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
	addPathDepsForProps(ctx, props)
}

func addPathDepsForProps(ctx BottomUpMutatorContext, props []interface{}) {
	// 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(m, 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 {
		var values []reflect.Value
		fieldsByIndex(v, i, &values)
		for _, sv := range values {
			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
}

// fieldsByIndex is similar to reflect.Value.FieldByIndex, but is more robust: it doesn't track
// nil pointers and it returns multiple values when there's slice of struct.
func fieldsByIndex(v reflect.Value, index []int, values *[]reflect.Value) {
	// leaf case
	if len(index) == 1 {
		if isSliceOfStruct(v) {
			for i := 0; i < v.Len(); i++ {
				*values = append(*values, v.Index(i).Field(index[0]))
			}
		} else {
			// Dereference it if it's a pointer.
			if v.Kind() == reflect.Ptr {
				if v.IsNil() {
					return
				}
				v = v.Elem()
			}
			*values = append(*values, v.Field(index[0]))
		}
		return
	}

	// recursion
	if v.Kind() == reflect.Ptr {
		// don't track nil pointer
		if v.IsNil() {
			return
		}
		v = v.Elem()
	} else if isSliceOfStruct(v) {
		// do the recursion for all elements
		for i := 0; i < v.Len(); i++ {
			fieldsByIndex(v.Index(i).Field(index[0]), index[1:], values)
		}
		return
	}
	fieldsByIndex(v.Field(index[0]), index[1:], values)
	return
}

func isSliceOfStruct(v reflect.Value) bool {
	return v.Kind() == reflect.Slice && v.Type().Elem().Kind() == reflect.Struct
}

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)
}