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

4 files changed, 96 insertions, 7 deletions

diff --git a/Android.bp b/Android.bp
index bb9ab74c..355dfd2e 100644
--- a/Android.bp
+++ b/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",
diff --git a/android/arch.go b/android/arch.go
index 2d38dafc..62acb09d 100644
--- a/android/arch.go
+++ b/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
 }
 
diff --git a/android/customizer.go b/android/customizer.go
new file mode 100644
index 00000000..056880da
--- /dev/null
+++ b/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)
+			}
+		}
+	}
+}
diff --git a/android/module.go b/android/module.go
index 03c06b42..fd37ca85 100644
--- a/android/module.go
+++ b/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 {