don't export systemserverclasspath_fragment if contents are empty

If a systemserverclasspath_fragment only contains libraries that have a
higher min_sdk_version than the target build release version, then we
should not export the systemserverclasspath_fragment. Before this
change, the fragment was exported with an empty `contents` property
which caused errors after being dropped as a prebuilt.

Bug: 289183551
Test: go test ./sdk
Change-Id: Ifefc6880228e4dd37f5e42b2bda31a83df785375

sdk/bootclasspath_fragment_sdk_test.go

@@ -1194,3 +1194,58 @@ java_sdk_library_import {
 			expectedSnapshot, expectedCopyRules, expectedStubFlagsInputs, "")
 	})
 }
+
+func TestSnapshotWithEmptyBootClasspathFragment(t *testing.T) {
+	result := android.GroupFixturePreparers(
+		prepareForSdkTestWithJava,
+		java.PrepareForTestWithJavaDefaultModules,
+		java.PrepareForTestWithJavaSdkLibraryFiles,
+		java.FixtureWithLastReleaseApis("mysdklibrary", "mynewsdklibrary"),
+		java.FixtureConfigureApexBootJars("myapex:mysdklibrary", "myapex:mynewsdklibrary"),
+		prepareForSdkTestWithApex,
+		// Add a platform_bootclasspath that depends on the fragment.
+		fixtureAddPlatformBootclasspathForBootclasspathFragment("myapex", "mybootclasspathfragment"),
+		android.FixtureMergeEnv(map[string]string{
+			"SOONG_SDK_SNAPSHOT_TARGET_BUILD_RELEASE": "S",
+		}),
+		android.FixtureWithRootAndroidBp(`
+			sdk {
+				name: "mysdk",
+				apexes: ["myapex"],
+			}
+			apex {
+				name: "myapex",
+				key: "myapex.key",
+				min_sdk_version: "S",
+				bootclasspath_fragments: ["mybootclasspathfragment"],
+			}
+			bootclasspath_fragment {
+				name: "mybootclasspathfragment",
+				apex_available: ["myapex"],
+				contents: ["mysdklibrary", "mynewsdklibrary"],
+				hidden_api: {
+					split_packages: [],
+				},
+			}
+			java_sdk_library {
+				name: "mysdklibrary",
+				apex_available: ["myapex"],
+				srcs: ["Test.java"],
+				shared_library: false,
+				public: {enabled: true},
+				min_sdk_version: "Tiramisu",
+			}
+			java_sdk_library {
+				name: "mynewsdklibrary",
+				apex_available: ["myapex"],
+				srcs: ["Test.java"],
+				compile_dex: true,
+				public: {enabled: true},
+				min_sdk_version: "Tiramisu",
+				permitted_packages: ["mynewsdklibrary"],
+			}
+		`),
+	).RunTest(t)
+
+	CheckSnapshot(t, result, "mysdk", "", checkAndroidBpContents(`// This is auto-generated. DO NOT EDIT.`))
+}

sdk/bp.go

@@ -311,13 +311,15 @@ func (t identityTransformation) transformProperty(_ string, value interface{}, t
 }
 
 func (m *bpModule) deepCopy() *bpModule {
-	return m.transform(deepCopyTransformer)
+	return transformModule(m, deepCopyTransformer)
 }
 
-func (m *bpModule) transform(transformer bpTransformer) *bpModule {
+func transformModule(m *bpModule, transformer bpTransformer) *bpModule {
 	transformedModule := transformer.transformModule(m)
+	if transformedModule != nil {
 		// Copy the contents of the returned property set into the module and then transform that.
 		transformedModule.bpPropertySet, _ = transformPropertySet(transformer, "", transformedModule.bpPropertySet, nil)
+	}
 	return transformedModule
 }
 

sdk/systemserverclasspath_fragment_sdk_test.go

@@ -86,6 +86,51 @@ func testSnapshotWithSystemServerClasspathFragment(t *testing.T, sdk string, tar
 	)
 }
 
