublicLibrary || isImportedApiLibrary {
+			// A stubs or LLNDK stubs variant.
+			if m.sanitize != nil {
+				m.sanitize.Properties.ForceDisable = true
+			}
+			if m.stl != nil {
+				m.stl.Properties.Stl = StringPtr("none")
+			}
+			m.Properties.PreventInstall = true
+			lib := moduleLibraryInterface(m)
+			allStubsVersions := library.allStubsVersions()
+			isLatest := len(allStubsVersions) > 0 && variation == allStubsVersions[len(allStubsVersions)-1]
+			lib.setBuildStubs(isLatest)
+		}
+		if variation != "" {
+			// A non-LLNDK stubs module is hidden from make
+			library.setStubsVersion(variation)
+			m.Properties.HideFromMake = true
+		} else {
+			// A non-LLNDK implementation module has a dependency to all stubs versions
+			for _, version := range library.allStubsVersions() {
+				ctx.AddVariationDependencies([]blueprint.Variation{{"version", version}},
+					stubImplDepTag, ctx.ModuleName())
+			}
+		}
+	} else if ok && m.SplitPerApiLevel() && m.IsSdkVariant() {
+		m.Properties.Sdk_version = StringPtr(variation)
+		m.Properties.Min_sdk_version = StringPtr(variation)
 	}
 }

--- a/cc/library_stub.go
+++ b/cc/library_stub.go
@@ -303,7 +303,7 @@ func (d *apiLibraryDecorator) hasStubsVariants() bool {
 	return d.hasApexStubs()
 }

-func (d *apiLibraryDecorator) stubsVersions(ctx android.BaseMutatorContext) []string {
+func (d *apiLibraryDecorator) stubsVersions(ctx android.BaseModuleContext) []string {
 	m, ok := ctx.Module().(*Module)

 	if !ok {
--- a/cc/ndk_library.go
+++ b/cc/ndk_library.go
@@ -133,7 +133,7 @@ func (stub *stubDecorator) implementationModuleName(name string) string {
 	return strings.TrimSuffix(name, ndkLibrarySuffix)
 }

-func ndkLibraryVersions(ctx android.BaseMutatorContext, from android.ApiLevel) []string {
+func ndkLibraryVersions(ctx android.BaseModuleContext, from android.ApiLevel) []string {
 	var versions []android.ApiLevel
 	versionStrs := []string{}
 	for _, version := range ctx.Config().AllSupportedApiLevels() {
@@ -147,7 +147,7 @@ func ndkLibraryVersions(ctx android.BaseMutatorContext, from android.ApiLevel) [
 	return versionStrs
 }

-func (this *stubDecorator) stubsVersions(ctx android.BaseMutatorContext) []string {
+func (this *stubDecorator) stubsVersions(ctx android.BaseModuleContext) []string {
 	if !ctx.Module().Enabled(ctx) {
 		return nil
 	}
--- a/cc/sdk.go
+++ b/cc/sdk.go
@@ -19,12 +19,86 @@ import (
 	"android/soong/genrule"
 )

