Propagate stubs to the SDK for libraries that have them.

Necessary to make the APEX build logic treat the libraries as API
boundaries rather than dependencies to bundle.

The .so files in the snapshots are the compiled stub libraries in this
case. They are strictly speaking redundant since they can be generated
from the .map.txt files in the snapshots, but doing that would require
extending the cc_prebuilt_library(_shared) module types with a full
compiler pass etc, and that would break a lot of assumptions in the cc
package.

Test: m nothing
Test: Create an SDK snapshot with Bionic libs, drop it into a
  master-art tree without bionic/ in it, build ART APEXes, and check
  that the Soong phase completes (specifically no errors about various
  APEX libs requiring libc that is not available to them).
Bug: 152481980
Change-Id: I31b928e6261198b6dd6f6b17196e714f07b64172

cc/cc.go

@@ -583,6 +583,13 @@ func (c *Module) GetDepsInLinkOrder() []android.Path {
 	return c.depsInLinkOrder
 }
 
+func (c *Module) StubsSymbolFile() android.OptionalPath {
+	if library, ok := c.linker.(*libraryDecorator); ok {
+		return library.stubsSymbolFile
+	}
+	return android.OptionalPath{}
+}
+
 func (c *Module) StubsVersions() []string {
 	if c.linker != nil {
 		if library, ok := c.linker.(*libraryDecorator); ok {

cc/library.go

@@ -367,6 +367,9 @@ type libraryDecorator struct {
 	// Location of the file that should be copied to dist dir when requested
 	distFile android.OptionalPath
 
+	// stubs.symbol_file
+	stubsSymbolFile android.OptionalPath
+
 	versionScriptPath android.ModuleGenPath
 
 	post_install_cmds []string
@@ -376,7 +379,7 @@ type libraryDecorator struct {
 	useCoreVariant       bool
 	checkSameCoreVariant bool
 
-	// Decorated interafaces
+	// Decorated interfaces
 	*baseCompiler
 	*baseLinker
 	*baseInstaller
@@ -603,6 +606,7 @@ func (library *libraryDecorator) shouldCreateSourceAbiDump(ctx ModuleContext) bo
 
 func (library *libraryDecorator) compile(ctx ModuleContext, flags Flags, deps PathDeps) Objects {
 	if library.buildStubs() {
+		library.stubsSymbolFile = android.OptionalPathForModuleSrc(ctx, library.Properties.Stubs.Symbol_file)
 		objs, versionScript := compileStubLibrary(ctx, flags, String(library.Properties.Stubs.Symbol_file), library.MutatedProperties.StubsVersion, "--apex")
 		library.versionScriptPath = versionScript
 		return objs

cc/library_sdk_member.go

@@ -269,12 +269,21 @@ func addPossiblyArchSpecificProperties(sdkModuleContext android.ModuleContext, b
 	for property, dirs := range includeDirs {
 		outputProperties.AddProperty(property, dirs)
 	}
+
+	if len(libInfo.StubsVersion) > 0 {
+		symbolFilePath := filepath.Join(nativeEtcDir, libInfo.StubsSymbolFile.Path().Base())
+		builder.CopyToSnapshot(libInfo.StubsSymbolFile.Path(), symbolFilePath)
+		stubsSet := outputProperties.AddPropertySet("stubs")
+		stubsSet.AddProperty("symbol_file", symbolFilePath)
+		stubsSet.AddProperty("versions", []string{libInfo.StubsVersion})
+	}
 }
 
 const (
 	nativeIncludeDir          = "include"
 	nativeGeneratedIncludeDir = "include_gen"
 	nativeStubDir             = "lib"
+	nativeEtcDir              = "etc"
 )
 
 // path to the native library. Relative to <sdk_root>/<api_dir>
@@ -335,6 +344,13 @@ type nativeLibInfoProperties struct {
 	// This field is exported as its contents may not be arch specific.
 	SystemSharedLibs []string
 
+	// The specific stubs version for the lib variant, or empty string if stubs
+	// are not in use.
+	StubsVersion string
+
+	// The stubs symbol file.
+	StubsSymbolFile android.OptionalPath
+
 	// outputFile is not exported as it is always arch specific.
 	outputFile android.Path
 }
@@ -370,6 +386,11 @@ func (p *nativeLibInfoProperties) PopulateFromVariant(ctx android.SdkMemberConte
 		p.SystemSharedLibs = specifiedDeps.systemSharedLibs
 	}
 	p.exportedGeneratedHeaders = ccModule.ExportedGeneratedHeaders()
+
+	if ccModule.HasStubsVariants() {
+		p.StubsVersion = ccModule.StubsVersion()
+		p.StubsSymbolFile = ccModule.StubsSymbolFile()
+	}
 }
 
 func (p *nativeLibInfoProperties) AddToPropertySet(ctx android.SdkMemberContext, propertySet android.BpPropertySet) {

sdk/cc_sdk_test.go

@@ -32,6 +32,7 @@ func testSdkWithCc(t *testing.T, bp string) *testSdkResult {
 		"arm64/include/Arm64Test.h":     nil,
 		"libfoo.so":                     nil,
 		"aidl/foo/bar/Test.aidl":        nil,
+		"some/where/stubslib.map.txt":   nil,
 	}
 	return testSdkWithFs(t, bp, fs)
 }
@@ -1739,3 +1740,65 @@ sdk_snapshot {
 }
 `))
 }
+
+func TestStubsLibrary(t *testing.T) {
+	result := testSdkWithCc(t, `
+		sdk {
+			name: "mysdk",
+			native_shared_libs: ["stubslib"],
+		}
+
+		cc_library {
+			name: "stubslib",
+			stubs: {
+				symbol_file: "some/where/stubslib.map.txt",
+				versions: ["1", "2", "3"],
+			},
+		}
+	`)
+
+	result.CheckSnapshot("mysdk", "",
+		checkAndroidBpContents(`
+// This is auto-generated. DO NOT EDIT.
+
+cc_prebuilt_library_shared {
+    name: "mysdk_stubslib@current",
+    sdk_member_name: "stubslib",
+    installable: false,
+    stubs: {
+        symbol_file: "etc/stubslib.map.txt",
+        versions: ["3"],
+    },
+    arch: {
+        arm64: {
+            srcs: ["arm64/lib/stubslib.so"],
+        },
+        arm: {
+            srcs: ["arm/lib/stubslib.so"],
+        },
+    },
+}
+
+cc_prebuilt_library_shared {
+    name: "stubslib",
+    prefer: false,
+    stubs: {
+        symbol_file: "etc/stubslib.map.txt",
+        versions: ["3"],
+    },
+    arch: {
+        arm64: {
+            srcs: ["arm64/lib/stubslib.so"],
+        },
+        arm: {
+            srcs: ["arm/lib/stubslib.so"],
+        },
+    },
+}
+
+sdk_snapshot {
+    name: "mysdk@current",
+    native_shared_libs: ["mysdk_stubslib@current"],
+}
+`))
+}