Add ApexModule interface for APEX-aware modules

ApexModule is the interface for APEX-aware modules. The module type apex
uses the interface to get APEX-specific information from other modules,
such as the list of APEXs that a module should be built for.

A module that is included in an APEX will be built specificaly for the
APEX. This is especially required for shared libraries; we shouldn't
just copy the artifacts built for platform, because they may be linking
against private (=unstable) symbols that are not available to APEXs
which are basically unbundled.

This CL, as a first step, makes cc.Module an APEX-aware module type.

Bug: 112672359
Test: m apex.test; the built apex has all the direct and transitive
shared lib dependencies of the libs and executables listed in Android.bp

Change-Id: I21f6a586654779984f0f5154b2a08b2adbf2168b

Android.bp

@@ -40,6 +40,7 @@ bootstrap_go_package {
     ],
     srcs: [
         "android/androidmk.go",
+        "android/apex.go",
         "android/api_levels.go",
         "android/arch.go",
         "android/config.go",

android/apex.go

@@ -0,0 +1,102 @@
+// Copyright 2018 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package android
+
+// ApexModule is the interface that a module type is expected to implement if
+// the module has to be built differently depending on whether the module
+// is destined for an apex or not (installed to one of the regular partitions).
+//
+// Native shared libraries are one such module type; when it is built for an
+// APEX, it should depend only on stable interfaces such as NDK, stable AIDL,
+// or C APIs from other APEXs.
+//
+// A module implementing this interface will be mutated into multiple
+// variations by the apex mutator if it is directly or indirectly included
+// in one or more APEXs. Specifically, if a module is included in apex.foo and
+// apex.bar then three apex variants are created: platform, apex.foo and
+// apex.bar. The platform variant is for the regular partitions
+// (e.g., /system or /vendor, etc.) while the other two are for the APEXs,
+// respectively.
+type ApexModule interface {
+	Module
+	apexModuleBase() *ApexModuleBase
+
+	// Marks that this module should be built for the APEX of the specified name
+	BuildForApex(apexName string)
+
+	// Tests whether this module will be built for the platform or not (= APEXs)
+	IsForPlatform() bool
+
+	// Returns the name of APEX that this module will be built for. Empty string
+	// is returned when 'IsForPlatform() == true'. Note that a module can be
+	// included to multiple APEXs, in which case, the module is mutated into
+	// multiple modules each of which for an APEX. This method returns the
+	// name of the APEX that a variant module is for.
+	ApexName() string
+
+	// Tests if this module can have APEX variants. APEX variants are
+	// created only for the modules that returns true here. This is useful
+	// for not creating APEX variants for shared libraries such as NDK stubs.
+	CanHaveApexVariants() bool
+
+	// Tests if this module can be installed to APEX as a file. For example,
+	// this would return true for shared libs while return false for static
+	// libs.
+	IsInstallableToApex() bool
+}
+
+type ApexProperties struct {
+	ApexName string `blueprint:"mutated"`
+}
+
+// Provides default implementation for the ApexModule interface. APEX-aware
+// modules are expected to include this struct and call InitApexModule().
+type ApexModuleBase struct {
+	ApexProperties ApexProperties
+
+	canHaveApexVariants bool
+}
+
+func (m *ApexModuleBase) apexModuleBase() *ApexModuleBase {
+	return m
+}
+
+func (m *ApexModuleBase) BuildForApex(apexName string) {
+	m.ApexProperties.ApexName = apexName
+}
+
+func (m *ApexModuleBase) IsForPlatform() bool {
+	return m.ApexProperties.ApexName == ""
+}
+
+func (m *ApexModuleBase) ApexName() string {
+	return m.ApexProperties.ApexName
+}
+
+func (m *ApexModuleBase) CanHaveApexVariants() bool {
+	return m.canHaveApexVariants
+}
+
+func (m *ApexModuleBase) IsInstallableToApex() bool {
+	// should be overriden if needed
+	return false
+}
+
+func InitApexModule(m ApexModule) {
+	base := m.apexModuleBase()
+	base.canHaveApexVariants = true
+
+	m.AddProperties(&base.ApexProperties)
+}

cc/androidmk.go

@@ -51,7 +51,7 @@ func (c *Module) subAndroidMk(data *android.AndroidMkData, obj interface{}) {
 }
 
 func (c *Module) AndroidMk() android.AndroidMkData {
-	if c.Properties.HideFromMake {
+	if c.Properties.HideFromMake || !c.IsForPlatform() {
 		return android.AndroidMkData{
 			Disabled: true,
 		}

cc/cc.go

@@ -320,6 +320,7 @@ var (
 type Module struct {
 	android.ModuleBase
 	android.DefaultableModuleBase
+	android.ApexModuleBase
 
 	Properties       BaseProperties
 	VendorProperties VendorProperties
@@ -416,6 +417,8 @@ func (c *Module) Init() android.Module {
 
 	android.InitDefaultableModule(c)
 
+	android.InitApexModule(c)
+
 	return c
 }
 
@@ -794,7 +797,7 @@ func (c *Module) GenerateAndroidBuildActions(actx android.ModuleContext) {
 		c.outputFile = android.OptionalPathForPath(outputFile)
 	}
 
-	if c.installer != nil && !c.Properties.PreventInstall && c.outputFile.Valid() {
+	if c.installer != nil && !c.Properties.PreventInstall && c.IsForPlatform() && c.outputFile.Valid() {
 		c.installer.install(ctx, c.outputFile.Path())
 		if ctx.Failed() {
 			return
@@ -1511,12 +1514,24 @@ func (c *Module) getMakeLinkType() string {
 	}
 }
 
+// Overrides ApexModule.IsInstallabeToApex()
+// Only shared libraries are installable to APEX.
+func (c *Module) IsInstallableToApex() bool {
+	if shared, ok := c.linker.(interface {
+		shared() bool
+	}); ok {
+		return shared.shared()
+	}
+	return false
+}
+
 //
 // Defaults
 //
 type Defaults struct {
 	android.ModuleBase
 	android.DefaultsModuleBase
+	android.ApexModuleBase
 }
 
 func (*Defaults) GenerateAndroidBuildActions(ctx android.ModuleContext) {
@@ -1558,6 +1573,7 @@ func DefaultsFactory(props ...interface{}) android.Module {
 	)
 
 	android.InitDefaultsModule(module)
+	android.InitApexModule(module)
 
 	return module
 }