y.go

// Copyright 2014 The y Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package y

import (
	"bytes"
	"container/heap"
	"fmt"
	"go/ast"
	"go/parser"
	"go/scanner"
	"go/token"
	"io"
	"sort"
	"strconv"
	"strings"

	yparser "github.com/chuanglian-dev/parser/yacc"
	"github.com/YKG/strutil"
)

const (
	intBits  = 1 << (^uint(0)>>32&1 + ^uint(0)>>16&1 + ^uint(0)>>8&1 + 3)
	bitShift = intBits>>6 + 5
	bitMask  = intBits - 1
)

var (
	assocStr = map[int]string{
		AssocLeft:       "%left",
		AssocRight:      "%right",
		AssocNone:       "%nonassoc",
		AssocPrecedence: "%precedence",
	}
	empty     = "ε"
	isTesting bool
)

// Max returns the larger of a and b.
func YMax(a, b int) int {
	if a > b {
		return a
	}

	return b
}

type action struct {
	kind int // 'a': accept, 'g': goto, 'r': reduce, 's': shift
	arg  int // a: N/A, r: rule#, g, s: state#
}

type actions []Action

func (a actions) Len() int { return len(a) }

func (a actions) Less(i, j int) bool {
	ni := a[i].Sym.Name
	nj := a[j].Sym.Name
	if ni < nj {
		return true
	}

	if ni > nj {
		return false
	}

	ti, ki := a[i].Kind()
	tj, kj := a[i].Kind()
	if ti < tj {
		return true
	}

	if ti > tj {
		return false
	}

	return ki < kj
}

func (a actions) Swap(i, j int) { a[i], a[j] = a[j], a[i] }

func newReduction(arg int) action {
	if arg == 0 {
		return action{'a', 0}
	}

	return action{'r', arg}
}

func (a action) String() string {
	switch a.kind {
	case 'a':
		return "accept"
	case 'g':
		return fmt.Sprintf("goto state %d", a.arg)
	case 'r':
		return fmt.Sprintf("reduce using rule %d", a.arg)
	case 's':
		return fmt.Sprintf("shift, and goto state %d", a.arg)
	default:
		panic("y: internal error 008")
	}
}

type item uint64 // LR 0 item

func newItem(rule, dot int) item { return item(uint64(rule)<<32 | uint64(dot)) }

func (i item) dot() int { return int(i & (1<<32 - 1)) }

func (i item) dump(y *y) string {
	var buf bytes.Buffer
	rule := y.Rules[i.rule()]
	buf.WriteString(fmt.Sprintf("%3d %s:", i.rule(), rule.Sym.Name))
	dot := i.dot()
	for _, v := range rule.Components[:dot] {
		buf.WriteString(" " + v)
	}
	buf.WriteString(" .")
	for _, v := range rule.Components[dot:] {
		buf.WriteString(" " + v)
	}
	return buf.String()
}

func (i item) next(y *y) *Symbol { return i.sym(y, i.dot()) }
func (i item) rule() int         { return int(i >> 32) }

func (i item) sym(y *y, dot int) *Symbol {
	rule := y.Rules[i.rule()]
	if dot < 0 {
		return rule.Sym
	}

	if dot == len(rule.Components) {
		return nil
	}

	return rule.syms[dot]
}

func (i item) syms(y *y) (r []*Symbol) {
	return y.Rules[i.rule()].syms
}

type item1 struct { // LR 1 item
	item item
	sym  *Symbol
}

func (i item1) dump(y *y) string {
	return fmt.Sprintf("%s, %s", i.item.dump(y), i.sym.Name)
}

type itemSet []item

func (s itemSet) add(i item) (itemSet, bool) { // true: s already has i
	l, ok := s.find(i)
	if ok {
		return s, true
	}

	s = append(s, 0)
	copy(s[l+1:], s[l:])
	s[l] = i
	return s, false
}

func (s itemSet) clone() itemSet { return append(itemSet(nil), s...) }

func (s itemSet) closure(y *y) (r itemSet) { // dragon 4.7, Fig. 4.33
	q, r := s.clone(), s.clone()
	for len(q) != 0 {
		item := q[len(q)-1]
		q = q[:len(q)-1]
		nx := item.next(y)
		if nx == nil || nx.IsTerminal {
			continue
		}

		for _, rule := range nx.Rules {
			s := newItem(rule.RuleNum, 0)
			var ok bool
			r, ok = r.add(s)
			if !ok {
				q = append(q, s)
			}
		}
	}
	return r
}

func (s itemSet) find(i item) (m int, _ bool) {
	l, h := 0, len(s)-1
	for l <= h {
		m = (l + h) >> 1
		switch j := s[m]; {
		case i > j:
			l = m + 1
		case i == j:
			return m, true
		default:
			h = m - 1
		}
	}
	return l, false
}

func (s itemSet) goTo(y *y, x *Symbol) (r itemSet) { // dragon 4.7, Example 4.35.
	if n := len(y.isPool); n != 0 {
		r = y.isPool[n-1][:0]
		y.isPool = y.isPool[:n-1]
	}
	for _, item := range s { //TODO cache item->nextSym
		if item.next(y) != x {
			continue
		}

		r = append(r, item+1)
	}
	return r
}

func (s itemSet) mustFind(i item) int {
	if m, ok := s.find(i); ok {
		return m
	}

	panic("y: internal error 011")
}

func (s itemSet) state(y *y) (int, bool) {
	id := y.id(s)
	n, ok := y.itemSets[id]
	if !ok {
		n = len(y.itemSets)
		y.itemSets[id] = n
		ns := newState(y, s)
		ns.id = n
		y.States = append(y.States, ns)
	}
	return n, ok
}

type itemSet1 map[item1]bool

func (s itemSet1) add(i item1) bool { // true: s already has i
	if i.sym.id == 0 {
		return true
	}

	if _, ok := s[i]; ok {
		return true
	}

	s[i] = true
	return false
}

type stateItem struct {
	state int
	i     int
}

type symSet []int

func (s symSet) add(t symSet, withEmpty bool) (r bool) { // true: s already has all items in t
	r = true
	for x, w := range t {
		if x == 0 && !withEmpty {
			w &^= 1
		}
		if w == 0 {
			continue
		}

		o := s[x]
		if w = o | w; w != o {
			s[x] = w
			r = false
		}
	}
	return r
}

func (s symSet) add1(t int) bool { // true: s already has t
	x, m := t>>bitShift, 1<<uint(t&bitMask)
	w := s[x]
	if w&m != 0 {
		return true
	}
	s[x] = w | m
	return false
}

func (s symSet) addEmpty() { s[0] |= 1 }

func (s symSet) clear() symSet {
	for i := range s {
		s[i] = 0
	}
	return s
}

func (s symSet) clone(y *y) symSet {
	r := y.newSymSet(-1)
	copy(r, s)
	return r
}

func (s symSet) len() (r int) {
	for _, w := range s {
		for bit := 0; bit < intBits && w != 0; bit, w = bit+1, w>>1 {
			if w&1 != 0 {
				r++
			}
		}
	}
	return r
}

func (s symSet) dump(y *y) string {
	var a []string
	for x, w := range s {
		for bit := 0; bit < intBits && w != 0; bit, w = bit+1, w>>1 {
			if w&1 != 0 {
				a = append(a, y.syms[x<<bitShift+bit].Name)
			}
		}
	}
	sort.Strings(a)
	return strings.Join(a, ", ")
}