-// sdkMutator sets a creates a platform and an SDK variant for modules
+// sdkTransitionMutator creates a platform and an SDK variant for modules
 // that set sdk_version, and ignores sdk_version for the platform
 // variant.  The SDK variant will be used for embedding in APKs
 // that may be installed on older platforms.  Apexes use their own
 // variants that enforce backwards compatibility.
-func sdkMutator(ctx android.BottomUpMutatorContext) {
+type sdkTransitionMutator struct{}
+
+func (sdkTransitionMutator) Split(ctx android.BaseModuleContext) []string {
+	if ctx.Os() != android.Android {
+		return []string{""}
+	}
+
+	switch m := ctx.Module().(type) {
+	case LinkableInterface:
+		if m.AlwaysSdk() {
+			if !m.UseSdk() && !m.SplitPerApiLevel() {
+				ctx.ModuleErrorf("UseSdk() must return true when AlwaysSdk is set, did the factory forget to set Sdk_version?")
+			}
+			return []string{"sdk"}
+		} else if m.UseSdk() || m.SplitPerApiLevel() {
+			return []string{"", "sdk"}
+		} else {
+			return []string{""}
+		}
+	case *genrule.Module:
+		if p, ok := m.Extra.(*GenruleExtraProperties); ok {
+			if String(p.Sdk_version) != "" {
+				return []string{"", "sdk"}
+			} else {
+				return []string{""}
+			}
+		}
+	case *CcApiVariant:
+		ccApiVariant, _ := ctx.Module().(*CcApiVariant)
+		if String(ccApiVariant.properties.Variant) == "ndk" {
+			return []string{"sdk"}
+		} else {
+			return []string{""}
+		}
+	}
+
+	return []string{""}
+}
+
+func (sdkTransitionMutator) OutgoingTransition(ctx android.OutgoingTransitionContext, sourceVariation string) string {
+	return sourceVariation
+}
+
+func (sdkTransitionMutator) IncomingTransition(ctx android.IncomingTransitionContext, incomingVariation string) string {
+	if ctx.Os() != android.Android {
+		return ""
+	}
+	switch m := ctx.Module().(type) {
+	case LinkableInterface:
+		if m.AlwaysSdk() {
+			return "sdk"
+		} else if m.UseSdk() || m.SplitPerApiLevel() {
+			return incomingVariation
+		}
+	case *genrule.Module:
+		if p, ok := m.Extra.(*GenruleExtraProperties); ok {
+			if String(p.Sdk_version) != "" {
+				return incomingVariation
+			}
+		}
+	case *CcApiVariant:
+		ccApiVariant, _ := ctx.Module().(*CcApiVariant)
+		if String(ccApiVariant.properties.Variant) == "ndk" {
+			return "sdk"
+		}
+	}
+
+	if ctx.IsAddingDependency() {
+		return incomingVariation
+	} else {
+		return ""
+	}
+}
+
+func (sdkTransitionMutator) Mutate(ctx android.BottomUpMutatorContext, variation string) {
 	if ctx.Os() != android.Android {
 		return
 	}
@@ -33,59 +107,45 @@ func sdkMutator(ctx android.BottomUpMutatorContext) {
 	case LinkableInterface:
 		ccModule, isCcModule := ctx.Module().(*Module)
 		if m.AlwaysSdk() {
-			if !m.UseSdk() && !m.SplitPerApiLevel() {
-				ctx.ModuleErrorf("UseSdk() must return true when AlwaysSdk is set, did the factory forget to set Sdk_version?")
+			if variation != "sdk" {
+				ctx.ModuleErrorf("tried to create variation %q for module with AlwaysSdk set, expected \"sdk\"", variation)
 			}
-			modules := ctx.CreateVariations("sdk")
-			modules[0].(*Module).Properties.IsSdkVariant = true
+
+			ccModule.Properties.IsSdkVariant = true
 		} else if m.UseSdk() || m.SplitPerApiLevel() {
-			modules := ctx.CreateVariations("", "sdk")
+			if variation == "" {
+				// Clear the sdk_version property for the platform (non-SDK) variant so later code
+				// doesn't get confused by it.
+				ccModule.Properties.Sdk_version = nil
+			} else {
+				// Mark the SDK variant.
+				ccModule.Properties.IsSdkVariant = true

-			// Clear the sdk_version property for the platform (non-SDK) variant so later code
-			// doesn't get confused by it.
-			modules[0].(*Module).Properties.Sdk_version = nil
-
-			// Mark the SDK variant.
-			modules[1].(*Module).Properties.IsSdkVariant = true
+				// SDK variant never gets installed because the variant is to be embedded in
+				// APKs, not to be installed to the platform.
+				ccModule.Properties.PreventInstall = true
+			}

 			if ctx.Config().UnbundledBuildApps() {
-				// For an unbundled apps build, hide the platform variant from Make
-				// so that other Make modules don't link against it, but against the
-				// SDK variant.
-				modules[0].(*Module).Properties.HideFromMake = true
+				if variation == "" {
+					// For an unbundled apps build, hide the platform variant from Make
+					// so that other Make modules don't link against it, but against the
+					// SDK variant.
+					ccModule.Properties.HideFromMake = true
+				}
 			} else {
-				// For a platform build, mark the SDK variant so that it gets a ".sdk" suffix when
-				// exposed to Make.
-				modules[1].(*Module).Properties.SdkAndPlatformVariantVisibleToMake = true
+				if variation == "sdk" {
+					// For a platform build, mark the SDK variant so that it gets a ".sdk" suffix when
+					// exposed to Make.
+					ccModule.Properties.SdkAndPlatformVariantVisibleToMake = true
+				}
 			}
-			// SDK variant never gets installed because the variant is to be embedded in
-			// APKs, not to be installed to the platform.
-			modules[1].(*Module).Properties.PreventInstall = true
-			ctx.AliasVariation("")
 		} else {
 			if isCcModule {
 				// Clear the sdk_version property for modules that don't have an SDK variant so
 				// later code doesn't get confused by it.
 				ccModule.Properties.Sdk_version = nil
 			}
-			ctx.CreateVariations("")
-			ctx.AliasVariation("")
-		}
-	case *genrule.Module:
-		if p, ok := m.Extra.(*GenruleExtraProperties); ok {
-			if String(p.Sdk_version) != "" {
-				ctx.CreateVariations("", "sdk")
-			} else {
-				ctx.CreateVariations("")
-			}
-			ctx.AliasVariation("")
-		}
-	case *CcApiVariant:
-		ccApiVariant, _ := ctx.Module().(*CcApiVariant)
-		if String(ccApiVariant.properties.Variant) == "ndk" {
-			ctx.CreateVariations("sdk")
-		} else {
-			ctx.CreateVariations("")
 		}
 	}
 }
--- a/dexpreopt/dexpreopt.go
+++ b/dexpreopt/dexpreopt.go
@@ -532,7 +532,7 @@ func OdexOnSystemOtherByName(name string, dexLocation string, global *GlobalConf
 	}

