Add path properties mutator

Add a mutator pass after DepsMutator that visits every property
struct in every module looking for properties that have a tag
`android:"path"`, and automatically add a SourceDepTag dependency
on any module references (":module-name") found.  Uses a cache to
store the mapping of property struct type to locations of
properties with the tag.

Test: android/path_properties_test.go
Change-Id: I38c0497843dde4890e9342c3a6f0b402c0720742

1 files changed, 123 insertions, 0 deletions

diff --git a/android/path_properties.go b/android/path_properties.go
new file mode 100644
index 000000000..5d8970927
--- /dev/null
+++ b/android/path_properties.go
@@ -0,0 +1,123 @@
+// Copyright 2019 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"
+	"reflect"
+
+	"github.com/google/blueprint/proptools"
+)
+
+func registerPathDepsMutator(ctx RegisterMutatorsContext) {
+	ctx.BottomUp("pathdeps", pathDepsMutator).Parallel()
+}
+
+// The pathDepsMutator automatically adds dependencies on any module that is listed with ":module" syntax in a
+// property that is tagged with android:"path".
+func pathDepsMutator(ctx BottomUpMutatorContext) {
+	m := ctx.Module().(Module)
+	if m == nil {
+		return
+	}
+
+	props := m.base().customizableProperties
+
+	for _, ps := range props {
+		pathProperties := pathPropertiesForPropertyStruct(ctx, ps)
+		pathProperties = FirstUniqueStrings(pathProperties)
+
+		var deps []string
+		for _, s := range pathProperties {
+			if m := SrcIsModule(s); m != "" {
+				deps = append(deps, m)
+			}
+		}
+
+		ctx.AddDependency(ctx.Module(), SourceDepTag, deps...)
+	}
+}
+
+// pathPropertiesForPropertyStruct uses the indexes of properties that are tagged with android:"path" to extract
+// all their values from a property struct, returning them as a single slice of strings..
+func pathPropertiesForPropertyStruct(ctx BottomUpMutatorContext, ps interface{}) []string {
+	v := reflect.ValueOf(ps)
+	if v.Kind() != reflect.Ptr || v.Elem().Kind() != reflect.Struct {
+		panic(fmt.Errorf("type %s is not a pointer to a struct", v.Type()))
+	}
+	if v.IsNil() {
+		return nil
+	}
+	v = v.Elem()
+
+	pathPropertyIndexes := pathPropertyIndexesForPropertyStruct(ps)
+
+	var ret []string
+
+	for _, i := range pathPropertyIndexes {
+		sv := fieldByIndex(v, i)
+		if !sv.IsValid() {
+			continue
+		}
+
+		if sv.Kind() == reflect.Ptr {
+			if sv.IsNil() {
+				continue
+			}
+			sv = sv.Elem()
+		}
+		switch sv.Kind() {
+		case reflect.String:
+			ret = append(ret, sv.String())
+		case reflect.Slice:
+			ret = append(ret, sv.Interface().([]string)...)
+		default:
+			panic(fmt.Errorf(`field %s in type %s has tag android:"path" but is not a string or slice of strings, it is a %s`,
+				v.Type().FieldByIndex(i).Name, v.Type(), sv.Type()))
+		}
+	}
+
+	return ret
+}
+
+// fieldByIndex is like reflect.Value.FieldByIndex, but returns an invalid reflect.Value when traversing a nil pointer
+// to a struct.
+func fieldByIndex(v reflect.Value, index []int) reflect.Value {
+	if len(index) == 1 {
+		return v.Field(index[0])
+	}
+	for _, x := range index {
+		if v.Kind() == reflect.Ptr {
+			if v.IsNil() {
+				return reflect.Value{}
+			}
+			v = v.Elem()
+		}
+		v = v.Field(x)
+	}
+	return v
+}
+
+var pathPropertyIndexesCache OncePer
+
+// pathPropertyIndexesForPropertyStruct returns a list of all of the indexes of properties in property struct type that
+// are tagged with android:"path".  Each index is a []int suitable for passing to reflect.Value.FieldByIndex.  The value
+// is cached in a global cache by type.
+func pathPropertyIndexesForPropertyStruct(ps interface{}) [][]int {
+	key := NewCustomOnceKey(reflect.TypeOf(ps))
+	return pathPropertyIndexesCache.Once(key, func() interface{} {
+		return proptools.PropertyIndexesWithTag(ps, "android", "path")
+	}).([][]int)
+}