func (s symSet) has(sym int) bool { return s[sym>>bitShift]&(1<<uint(sym&bitMask)) != 0 }

func (s symSet) hasEmpty() bool { return s[0]&1 != 0 }

func (s symSet) remove(t int) {
	s[t>>bitShift] &^= 1 << uint(t&bitMask)
}

type trans struct {
	item
	*Symbol
}

type typeDecl struct {
	token.Pos
	typeName string
}

type percTypeLit struct {
	pos token.Pos
	lit string
}

type y struct {
	*Parser
	acceptSym       *Symbol                  //
	allocVal        int                      //
	allocatedValues map[int]bool             //
	ast             *yparser.Specification   //
	clsCache        map[item]map[item]symSet //
	clsQueue        []item1                  // Non reentrant item1.closure todo list.
	clsSyms         []*Symbol                // Non reentrant item1.closure buffer.
	dummySym        *Symbol                  //
	emptySym        *Symbol                  //
	endSym          *Symbol                  //
	entries         int                      // Number of used cells in the parse table.
	errSym          *Symbol                  //
	errors          scanner.ErrorList        //
	firstRule       int                      //
	fset            *token.FileSet           //
	idBuf           []byte                   // Non reentrant id() buffer.
	isPool          []itemSet                //
	itemSets        map[string]int           //
	noSym           *Symbol                  //
	nonTerminals    map[string]token.Pos     //
	opts            *Options                 //
	percTypeLits    map[string]*percTypeLit  // nm: *percTypeLit
	percTypeLitPos  map[string]token.Pos     // lit: *percTypeLit
	precedence      int                      //
	ssPool          []symSet                 //
	symSetCap       int                      //
	symTypes        map[string]typeDecl      //
	syms            []*Symbol                //
	symsUsed        map[string]token.Pos     //
	synthRule       int                      //
	types           map[string]token.Pos     // %union fields
	typesUsed       map[string]token.Pos     //
	unionPos        token.Pos                //
	zeroPathsValid  bool                     // States paths to state 0 determined.
}

func newY(fset *token.FileSet, ast *yparser.Specification, opts *Options) *y {
	r := &y{
		Parser:          newParser(),
		acceptSym:       &Symbol{Name: "$accept"},
		allocatedValues: map[int]bool{},
		ast:             ast,
		clsCache:        map[item]map[item]symSet{},
		dummySym:        &Symbol{Name: "#", IsTerminal: true},
		emptySym:        &Symbol{Name: empty, IsTerminal: true},
		endSym:          &Symbol{Name: "$end", IsTerminal: true, Precedence: -1},
		errSym:          &Symbol{Name: "error", IsTerminal: true},
		fset:            fset,
		idBuf:           make([]byte, 1024),
		itemSets:        map[string]int{},
		noSym:           &Symbol{Name: "$default", Value: -1},
		nonTerminals:    map[string]token.Pos{},
		opts:            opts,
		percTypeLitPos:  map[string]token.Pos{},
		percTypeLits:    map[string]*percTypeLit{},
		types:           map[string]token.Pos{},
		typesUsed:       map[string]token.Pos{},
	}
	r.symsUsed = map[string]token.Pos{r.errSym.Name: 0, r.noSym.Name: 0}
	r.endSym.Value = r.allocValue()
	r.errSym.Value = r.allocValue()
	r.LiteralStrings = map[string]*Symbol{}
	r.Syms = map[string]*Symbol{
		r.acceptSym.Name: r.acceptSym,
		r.dummySym.Name:  r.dummySym,
		r.emptySym.Name:  r.emptySym,
		r.endSym.Name:    r.endSym,
		r.errSym.Name:    r.errSym,
		r.noSym.Name:     r.noSym,
	}
	return r
}

func processAST(fset *token.FileSet, ast *yparser.Specification, opts *Options) (*y, error) {
	var err error
	if opts, err = opts.boot(fset); err != nil {
		return nil, err
	}

	y := newY(fset, ast, opts)
	if err := y.defs(); err != nil {
		return nil, err
	}

	if t := ast.Tail; t != nil {
		y.Tail = t.Value
	}
	if err := y.rules0(); err != nil {
		return nil, err
	}

	m := map[int]*Symbol{}
	a := make([]string, 0, len(y.Syms))
	for nm := range y.Syms {
		a = append(a, nm)
	}
	sort.Strings(a)
	for _, sym := range y.Syms {
		nm := sym.Name
		if v := sym.Value; v >= 0 {
			ex := m[v]
			if ex != nil && ex != sym {
				y.err(sym.Pos, "symbol %s has the same value (%d) as symbol %s at %s.", sym, v, ex, y.pos(ex.Pos))
				continue
			}

			if nm == "#" || nm == "ε" || nm == "$accept" {
				continue
			}

			m[v] = sym
		}
	}
	for _, nm := range a {
		sym := y.Syms[nm]
		if nm == "" || nm == "ε" || nm == "#" || nm[0] == '$' && nm[1] != '@' && sym != y.noSym { // internal symbols
			continue
		}

		if sym.Value < 0 {
			sym.Value = y.allocValue()
		}
	}
	if err := y.error(); err != nil {
		return nil, y.error()
	}

	y.follows()
	y.states0()
	y.lookaheads()
	y.reductions()
	y.conflicts()
	y.Table = make([][]Action, len(y.States))
	for i, state := range y.States {
		a := make([]Action, 0, len(state.actions)+len(state.gotos))
		for sym, acts := range state.actions {
			act := acts[0]
			switch act.kind {
			case 'a':
				a = append(a, Action{y.endSym, 0})
			case 's':
				a = append(a, Action{sym, act.arg})
			case 'r':
				a = append(a, Action{sym, -act.arg})
			default:
				panic("y: internal error 005")
			}
		}
		for sym, act := range state.gotos {
			a = append(a, Action{sym, act.arg})
		}
		y.Table[i] = a
	}
	if w := opts.Report; w != nil {
		y.report(w)
	}
	if y.opts.Reducible {
		y.reducible()
	}
	return y, y.xerrors()
}

func (y *y) addRule(r *Rule) *Rule {
	r.Sym.Rules = append(r.Sym.Rules, r)
	r.RuleNum = len(y.Rules)
	y.Rules = append(y.Rules, r)
	return r
}

func (y *y) allocValue() (n int) {
	for {
		switch n = y.allocVal; {
		case n == 0:
			n = 0xe000 // Private Use Area.
		case n == 0xf8ff:
			n = 0xf0000 // Supplemental Private Use Area-A.
		case n == 0xffffd:
			n = 0x100000 // Supplemental Private Use Area-B.
		case n == 0x10fffd:
			panic("y: internal error 012")
		default:
			n++
		}
		y.allocVal = n
		if !y.allocatedValues[n] {
			y.allocatedValues[n] = true
			return n
		}
	}
}

func (y *y) closure(i item) (r map[item]symSet) { // Result symSets must not be mutated.
	if r, ok := y.clsCache[i]; ok {
		return r
	}

	r = y.closure0(map[item]symSet{i: y.newSymSet(y.dummySym.id)}, append(y.clsQueue[:0], item1{i, y.dummySym}))
	y.clsCache[i] = r
	return r
}

