Migrate sanitizers to transition mutators.

The logic is not 100% provably the same since HEAD was quite
confusing at some points, but I did make an effort to preserve
functional equivalence.

In case that effort was not enough, it should be pretty easy to
tweak the logic at HEAD since it's still quite malleable.

Bug: 231370928
Test: Presubmits.
Change-Id: I17b2efbfb5c4d0aedd922caed54ff8d857e578df

android/mutator.go

@@ -93,6 +93,7 @@ type RegisterMutatorsContext interface {
 	TopDown(name string, m TopDownMutator) MutatorHandle
 	BottomUp(name string, m BottomUpMutator) MutatorHandle
 	BottomUpBlueprint(name string, m blueprint.BottomUpMutator) MutatorHandle
+	Transition(name string, m TransitionMutator)
 }
 
 type RegisterMutatorFunc func(RegisterMutatorsContext)
@@ -421,6 +422,124 @@ func (x *registerMutatorsContext) BottomUpBlueprint(name string, m blueprint.Bot
 	return mutator
 }
 
+type IncomingTransitionContext interface {
+	// Module returns the target of the dependency edge for which the transition
+	// is being computed
+	Module() Module
+
+	// Config returns the configuration for the build.
+	Config() Config
+}
+
+type OutgoingTransitionContext interface {
+	// Module returns the target of the dependency edge for which the transition
+	// is being computed
+	Module() Module
+
+	// DepTag() Returns the dependency tag through which this dependency is
+	// reached
+	DepTag() blueprint.DependencyTag
+}
+type TransitionMutator interface {
+	// Split returns the set of variations that should be created for a module no
+	// matter who depends on it. Used when Make depends on a particular variation
+	// or when the module knows its variations just based on information given to
+	// it in the Blueprint file. This method should not mutate the module it is
+	// called on.
+	Split(ctx BaseModuleContext) []string
+
+	// OutCalled on a module to determine which variation it wants from its direct
+	// dependencies. The dependency itself can override this decision. This method
+	// should not mutate the module itself.
+	OutgoingTransition(ctx OutgoingTransitionContext, sourceVariation string) string
+
+	// Called on a module to determine which variation it should be in based on
+	// the variation modules that depend on it want. This gives the module a final
+	// say about its own variations. This method should not mutate the module
+	// itself.
+	IncomingTransition(ctx IncomingTransitionContext, incomingVariation string) string
+
+	// Called after a module was split into multiple variations on each variation.
+	// It should not split the module any further but adding new dependencies is
+	// fine. Unlike all the other methods on TransitionMutator, this method is
+	// allowed to mutate the module.
+	Mutate(ctx BottomUpMutatorContext, variation string)
+}
+
+type androidTransitionMutator struct {
+	finalPhase          bool
+	bazelConversionMode bool
+	mutator             TransitionMutator
+}
+
+func (a *androidTransitionMutator) Split(ctx blueprint.BaseModuleContext) []string {
+	if m, ok := ctx.Module().(Module); ok {
+		moduleContext := m.base().baseModuleContextFactory(ctx)
+		moduleContext.bazelConversionMode = a.bazelConversionMode
+		return a.mutator.Split(&moduleContext)
+	} else {
+		return []string{""}
+	}
+}
+
+type outgoingTransitionContextImpl struct {
+	bp blueprint.OutgoingTransitionContext
+}
+
+func (c *outgoingTransitionContextImpl) Module() Module {
+	return c.bp.Module().(Module)
+}
+
+func (c *outgoingTransitionContextImpl) DepTag() blueprint.DependencyTag {
+	return c.bp.DepTag()
+}
+
+func (a *androidTransitionMutator) OutgoingTransition(ctx blueprint.OutgoingTransitionContext, sourceVariation string) string {
+	if _, ok := ctx.Module().(Module); ok {
+		return a.mutator.OutgoingTransition(&outgoingTransitionContextImpl{bp: ctx}, sourceVariation)
+	} else {
+		return ""
+	}
+}
+
+type incomingTransitionContextImpl struct {
+	bp blueprint.IncomingTransitionContext
+}
+
+func (c *incomingTransitionContextImpl) Module() Module {
+	return c.bp.Module().(Module)
+}
+
+func (c *incomingTransitionContextImpl) Config() Config {
+	return c.bp.Config().(Config)
+}
+
+func (a *androidTransitionMutator) IncomingTransition(ctx blueprint.IncomingTransitionContext, incomingVariation string) string {
+	if _, ok := ctx.Module().(Module); ok {
+		return a.mutator.IncomingTransition(&incomingTransitionContextImpl{bp: ctx}, incomingVariation)
+	} else {
+		return ""
+	}
+}
+
+func (a *androidTransitionMutator) Mutate(ctx blueprint.BottomUpMutatorContext, variation string) {
+	if am, ok := ctx.Module().(Module); ok {
+		a.mutator.Mutate(bottomUpMutatorContextFactory(ctx, am, a.finalPhase, a.bazelConversionMode), variation)
+	}
+}
+
+func (x *registerMutatorsContext) Transition(name string, m TransitionMutator) {
+	atm := &androidTransitionMutator{
+		finalPhase:          x.finalPhase,
+		bazelConversionMode: x.bazelConversionMode,
+		mutator:             m,
+	}
+	mutator := &mutator{
+		name:              name,
+		transitionMutator: atm}
+	x.mutators = append(x.mutators, mutator)
+}
+
 func (x *registerMutatorsContext) mutatorName(name string) string {
 	if x.bazelConversionMode {
 		return name + "_bp2build"
@@ -456,6 +575,8 @@ func (mutator *mutator) register(ctx *Context) {
 		handle = blueprintCtx.RegisterBottomUpMutator(mutator.name, mutator.bottomUpMutator)
 	} else if mutator.topDownMutator != nil {
 		handle = blueprintCtx.RegisterTopDownMutator(mutator.name, mutator.topDownMutator)
+	} else if mutator.transitionMutator != nil {
+		blueprintCtx.RegisterTransitionMutator(mutator.name, mutator.transitionMutator)
 	}
 	if mutator.parallel {
 		handle.Parallel()