android/path_properties.go

// 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"
)

// This file implements support for automatically adding dependencies on any module referenced
// with the ":module" module reference syntax in a property that is annotated with `android:"path"`.
// The dependency is used by android.PathForModuleSrc to convert the module reference into the path
// to the output file of the referenced module.

func registerPathDepsMutator(ctx RegisterMutatorsContext) {
	ctx.BottomUp("pathdeps", pathDepsMutator).Parallel()
}

// The pathDepsMutator automatically adds dependencies on any module that is listed with the
// ":module" module reference syntax in a property that is tagged with `android:"path"`.
func pathDepsMutator(ctx BottomUpMutatorContext) {
	props := ctx.Module().base().generalProperties

	// Iterate through each property struct of the module extracting the contents of all properties
	// tagged with `android:"path"`.
	var pathProperties []string
	for _, ps := range props {
		pathProperties = append(pathProperties, pathPropertiesForPropertyStruct(ps)...)
	}

	// Remove duplicates to avoid multiple dependencies.
	pathProperties = FirstUniqueStrings(pathProperties)

	// Add dependencies to anything that is a module reference.
	for _, s := range pathProperties {
		if m, t := SrcIsModuleWithTag(s); m != "" {
			ctx.AddDependency(ctx.Module(), sourceOrOutputDepTag(t), m)
		}
	}
}

// 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(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 the property struct is a nil pointer it can't have any paths set in it.
	if v.IsNil() {
		return nil
	}

	// v is now the reflect.Value for the concrete property struct.
	v = v.Elem()

	// Get or create the list of indexes of properties that are tagged with `android:"path"`.
	pathPropertyIndexes := pathPropertyIndexesForPropertyStruct(ps)

	var ret []string

	for _, i := range pathPropertyIndexes {
		// Turn an index into a field.
		sv := fieldByIndex(v, i)
		if !sv.IsValid() {
			// Skip properties inside a nil pointer.
			continue
		}

		// If the field is a non-nil pointer step into it.
		if sv.Kind() == reflect.Ptr {
			if sv.IsNil() {
				continue
			}
			sv = sv.Elem()
		}

		// Collect paths from all strings and slices of strings.
		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)
}