+func TestSnapshotWithEmptySystemServerClasspathFragment(t *testing.T) {
+	commonSdk := `
+		apex {
+			name: "myapex",
+			key: "myapex.key",
+			min_sdk_version: "Tiramisu",
+			systemserverclasspath_fragments: ["mysystemserverclasspathfragment"],
+		}
+		systemserverclasspath_fragment {
+			name: "mysystemserverclasspathfragment",
+			apex_available: ["myapex"],
+			contents: ["mysdklibrary"],
+		}
+		java_sdk_library {
+			name: "mysdklibrary",
+			apex_available: ["myapex"],
+			srcs: ["Test.java"],
+			min_sdk_version: "34", // UpsideDownCake
+		}
+		sdk {
+			name: "mysdk",
+			apexes: ["myapex"],
+		}
+	`
+
+	result := android.GroupFixturePreparers(
+		prepareForSdkTestWithJava,
+		java.PrepareForTestWithJavaDefaultModules,
+		java.PrepareForTestWithJavaSdkLibraryFiles,
+		java.FixtureWithLastReleaseApis("mysdklibrary"),
+		dexpreopt.FixtureSetApexSystemServerJars("myapex:mysdklibrary"),
+		android.FixtureModifyEnv(func(env map[string]string) {
+			// targeting Tiramisu here means that we won't export mysdklibrary
+			env["SOONG_SDK_SNAPSHOT_TARGET_BUILD_RELEASE"] = "Tiramisu"
+		}),
+		android.FixtureModifyProductVariables(func(variables android.FixtureProductVariables) {
+			variables.Platform_version_active_codenames = []string{"UpsideDownCake"}
+		}),
+		prepareForSdkTestWithApex,
+		android.FixtureWithRootAndroidBp(commonSdk),
+	).RunTest(t)
+
+	CheckSnapshot(t, result, "mysdk", "", checkAndroidBpContents(`// This is auto-generated. DO NOT EDIT.`))
+}
+
 func TestSnapshotWithSystemServerClasspathFragment(t *testing.T) {
 
 	commonSdk := `

sdk/update.go

@@ -455,12 +455,15 @@ be unnecessary as every module in the sdk already has its own licenses property.
 
 	for _, module := range builder.prebuiltOrder {
 		// Prune any empty property sets.
-		module = module.transform(pruneEmptySetTransformer{})
+		module = transformModule(module, pruneEmptySetTransformer{})
 
 		// Transform the module module to make it suitable for use in the snapshot.
-		module.transform(snapshotTransformer)
+		module = transformModule(module, snapshotTransformer)
+		module = transformModule(module, emptyClasspathContentsTransformation{})
+		if module != nil {
 			bpFile.AddModule(module)
 		}
+	}
 
 	// generate Android.bp
 	bp = newGeneratedFile(ctx, "snapshot", "Android.bp")
@@ -835,9 +838,11 @@ type snapshotTransformation struct {
 }
 
 func (t snapshotTransformation) transformModule(module *bpModule) *bpModule {
+	if module != nil {
 		// If the module is an internal member then use a unique name for it.
 		name := module.Name()
 		module.setProperty("name", t.builder.snapshotSdkMemberName(name, true))
+	}
 	return module
 }
 
@@ -850,6 +855,25 @@ func (t snapshotTransformation) transformProperty(_ string, value interface{}, t
 	}
 }
 
+type emptyClasspathContentsTransformation struct {
+	identityTransformation
+}
+
+func (t emptyClasspathContentsTransformation) transformModule(module *bpModule) *bpModule {
+	classpathModuleTypes := []string{
+		"prebuilt_bootclasspath_fragment",
+		"prebuilt_systemserverclasspath_fragment",
+	}
+	if module != nil && android.InList(module.moduleType, classpathModuleTypes) {
+		if contents, ok := module.bpPropertySet.properties["contents"].([]string); ok {
+			if len(contents) == 0 {
+				return nil
+			}
+		}
+	}
+	return module
+}
+
 type pruneEmptySetTransformer struct {
 	identityTransformation
 }