Add PropertyCustomizer

Allow any module factory to insert a PropertyCustomizer on the module,
which will be called before any other mutators.  The PropertyCustomizer
can append or prepend to any properties, allowing module types to extend
other module types by modifying the public, stable interface provided by
the properties.

Change-Id: Idff02be80d939a70df1c6bbccffdd1f04ff975d2

Android.bp

@@ -94,6 +94,7 @@ bootstrap_go_package {
         "android/androidmk.go",
         "android/arch.go",
         "android/config.go",
+        "android/customizer.go",
         "android/defaults.go",
         "android/defs.go",
         "android/glob.go",

android/arch.go

@@ -24,13 +24,6 @@ import (
 	"github.com/google/blueprint/proptools"
 )
 
-func init() {
-	RegisterBottomUpMutator("defaults_deps", defaultsDepsMutator).Parallel()
-	RegisterTopDownMutator("defaults", defaultsMutator).Parallel()
-
-	RegisterBottomUpMutator("arch", ArchMutator).Parallel()
-}
-
 var (
 	Arm    = newArch("arm", "lib32")
 	Arm64  = newArch("arm64", "lib64")
@@ -490,6 +483,8 @@ func InitArchModule(m Module,
 		allProperties = append(allProperties, asp)
 	}
 
+	base.customizableProperties = allProperties
+
 	return m, allProperties
 }
 

android/customizer.go

@@ -0,0 +1,77 @@
+// Copyright 2016 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 "github.com/google/blueprint/proptools"
+
+type CustomizePropertiesContext interface {
+	BaseContext
+	AppendProperties(...interface{})
+	PrependProperties(...interface{})
+}
+
+type customizePropertiesContext struct {
+	BaseContext
+
+	module *ModuleBase
+}
+
+type PropertyCustomizer interface {
+	CustomizeProperties(CustomizePropertiesContext)
+}
+
+func customizerMutator(ctx TopDownMutatorContext) {
+	if m, ok := ctx.Module().(Module); ok {
+		a := m.base()
+		if len(a.customizers) > 0 {
+			mctx := &customizePropertiesContext{
+				BaseContext: ctx,
+				module:      a,
+			}
+			for _, c := range a.customizers {
+				c.CustomizeProperties(mctx)
+				if mctx.Failed() {
+					return
+				}
+			}
+		}
+	}
+}
+
+func (ctx *customizePropertiesContext) AppendProperties(props ...interface{}) {
+	for _, p := range props {
+		err := proptools.AppendMatchingProperties(ctx.module.customizableProperties, p, nil)
+		if err != nil {
+			if propertyErr, ok := err.(*proptools.ExtendPropertyError); ok {
+				ctx.PropertyErrorf(propertyErr.Property, "%s", propertyErr.Err.Error())
+			} else {
+				panic(err)
+			}
+		}
+	}
+}
+
+func (ctx *customizePropertiesContext) PrependProperties(props ...interface{}) {
+	for _, p := range props {
+		err := proptools.PrependMatchingProperties(ctx.module.customizableProperties, p, nil)
+		if err != nil {
+			if propertyErr, ok := err.(*proptools.ExtendPropertyError); ok {
+				ctx.PropertyErrorf(propertyErr.Property, "%s", propertyErr.Err.Error())
+			} else {
+				panic(err)
+			}
+		}
+	}
+}

android/module.go

@@ -25,6 +25,14 @@ import (
 	"github.com/google/blueprint"
 )
 
+func init() {
+	RegisterTopDownMutator("customizer", customizerMutator).Parallel()
+	RegisterBottomUpMutator("defaults_deps", defaultsDepsMutator).Parallel()
+	RegisterTopDownMutator("defaults", defaultsMutator).Parallel()
+
+	RegisterBottomUpMutator("arch", ArchMutator).Parallel()
+}
+
 var (
 	DeviceSharedLibrary = "shared_library"
 	DeviceStaticLibrary = "static_library"
@@ -188,6 +196,11 @@ func InitAndroidArchModule(m Module, hod HostOrDeviceSupported, defaultMultilib
 	return InitArchModule(m, propertyStructs...)
 }
 
+func AddCustomizer(m blueprint.Module, c PropertyCustomizer) {
+	base := m.(Module).base()
+	base.customizers = append(base.customizers, c)
+}
+
 // A AndroidModuleBase object contains the properties that are common to all Android
 // modules.  It should be included as an anonymous field in every module
 // struct definition.  InitAndroidModule should then be called from the module's
@@ -238,6 +251,7 @@ type ModuleBase struct {
 	hostAndDeviceProperties hostAndDeviceProperties
 	generalProperties       []interface{}
 	archProperties          []*archProperties
+	customizableProperties  []interface{}
 
 	noAddressSanitizer bool
 	installFiles       Paths
@@ -248,6 +262,8 @@ type ModuleBase struct {
 	installTarget    string
 	checkbuildTarget string
 	blueprintDir     string
+
+	customizers []PropertyCustomizer
 }
 
 func (a *ModuleBase) base() *ModuleBase {