 	for _, f := range global.PatternsOnSystemOther {
-		if makefileMatch("/" + f, dexLocation) || makefileMatch(filepath.Join(SystemPartition, f), dexLocation) {
+		if makefileMatch("/"+f, dexLocation) || makefileMatch(filepath.Join(SystemPartition, f), dexLocation) {
 			return true
 		}
 	}
--- a/python/python.go
+++ b/python/python.go
@@ -38,7 +38,7 @@ func registerPythonMutators(ctx android.RegistrationContext) {

 // Exported to support other packages using Python modules in tests.
 func RegisterPythonPreDepsMutators(ctx android.RegisterMutatorsContext) {
-	ctx.BottomUp("python_version", versionSplitMutator()).Parallel()
+	ctx.Transition("python_version", &versionSplitTransitionMutator{})
 }

 // the version-specific properties that apply to python modules.
@@ -245,7 +245,6 @@ var (
 	protoExt                 = ".proto"
 	pyVersion2               = "PY2"
 	pyVersion3               = "PY3"
-	pyVersion2And3           = "PY2ANDPY3"
 	internalPath             = "internal"
 )

@@ -253,46 +252,68 @@ type basePropertiesProvider interface {
 	getBaseProperties() *BaseProperties
 }

-// versionSplitMutator creates version variants for modules and appends the version-specific
-// properties for a given variant to the properties in the variant module
-func versionSplitMutator() func(android.BottomUpMutatorContext) {
-	return func(mctx android.BottomUpMutatorContext) {
-		if base, ok := mctx.Module().(basePropertiesProvider); ok {
-			props := base.getBaseProperties()
-			var versionNames []string
-			// collect version specific properties, so that we can merge version-specific properties
-			// into the module's overall properties
-			var versionProps []VersionProperties
-			// PY3 is first so that we alias the PY3 variant rather than PY2 if both
-			// are available
-			if proptools.BoolDefault(props.Version.Py3.Enabled, true) {
-				versionNames = append(versionNames, pyVersion3)
-				versionProps = append(versionProps, props.Version.Py3)
-			}
-			if proptools.BoolDefault(props.Version.Py2.Enabled, false) {
-				if !mctx.DeviceConfig().BuildBrokenUsesSoongPython2Modules() &&
-					mctx.ModuleName() != "py2-cmd" &&
-					mctx.ModuleName() != "py2-stdlib" {
-					mctx.PropertyErrorf("version.py2.enabled", "Python 2 is no longer supported, please convert to python 3. This error can be temporarily overridden by setting BUILD_BROKEN_USES_SOONG_PYTHON2_MODULES := true in the product configuration")
-				}
-				versionNames = append(versionNames, pyVersion2)
-				versionProps = append(versionProps, props.Version.Py2)
-			}
-			modules := mctx.CreateLocalVariations(versionNames...)
-			// Alias module to the first variant
-			if len(versionNames) > 0 {
-				mctx.AliasVariation(versionNames[0])
-			}
-			for i, v := range versionNames {
-				// set the actual version for Python module.
-				newProps := modules[i].(basePropertiesProvider).getBaseProperties()
-				newProps.Actual_version = v
-				// append versioned properties for the Python module to the overall properties
-				err := proptools.AppendMatchingProperties([]interface{}{newProps}, &versionProps[i], nil)
-				if err != nil {
-					panic(err)
-				}
+type versionSplitTransitionMutator struct{}
+
+func (versionSplitTransitionMutator) Split(ctx android.BaseModuleContext) []string {
+	if base, ok := ctx.Module().(basePropertiesProvider); ok {
+		props := base.getBaseProperties()
+		var variants []string
