Convert trivial TopDown mutators to BottomUp

Many TopDown mutators can be easily converted to BottomUp mutators,
which are easier to handle for incremental and partial analysis.

Bug: 367784740
Test: all soong tests pass
Test: no change to build.ninja
Flag: EXEMPT refactor
Change-Id: I82955e844ed0eb6680854678c0744ac5398eb7ba
diff --git a/android/defaults.go b/android/defaults.go
index 0d51d9d..d3dbaed 100644
--- a/android/defaults.go
+++ b/android/defaults.go
@@ -69,7 +69,7 @@
 
 	// Apply defaults from the supplied Defaults to the property structures supplied to
 	// setProperties(...).
-	applyDefaults(TopDownMutatorContext, []Defaults)
+	applyDefaults(BottomUpMutatorContext, []Defaults)
 
 	// Set the hook to be called after any defaults have been applied.
 	//
@@ -209,7 +209,7 @@
 
 var _ Defaults = (*DefaultsModuleBase)(nil)
 
-func (defaultable *DefaultableModuleBase) applyDefaults(ctx TopDownMutatorContext,
+func (defaultable *DefaultableModuleBase) applyDefaults(ctx BottomUpMutatorContext,
 	defaultsList []Defaults) {
 
 	for _, defaults := range defaultsList {
@@ -226,7 +226,7 @@
 // Product variable properties need special handling, the type of the filtered product variable
 // property struct may not be identical between the defaults module and the defaultable module.
 // Use PrependMatchingProperties to apply whichever properties match.
-func (defaultable *DefaultableModuleBase) applyDefaultVariableProperties(ctx TopDownMutatorContext,
+func (defaultable *DefaultableModuleBase) applyDefaultVariableProperties(ctx BottomUpMutatorContext,
 	defaults Defaults, defaultableProp interface{}) {
 	if defaultableProp == nil {
 		return
@@ -254,7 +254,7 @@
 	}
 }
 
-func (defaultable *DefaultableModuleBase) applyDefaultProperties(ctx TopDownMutatorContext,
+func (defaultable *DefaultableModuleBase) applyDefaultProperties(ctx BottomUpMutatorContext,
 	defaults Defaults, defaultableProp interface{}) {
 
 	for _, def := range defaults.properties() {
@@ -273,7 +273,7 @@
 
 func RegisterDefaultsPreArchMutators(ctx RegisterMutatorsContext) {
 	ctx.BottomUp("defaults_deps", defaultsDepsMutator).Parallel()
-	ctx.TopDown("defaults", defaultsMutator).Parallel()
+	ctx.BottomUp("defaults", defaultsMutator).Parallel()
 }
 
 func defaultsDepsMutator(ctx BottomUpMutatorContext) {
@@ -282,8 +282,12 @@
 	}
 }
 
-func defaultsMutator(ctx TopDownMutatorContext) {
+func defaultsMutator(ctx BottomUpMutatorContext) {
 	if defaultable, ok := ctx.Module().(Defaultable); ok {
+		if _, isDefaultsModule := ctx.Module().(Defaults); isDefaultsModule {
+			// Don't squash transitive defaults into defaults modules
+			return
+		}
 		defaults := defaultable.defaults().Defaults
 		if len(defaults) > 0 {
 			var defaultsList []Defaults