Add a new SingletonModule type

A SingletonModule is halfway between a Singleton and a Module.  It has
access to visiting other modules via its GenerateSingletonBuildActions
method, but must be defined in an Android.bp file and can also be
depended on like a module.

Bug: 176904285
Test: singleton_module_test.go
Change-Id: I1b2bfdfb3927c1eabf431c53213cb7c581e33ca4

android/Android.bp

@@ -59,6 +59,7 @@ bootstrap_go_package {
         "sandbox.go",
         "sdk.go",
         "singleton.go",
+        "singleton_module.go",
         "soong_config_modules.go",
         "test_suites.go",
         "testing.go",
@@ -95,6 +96,7 @@ bootstrap_go_package {
         "paths_test.go",
         "prebuilt_test.go",
         "rule_builder_test.go",
+        "singleton_module_test.go",
         "soong_config_modules_test.go",
         "util_test.go",
         "variable_test.go",

android/makevars.go

@@ -134,8 +134,6 @@ func RegisterMakeVarsProvider(pctx PackageContext, provider MakeVarsProvider) {
 
 // SingletonMakeVarsProvider is a Singleton with an extra method to provide extra values to be exported to Make.
 type SingletonMakeVarsProvider interface {
-	Singleton
-
 	// MakeVars uses a MakeVarsContext to provide extra values to be exported to Make.
 	MakeVars(ctx MakeVarsContext)
 }

android/register.go

@@ -16,6 +16,7 @@ package android
 
 import (
 	"fmt"
+	"reflect"
 
 	"github.com/google/blueprint"
 )
@@ -26,6 +27,7 @@ type moduleType struct {
 }
 
 var moduleTypes []moduleType
+var moduleTypesForDocs = map[string]reflect.Value{}
 
 type singleton struct {
 	name    string
@@ -69,6 +71,16 @@ func SingletonFactoryAdaptor(ctx *Context, factory SingletonFactory) blueprint.S
 
 func RegisterModuleType(name string, factory ModuleFactory) {
 	moduleTypes = append(moduleTypes, moduleType{name, factory})
+	RegisterModuleTypeForDocs(name, reflect.ValueOf(factory))
+}
+
+// RegisterModuleTypeForDocs associates a module type name with a reflect.Value of the factory
+// function that has documentation for the module type.  It is normally called automatically
+// by RegisterModuleType, but can be called manually after RegisterModuleType in order to
+// override the factory method used for documentation, for example if the method passed to
+// RegisterModuleType was a lambda.
+func RegisterModuleTypeForDocs(name string, factory reflect.Value) {
+	moduleTypesForDocs[name] = factory
 }
 
 func RegisterSingletonType(name string, factory SingletonFactory) {
@@ -142,12 +154,17 @@ func ModuleTypeFactories() map[string]ModuleFactory {
 	return ret
 }
 
+func ModuleTypeFactoriesForDocs() map[string]reflect.Value {
+	return moduleTypesForDocs
+}
+
 // Interface for registering build components.
 //
 // Provided to allow registration of build components to be shared between the runtime
 // and test environments.
 type RegistrationContext interface {
 	RegisterModuleType(name string, factory ModuleFactory)
+	RegisterSingletonModuleType(name string, factory SingletonModuleFactory)
 	RegisterSingletonType(name string, factory SingletonFactory)
 	PreArchMutators(f RegisterMutatorFunc)
 
@@ -186,8 +203,9 @@ var InitRegistrationContext RegistrationContext = &initRegistrationContext{
 var _ RegistrationContext = (*TestContext)(nil)
 
 type initRegistrationContext struct {
-	moduleTypes    map[string]ModuleFactory
-	singletonTypes map[string]SingletonFactory
+	moduleTypes        map[string]ModuleFactory
+	singletonTypes     map[string]SingletonFactory
+	moduleTypesForDocs map[string]reflect.Value
 }
 
 func (ctx *initRegistrationContext) RegisterModuleType(name string, factory ModuleFactory) {
@@ -196,6 +214,17 @@ func (ctx *initRegistrationContext) RegisterModuleType(name string, factory Modu
 	}
 	ctx.moduleTypes[name] = factory
 	RegisterModuleType(name, factory)
+	RegisterModuleTypeForDocs(name, reflect.ValueOf(factory))
+}
+
+func (ctx *initRegistrationContext) RegisterSingletonModuleType(name string, factory SingletonModuleFactory) {
+	s, m := SingletonModuleFactoryAdaptor(name, factory)
+	ctx.RegisterSingletonType(name, s)
+	ctx.RegisterModuleType(name, m)
+	// Overwrite moduleTypesForDocs with the original factory instead of the lambda returned by
+	// SingletonModuleFactoryAdaptor so that docs can find the module type documentation on the
+	// factory method.
+	RegisterModuleTypeForDocs(name, reflect.ValueOf(factory))
 }
 
