Add override_module.

This new module type replaces the inherit-package function in make by
allowing developers to override the name, the certificate, and the
manifest package name of an android_app module.

Bug: 122957760
Fixes: 123640028
Test: app_test.go + BrowserGoogle
Change-Id: Iefe447e7078b25039233221361ef95c83a29973a

android/override_module.go

@@ -0,0 +1,97 @@
+package android
+
+import (
+	"github.com/google/blueprint/proptools"
+	"sync"
+)
+
+func init() {
+	RegisterModuleType("override_module", OverrideModuleFactory)
+}
+
+type OverrideModule struct {
+	ModuleBase
+	properties OverrideModuleProperties
+}
+
+type OverrideModuleProperties struct {
+	// base module to override
+	Base *string
+
+	// file path or module name (in the form ":module") of a certificate to override with
+	Certificate *string
+
+	// manifest package name to override with
+	Manifest_package_name *string
+}
+
+// TODO(jungjw): Work with the mainline team to see if we can deprecate all PRODUCT_*_OVERRIDES vars
+// and hand over overriding values directly to base module code.
+func processOverrides(ctx LoadHookContext, p *OverrideModuleProperties) {
+	base := proptools.String(p.Base)
+	if base == "" {
+		ctx.PropertyErrorf("base", "base module name must be provided")
+	}
+
+	config := ctx.DeviceConfig()
+	if other, loaded := config.moduleNameOverrides().LoadOrStore(base, ctx.ModuleName()); loaded {
+		ctx.ModuleErrorf("multiple overriding modules for %q, the other: %q", base, other.(string))
+	}
+
+	if p.Certificate != nil {
+		config.certificateOverrides().Store(base, *p.Certificate)
+	}
+
+	if p.Manifest_package_name != nil {
+		config.manifestPackageNameOverrides().Store(base, *p.Manifest_package_name)
+	}
+}
+
+func (i *OverrideModule) DepsMutator(ctx BottomUpMutatorContext) {
+	base := *i.properties.Base
+	// Right now, we add a dependency only to check the base module exists, and so are not using a tag here.
+	// TODO(jungjw): Add a tag and check the base module type once we finalize supported base module types.
+	ctx.AddDependency(ctx.Module(), nil, base)
+}
+
+func (i *OverrideModule) GenerateAndroidBuildActions(ctx ModuleContext) {
+	// All the overrides happen in the base module.
+	// TODO(jungjw): Check the base module type.
+}
+
+// override_module overrides an existing module with the specified properties.
+//
+// Currently, only android_app is officially supported.
+func OverrideModuleFactory() Module {
+	m := &OverrideModule{}
+	AddLoadHook(m, func(ctx LoadHookContext) {
+		processOverrides(ctx, &m.properties)
+	})
+	m.AddProperties(&m.properties)
+	InitAndroidModule(m)
+	return m
+}
+
+var moduleNameOverridesKey = NewOnceKey("moduleNameOverrides")
+
+func (c *deviceConfig) moduleNameOverrides() *sync.Map {
+	return c.Once(moduleNameOverridesKey, func() interface{} {
+		return &sync.Map{}
+	}).(*sync.Map)
+}
+
+var certificateOverridesKey = NewOnceKey("certificateOverrides")
+
+func (c *deviceConfig) certificateOverrides() *sync.Map {
+	return c.Once(certificateOverridesKey, func() interface{} {
+		return &sync.Map{}
+	}).(*sync.Map)
+}
+
+var manifestPackageNameOverridesKey = NewOnceKey("manifestPackageNameOverrides")
+
+func (c *deviceConfig) manifestPackageNameOverrides() *sync.Map {
+	return c.Once(manifestPackageNameOverridesKey, func() interface{} {
+		return &sync.Map{}
+	}).(*sync.Map)
+}