+		// PY3 is first so that we alias the PY3 variant rather than PY2 if both
+		// are available
+		if proptools.BoolDefault(props.Version.Py3.Enabled, true) {
+			variants = append(variants, pyVersion3)
+		}
+		if proptools.BoolDefault(props.Version.Py2.Enabled, false) {
+			if !ctx.DeviceConfig().BuildBrokenUsesSoongPython2Modules() &&
+				ctx.ModuleName() != "py2-cmd" &&
+				ctx.ModuleName() != "py2-stdlib" {
+				ctx.PropertyErrorf("version.py2.enabled", "Python 2 is no longer supported, please convert to python 3. This error can be temporarily overridden by setting BUILD_BROKEN_USES_SOONG_PYTHON2_MODULES := true in the product configuration")
 			}
+			variants = append(variants, pyVersion2)
+		}
+		return variants
+	}
+	return []string{""}
+}
+
+func (versionSplitTransitionMutator) OutgoingTransition(ctx android.OutgoingTransitionContext, sourceVariation string) string {
+	return ""
+}
+
+func (versionSplitTransitionMutator) IncomingTransition(ctx android.IncomingTransitionContext, incomingVariation string) string {
+	if incomingVariation != "" {
+		return incomingVariation
+	}
+	if base, ok := ctx.Module().(basePropertiesProvider); ok {
+		props := base.getBaseProperties()
+		if proptools.BoolDefault(props.Version.Py3.Enabled, true) {
+			return pyVersion3
+		} else {
+			return pyVersion2
+		}
+	}
+
+	return ""
+}
+
+func (versionSplitTransitionMutator) Mutate(ctx android.BottomUpMutatorContext, variation string) {
+	if variation == "" {
+		return
+	}
+	if base, ok := ctx.Module().(basePropertiesProvider); ok {
+		props := base.getBaseProperties()
+		props.Actual_version = variation
+
+		var versionProps *VersionProperties
+		if variation == pyVersion3 {
+			versionProps = &props.Version.Py3
+		} else if variation == pyVersion2 {
+			versionProps = &props.Version.Py2
+		}
+
+		err := proptools.AppendMatchingProperties([]interface{}{props}, versionProps, nil)
+		if err != nil {
+			panic(err)
 		}
 	}
 }
--- a/rust/coverage.go
+++ b/rust/coverage.go
@@ -47,7 +47,7 @@ func (cov *coverage) deps(ctx DepsContext, deps Deps) Deps {

 		// no_std modules are missing libprofiler_builtins which provides coverage, so we need to add it as a dependency.
 		if rustModule, ok := ctx.Module().(*Module); ok && rustModule.compiler.noStdlibs() {
-			ctx.AddVariationDependencies([]blueprint.Variation{{Mutator: "rust_libraries", Variation: "rlib"}, {Mutator: "link", Variation: ""}}, rlibDepTag, ProfilerBuiltins)
+			ctx.AddVariationDependencies([]blueprint.Variation{{Mutator: "rust_libraries", Variation: "rlib"}}, rlibDepTag, ProfilerBuiltins)
 		}
 	}

--- a/rust/library.go
+++ b/rust/library.go
@@ -20,6 +20,8 @@ import (
 	"regexp"
 	"strings"

+	"github.com/google/blueprint"
+
 	"android/soong/android"
 	"android/soong/cc"
 )
@@ -692,31 +694,28 @@ func validateLibraryStem(ctx BaseModuleContext, filename string, crate_name stri
 	}
 }

-// LibraryMutator mutates the libraries into variants according to the
-// build{Rlib,Dylib} attributes.
-func LibraryMutator(mctx android.BottomUpMutatorContext) {
-	// Only mutate on Rust libraries.
-	m, ok := mctx.Module().(*Module)
+type libraryTransitionMutator struct{}
+
+func (libraryTransitionMutator) Split(ctx android.BaseModuleContext) []string {
+	m, ok := ctx.Module().(*Module)
 	if !ok || m.compiler == nil {
-		return
+		return []string{""}
 	}
 	library, ok := m.compiler.(libraryInterface)
 	if !ok {
-		return
+		return []string{""}
 	}