func (y *y) closure0(j map[item]symSet, q []item1) map[item]symSet { // dragon 4.7, Fig. 4.38; not reentrant.
	ySyms := y.clsSyms
	for len(q) != 0 {
		i := q[len(q)-1]
		q = q[:len(q)-1]
		bb := i.item.syms(y)[i.item.dot():]
		if len(bb) == 0 {
			continue
		}

		rules := bb[0].Rules
		ySyms = append(ySyms[:0], bb[1:]...)
		ySyms = append(ySyms, i.sym)
		symSet := y.first(ySyms)
		for x, w := range symSet {
			for bit := 0; bit < intBits && w != 0; bit, w = bit+1, w>>1 {
				if w&1 == 0 {
					continue
				}

				for _, p := range rules {
					nii := newItem(p.RuleNum, 0)
					ni := item1{nii, y.syms[x<<bitShift+bit]}
					switch v, ok := j[nii]; {
					case !ok:
						j[nii] = y.newSymSet(ni.sym.id)
						q = append(q, ni)
					default:
						if v.add1(ni.sym.id) {
							break
						}

						j[nii] = v
						q = append(q, ni)
					}
				}
			}
		}
		y.ssPool = append(y.ssPool, symSet.clear())
	}
	y.clsSyms = ySyms
	y.clsQueue = q
	return j
}

func (y *y) conflicts() error {
	for si, state := range y.States {
		for sym, acts := range state.actions {
			if len(acts) < 2 {
				continue
			}

			delete(state.actions, sym)
			var s, r []action
			for _, act := range acts {
				switch act.kind {
				case 's':
					s = append(s, act)
				case 'r':
					r = append(r, act)
				default:
					panic("internal error")
				}
			}
			if len(s) > 1 {
				panic("internal error")
			}

			sort.Slice(r, func(i, j int) bool { return r[i].arg < r[j].arg })
			var in, out [][2]action
			if len(s) != 0 {
				s := s[0]
				for _, r := range r {
					in = append(in, [2]action{s, r})
				}
			}
			for i, r1 := range r {
				for _, r2 := range r[i+1:] {
					in = append(in, [2]action{r1, r2})
				}
			}
			for _, conflict := range in {
				switch resolved, asShift := y.resolve(state, si, sym, conflict); {
				case !resolved:
					out = append(out, conflict)
				case asShift:
					if conflict[0].kind != 's' {
						break
					}

					r := conflict[1].arg
					dot := len(y.Rules[r].Components)
					item := newItem(r, dot)
					switch dot {
					case 0:
						state.xla[state.xitems.mustFind(item)].remove(sym.id)
					default:
						state.lookahead[state.kernel.mustFind(item)].remove(sym.id)
					}
				}
			}
			ret := map[action]bool{}
			var sr, rr bool
			for _, conflict := range out {
				ret[conflict[0]], ret[conflict[1]] = true, true
				if conflict[0].kind == 's' {
					sr = true
					continue
				}

				rr = true
			}
			if sr {
				y.ConflictsSR++
			}
			if rr {
				y.ConflictsRR++
			}
			var sa, ra []action
			for action := range ret {
				if action.kind == 's' {
					sa = append(sa, action)
					continue
				}

				ra = append(ra, action)
			}
			sort.Slice(ra, func(i, j int) bool { return ra[i].arg < ra[j].arg })
			state.actions[sym] = append(state.actions[sym], sa...)
			state.actions[sym] = append(state.actions[sym], ra...)
		}
		sort.Strings(state.resolved)
	}
	if !y.opts.AllowConflicts {
		if y.ConflictsSR != 0 {
			y.err(0, "conflicts: %d shift/reduce", y.ConflictsSR)
		}
		if y.ConflictsRR != 0 {
			y.err(0, "conflicts: %d reduce/reduce", y.ConflictsRR)
		}
	}
	if y.opts.noDefault {
		return y.error()
	}

	for si, state := range y.States {
		var valid bool
		var la symSet
		max := 0
		for i, item := range state.kernel {
			if item.next(y) != nil || si == 1 && item == 1 {
				continue
			}

			if n := state.lookahead[i].len(); !valid || n < max {
				max = n
				la = state.lookahead[i]
				valid = true
			}
		}
		for i := range state.xitems {
			if n := state.xla[i].len(); !valid || n < max {
				max = n
				la = state.xla[i]
				valid = true
			}
		}

		if !valid {
			continue
		}

		// Collapse la reductions.
		redn := -1
		for sym, actions := range state.actions {
			action := actions[0]
			if action.kind != 'r' {
				continue
			}

			if redn < 0 && la.has(sym.id) {
				redn = action.arg
			}

			switch actions = actions[1:]; len(actions) {
			case 0:
				delete(state.actions, sym)
			default:
				state.actions[sym] = actions
			}

		}
		state.actions[y.noSym] = []action{{'r', redn}}
	}
	return y.error()
}

func (y *y) defs() error {
	types := map[string]typeDecl{}
	var buf bytes.Buffer
	defer func() {
		y.Prologue = buf.String()
		y.symTypes = types
	}()

	y.Definitions = y.ast.Defs
	for _, def := range y.ast.Defs {
		isAssoc := false
		switch def.Case {
		case 0: // START IDENTIFIER
			nm := def.Token2.Val
			y.Start = nm
			y.nonTerminals[nm] = def.Token2.Pos()
			y.useSym(nm, def.Token2.Pos())
		case 1: // UNION
			if ex := y.unionPos; ex != 0 {
				y.err(def.Token.Pos(), "duplicate %%union: previous at %v", y.pos(ex))
				break
			}

			y.unionPos = def.Pos()
			src := def.Value
			for len(src) != 0 && src[0] != '{' {
				src = src[1:]
			}
			if len(src) != 0 {
				src = src[1:]
			}
			for len(src) != 0 && (src[0] == '\n' || src[0] == '\r') {
				src = src[1:]
			}
			src = fmt.Sprintf("struct {\n\tyys    int\n%s{}", src)
			expr, err := parser.ParseExpr(src)
			if err != nil {
				y.err(def.Pos(), "invalid %%union:\n%s\n%v", src, err)
				break
			}

			y.Union, y.UnionSrc = expr.(*ast.CompositeLit).Type.(*ast.StructType), src[:len(src)-2]
			for _, fields := range y.Union.Fields.List[1:] {
				for _, nm := range fields.Names {
					switch ex, ok := y.types[nm.Name]; {
					case !ok:
						y.types[nm.Name] = def.Pos()
					default:
						y.err(def.Pos(), "union field %s already declared: %s", nm, y.pos(ex))
					}
				}
			}
		case 2: // LCURL RCURL
			buf.WriteString(def.Value)
		case 3: // ReservedWord Tag NameList
			switch def.ReservedWord.Case {
			case
				1, // LEFT
				2, // RIGHT
				3, // NONASSOC
				5: // PRECEDENCE
				y.precedence++
				isAssoc = true
				fallthrough
			case 0: // TOKEN
				var typ string
				if tag := def.Tag; tag != nil {
					typ = def.Tag.Token2.Val
					y.useType(def.Tag.Token2.Pos(), typ)
				}
				assoc := AssocNotSpecified
				switch def.ReservedWord.Token.Char.Rune {
				case yparser.LEFT:
					assoc = AssocLeft
				case yparser.RIGHT:
					assoc = AssocRight
				case yparser.NONASSOC:
					assoc = AssocNone
				case yparser.PRECEDENCE:
					assoc = AssocPrecedence
				}
				var assocDef AssocDef
				assocDef.Associativity = assoc
				for _, nmno := range def.Nlist {
					var name string
					num := nmno.Number