 func (ctx *initRegistrationContext) RegisterSingletonType(name string, factory SingletonFactory) {

android/singleton_module.go

@@ -0,0 +1,146 @@
+// Copyright 2020 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
+
+import (
+	"fmt"
+	"sync"
+
+	"github.com/google/blueprint"
+)
+
+// A SingletonModule is halfway between a Singleton and a Module.  It has access to visiting
+// other modules via its GenerateSingletonBuildActions method, but must be defined in an Android.bp
+// file and can also be depended on like a module.  It must be used zero or one times in an
+// Android.bp file, and it can only have a single variant.
+//
+// The SingletonModule's GenerateAndroidBuildActions method will be called before any normal or
+// singleton module that depends on it, but its GenerateSingletonBuildActions method will be called
+// after all modules, in registration order with other singletons and singleton modules.
+// GenerateAndroidBuildActions and GenerateSingletonBuildActions will not be called if the
+// SingletonModule was not instantiated in an Android.bp file.
+//
+// Since the SingletonModule rules likely depend on the modules visited during
+// GenerateSingletonBuildActions, the GenerateAndroidBuildActions is unlikely to produce any
+// rules directly.  Instead, it will probably set some providers to paths that will later have rules
+// generated to produce them in GenerateSingletonBuildActions.
+//
+// The expected use case for a SingletonModule is a module that produces files that depend on all
+// modules in the tree and will be used by other modules.  For example it could produce a text
+// file that lists all modules that meet a certain criteria, and that text file could be an input
+// to another module.  Care must be taken that the ninja rules produced by the SingletonModule
+// don't produce a cycle by referencing output files of rules of modules that depend on the
+// SingletonModule.
+//
+// A SingletonModule must embed a SingletonModuleBase struct, and its factory method must be
+// registered with RegisterSingletonModuleType from an init() function.
+//
+// A SingletonModule can also implement SingletonMakeVarsProvider to export values to Make.
+type SingletonModule interface {
+	Module
+	GenerateSingletonBuildActions(SingletonContext)
+	singletonModuleBase() *SingletonModuleBase
+}
+
+// SingletonModuleBase must be embedded into implementers of the SingletonModule interface.
+type SingletonModuleBase struct {
+	ModuleBase
+
+	lock    sync.Mutex
+	bp      string
+	variant string
+}
+
+// GenerateBuildActions wraps the ModuleBase GenerateBuildActions method, verifying it was only
+// called once to prevent multiple variants of a SingletonModule.
+func (smb *SingletonModuleBase) GenerateBuildActions(ctx blueprint.ModuleContext) {
+	smb.lock.Lock()
+	if smb.variant != "" {
+		ctx.ModuleErrorf("GenerateAndroidBuildActions already called for variant %q, SingletonModules can only  have one variant", smb.variant)
+	}
+	smb.variant = ctx.ModuleSubDir()
+	smb.lock.Unlock()
+
+	smb.ModuleBase.GenerateBuildActions(ctx)
+}
+
+// InitAndroidSingletonModule must be called from the SingletonModule's factory function to
+// initialize SingletonModuleBase.
+func InitAndroidSingletonModule(sm SingletonModule) {
+	InitAndroidModule(sm)
+}
+
+// singletonModuleBase retrieves the embedded SingletonModuleBase from a SingletonModule.
+func (smb *SingletonModuleBase) singletonModuleBase() *SingletonModuleBase { return smb }
+
+// SingletonModuleFactory is a factory method that returns a SingletonModule.
+type SingletonModuleFactory func() SingletonModule
+
+// SingletonModuleFactoryAdaptor converts a SingletonModuleFactory into a SingletonFactory and a
+// ModuleFactory.
+func SingletonModuleFactoryAdaptor(name string, factory SingletonModuleFactory) (SingletonFactory, ModuleFactory) {
+	// The sm variable acts as a static holder of the only SingletonModule instance.  Calls to the
+	// returned SingletonFactory and ModuleFactory lambdas will always return the same sm value.
+	// The SingletonFactory is only expected to be called once, but the ModuleFactory may be
+	// called multiple times if the module is replaced with a clone of itself at the end of
+	// blueprint.ResolveDependencies.
+	var sm SingletonModule
+	s := func() Singleton {
+		sm = factory()
+		return &singletonModuleSingletonAdaptor{sm}
+	}
+	m := func() Module {
+		if sm == nil {
+			panic(fmt.Errorf("Singleton %q for SingletonModule was not instantiated", name))
+		}
+
+		// Check for multiple uses of a SingletonModule in a LoadHook.  Checking directly in the
+		// factory would incorrectly flag when the factory was called again when the module is
+		// replaced with a clone of itself at the end of blueprint.ResolveDependencies.
+		AddLoadHook(sm, func(ctx LoadHookContext) {
+			smb := sm.singletonModuleBase()
+			smb.lock.Lock()
+			defer smb.lock.Unlock()
+			if smb.bp != "" {
+				ctx.ModuleErrorf("Duplicate SingletonModule %q, previously used in %s", name, smb.bp)
+			}
+			smb.bp = ctx.BlueprintsFile()
+		})
+		return sm
+	}
+	return s, m
+}
+
+// singletonModuleSingletonAdaptor makes a SingletonModule into a Singleton by translating the
+// GenerateSingletonBuildActions method to Singleton.GenerateBuildActions.
+type singletonModuleSingletonAdaptor struct {
+	sm SingletonModule
+}
+
+// GenerateBuildActions calls the SingletonModule's GenerateSingletonBuildActions method, but only
+// if the module was defined in an Android.bp file.
+func (smsa *singletonModuleSingletonAdaptor) GenerateBuildActions(ctx SingletonContext) {
+	if smsa.sm.singletonModuleBase().bp != "" {
+		smsa.sm.GenerateSingletonBuildActions(ctx)
+	}
+}
+
+func (smsa *singletonModuleSingletonAdaptor) MakeVars(ctx MakeVarsContext) {
+	if smsa.sm.singletonModuleBase().bp != "" {
+		if makeVars, ok := smsa.sm.(SingletonMakeVarsProvider); ok {
+			makeVars.MakeVars(ctx)
+		}
+	}
+}