 	// Don't produce rlib/dylib/source variants for shared or static variants
 	if library.shared() || library.static() {
-		return
+		return []string{""}
 	}

 	var variants []string
 	// The source variant is used for SourceProvider modules. The other variants (i.e. rlib and dylib)
 	// depend on this variant. It must be the first variant to be declared.
-	sourceVariant := false
 	if m.sourceProvider != nil {
-		variants = append(variants, "source")
-		sourceVariant = true
+		variants = append(variants, sourceVariation)
 	}
 	if library.buildRlib() {
 		variants = append(variants, rlibVariation)
@@ -726,92 +725,134 @@ func LibraryMutator(mctx android.BottomUpMutatorContext) {
 	}

 	if len(variants) == 0 {
-		return
+		return []string{""}
 	}
-	modules := mctx.CreateLocalVariations(variants...)

-	// The order of the variations (modules) matches the variant names provided. Iterate
-	// through the new variation modules and set their mutated properties.
-	var emptyVariant = false
-	var rlibVariant = false
-	for i, v := range modules {
-		switch variants[i] {
-		case rlibVariation:
-			v.(*Module).compiler.(libraryInterface).setRlib()
-			rlibVariant = true
-		case dylibVariation:
-			v.(*Module).compiler.(libraryInterface).setDylib()
-			if v.(*Module).ModuleBase.ImageVariation().Variation == android.VendorRamdiskVariation {
-				// TODO(b/165791368)
-				// Disable dylib Vendor Ramdisk variations until we support these.
-				v.(*Module).Disable()
-			}
+	return variants
+}

-		case "source":
-			v.(*Module).compiler.(libraryInterface).setSource()
-			// The source variant does not produce any library.
-			// Disable the compilation steps.
-			v.(*Module).compiler.SetDisabled()
-		case "":
-			emptyVariant = true
+func (libraryTransitionMutator) OutgoingTransition(ctx android.OutgoingTransitionContext, sourceVariation string) string {
+	return ""
+}
+
+func (libraryTransitionMutator) IncomingTransition(ctx android.IncomingTransitionContext, incomingVariation string) string {
+	m, ok := ctx.Module().(*Module)
+	if !ok || m.compiler == nil {
+		return ""
+	}
+	library, ok := m.compiler.(libraryInterface)
+	if !ok {
+		return ""
+	}
+
+	if incomingVariation == "" {
+		if m.sourceProvider != nil {
+			return sourceVariation
+		}
+		if library.shared() {
+			return ""
+		}
+		if library.buildRlib() {
+			return rlibVariation
+		}
+		if library.buildDylib() {
+			return dylibVariation
 		}
 	}
+	return incomingVariation
+}

-	if rlibVariant && library.isFFILibrary() {
-		// If an rlib variant is set and this is an FFI library, make it the
-		// default variant so CC can link against it appropriately.
-		mctx.AliasVariation(rlibVariation)
-	} else if emptyVariant {
-		// If there's an empty variant, alias it so it is the default variant
-		mctx.AliasVariation("")
+func (libraryTransitionMutator) Mutate(ctx android.BottomUpMutatorContext, variation string) {
+	m, ok := ctx.Module().(*Module)
+	if !ok || m.compiler == nil {
+		return
+	}
+	library, ok := m.compiler.(libraryInterface)
+	if !ok {
+		return
+	}
+
+	switch variation {
+	case rlibVariation:
+		library.setRlib()
+	case dylibVariation:
+		library.setDylib()
+		if m.ModuleBase.ImageVariation().Variation == android.VendorRamdiskVariation {
+			// TODO(b/165791368)
+			// Disable dylib Vendor Ramdisk variations until we support these.
+			m.Disable()
+		}
+
+	case sourceVariation:
+		library.setSource()
+		// The source variant does not produce any library.
+		// Disable the compilation steps.
+		m.compiler.SetDisabled()
 	}

 	// If a source variant is created, add an inter-variant dependency
 	// between the other variants and the source variant.
-	if sourceVariant {
-		sv := modules[0]
-		for _, v := range modules[1:] {
-			if !v.Enabled(mctx) {
-				continue
-			}
-			mctx.AddInterVariantDependency(sourceDepTag, v, sv)
-		}
-		// Alias the source variation so it can be named directly in "srcs" properties.
-		mctx.AliasVariation("source")
+	if m.sourceProvider != nil && variation != sourceVariation {
+		ctx.AddVariationDependencies(
+			[]blueprint.Variation{
+				{"rust_libraries", sourceVariation},
+			},
+			sourceDepTag, ctx.ModuleName())
 	}
 }