					switch x := nmno.Identifier.(type) {
					case int:
						name = fmt.Sprintf("%q", x)
						if num < 0 {
							num = x
						}
					case string:
						name = x
					default:
						panic("internal error")
					}

					t := &Symbol{
						Associativity: assoc,
						ExplicitValue: num,
						IsTerminal:    true,
						Name:          name,
						Pos:           nmno.Token.Pos(),
						Precedence:    -1,
						Type:          typ,
						Value:         num,
					}
					ls := ""
					if n := nmno.LiteralStringOpt; n != nil {
						ls = n.Token.Val
						if ex, ok := y.LiteralStrings[ls]; ok {
							y.err(n.Token.Pos(), "literal strings must be unique, previous association with name at %v: %s", y.fset.Position(ex.Pos), ls)
						} else {
							y.LiteralStrings[ls] = t
							y.percTypeLitPos[ls] = t.Pos
							t.LiteralString = ls
						}
					}
					if isAssoc {
						assocDef.Syms = append(assocDef.Syms, t)
					}

					switch def.ReservedWord.Token.Char.Rune {
					case yparser.LEFT, yparser.RIGHT, yparser.NONASSOC, yparser.PRECEDENCE:
						t.Precedence = y.precedence
					}

					ex, ok := y.Syms[name]
					if !ok {
						if t.Value < 0 {
							t.Value = y.allocValue()
						} else {
							y.allocatedValues[t.Value] = true
						}
						y.Syms[name] = t
						continue
					}

					// Merge the declarations, if possible.
					if n := t.Associativity; n != AssocNotSpecified {
						switch o := ex.Associativity; {
						case o == AssocNotSpecified:
							ex.Associativity = n
						case n != o:
							y.err(
								t.Pos,
								"%s: conflict with previous associativity declaration at %v",
								name, y.pos(ex.Pos),
							)
						}
					}

					if n := t.Precedence; n >= 0 {
						switch o := ex.Precedence; {
						case o < 0:
							ex.Precedence = n
						case n != o:
							y.err(
								t.Pos,
								"%s: conflict with previous precedence declaration at %v",
								name, y.pos(ex.Pos),
							)
						}
					}

					if n := t.Type; n != "" {
						switch o := ex.Type; {
						case o == "":
							ex.Type = n
						case n != o:
							y.err(
								t.Pos,
								"%s: conflict with previous type declaration at %v",
								name, y.pos(ex.Pos),
							)
						}
					}

					if n := t.Value; n >= 0 {
						switch o := ex.Value; {
						case o < 0:
							ex.Value = n
						case n != o:
							y.err(
								t.Pos,
								"%s: conflict with previous value declaration at %v",
								name, y.pos(ex.Pos),
							)
						}
					}
				}
				if isAssoc {
					y.AssocDefs = append(y.AssocDefs, &assocDef)
				}
			case 4: // TYPE
				typ := ""
				if tag := def.Tag; tag != nil {
					typ = tag.Token2.Val
					y.useType(def.Tag.Token2.Pos(), typ)
				}
				for _, nmno := range def.Nlist {
					if x, ok := nmno.Identifier.(int); ok {
						var name string
						num := nmno.Number

						name = fmt.Sprintf("%q", x)
						if num < 0 {
							num = x
						}

						t := &Symbol{
							Associativity: AssocNotSpecified,
							ExplicitValue: num,
							IsTerminal:    true,
							Name:          name,
							Pos:           nmno.Token.Pos(),
							Precedence:    -1,
							Type:          typ,
							Value:         num,
						}
						ls := ""
						if n := nmno.LiteralStringOpt; n != nil {
							ls = n.Token.Val
							if ex, ok := y.LiteralStrings[ls]; ok {
								y.err(n.Token.Pos(), "literal strings must be unique, previous association with name at %v: %s", y.fset.Position(ex.Pos), ls)
							} else {
								y.LiteralStrings[ls] = t
								y.percTypeLitPos[ls] = t.Pos
								t.LiteralString = ls
							}
						}
						ex, ok := y.Syms[name]
						if !ok {
							if t.Value < 0 {
								t.Value = y.allocValue()
							} else {
								y.allocatedValues[t.Value] = true
							}
							y.Syms[name] = t
							continue
						}

						// Merge the declarations, if possible.
						if n := t.Associativity; n != AssocNotSpecified {
							switch o := ex.Associativity; {
							case o == AssocNotSpecified:
								ex.Associativity = n
							case n != o:
								y.err(
									t.Pos,
									"%s: conflict with previous associativity declaration at %v",
									name, y.pos(ex.Pos),
								)
							}
						}

						if n := t.Precedence; n >= 0 {
							switch o := ex.Precedence; {
							case o < 0:
								ex.Precedence = n
							case n != o:
								y.err(
									t.Pos,
									"%s: conflict with previous precedence declaration at %v",
									name, y.pos(ex.Pos),
								)
							}
						}

						if n := t.Type; n != "" {
							switch o := ex.Type; {
							case o == "":
								ex.Type = n
							case n != o:
								y.err(
									t.Pos,
									"%s: conflict with previous type declaration at %v",
									name, y.pos(ex.Pos),
								)
							}
						}

						if n := t.Value; n >= 0 {
							switch o := ex.Value; {
							case o < 0:
								ex.Value = n
							case n != o:
								y.err(
									t.Pos,
									"%s: conflict with previous value declaration at %v",
									name, y.pos(ex.Pos),
								)
							}
						}
						continue
					}

					nm := nmno.Identifier.(string)
					if ex, ok := types[nm]; ok {
						y.err(nmno.Token.Pos(), "%%type: previous declaration at %v", y.pos(ex.Pos))
						continue
					}

					types[nm] = typeDecl{nmno.Token.Pos(), typ}
					y.useSym(nm, nmno.Token.Pos())
					ls := ""
					if n := nmno.LiteralStringOpt; n != nil {
						ls = n.Token.Val
						y.percTypeLits[nm] = &percTypeLit{nmno.Token.Pos(), ls}
						if ex, ok := y.percTypeLitPos[ls]; ok {
							y.err(n.Token.Pos(), "literal strings must be unique, previous association with name at %v: %s", y.fset.Position(ex), ls)
						} else {
							y.percTypeLitPos[ls] = nmno.Token.Pos()
						}
					}
				}
			default:
				panic("internal error")
			}
		case 4: // ReservedWord Tag (No NameList)
		case 5: // ERROR_VERBOSE
			y.ErrorVerbose = true
		default:
			fmt.Println(def.Case)
			panic("internal error")
		}
	}
	return y.error()
}

func (y *y) err(pos token.Pos, format string, arg ...interface{}) error {
	return y.errp(y.pos(pos), format, arg...)
}

func (y *y) errp(pos token.Position, format string, arg ...interface{}) error {
	y.errors.Add(pos, fmt.Sprintf(format, arg...))
	return y.errors[len(y.errors)-1]
}

func (y *y) error() error {
	if len(y.errors) == 0 {
		return nil
	}

	y.errors.Sort()
	return y.errors.Err()
}

func (y *y) first(x []*Symbol) (r symSet) { // dragon, 4.4
	r = y.newSymSet(-1)
	for _, sym := range x {
		f1 := sym.first(y)
		r.add(f1, false)
		if !f1.hasEmpty() {
			return r
		}
	}