android/singleton_module_test.go

@@ -0,0 +1,149 @@
+// Copyright 2021 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
+
+import (
+	"reflect"
+	"strings"
+	"testing"
+)
+
+type testSingletonModule struct {
+	SingletonModuleBase
+	ops []string
+}
+
+func (tsm *testSingletonModule) GenerateAndroidBuildActions(ctx ModuleContext) {
+	tsm.ops = append(tsm.ops, "GenerateAndroidBuildActions")
+}
+
+func (tsm *testSingletonModule) GenerateSingletonBuildActions(ctx SingletonContext) {
+	tsm.ops = append(tsm.ops, "GenerateSingletonBuildActions")
+}
+
+func (tsm *testSingletonModule) MakeVars(ctx MakeVarsContext) {
+	tsm.ops = append(tsm.ops, "MakeVars")
+}
+
+func testSingletonModuleFactory() SingletonModule {
+	tsm := &testSingletonModule{}
+	InitAndroidSingletonModule(tsm)
+	return tsm
+}
+
+func runSingletonModuleTest(bp string) (*TestContext, []error) {
+	config := TestConfig(buildDir, nil, bp, nil)
+	// Enable Kati output to test SingletonModules with MakeVars.
+	config.katiEnabled = true
+	ctx := NewTestContext(config)
+	ctx.RegisterSingletonModuleType("test_singleton_module", testSingletonModuleFactory)
+	ctx.RegisterSingletonType("makevars", makeVarsSingletonFunc)
+	ctx.Register()
+
+	_, errs := ctx.ParseBlueprintsFiles("Android.bp")
+	if len(errs) > 0 {
+		return ctx, errs
+	}
+
+	_, errs = ctx.PrepareBuildActions(config)
+	return ctx, errs
+}
+
+func TestSingletonModule(t *testing.T) {
+	bp := `
+		test_singleton_module {
+			name: "test_singleton_module",
+		}
+	`
+	ctx, errs := runSingletonModuleTest(bp)
+	if len(errs) > 0 {
+		t.Fatal(errs)
+	}
+
+	ops := ctx.ModuleForTests("test_singleton_module", "").Module().(*testSingletonModule).ops
+	wantOps := []string{"GenerateAndroidBuildActions", "GenerateSingletonBuildActions", "MakeVars"}
+	if !reflect.DeepEqual(ops, wantOps) {
+		t.Errorf("Expected operations %q, got %q", wantOps, ops)
+	}
+}
+
+func TestDuplicateSingletonModule(t *testing.T) {
+	bp := `
+		test_singleton_module {
+			name: "test_singleton_module",
+		}
+
+		test_singleton_module {
+			name: "test_singleton_module2",
+		}
+	`
+	_, errs := runSingletonModuleTest(bp)
+	if len(errs) == 0 {
+		t.Fatal("expected duplicate SingletonModule error")
+	}
+	if len(errs) != 1 || !strings.Contains(errs[0].Error(), `Duplicate SingletonModule "test_singleton_module", previously used in`) {
+		t.Fatalf("expected duplicate SingletonModule error, got %q", errs)
+	}
+}
+
+func TestUnusedSingletonModule(t *testing.T) {
+	bp := ``
+	ctx, errs := runSingletonModuleTest(bp)
+	if len(errs) > 0 {
+		t.Fatal(errs)
+	}
+
+	singleton := ctx.SingletonForTests("test_singleton_module").Singleton()