-func LibstdMutator(mctx android.BottomUpMutatorContext) {
-	if m, ok := mctx.Module().(*Module); ok && m.compiler != nil && !m.compiler.Disabled() {
-		switch library := m.compiler.(type) {
-		case libraryInterface:
-			// Only create a variant if a library is actually being built.
-			if library.rlib() && !library.sysroot() {
-				// If this is a rust_ffi variant it only needs rlib-std
-				if library.isFFILibrary() {
-					variants := []string{"rlib-std"}
-					modules := mctx.CreateLocalVariations(variants...)
-					rlib := modules[0].(*Module)
-					rlib.compiler.(libraryInterface).setRlibStd()
-					rlib.Properties.RustSubName += RlibStdlibSuffix
-					mctx.AliasVariation("rlib-std")
-				} else {
-					variants := []string{"rlib-std", "dylib-std"}
-					modules := mctx.CreateLocalVariations(variants...)
+type libstdTransitionMutator struct{}

-					rlib := modules[0].(*Module)
-					dylib := modules[1].(*Module)
-					rlib.compiler.(libraryInterface).setRlibStd()
-					dylib.compiler.(libraryInterface).setDylibStd()
-					if dylib.ModuleBase.ImageVariation().Variation == android.VendorRamdiskVariation {
-						// TODO(b/165791368)
-						// Disable rlibs that link against dylib-std on vendor ramdisk variations until those dylib
-						// variants are properly supported.
-						dylib.Disable()
-					}
-					rlib.Properties.RustSubName += RlibStdlibSuffix
+func (libstdTransitionMutator) Split(ctx android.BaseModuleContext) []string {
+	if m, ok := ctx.Module().(*Module); ok && m.compiler != nil && !m.compiler.Disabled() {
+		// Only create a variant if a library is actually being built.
+		if library, ok := m.compiler.(libraryInterface); ok {
+			if library.rlib() && !library.sysroot() {
+				if library.isFFILibrary() {
+					return []string{"rlib-std"}
+				} else {
+					return []string{"rlib-std", "dylib-std"}
 				}
 			}
 		}
 	}
+	return []string{""}
+}
+
+func (libstdTransitionMutator) OutgoingTransition(ctx android.OutgoingTransitionContext, sourceVariation string) string {
+	return ""
+}
+
+func (libstdTransitionMutator) IncomingTransition(ctx android.IncomingTransitionContext, incomingVariation string) string {
+	if m, ok := ctx.Module().(*Module); ok && m.compiler != nil && !m.compiler.Disabled() {
+		if library, ok := m.compiler.(libraryInterface); ok {
+			if library.shared() {
+				return ""
+			}
+			if library.rlib() && !library.sysroot() {
+				if incomingVariation != "" {
+					return incomingVariation
+				}
+				return "rlib-std"
+			}
+		}
+	}
+	return ""
+}
+
+func (libstdTransitionMutator) Mutate(ctx android.BottomUpMutatorContext, variation string) {
+	if variation == "rlib-std" {
+		rlib := ctx.Module().(*Module)
+		rlib.compiler.(libraryInterface).setRlibStd()
+		rlib.Properties.RustSubName += RlibStdlibSuffix
+	} else if variation == "dylib-std" {
+		dylib := ctx.Module().(*Module)
+		dylib.compiler.(libraryInterface).setDylibStd()
+		if dylib.ModuleBase.ImageVariation().Variation == android.VendorRamdiskVariation {
+			// TODO(b/165791368)
+			// Disable rlibs that link against dylib-std on vendor ramdisk variations until those dylib
+			// variants are properly supported.
+			dylib.Disable()
+		}
+	}
 }
--- a/rust/rust.go
+++ b/rust/rust.go
@@ -37,20 +37,24 @@ var pctx = android.NewPackageContext("android/soong/rust")

 func init() {
 	android.RegisterModuleType("rust_defaults", defaultsFactory)
-	android.PreDepsMutators(func(ctx android.RegisterMutatorsContext) {
-		ctx.BottomUp("rust_libraries", LibraryMutator).Parallel()
-		ctx.BottomUp("rust_stdlinkage", LibstdMutator).Parallel()
-		ctx.BottomUp("rust_begin", BeginMutator).Parallel()
-	})
-	android.PostDepsMutators(func(ctx android.RegisterMutatorsContext) {
-		ctx.BottomUp("rust_sanitizers", rustSanitizerRuntimeMutator).Parallel()
-	})
+	android.PreDepsMutators(registerPreDepsMutators)
+	android.PostDepsMutators(registerPostDepsMutators)
 	pctx.Import("android/soong/android")
 	pctx.Import("android/soong/rust/config")
 	pctx.ImportAs("cc_config", "android/soong/cc/config")
 	android.InitRegistrationContext.RegisterParallelSingletonType("kythe_rust_extract", kytheExtractRustFactory)
 }