	r.addEmpty()
	return r
}

func (y *y) follows() { // dragon, 4.4
	y.acceptSym.follow = y.newSymSet(y.endSym.id) // 1.
	for {
		changed := false

		for _, sym := range y.Syms {
			if sym.IsTerminal {
				continue
			}

			for _, rule := range sym.Rules {
				a := rule.Sym
				if len(a.follow) == 0 {
					a.follow = y.newSymSet(-1)
				}
				syms := rule.syms
				n := len(syms)
				for dot, b := range syms {
					if len(b.follow) == 0 {
						b.follow = y.newSymSet(-1)
					}
					f3 := false
					if dot < n-1 { // 2.
						beta := syms[dot+1]
						f := beta.first(y)
						if !b.follow.add(f, false) {
							changed = true
						}
						f3 = f.hasEmpty()
					}
					if dot == n-1 || f3 { // 3.
						if !b.follow.add(a.follow, true) {
							changed = true
						}
					}
				}
			}
		}

		if !changed {
			break
		}
	}
}

func (y *y) id(s itemSet) string { // Not reentrant.
	b := y.idBuf[:0] //TODO try compute size in advance using log2
	for _, item := range s {
		r, d := item.rule(), item.dot()
		if r != 0 && d == 0 {
			continue
		}

		for r != 0 {
			b = append(b, byte(r)&0x7f)
			r >>= 7
		}
		b = append(b, 0x80)
		for d != 0 {
			b = append(b, byte(d)&0x7f)
			d >>= 7
		}
		b = append(b, 0x81)
	}
	y.idBuf = b
	return string(b)
}

func (y *y) lookaheads() {
	di := y.dummySym.id
	dx, dm := di>>bitShift, 1<<uint(di&bitMask) //TODO static const
	y.States[0].lookahead[0] = y.newSymSet(y.endSym.id)
	q := make([]stateItem, 0, len(y.States))
	m := make(map[stateItem]bool, len(y.States))
	for s, state := range y.States {
		for i := range state.kernel {
			si := stateItem{s, i}
			q = append(q, si)
			m[si] = true
		}
	}
	for len(q) != 0 {
		j := q[len(q)-1]
		q = q[:len(q)-1]
		delete(m, j)
		state, i := y.States[j.state], j.i
		item := state.kernel[i]
		if item.dot() == 0 && item.rule() != 0 {
			continue
		}

		for item, syms := range y.closure(item) {
			sym := item.next(y)
			if sym == nil {
				continue
			}

			j := state.trans[trans{item, sym}]
			gs := y.States[j.state]
			v := gs.lookahead[j.i]
			if v == nil {
				v = y.newSymSet(-1)
			}

			if syms[dx]&dm != 0 {
				syms = syms.clone(y) // Must not mutate.
				syms[dx] &^= dm
				syms.add(state.lookahead[i], false)
			}
			if !v.add(syms, false) && !m[j] {
				m[j] = true
				q = append(q, j)
			}
			gs.lookahead[j.i] = v
		}
	}
}

func (y *y) newSymSet(sym int) symSet {
	var r symSet
	switch n := len(y.ssPool); {
	case n != 0:
		r = y.ssPool[n-1]
		y.ssPool = y.ssPool[:n-1]
	default:
		r = make(symSet, y.symSetCap)
	}
	if sym >= 0 {
		r[sym>>bitShift] = 1 << uint(sym&bitMask)
	}
	return r
}

func (y *y) pos(po token.Pos) token.Position { return y.fset.Position(po) }

func (y *y) reducible() error {
	for si, state := range y.States {
		for _, actions := range state.actions {
			action := actions[0]
			if action.kind != 'r' {
				continue
			}

			rule := y.Rules[action.arg]
			if len(state.Reduce0(rule)) == 0 {
				y.errp(y.pos(rule.Sym.Pos), "no token string reduces %s in state %d", rule.Sym, si)
			}
		}
	}
	return y.error()
}

func (y *y) reductions() {
	defaultLA := y.newSymSet(y.noSym.id)
	for _, state := range y.States {
		for i, item := range state.kernel {
			if item.next(y) != nil {
				continue
			}

			// Item reduces a rule.
			la := state.lookahead[i]
			if len(la) == 0 {
				la = defaultLA
			}
			for x, w := range la {
				for bit := 0; bit < intBits && w != 0; bit, w = bit+1, w>>1 {
					if w&1 == 0 {
						continue
					}

					sym := y.syms[x<<bitShift+bit]
					state.actions[sym] = append(state.actions[sym], newReduction(item.rule()))
					y.entries++
				}
			}
		}

		if len(state.xitems) == 0 {
			continue
		}

		cls := state.kernel.closure(y)
		las := make([]symSet, len(cls))
		m := map[*Symbol][]int{}
		for i, item := range cls {
			rsym := item.sym(y, -1)
			m[rsym] = append(m[rsym], i)
		}
		for i, item := range state.kernel {
			j := cls.mustFind(item)
			las[j] = state.lookahead[i].clone(y)
		}
		for {
			changed := false
			for i, item := range cls {
				sym := item.next(y)
				if sym == nil || sym.IsTerminal {
					continue
				}

				targ, ok := m[sym]
				if !ok {
					continue
				}

				var la symSet
				switch nsym := (item + 1).next(y); {
				case nsym == nil:
					la = las[i]
				default:
					la = y.first(item.syms(y)[item.dot()+1:])
					if la.hasEmpty() {
						la.add(las[i], false)
					}
				}

				for _, i := range targ {
					v := las[i]
					if len(v) == 0 {
						v = y.newSymSet(-1)
					}

					if !v.add(la, false) {
						las[i] = v
						changed = true
					}
				}
			}

			if !changed {
				break
			}
		}
		for i, item := range state.xitems {
			j := cls.mustFind(item)
			state.xla[i] = las[j]
			las[j] = nil
		}
		for _, v := range las {
			if len(v) != 0 {
				y.ssPool = append(y.ssPool, v.clear())
			}
		}
		for i, item := range state.xitems {
			for x, w := range state.xla[i] {
				for bit := 0; bit < intBits && w != 0; bit, w = bit+1, w>>1 {
					if w&1 == 0 {
						continue
					}

					sym := y.syms[x<<bitShift+bit]
					state.actions[sym] = append(state.actions[sym], newReduction(item.rule()))
					y.entries++
				}
			}
		}
	}
}

func (y *y) report(w io.Writer) {
	f := strutil.IndentFormatter(w, "  ")
	if y.opts.debugSyms {
		var a []string
		max := 0
		for _, v := range y.syms {
			max = YMax(max, len(v.Name))
		}
		for _, v := range y.syms {
			a = append(a, fmt.Sprintf("%[2]*[1]s val %6[3]d, id %3[5]d, type %[4]q",
				v.Name, -max-1, v.Value, v.Type, v.id),
			)
		}
		sort.Strings(a)
		for _, v := range a {
			f.Format("%s\n", v)
		}
	}
	for si, state := range y.States {
		f.Format("state %d //", si)

		syms, la := state.Syms0()
		for _, s := range syms {
			switch {
			case s == nil:
				f.Format(" <?>")
			case !s.IsTerminal:
				f.Format(" <%s>", s)
			default:
				f.Format(" %s", s)
			}
		}
		if la != nil {
			f.Format(" [%s]", la)
		}
		f.Format("%i\n\n")