+	sm := singleton.(*singletonModuleSingletonAdaptor).sm
+	ops := sm.(*testSingletonModule).ops
+	if ops != nil {
+		t.Errorf("Expected no operations, got %q", ops)
+	}
+}
+
+func testVariantSingletonModuleMutator(ctx BottomUpMutatorContext) {
+	if _, ok := ctx.Module().(*testSingletonModule); ok {
+		ctx.CreateVariations("a", "b")
+	}
+}
+
+func TestVariantSingletonModule(t *testing.T) {
+	bp := `
+		test_singleton_module {
+			name: "test_singleton_module",
+		}
+	`
+
+	config := TestConfig(buildDir, nil, bp, nil)
+	ctx := NewTestContext(config)
+	ctx.PreDepsMutators(func(ctx RegisterMutatorsContext) {
+		ctx.BottomUp("test_singleton_module_mutator", testVariantSingletonModuleMutator)
+	})
+	ctx.RegisterSingletonModuleType("test_singleton_module", testSingletonModuleFactory)
+	ctx.Register()
+
+	_, errs := ctx.ParseBlueprintsFiles("Android.bp")
+
+	if len(errs) == 0 {
+		_, errs = ctx.PrepareBuildActions(config)
+	}
+
+	if len(errs) == 0 {
+		t.Fatal("expected duplicate SingletonModule error")
+	}
+	if len(errs) != 1 || !strings.Contains(errs[0].Error(), `GenerateAndroidBuildActions already called for variant`) {
+		t.Fatalf("expected duplicate SingletonModule error, got %q", errs)
+	}
+}

android/testing.go

@@ -103,6 +103,12 @@ func (ctx *TestContext) RegisterModuleType(name string, factory ModuleFactory) {
 	ctx.Context.RegisterModuleType(name, ModuleFactoryAdaptor(factory))
 }
 
+func (ctx *TestContext) RegisterSingletonModuleType(name string, factory SingletonModuleFactory) {
+	s, m := SingletonModuleFactoryAdaptor(name, factory)
+	ctx.RegisterSingletonType(name, s)
+	ctx.RegisterModuleType(name, m)
+}
+
 func (ctx *TestContext) RegisterSingletonType(name string, factory SingletonFactory) {
 	ctx.Context.RegisterSingletonType(name, SingletonFactoryAdaptor(ctx.Context, factory))
 }

cmd/soong_build/writedocs.go

@@ -20,7 +20,6 @@ import (
 	"html/template"
 	"io/ioutil"
 	"path/filepath"
-	"reflect"
 	"sort"
 
 	"github.com/google/blueprint/bootstrap"
@@ -97,12 +96,8 @@ func moduleTypeDocsToTemplates(moduleTypeList []*bpdoc.ModuleType) []moduleTypeT
 }
 
 func getPackages(ctx *android.Context) ([]*bpdoc.Package, error) {
-	moduleTypeFactories := android.ModuleTypeFactories()
-	bpModuleTypeFactories := make(map[string]reflect.Value)
-	for moduleType, factory := range moduleTypeFactories {
-		bpModuleTypeFactories[moduleType] = reflect.ValueOf(factory)
-	}
-	return bootstrap.ModuleTypeDocs(ctx.Context, bpModuleTypeFactories)
+	moduleTypeFactories := android.ModuleTypeFactoriesForDocs()
+	return bootstrap.ModuleTypeDocs(ctx.Context, moduleTypeFactories)
 }
 
 func writeDocs(ctx *android.Context, filename string) error {