Allow Singletons to export Make variables

Register any Singletons that implement a MakeVars method as
MakeVarsProviders, and convert the hiddenapi singleton to
use it.

Test: m checkbuild
Change-Id: I6a2044ad34ef46a8b267762ddfeb51aa01d7734d

android/makevars.go

@@ -90,6 +90,25 @@ func RegisterMakeVarsProvider(pctx PackageContext, provider MakeVarsProvider) {
 	makeVarsProviders = append(makeVarsProviders, makeVarsProvider{pctx, provider})
 }
 
+// SingletonMakeVarsProvider is a Singleton with an extra method to provide extra values to be exported to Make.
+type SingletonMakeVarsProvider interface {
+	Singleton
+
+	// MakeVars uses a MakeVarsContext to provide extra values to be exported to Make.
+	MakeVars(ctx MakeVarsContext)
+}
+
+// registerSingletonMakeVarsProvider adds a singleton that implements SingletonMakeVarsProvider to the list of
+// MakeVarsProviders to run.
+func registerSingletonMakeVarsProvider(singleton SingletonMakeVarsProvider) {
+	makeVarsProviders = append(makeVarsProviders, makeVarsProvider{pctx, SingletonmakeVarsProviderAdapter(singleton)})
+}
+
+// SingletonmakeVarsProviderAdapter converts a SingletonMakeVarsProvider to a MakeVarsProvider.
+func SingletonmakeVarsProviderAdapter(singleton SingletonMakeVarsProvider) MakeVarsProvider {
+	return func(ctx MakeVarsContext) { singleton.MakeVars(ctx) }
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 func makeVarsSingletonFunc() Singleton {

android/register.go

@@ -58,6 +58,9 @@ type SingletonFactory func() Singleton
 func SingletonFactoryAdaptor(factory SingletonFactory) blueprint.SingletonFactory {
 	return func() blueprint.Singleton {
 		singleton := factory()
+		if makevars, ok := singleton.(SingletonMakeVarsProvider); ok {
+			registerSingletonMakeVarsProvider(makevars)
+		}
 		return singletonAdaptor{singleton}
 	}
 }