		switch {
		case y.opts.Closures:
			for _, item := range state.kernel.closure(y) {
				rule := y.Rules[item.rule()]
				f.Format("%v", item.dump(y))
				if y.opts.LA || item.next(y) == nil {
					switch i, ok := state.kernel.find(item); {
					case ok:
						f.Format("  [%s]", state.lookahead[i].dump(y))
					default:
						if i, ok := state.xitems.find(item); ok {
							f.Format("  [%s]", state.xla[i].dump(y))
						}
					}
				}
				if as := assocStr[rule.Associativity]; as != "" || rule.Precedence >= 0 {
					f.Format("  // assoc %s, prec %d", as, rule.Precedence)
				}
				f.Format("\n")
			}
		default:
			for i, item := range state.kernel {
				rule := y.Rules[item.rule()]
				f.Format("%v", item.dump(y))
				if y.opts.LA || item.dot() == len(rule.Components) {
					f.Format("  [%s]", state.lookahead[i].dump(y))
				}
				if as := assocStr[rule.Associativity]; as != "" || rule.Precedence >= 0 {
					f.Format("  // assoc %s, prec %d", as, rule.Precedence)
				}
				f.Format("\n")
			}
			for i, item := range state.xitems {
				rule := y.Rules[item.rule()]
				f.Format("%v  [%s]", item.dump(y), state.xla[i].dump(y))
				if as := assocStr[rule.Associativity]; as != "" || rule.Precedence >= 0 {
					f.Format(" // assoc %s, prec %d", as, rule.Precedence)
				}
				f.Format("\n")
			}
		}

		f.Format("%i\n")
		a := []string{}
		var w int
		for sym := range state.actions {
			w = YMax(w, len(sym.Name))
			a = append(a, sym.Name)
		}
		sort.Strings(a)
		type conflict struct {
			sym  *Symbol
			acts []action
		}
		var conflicts []conflict
		for _, nm := range a {
			sym := y.Syms[nm]
			acts := state.actions[sym]
			act := acts[0]
			f.Format("%-*s  %v", w, nm, act)
			if act.kind == 'r' {
				f.Format(" (%s)", y.Rules[act.arg].Sym.Name)
			}
			if len(acts) > 1 {
				conflicts = append(conflicts, conflict{sym, acts})
			}
			f.Format("\n")
		}
		a = a[:0]
		w = 0
		for sym := range state.gotos {
			w = YMax(w, len(sym.Name))
			a = append(a, sym.Name)
		}
		sort.Strings(a)
		for i, nm := range a {
			if i == 0 {
				f.Format("\n")
			}
			f.Format("%-*s  %v\n", w, nm, state.gotos[y.Syms[nm]])
		}
		for i, conflict := range conflicts {
			if i == 0 {
				if len(state.gotos) != 0 {
					f.Format("\n")
				}
			}
			sym := conflict.sym
			nm := sym.Name
			f.Format("conflict on %v", nm)
			for _, act := range conflict.acts {
				f.Format(", %s", act.String())
			}
			if as := assocStr[sym.Associativity]; as != "" || sym.Precedence >= 0 {
				f.Format(" // %v: assoc %s, prec %d", nm, assocStr[sym.Associativity], sym.Precedence)
			}
			f.Format("\n")
		}
		if len(state.resolved) != 0 {
			f.Format("\n")
		}
		for _, v := range state.resolved {
			f.Format("%s\n", v)
		}
		f.Format("%u%u\n")
	}
}

func (y *y) resolve(s *State, si int, sym *Symbol, conflict [2]action) (resolved, asShift bool) {
	switch conflict[0].kind {
	case 's':
		rrule := y.Rules[conflict[1].arg]
		sprec, rprec := sym.Precedence, rrule.Precedence
		if sprec < 0 || rprec < 0 {
			break
		}

		var explain string
		defer func() {
			if y.opts.Resolved && resolved {
				s.resolved = append(s.resolved, explain)
			}
		}()

		switch {
		case sprec > rprec:
			explain = fmt.Sprintf(
				"Conflict between rule %d and token %s resolved as shift (%s < %s).",
				rrule.RuleNum, sym, rrule.PrecSym, sym,
			)
			s.actions[sym] = append(s.actions[sym], conflict[0])
			return true, true
		case sprec < rprec:
			explain = fmt.Sprintf(
				"Conflict between rule %d and token %s resolved as reduce (%s < %s).",
				rrule.RuleNum, sym, sym, rrule.PrecSym,
			)
			s.actions[sym] = append(s.actions[sym], conflict[1])
			return true, false
		case sym.Associativity == AssocLeft:
			explain = fmt.Sprintf(
				"Conflict between rule %d and token %s resolved as reduce (%%left %s).",
				rrule.RuleNum, sym, sym,
			)
			s.actions[sym] = append(s.actions[sym], conflict[1])
			return true, false
		case sym.Associativity == AssocRight:
			explain = fmt.Sprintf(
				"Conflict between rule %d and token %s resolved as shift (%%right %s).",
				rrule.RuleNum, sym, sym,
			)
			s.actions[sym] = append(s.actions[sym], conflict[0])
			return true, true
		case sym.Associativity == AssocNone:
			y.err(sym.Pos, "%nonassoc symbol %s conflict in state %d", sym, si)
		}
	case 'r':
		// nop
	default:
		panic("y: internal error 009")
	}
	return false, false
}

func (y *y) litSym(s string) string {
	if s[0] != '"' {
		return s
	}

	x := y.LiteralStrings[s]
	if x == nil {
		return s
	}

	return x.Name
}

func (y *y) rules0() error {
	y.addRule(&Rule{
		Components: []string{""},
		Precedence: -1,
		Sym:        y.acceptSym,
	})
	post := map[string]token.Pos{}

	for _, prule := range y.ast.Rules {
		nm := prule.Name.Val
		if nm == "error" {
			y.err(prule.Name.Pos(), "a rule cannot use the reserved name error")
			continue
		}

		ruleSym := y.Syms[nm]
		if ruleSym == nil {
			ruleSym = &Symbol{Name: nm, Pos: prule.Name.Pos(), Value: -1}
			y.Syms[nm] = ruleSym
		}
		lit := y.percTypeLits[nm]
		if lit != nil {
			ls := lit.lit
			y.LiteralStrings[ls] = ruleSym
			ruleSym.LiteralString = ls
		}
		ruleSym.Type = y.symTypes[ruleSym.Name].typeName
		r := &Rule{
			Body:         prule.Body,
			MaxParentDlr: -1,
			Precedence:   -1,
			Sym:          ruleSym,
			Token:        prule.Token,
			pos:          prule.Name.Pos(),
		}
		if prule.Case == 0 {
			r.Name = prule.Name
		}

