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package toml
// Struct field handling is adapted from code in encoding/json:
//
// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the Go distribution.
import (
"reflect"
"sort"
"sync"
)
// A field represents a single field found in a struct.
type field struct {
name string // the name of the field (`toml` tag included)
tag bool // whether field has a `toml` tag
index []int // represents the depth of an anonymous field
typ reflect.Type // the type of the field
}
// byName sorts field by name, breaking ties with depth,
// then breaking ties with "name came from toml tag", then
// breaking ties with index sequence.
type byName []field
func (x byName) Len() int { return len(x) }
func (x byName) Swap(i, j int) { x[i], x[j] = x[j], x[i] }
func (x byName) Less(i, j int) bool {
if x[i].name != x[j].name {
return x[i].name < x[j].name
}
if len(x[i].index) != len(x[j].index) {
return len(x[i].index) < len(x[j].index)
}
if x[i].tag != x[j].tag {
return x[i].tag
}
return byIndex(x).Less(i, j)
}
// byIndex sorts field by index sequence.
type byIndex []field
func (x byIndex) Len() int { return len(x) }
func (x byIndex) Swap(i, j int) { x[i], x[j] = x[j], x[i] }
func (x byIndex) Less(i, j int) bool {
for k, xik := range x[i].index {
if k >= len(x[j].index) {
return false
}
if xik != x[j].index[k] {
return xik < x[j].index[k]
}
}
return len(x[i].index) < len(x[j].index)
}
// typeFields returns a list of fields that TOML should recognize for the given
// type. The algorithm is breadth-first search over the set of structs to
// include - the top struct and then any reachable anonymous structs.
func typeFields(t reflect.Type) []field {
// Anonymous fields to explore at the current level and the next.
current := []field{}
next := []field{{typ: t}}
// Count of queued names for current level and the next.
count := map[reflect.Type]int{}
nextCount := map[reflect.Type]int{}
// Types already visited at an earlier level.
visited := map[reflect.Type]bool{}
// Fields found.
var fields []field
for len(next) > 0 {
current, next = next, current[:0]
count, nextCount = nextCount, map[reflect.Type]int{}
for _, f := range current {
if visited[f.typ] {
continue
}
visited[f.typ] = true
// Scan f.typ for fields to include.
for i := 0; i < f.typ.NumField(); i++ {
sf := f.typ.Field(i)
if sf.PkgPath != "" && !sf.Anonymous { // unexported
continue
}
opts := getOptions(sf.Tag)
if opts.skip {
continue
}
index := make([]int, len(f.index)+1)
copy(index, f.index)
index[len(f.index)] = i
ft := sf.Type
if ft.Name() == "" && ft.Kind() == reflect.Ptr {
// Follow pointer.
ft = ft.Elem()
}
// Record found field and index sequence.
if opts.name != "" || !sf.Anonymous || ft.Kind() != reflect.Struct {
tagged := opts.name != ""
name := opts.name
if name == "" {
name = sf.Name
}
fields = append(fields, field{name, tagged, index, ft})
if count[f.typ] > 1 {
// If there were multiple instances, add a second,
// so that the annihilation code will see a duplicate.
// It only cares about the distinction between 1 or 2,
// so don't bother generating any more copies.
fields = append(fields, fields[len(fields)-1])
}
continue
}
// Record new anonymous struct to explore in next round.
nextCount[ft]++
if nextCount[ft] == 1 {
f := field{name: ft.Name(), index: index, typ: ft}
next = append(next, f)
}
}
}
}
sort.Sort(byName(fields))
// Delete all fields that are hidden by the Go rules for embedded fields,
// except that fields with TOML tags are promoted.
// The fields are sorted in primary order of name, secondary order
// of field index length. Loop over names; for each name, delete
// hidden fields by choosing the one dominant field that survives.
out := fields[:0]
for advance, i := 0, 0; i < len(fields); i += advance {
// One iteration per name.
// Find the sequence of fields with the name of this first field.
fi := fields[i]
name := fi.name
for advance = 1; i+advance < len(fields); advance++ {
fj := fields[i+advance]
if fj.name != name {
break
}
}
if advance == 1 { // Only one field with this name
out = append(out, fi)
continue
}
dominant, ok := dominantField(fields[i : i+advance])
if ok {
out = append(out, dominant)
}
}
fields = out
sort.Sort(byIndex(fields))
return fields
}
// dominantField looks through the fields, all of which are known to
// have the same name, to find the single field that dominates the
// others using Go's embedding rules, modified by the presence of
// TOML tags. If there are multiple top-level fields, the boolean
// will be false: This condition is an error in Go and we skip all
// the fields.
func dominantField(fields []field) (field, bool) {
// The fields are sorted in increasing index-length order. The winner
// must therefore be one with the shortest index length. Drop all
// longer entries, which is easy: just truncate the slice.
length := len(fields[0].index)
tagged := -1 // Index of first tagged field.
for i, f := range fields {
if len(f.index) > length {
fields = fields[:i]
break
}
if f.tag {
if tagged >= 0 {
// Multiple tagged fields at the same level: conflict.
// Return no field.
return field{}, false
}
tagged = i
}
}
if tagged >= 0 {
return fields[tagged], true
}
// All remaining fields have the same length. If there's more than one,
// we have a conflict (two fields named "X" at the same level) and we
// return no field.
if len(fields) > 1 {
return field{}, false
}
return fields[0], true
}
var fieldCache struct {
sync.RWMutex
m map[reflect.Type][]field
}
// cachedTypeFields is like typeFields but uses a cache to avoid repeated work.
func cachedTypeFields(t reflect.Type) []field {
fieldCache.RLock()
f := fieldCache.m[t]
fieldCache.RUnlock()
if f != nil {
return f
}
// Compute fields without lock.
// Might duplicate effort but won't hold other computations back.
f = typeFields(t)
if f == nil {
f = []field{}
}
fieldCache.Lock()
if fieldCache.m == nil {
fieldCache.m = map[reflect.Type][]field{}
}
fieldCache.m[t] = f
fieldCache.Unlock()
return f
}