genrule: let Android.bp file specify exported header dirs

Instead of exporting the generated sources dir as headers, let
the Android.bp file specify subdirectories as exported.

Test: m -j checkbuild
Change-Id: I18dd900d63ce7485c8fbfcc39dc77abad6f733d7
diff --git a/genrule/genrule.go b/genrule/genrule.go
index b1ce804..bb78b1f 100644
--- a/genrule/genrule.go
+++ b/genrule/genrule.go
@@ -34,7 +34,7 @@
 
 type SourceFileGenerator interface {
 	GeneratedSourceFiles() android.Paths
-	GeneratedHeaderDir() android.Path
+	GeneratedHeaderDirs() android.Paths
 }
 
 type HostToolProvider interface {
@@ -65,6 +65,9 @@
 
 	// Local file that is used as the tool
 	Tool_files []string
+
+	// List of directories to export generated headers from
+	Export_include_dirs []string
 }
 
 type generator struct {
@@ -77,7 +80,7 @@
 	deps android.Paths
 	rule blueprint.Rule
 
-	genPath android.Path
+	exportedIncludeDirs android.Paths
 
 	outputFiles android.Paths
 }
@@ -93,8 +96,8 @@
 	return g.outputFiles
 }
 
-func (g *generator) GeneratedHeaderDir() android.Path {
-	return g.genPath
+func (g *generator) GeneratedHeaderDirs() android.Paths {
+	return g.exportedIncludeDirs
 }
 
 func (g *generator) DepsMutator(ctx android.BottomUpMutatorContext) {
@@ -113,7 +116,14 @@
 		return
 	}
 
-	g.genPath = android.PathForModuleGen(ctx, "")
+	if len(g.properties.Export_include_dirs) > 0 {
+		for _, dir := range g.properties.Export_include_dirs {
+			g.exportedIncludeDirs = append(g.exportedIncludeDirs,
+				android.PathForModuleGen(ctx, ctx.ModuleDir(), dir))
+		}
+	} else {
+		g.exportedIncludeDirs = append(g.exportedIncludeDirs, android.PathForModuleGen(ctx, ""))
+	}
 
 	tools := map[string]android.Path{}
 
@@ -166,7 +176,7 @@
 			}
 			return "${depfile}", nil
 		case "genDir":
-			return g.genPath.String(), nil
+			return android.PathForModuleGen(ctx, "").String(), nil
 		default:
 			if strings.HasPrefix(name, "location ") {
 				label := strings.TrimSpace(strings.TrimPrefix(name, "location "))