		// Make $n have index n.
		pcomponents := append([]interface{}{nil}, prule.Body...)
		if pr := prule.Precedence; pr != nil {
			for pr != nil && pr.Case == 3 { // Precedence ';'
				pr = pr.Precedence
			}

			if pr != nil {
				var nm string
				switch x := pr.Identifier.(type) {
				case int:
					nm = fmt.Sprintf("%q", x)
				case string:
					nm = y.litSym(x)
				default:
					panic("internal error")
				}

				s, ok := y.Syms[nm]
				if !ok {
					y.err(pr.Token2.Pos(), "%%prec: undefined symbol (1) %s", nm) //TODO -(1)
					continue
				}

				if !s.IsTerminal {
					y.err(pr.Token2.Pos(), "must be a terminal: %s", nm)
					continue
				}

				r.Associativity, r.Precedence = s.Associativity, s.Precedence
				r.PrecSym = s
				r.ExplicitPrecSym = s
			}
		}

		var finalAct *yparser.Action
		var components []string
		for i, item := range pcomponents {
			switch x := item.(type) {
			case nil:
				// no $0 component
			case string:
				x = y.litSym(x)
				y.useSym(x, prule.Name.Pos())
				if len(components) == 0 && x == r.Sym.Name {
					r.Sym.IsLeftRecursive = true
				}
				components = append(components, x)
				sym := y.Syms[x]
				if sym == nil || sym.Type != "" {
					break
				}

				sym.Type = y.symTypes[x].typeName
			case *yparser.Action:
				for _, v := range x.Values {
					n := v.Num
					tag := v.Tag
					if v.Type == yparser.ActionValueDlrDlr && ruleSym.Type == "" && !y.opts.AllowTypeErrors {
						y.err(v.Pos, "$$ of %s has no declared type", ruleSym)
					}
					if v.Type == yparser.ActionValueDlrNum || v.Type == yparser.ActionValueDlrTagNum {
						switch {
						case n < 1 || n >= len(pcomponents):
							y.err(v.Pos, "undefined: $%d", n)
						case n >= i:
							y.err(v.Pos, "not accessible here: $%d", n)
						case v.Type == yparser.ActionValueDlrNum:
							csym := components[n-1]
							if _, ok := post[csym]; !ok {
								post[csym] = v.Pos
							}
						}
					}
					if v.Type == yparser.ActionValueDlrTagDlr || v.Type == yparser.ActionValueDlrTagNum {
						switch _, ok := y.types[tag]; {
						case ok:
							y.useType(v.Pos, tag)
						default:
							y.err(v.Pos, "undefined type %s", tag)
						}
					}
				}

				if i == len(pcomponents)-1 {
					finalAct = x
					break
				}

				y.synthRule++
				s := &Symbol{Name: fmt.Sprintf("$@%d", y.synthRule), Value: -1}
				y.Syms[s.Name] = s
				y.addRule(&Rule{
					Action:       x,
					MaxParentDlr: i - 1,
					Parent:       r,
					Sym:          s,
					maxDlr:       -1,
					Precedence:   -1,
				})
				components = append(components, s.Name)
			case int: // literal
				nm := fmt.Sprintf("%q", x)
				components = append(components, nm)
				pcomponents[i] = nm
				s := y.Syms[nm]
				if s != nil {
					break
				}

				s = &Symbol{Name: nm, IsTerminal: true, Precedence: -1, Value: x}
				y.Syms[nm] = s
			default:
				panic("internal error")
			}
		}
		r.Action = finalAct
		r.maxDlr = len(pcomponents) - 1
		r.Components = components
		if len(components) != 0 && components[len(components)-1] == r.Sym.Name {
			r.Sym.IsRightRecursive = true
		}
		y.addRule(r)
		if r.Sym.Type != "" && r.Action == nil && len(components) == 0 {
			y.err(prule.Token.Pos(), "empty rule for typed nonterminal, and no action")
		}

		if y.firstRule == 0 {
			y.firstRule = r.RuleNum
		}
	}

	if y.Start == "" {
		y.Start = y.Rules[y.firstRule].Sym.Name
	}
	y.useSym(y.Start, y.ast.Rules[0].Token.Pos())
	y.Rules[0].Components[0] = y.Start

	for _, rule := range y.Rules {
		if rule.Precedence >= 0 {
			continue
		}

		components := rule.Components
		if len(components) == 0 {
			rule.Sym.derivesE = true
			rule.Sym.derivesEValid = true
			continue
		}

		for i := len(components) - 1; i >= 0; i-- {
			if sym := y.Syms[components[i]]; sym != nil && sym.IsTerminal {
				rule.Associativity, rule.Precedence = sym.Associativity, sym.Precedence
				rule.PrecSym = sym
				break
			}
		}
	}

	for nm, pos := range y.typesUsed {
		if _, ok := y.types[nm]; !ok {
			y.err(pos, "undefined type %s", nm)
		}
	}

	for nm, pos := range post {
		sym := y.Syms[nm]
		if (sym == nil || sym.Type == "") && !y.opts.AllowTypeErrors {
			y.err(pos, "%s has no declared type", nm)
		}
	}

	//TODO for nm, pos := range y.types {
	//TODO 	if _, ok := y.typesUsed[nm]; !ok {
	//TODO 		y.err(pos, "type declared and not used: %s", nm)
	//TODO 	}
	//TODO }

	for nm, pos := range y.symsUsed {
		if _, ok := y.Syms[nm]; !ok {
			y.err(pos, "undefined symbol %s", nm)
		}
	}

	y.syms = make([]*Symbol, len(y.Syms))
	y.syms[0] = y.emptySym
	x := 1
	a := make([]string, 0, len(y.Syms))
	for nm := range y.Syms {
		a = append(a, nm)
	}
	sort.Strings(a)
	for _, nm := range a {
		s := y.Syms[nm]
		if s != y.emptySym {
			s.id = x
			y.syms[x] = s
			x++
		}
		if nm[0] == '$' || s.IsTerminal {
			continue
		}

		if _, ok := y.symsUsed[nm]; !ok {
			y.err(s.Pos, "non terminal declared and not used: %s", nm)
		}
	}
	y.symSetCap = (len(y.syms) + intBits - 1) / intBits
	for nm := range y.nonTerminals {
		nt, ok := y.Syms[nm]
		if !ok {
			continue
		}

		if nt.IsTerminal {
			y.err(nt.Pos, "expected %s to be a non terminal", nt)
		}

	}

	for _, rule := range y.Rules {
		rule.syms = make([]*Symbol, len(rule.Components))
		for i, v := range rule.Components {
			rule.syms[i] = y.Syms[v]
		}
		if y.opts.AllowTypeErrors {
			continue
		}

		if e := rule.Sym.Type; e != "" && rule.Action == nil && len(rule.Components) != 0 {
			if g := y.Syms[rule.Components[0]].Type; g != e {
				y.err(rule.pos, "type clash on default action: <%s> != <%s>", e, g)
			}
		}
	}
	return y.error()
}

func (y *y) states0() {
	itemSet{0}.state(y)
	syms := y.newSymSet(-1)
	q := []int{0}
	for len(q) != 0 {
		s := q[len(q)-1]
		state := y.States[s]
		q = q[:len(q)-1]
		cls := state.kernel.closure(y)
		syms.clear()
		for _, item := range cls {
			sym := item.next(y)
			if sym == nil { // reduction
				if len(item.syms(y)) == 0 { // rule -> ε
					state.xitems = append(state.xitems, item)
				}
				continue
			}

			goTo := cls.goTo(y, sym)
			n, ok := goTo.state(y)
			if !ok {
				q = append(q, n)
			} else {
				y.isPool = append(y.isPool, goTo)
			}

			state.trans[trans{item, sym}] = stateItem{n, goTo.mustFind(item + 1)}
			if syms.add1(sym.id) {
				continue
			}