+func registerPreDepsMutators(ctx android.RegisterMutatorsContext) {
+	ctx.Transition("rust_libraries", &libraryTransitionMutator{})
+	ctx.Transition("rust_stdlinkage", &libstdTransitionMutator{})
+	ctx.BottomUp("rust_begin", BeginMutator).Parallel()
+}
+
+func registerPostDepsMutators(ctx android.RegisterMutatorsContext) {
+	ctx.BottomUp("rust_sanitizers", rustSanitizerRuntimeMutator).Parallel()
+}
+
 type Flags struct {
 	GlobalRustFlags []string // Flags that apply globally to rust
 	GlobalLinkFlags []string // Flags that apply globally to linker
@@ -1128,10 +1132,11 @@ type autoDep struct {
 }

 var (
-	rlibVariation  = "rlib"
-	dylibVariation = "dylib"
-	rlibAutoDep    = autoDep{variation: rlibVariation, depTag: rlibDepTag}
-	dylibAutoDep   = autoDep{variation: dylibVariation, depTag: dylibDepTag}
+	sourceVariation = "source"
+	rlibVariation   = "rlib"
+	dylibVariation  = "dylib"
+	rlibAutoDep     = autoDep{variation: rlibVariation, depTag: rlibDepTag}
+	dylibAutoDep    = autoDep{variation: dylibVariation, depTag: dylibDepTag}
 )

 type autoDeppable interface {
@@ -1613,7 +1618,6 @@ func (mod *Module) DepsMutator(actx android.BottomUpMutatorContext) {
 	}

 	rlibDepVariations := commonDepVariations
-	rlibDepVariations = append(rlibDepVariations, blueprint.Variation{Mutator: "link", Variation: ""})

 	if lib, ok := mod.compiler.(libraryInterface); !ok || !lib.sysroot() {
 		rlibDepVariations = append(rlibDepVariations,
@@ -1629,7 +1633,6 @@ func (mod *Module) DepsMutator(actx android.BottomUpMutatorContext) {

 	// dylibs
 	dylibDepVariations := append(commonDepVariations, blueprint.Variation{Mutator: "rust_libraries", Variation: dylibVariation})
-	dylibDepVariations = append(dylibDepVariations, blueprint.Variation{Mutator: "link", Variation: ""})

 	for _, lib := range deps.Dylibs {
 		actx.AddVariationDependencies(dylibDepVariations, dylibDepTag, lib)
@@ -1650,7 +1653,6 @@ func (mod *Module) DepsMutator(actx android.BottomUpMutatorContext) {
 					// otherwise select the rlib variant.
 					autoDepVariations := append(commonDepVariations,
 						blueprint.Variation{Mutator: "rust_libraries", Variation: autoDep.variation})
-					autoDepVariations = append(autoDepVariations, blueprint.Variation{Mutator: "link", Variation: ""})
 					if actx.OtherModuleDependencyVariantExists(autoDepVariations, lib) {
 						actx.AddVariationDependencies(autoDepVariations, autoDep.depTag, lib)

@@ -1664,8 +1666,7 @@ func (mod *Module) DepsMutator(actx android.BottomUpMutatorContext) {
 		} else if _, ok := mod.sourceProvider.(*protobufDecorator); ok {
 			for _, lib := range deps.Rustlibs {
 				srcProviderVariations := append(commonDepVariations,
-					blueprint.Variation{Mutator: "rust_libraries", Variation: "source"})
-				srcProviderVariations = append(srcProviderVariations, blueprint.Variation{Mutator: "link", Variation: ""})
+					blueprint.Variation{Mutator: "rust_libraries", Variation: sourceVariation})

