Enforce hidden api usage in vendor (soong)

From aosp/588578, if vendor app doesn't fill sdk_version, build scirpt overwrites system_current to sdk_version.
But there is no similar enforcement in soong.

So, as make does, sdkVersion() returns "system_current" if it is device-specific or soc-specific module. and sdk_version is not filled.

Test: pass soong test
Bug: 132780927

Change-Id: I69bb3d7bfcf7c27c2db4d0efbe046f9c7879b4bc

java/aar.go

@@ -499,7 +499,7 @@ type AARImport struct {
 }
 
 func (a *AARImport) sdkVersion() string {
-	return String(a.properties.Sdk_version)
+	return proptools.StringDefault(a.properties.Sdk_version, defaultSdkVersion(a))
 }
 
 func (a *AARImport) minSdkVersion() string {

java/droiddoc.go

@@ -23,6 +23,7 @@ import (
 	"strings"
 
 	"github.com/google/blueprint"
+	"github.com/google/blueprint/proptools"
 )
 
 var (
@@ -523,7 +524,7 @@ func JavadocHostFactory() android.Module {
 var _ android.OutputFileProducer = (*Javadoc)(nil)
 
 func (j *Javadoc) sdkVersion() string {
-	return String(j.properties.Sdk_version)
+	return proptools.StringDefault(j.properties.Sdk_version, defaultSdkVersion(j))
 }
 
 func (j *Javadoc) minSdkVersion() string {

java/java.go

@@ -426,6 +426,18 @@ var (
 	usesLibTag            = dependencyTag{name: "uses-library"}
 )
 
+func defaultSdkVersion(ctx checkVendorModuleContext) string {
+	if ctx.SocSpecific() || ctx.DeviceSpecific() {
+		return "system_current"
+	}
+	return ""
+}
+
+type checkVendorModuleContext interface {
+	SocSpecific() bool
+	DeviceSpecific() bool
+}
+
 type sdkDep struct {
 	useModule, useFiles, useDefaultLibs, invalidVersion bool
 
@@ -465,7 +477,7 @@ func (j *Module) shouldInstrumentStatic(ctx android.BaseModuleContext) bool {
 }
 
 func (j *Module) sdkVersion() string {
-	return String(j.deviceProperties.Sdk_version)
+	return proptools.StringDefault(j.deviceProperties.Sdk_version, defaultSdkVersion(j))
 }
 
 func (j *Module) minSdkVersion() string {
@@ -1869,7 +1881,7 @@ type Import struct {
 }
 
 func (j *Import) sdkVersion() string {
-	return String(j.properties.Sdk_version)
+	return proptools.StringDefault(j.properties.Sdk_version, defaultSdkVersion(j))
 }
 
 func (j *Import) minSdkVersion() string {

java/java_test.go

@@ -282,6 +282,32 @@ func TestSimple(t *testing.T) {
 	}
 }
 
+func TestSdkVersion(t *testing.T) {
+	ctx := testJava(t, `
+		java_library {
+			name: "foo",
+			srcs: ["a.java"],
+			vendor: true,
+		}
+
+		java_library {
+			name: "bar",
+			srcs: ["b.java"],
+		}
+	`)
+
+	foo := ctx.ModuleForTests("foo", "android_common").Module().(*Library)
+	bar := ctx.ModuleForTests("bar", "android_common").Module().(*Library)
+
+	if foo.sdkVersion() != "system_current" {
+		t.Errorf("If sdk version of vendor module is empty, it must change to system_current.")
+	}
+
+	if bar.sdkVersion() != "" {
+		t.Errorf("If sdk version of non-vendor module is empty, it keeps empty.")
+	}
+}
+
 func TestArchSpecific(t *testing.T) {
 	ctx := testJava(t, `
 		java_library {