			switch {
			case sym.IsTerminal:
				state.actions[sym] = append(state.actions[sym], action{'s', n})
			default:
				state.gotos[sym] = action{'g', n}
			}
		}
		y.entries += len(state.actions) + len(state.gotos)
		state.xla = make([]symSet, len(state.xitems))
	}
}

func (y *y) useSym(nm string, pos token.Pos) {
	if _, ok := y.symsUsed[nm]; ok {
		return
	}

	y.symsUsed[nm] = pos
}

func (y *y) useType(pos token.Pos, name string) {
	if name == "" {
		return
	}

	if _, ok := y.typesUsed[name]; ok {
		return
	}

	y.typesUsed[name] = pos
}

func (y *y) xerrors() error {
	n := len(y.opts.XErrorsSrc)
	if n == 0 {
		return y.error()
	}

	if y.opts.XErrorsName == "" {
		y.opts.XErrorsName = "<xerrors>"
	}
	var s scanner.Scanner
	s.Init(
		y.fset.AddFile(y.opts.XErrorsName, -1, n),
		y.opts.XErrorsSrc,
		func(pos token.Position, msg string) {
			y.errp(pos, msg)
		},
		0, // Ignore comments
	)

	var stateSet []int
	var stateSets [][]int
	var example []string
	var examples [][]string
	m := map[string]string{}
	var list []XError
	acceptInt := true
examples:
	for {
		switch pos, tok, lit := s.Scan(); tok {
		case token.INT:
			if !acceptInt {
				y.err(pos, "state number not accepted here")
				break
			}

			n, err := strconv.ParseUint(lit, 10, 31)
			if err != nil {
				y.err(pos, "%v", err)
				break
			}

			stateSet = append(stateSet, int(n))
		case token.IDENT:
			acceptInt = false
			sym, ok := y.Syms[lit]
			if !ok {
				y.err(pos, "undefined symbol %s", lit)
				break
			}

			if !sym.IsTerminal {
				y.err(pos, "not a terminal symbol: %s", lit)
				break
			}

			if lit == "error" {
				lit = ""
			}
			example = append(example, lit)
		case token.CHAR:
			acceptInt = false
			t, err := strconv.Unquote(lit)
			if err != nil {
				y.err(pos, "%v", err)
				break
			}

			nm := fmt.Sprintf("%q", []rune(t)[0])
			if _, ok := y.Syms[nm]; !ok {
				y.Syms[nm] = &Symbol{Name: nm, IsTerminal: true, Precedence: -1, Value: int([]rune(lit)[0])}
			}
			example = append(example, nm)
		case token.OR: // '|'
			stateSets = append(stateSets, stateSet)
			stateSet = nil
			examples = append(examples, example)
			example = nil
		case token.STRING:
			acceptInt = true
			parse := func(toks []string) (stack []int, la *Symbol, ok bool) {
				lex := func() *Symbol {
					if la != nil {
						return la
					}

					if len(toks) == 0 {
						la = y.endSym
						return la
					}

					la = y.Syms[toks[0]]
					toks = toks[1:]
					return la
				}

				stack = []int{0}
				for {
					state := y.States[stack[len(stack)-1]]
					tok := lex()
					var action action
					actions, ok := state.actions[tok]
					if !ok {
						return stack, la, true
					}

					action = actions[0]
					switch action.kind {
					case 'a':
						return stack, la, false
					case 's':
						la = nil
						stack = append(stack, action.arg)
					case 'r':
						rule := y.Rules[action.arg]
						stack = stack[:len(stack)-len(rule.Components)]
						stack = append(stack, y.States[stack[len(stack)-1]].gotos[rule.Sym].arg)
					default:
						panic("y: internal error 010")
					}
				}
			}
			lit := lit[1 : len(lit)-1]
			stateSets = append(stateSets, stateSet)
			for i, example := range append(examples, example) {
				stateSet := stateSets[i]
				if len(stateSet) != 0 {
					if len(example) == 0 {
						example = []string{"$end"}
					}

					last := example[len(example)-1]
					la := y.Syms[last]
					for _, state := range stateSet {
						xe := XError{[]int{state}, la, lit}
						list = append(list, xe)
						m[xe.mapKey()] = lit
					}
					continue
				}

				stack, la, ok := parse(example)
				if !ok {
					y.err(pos, "parser unexpectedly accepts xerror example: %v %s", example, lit)
					continue
				}

				xe := XError{stack, la, lit}
				list = append(list, xe)
				m[xe.mapKey()] = lit
			}
			example = example[:0]
			examples = examples[:0]
			stateSet = stateSet[:0]
			stateSets = stateSets[:0]
		case token.EOF:
			break examples
		case token.ILLEGAL:
			y.err(pos, "illegal token %s (%q)", tok, lit)
			break examples
		case token.SEMICOLON:
			if lit == "\n" {
				break
			}

			fallthrough
		default:
			y.err(pos, "unexpected token %s (%q)", tok, lit)
			break examples
		}
	}
	for _, v := range list {
		if m[v.mapKey()] == v.Msg {
			y.XErrors = append(y.XErrors, v)
		}
	}
	return y.error()
}

func (y *y) zeroPaths() {
	if y.zeroPathsValid {
		return
	}

	var h zpHeap
	s0 := y.States[0]
	m := make([]bool, len(y.States))
	h.add(y, s0)
	m[0] = true
	for n := len(y.States) - 1; n != 0 && h.Len() != 0; {
		e := heap.Pop(&h).(*zpElem)
		d := e.dest
		if d.psym == nil {
			d.parent = e.src
			d.psym = e.sym
			d.distance = e.distance
			n--
		}
		if di := d.id; !m[di] {
			m[di] = true
			h.add(y, d)
		}
	}
	y.zeroPathsValid = true
}

type zpElem struct {
	src, dest *State
	sym       *Symbol
	distance  int
}

func (z *zpElem) less(b *zpElem) bool {
	if z.distance < b.distance {
		return true
	}

	if z.distance > b.distance {
		return false
	}

	if z.sym.Name < b.sym.Name {
		return true
	}

	if z.sym.Name > b.sym.Name {
		return false
	}

	return z.src.id < z.dest.id
}

type zpHeap []*zpElem

func (z zpHeap) Len() int            { return len(z) }
func (z zpHeap) Less(i, j int) bool  { return z[i].less(z[j]) }
func (z zpHeap) Swap(i, j int)       { z[i], z[j] = z[j], z[i] }
func (z *zpHeap) Push(x interface{}) { *z = append(*z, x.(*zpElem)) }

func (z *zpHeap) Pop() interface{} {
	s := *z
	r := s[len(s)-1]
	*z = s[:len(s)-1]
	return r
}

func (z *zpHeap) add(y *y, s *State) {
	var a []string
	for sym := range s.actions {
		a = append(a, sym.Name)
	}
	sort.Strings(a)
	for _, nm := range a {
		sym := y.Syms[nm]
		actions := s.actions[sym]
		action := actions[0]
		if action.kind == 's' {
			heap.Push(z, &zpElem{s, y.States[action.arg], sym, s.distance + len(sym.MinString())})
		}
	}
	a = a[:0]
	for sym := range s.gotos {
		a = append(a, sym.Name)
	}
	sort.Strings(a)
	for _, nm := range a {
		sym := y.Syms[nm]
		action := s.gotos[sym]
		heap.Push(z, &zpElem{s, y.States[action.arg], sym, s.distance + len(sym.MinString())})
	}
}