Add support for merging defaults soong_config_module_types into bp2build

select statements.

This supports defaults from the same or different namespaces, and
transitively defaults as well.

Test: soong unit tests
Test: CI
Change-Id: I99435bacfcfbfe20ad753b8021a1779531d7595a

android/defaults.go

@@ -213,10 +213,60 @@ func InitDefaultsModule(module DefaultsModule) {
 
 var _ Defaults = (*DefaultsModuleBase)(nil)
 
+// applyNamespacedVariableDefaults only runs in bp2build mode for
+// defaultable/defaults modules. Its purpose is to merge namespaced product
+// variable props from defaults deps, even if those defaults are custom module
+// types created from soong_config_module_type, e.g. one that's wrapping a
+// cc_defaults or java_defaults.
+func applyNamespacedVariableDefaults(defaultDep Defaults, ctx TopDownMutatorContext) {
+	var dep, b Bazelable
+
+	dep, ok := defaultDep.(Bazelable)
+	if !ok {
+		if depMod, ok := defaultDep.(Module); ok {
+			// Track that this dependency hasn't been converted to bp2build yet.
+			ctx.AddUnconvertedBp2buildDep(depMod.Name())
+			return
+		} else {
+			panic("Expected default dep to be a Module.")
+		}
+	}
+
+	b, ok = ctx.Module().(Bazelable)
+	if !ok {
+		return
+	}
+
+	// namespacedVariableProps is a map from namespaces (e.g. acme, android,
+	// vendor_foo) to a slice of soong_config_variable struct pointers,
+	// containing properties for that particular module.
+	src := dep.namespacedVariableProps()
+	dst := b.namespacedVariableProps()
+	if dst == nil {
+		dst = make(namespacedVariableProperties)
+	}
+
+	// Propagate all soong_config_variable structs from the dep. We'll merge the
+	// actual property values later in variable.go.
+	for namespace := range src {
+		if dst[namespace] == nil {
+			dst[namespace] = []interface{}{}
+		}
+		for _, i := range src[namespace] {
+			dst[namespace] = append(dst[namespace], i)
+		}
+	}
+
+	b.setNamespacedVariableProps(dst)
+}
+
 func (defaultable *DefaultableModuleBase) applyDefaults(ctx TopDownMutatorContext,
 	defaultsList []Defaults) {
 
 	for _, defaults := range defaultsList {
+		if ctx.Config().runningAsBp2Build {
+			applyNamespacedVariableDefaults(defaults, ctx)
+		}
 		for _, prop := range defaultable.defaultableProperties {
 			if prop == defaultable.defaultableVariableProperties {
 				defaultable.applyDefaultVariableProperties(ctx, defaults, prop)