Use system stubs for framework-doc-system-stubs.

The target is used to generate api_versions.xml file used by Android
Lint, point it to the system stubs in prebuilts/sdk/.

Bug: 190665366
Test: m framework-doc-system-stubs
Change-Id: I27fbad9eb1d84792901974674cbd85f0994bc9f1

java/droidstubs.go

@@ -128,12 +128,15 @@ type DroidstubsProperties struct {
 	// whicih can be used for scheduling purposes
 	High_mem *bool
 
-	// is set to true, Metalava will allow framework SDK to contain API levels annotations.
+	// if set to true, Metalava will allow framework SDK to contain API levels annotations.
 	Api_levels_annotations_enabled *bool
 
 	// the dirs which Metalava extracts API levels annotations from.
 	Api_levels_annotations_dirs []string
 
+	// the sdk kind which Metalava extracts API levels annotations from. Supports 'public' and 'system' for now; defaults to public.
+	Api_levels_sdk_type *string
+
 	// the filename which Metalava extracts API levels annotations from. Defaults to android.jar.
 	Api_levels_jar_filename *string
 
@@ -367,6 +370,7 @@ func (d *Droidstubs) apiLevelsAnnotationsFlags(ctx android.ModuleContext, cmd *a
 
 	filename := proptools.StringDefault(d.properties.Api_levels_jar_filename, "android.jar")
 
+	var dirs []string
 	ctx.VisitDirectDepsWithTag(metalavaAPILevelsAnnotationsDirTag, func(m android.Module) {
 		if t, ok := m.(*ExportedDroiddocDir); ok {
 			for _, dep := range t.deps {
@@ -383,12 +387,32 @@ func (d *Droidstubs) apiLevelsAnnotationsFlags(ctx android.ModuleContext, cmd *a
 					cmd.Implicit(dep)
 				}
 			}
-			cmd.FlagWithArg("--android-jar-pattern ", t.dir.String()+"/%/public/"+filename)
+
+			dirs = append(dirs, t.dir.String())
 		} else {
 			ctx.PropertyErrorf("api_levels_annotations_dirs",
 				"module %q is not a metalava api-levels-annotations dir", ctx.OtherModuleName(m))
 		}
 	})
+
+	// Add all relevant --android-jar-pattern patterns for Metalava.
+	// When parsing a stub jar for a specific version, Metalava picks the first pattern that defines
+	// an actual file present on disk (in the order the patterns were passed). For system APIs for
+	// privileged apps that are only defined since API level 21 (Lollipop), fallback to public stubs
+	// for older releases.
+	if sdkType := proptools.StringDefault(d.properties.Api_levels_sdk_type, "public"); sdkType != "public" {
+		if sdkType != "system" {
+			ctx.PropertyErrorf("api_levels_sdk_type", "only 'public' and 'system' are supported")
+		}
+		// If building non public stubs, add all sdkType patterns first...
+		for _, dir := range dirs {
+			cmd.FlagWithArg("--android-jar-pattern ", fmt.Sprintf("%s/%%/%s/%s", dir, sdkType, filename))
+		}
+	}
+	for _, dir := range dirs {
+		// ... and fallback to public ones, for Metalava to use if needed.
+		cmd.FlagWithArg("--android-jar-pattern ", fmt.Sprintf("%s/%%/%s/%s", dir, "public", filename))
+	}
 }
 
 func metalavaCmd(ctx android.ModuleContext, rule *android.RuleBuilder, javaVersion javaVersion, srcs android.Paths,

java/droidstubs_test.go

@@ -16,6 +16,7 @@ package java
 
 import (
 	"reflect"
+	"regexp"
 	"strings"
 	"testing"
 
@@ -81,6 +82,46 @@ func TestDroidstubs(t *testing.T) {
 	}
 }
 
+func TestSystemDroidstubs(t *testing.T) {
+	ctx, _ := testJavaWithFS(t, `
+		droiddoc_exported_dir {
+			name: "some-exported-dir",
+			path: "somedir",
+		}
+
+		droiddoc_exported_dir {
+			name: "some-other-exported-dir",
+			path: "someotherdir",
+		}
+
+		droidstubs {
+			name: "foo-stubs",
+			srcs: ["foo-doc/a.java"],
+			api_levels_annotations_dirs: [
+				"some-exported-dir",
+				"some-other-exported-dir",
+			],
+			api_levels_annotations_enabled: true,
+            api_levels_sdk_type: "system",
+		}
+		`,
+		map[string][]byte{
+			"foo-doc/a.java": nil,
+		})
+
+	m := ctx.ModuleForTests("foo-stubs", "android_common")
+	manifest := m.Output("metalava.sbox.textproto")
+	cmd := String(android.RuleBuilderSboxProtoForTests(t, manifest).Commands[0].Command)
+	r := regexp.MustCompile(`--android-jar-pattern [^ ]+/android.jar`)
+	matches := r.FindAllString(cmd, -1)
+	android.AssertArrayString(t, "order of patterns", []string{
+		"--android-jar-pattern somedir/%/system/android.jar",
+		"--android-jar-pattern someotherdir/%/system/android.jar",
+		"--android-jar-pattern somedir/%/public/android.jar",
+		"--android-jar-pattern someotherdir/%/public/android.jar",
+	}, matches)
+}
+
 func TestDroidstubsSandbox(t *testing.T) {
 	ctx, _ := testJavaWithFS(t, `
 		genrule {