 				// Only add rustlib dependencies if they're source providers themselves.
 				// This is used to track which crate names need to be added to the source generated
@@ -1681,7 +1682,7 @@ func (mod *Module) DepsMutator(actx android.BottomUpMutatorContext) {
 	if deps.Stdlibs != nil {
 		if mod.compiler.stdLinkage(ctx) == RlibLinkage {
 			for _, lib := range deps.Stdlibs {
-				actx.AddVariationDependencies(append(commonDepVariations, []blueprint.Variation{{Mutator: "rust_libraries", Variation: "rlib"}, {Mutator: "link", Variation: ""}}...),
+				actx.AddVariationDependencies(append(commonDepVariations, []blueprint.Variation{{Mutator: "rust_libraries", Variation: "rlib"}}...),
 					rlibDepTag, lib)
 			}
 		} else {
--- a/rust/rust_test.go
+++ b/rust/rust_test.go
@@ -60,6 +60,7 @@ var rustMockedFiles = android.MockFS{
 // testRust returns a TestContext in which a basic environment has been setup.
 // This environment contains a few mocked files. See rustMockedFiles for the list of these files.
 func testRust(t *testing.T, bp string) *android.TestContext {
+	t.Helper()
 	skipTestIfOsNotSupported(t)
 	result := android.GroupFixturePreparers(
 		prepareForRustTest,
--- a/rust/testing.go
+++ b/rust/testing.go
@@ -200,15 +200,8 @@ func registerRequiredBuildComponentsForTest(ctx android.RegistrationContext) {
 	ctx.RegisterModuleType("rust_prebuilt_library", PrebuiltLibraryFactory)
 	ctx.RegisterModuleType("rust_prebuilt_dylib", PrebuiltDylibFactory)
 	ctx.RegisterModuleType("rust_prebuilt_rlib", PrebuiltRlibFactory)
-	ctx.PreDepsMutators(func(ctx android.RegisterMutatorsContext) {
-		// rust mutators
-		ctx.BottomUp("rust_libraries", LibraryMutator).Parallel()
-		ctx.BottomUp("rust_stdlinkage", LibstdMutator).Parallel()
-		ctx.BottomUp("rust_begin", BeginMutator).Parallel()
-	})
+	ctx.PreDepsMutators(registerPreDepsMutators)
 	ctx.RegisterParallelSingletonType("rust_project_generator", rustProjectGeneratorSingleton)
 	ctx.RegisterParallelSingletonType("kythe_rust_extract", kytheExtractRustFactory)
-	ctx.PostDepsMutators(func(ctx android.RegisterMutatorsContext) {
-		ctx.BottomUp("rust_sanitizers", rustSanitizerRuntimeMutator).Parallel()
-	})
+	ctx.PostDepsMutators(registerPostDepsMutators)
 }
--- a/ui/build/paths/config.go
+++ b/ui/build/paths/config.go
@@ -86,28 +86,28 @@ func GetConfig(name string) PathConfig {
 // This list specifies whether a particular binary from $PATH is allowed to be
 // run during the build. For more documentation, see path_interposer.go .
 var Configuration = map[string]PathConfig{
-	"bash":           Allowed,
-	"diff":           Allowed,
-	"dlv":            Allowed,
-	"expr":           Allowed,
-	"fuser":          Allowed,
-	"gcert":          Allowed,
-	"gcertstatus":    Allowed,
-	"gcloud":         Allowed,
-	"git":            Allowed,
-	"hexdump":        Allowed,
-	"jar":            Allowed,
-	"java":           Allowed,
-	"javap":          Allowed,
-	"lsof":           Allowed,
-	"openssl":        Allowed,
-	"pstree":         Allowed,
-	"rsync":          Allowed,
-	"sh":             Allowed,
-	"stubby":         Allowed,
-	"tr":             Allowed,
-	"unzip":          Allowed,
-	"zip":            Allowed,
+	"bash":        Allowed,
+	"diff":        Allowed,
+	"dlv":         Allowed,
+	"expr":        Allowed,
+	"fuser":       Allowed,
+	"gcert":       Allowed,
+	"gcertstatus": Allowed,
+	"gcloud":      Allowed,
+	"git":         Allowed,
+	"hexdump":     Allowed,
+	"jar":         Allowed,
+	"java":        Allowed,
+	"javap":       Allowed,
+	"lsof":        Allowed,
+	"openssl":     Allowed,
+	"pstree":      Allowed,
+	"rsync":       Allowed,
+	"sh":          Allowed,
+	"stubby":      Allowed,
+	"tr":          Allowed,
+	"unzip":       Allowed,
+	"zip":         Allowed,

 	// Host toolchain is removed. In-tree toolchain should be used instead.
 	// GCC also can't find cc1 with this implementation.