return &PosBase{pos, filename, sat32(line), sat32(col), trimmed}
}

func (base *PosBase) IsFileBase() bool {
	if base == nil {
		return false
	}
	return base.pos.base == base
}

func (base *PosBase) Pos() (_ Pos) {
	if base == nil {
		return
	}
	return base.pos
}

func (base *PosBase) Filename() string {
	if base == nil {

	if !pos.IsKnown() {
		return src.NoXPos
	}

	posBase := m.makeSrcPosBase(pos.Base())
	return base.Ctxt.PosTable.XPos(src.MakePos(posBase, pos.Line(), pos.Col()))
}

// makeSrcPosBase translates from a *syntax.PosBase to a *src.PosBase.
func (m *posMap) makeSrcPosBase(b0 *syntax.PosBase) *src.PosBase {
	// fast path: most likely PosBase hasn't changed
	if m.cache.last == b0 {
		return m.cache.base
	}

	return buf.String()
}

// ----------------------------------------------------------------------------
// PosBase

// A PosBase encodes a filename and base position.
// Typically, each file and line directive introduce a PosBase.
type PosBase struct {
	pos         Pos    // position at which the relative position is (line, col)

package lex

import (
	"text/scanner"

	"cmd/internal/src"
)

// A Slice reads from a slice of Tokens.
type Slice struct {
	tokens []Token
	base   *src.PosBase
	line   int
	pos    int
}

func NewSlice(base *src.PosBase, line int, tokens []Token) *Slice {
	return &Slice{
		tokens: tokens,
		base:   base,
		line:   line,
		pos:    -1, // Next will advance to zero.
	}
}

type PosTable struct {
	baseList []*PosBase
	indexMap map[*PosBase]int
	nameMap  map[string]int // Maps file symbol name to index for debug information.
}

// XPos returns the corresponding XPos for the given pos,
// adding pos to t if necessary.
func (t *PosTable) XPos(pos Pos) XPos {
	return XPos{t.baseIndex(pos.base), pos.lico}
}

func (t *PosTable) baseIndex(base *PosBase) int32 {
	if base == nil {
		return 0

func (s *Stack) Text() string {
	return s.tr[len(s.tr)-1].Text()
}

func (s *Stack) File() string {
	return s.Base().Filename()
}

func (s *Stack) Base() *src.PosBase {
	return s.tr[len(s.tr)-1].Base()
}

func (s *Stack) SetBase(base *src.PosBase) {
	s.tr[len(s.tr)-1].SetBase(base)
}

func (s *Stack) Line() int {
	return s.tr[len(s.tr)-1].Line()
}

func (s *Stack) Col() int {

	case ROT:
		return "@>"
	}
	return t.s.TokenText()
}

func (t *Tokenizer) File() string {
	return t.base.Filename()
}

func (t *Tokenizer) Base() *src.PosBase {
	return t.base
}

func (t *Tokenizer) SetBase(base *src.PosBase) {
	t.base = base
}

func (t *Tokenizer) Line() int {
	return t.line
}

func (t *Tokenizer) Col() int {
	return t.s.Pos().Column
}

	Text() string
	// File reports the source file name of the token.
	File() string
	// Base reports the position base of the token.
	Base() *src.PosBase
	// SetBase sets the position base.
	SetBase(*src.PosBase)
	// Line reports the source line number of the token.
	Line() int
	// Col reports the source column number of the token.
	Col() int
	// Close does any teardown required.
	Close()
}

	}

	// TODO(mdempsky): Delta encoding.
	posBase := r.posBase()
	line := r.Uint()
	col := r.Uint()
	return r.p.fake.pos(posBase, int(line), int(col))
}

func (r *reader) posBase() string {
	return r.p.posBaseIdx(r.Reloc(pkgbits.RelocPosBase))
}

func (pr *pkgReader) posBaseIdx(idx pkgbits.Index) string {
	if b := pr.posBases[idx]; b != "" {
		return b
	}

	var filename string

// is unknown (line, col = 0, 0). If there are no matching comments,
// the result is nil.
func CommentMap(src io.Reader, rx *regexp.Regexp) (res map[uint][]Error) {
	// position of previous token
	var base *PosBase
	var prev struct{ line, col uint }

	var s scanner
	s.init(src, func(_, _ uint, text string) {
		if text[0] != '/' {
			return // not a comment, ignore
		}
		if text[1] == '*' {