Adding upstream version 1.16.10.upstream/1.16.10upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

3 files changed, 1848 insertions, 0 deletions

diff --git a/src/text/scanner/example_test.go b/src/text/scanner/example_test.go
new file mode 100644
index 0000000..5e8c3fb
--- /dev/null
+++ b/src/text/scanner/example_test.go
@@ -0,0 +1,140 @@
+// Copyright 2018 The Go 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 scanner_test
+
+import (
+	"fmt"
+	"strings"
+	"text/scanner"
+	"unicode"
+)
+
+func Example() {
+	const src = `
+// This is scanned code.
+if a > 10 {
+	someParsable = text
+}`
+
+	var s scanner.Scanner
+	s.Init(strings.NewReader(src))
+	s.Filename = "example"
+	for tok := s.Scan(); tok != scanner.EOF; tok = s.Scan() {
+		fmt.Printf("%s: %s\n", s.Position, s.TokenText())
+	}
+
+	// Output:
+	// example:3:1: if
+	// example:3:4: a
+	// example:3:6: >
+	// example:3:8: 10
+	// example:3:11: {
+	// example:4:2: someParsable
+	// example:4:15: =
+	// example:4:17: text
+	// example:5:1: }
+}
+
+func Example_isIdentRune() {
+	const src = "%var1 var2%"
+
+	var s scanner.Scanner
+	s.Init(strings.NewReader(src))
+	s.Filename = "default"
+
+	for tok := s.Scan(); tok != scanner.EOF; tok = s.Scan() {
+		fmt.Printf("%s: %s\n", s.Position, s.TokenText())
+	}
+
+	fmt.Println()
+	s.Init(strings.NewReader(src))
+	s.Filename = "percent"
+
+	// treat leading '%' as part of an identifier
+	s.IsIdentRune = func(ch rune, i int) bool {
+		return ch == '%' && i == 0 || unicode.IsLetter(ch) || unicode.IsDigit(ch) && i > 0
+	}
+
+	for tok := s.Scan(); tok != scanner.EOF; tok = s.Scan() {
+		fmt.Printf("%s: %s\n", s.Position, s.TokenText())
+	}
+
+	// Output:
+	// default:1:1: %
+	// default:1:2: var1
+	// default:1:7: var2
+	// default:1:11: %
+	//
+	// percent:1:1: %var1
+	// percent:1:7: var2
+	// percent:1:11: %
+}
+
+func Example_mode() {
+	const src = `
+    // Comment begins at column 5.
+
+This line should not be included in the output.
+
+/*
+This multiline comment
+should be extracted in
+its entirety.
+*/
+`
+
+	var s scanner.Scanner
+	s.Init(strings.NewReader(src))
+	s.Filename = "comments"
+	s.Mode ^= scanner.SkipComments // don't skip comments
+
+	for tok := s.Scan(); tok != scanner.EOF; tok = s.Scan() {
+		txt := s.TokenText()
+		if strings.HasPrefix(txt, "//") || strings.HasPrefix(txt, "/*") {
+			fmt.Printf("%s: %s\n", s.Position, txt)
+		}
+	}
+
+	// Output:
+	// comments:2:5: // Comment begins at column 5.
+	// comments:6:1: /*
+	// This multiline comment
+	// should be extracted in
+	// its entirety.
+	// */
+}
+
+func Example_whitespace() {
+	// tab-separated values
+	const src = `aa	ab	ac	ad
+ba	bb	bc	bd
+ca	cb	cc	cd
+da	db	dc	dd`
+
+	var (
+		col, row int
+		s        scanner.Scanner
+		tsv      [4][4]string // large enough for example above
+	)
+	s.Init(strings.NewReader(src))
+	s.Whitespace ^= 1<<'\t' | 1<<'\n' // don't skip tabs and new lines
+
+	for tok := s.Scan(); tok != scanner.EOF; tok = s.Scan() {
+		switch tok {
+		case '\n':
+			row++
+			col = 0
+		case '\t':
+			col++
+		default:
+			tsv[row][col] = s.TokenText()
+		}
+	}
+
+	fmt.Print(tsv)
+
+	// Output:
+	// [[aa ab ac ad] [ba bb bc bd] [ca cb cc cd] [da db dc dd]]
+}
diff --git a/src/text/scanner/scanner.go b/src/text/scanner/scanner.go
new file mode 100644
index 0000000..e0847a7
--- /dev/null
+++ b/src/text/scanner/scanner.go
@@ -0,0 +1,793 @@
+// Copyright 2009 The Go 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 scanner provides a scanner and tokenizer for UTF-8-encoded text.
+// It takes an io.Reader providing the source, which then can be tokenized
+// through repeated calls to the Scan function. For compatibility with
+// existing tools, the NUL character is not allowed. If the first character
+// in the source is a UTF-8 encoded byte order mark (BOM), it is discarded.
+//
+// By default, a Scanner skips white space and Go comments and recognizes all
+// literals as defined by the Go language specification. It may be
+// customized to recognize only a subset of those literals and to recognize
+// different identifier and white space characters.
+package scanner
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+	"unicode"
+	"unicode/utf8"
+)
+
+// A source position is represented by a Position value.
+// A position is valid if Line > 0.
+type Position struct {
+	Filename string // filename, if any
+	Offset   int    // byte offset, starting at 0
+	Line     int    // line number, starting at 1
+	Column   int    // column number, starting at 1 (character count per line)
+}
+
+// IsValid reports whether the position is valid.
+func (pos *Position) IsValid() bool { return pos.Line > 0 }
+
+func (pos Position) String() string {
+	s := pos.Filename
+	if s == "" {
+		s = "<input>"
+	}
+	if pos.IsValid() {
+		s += fmt.Sprintf(":%d:%d", pos.Line, pos.Column)
+	}
+	return s
+}
+
+// Predefined mode bits to control recognition of tokens. For instance,
+// to configure a Scanner such that it only recognizes (Go) identifiers,
+// integers, and skips comments, set the Scanner's Mode field to:
+//
+//	ScanIdents | ScanInts | SkipComments
+//
+// With the exceptions of comments, which are skipped if SkipComments is
+// set, unrecognized tokens are not ignored. Instead, the scanner simply
+// returns the respective individual characters (or possibly sub-tokens).
+// For instance, if the mode is ScanIdents (not ScanStrings), the string
+// "foo" is scanned as the token sequence '"' Ident '"'.
+//
+// Use GoTokens to configure the Scanner such that it accepts all Go
+// literal tokens including Go identifiers. Comments will be skipped.
+//
+const (
+	ScanIdents     = 1 << -Ident
+	ScanInts       = 1 << -Int
+	ScanFloats     = 1 << -Float // includes Ints and hexadecimal floats
+	ScanChars      = 1 << -Char
+	ScanStrings    = 1 << -String
+	ScanRawStrings = 1 << -RawString
+	ScanComments   = 1 << -Comment
+	SkipComments   = 1 << -skipComment // if set with ScanComments, comments become white space
+	GoTokens       = ScanIdents | ScanFloats | ScanChars | ScanStrings | ScanRawStrings | ScanComments | SkipComments
+)
+
+// The result of Scan is one of these tokens or a Unicode character.
+const (
+	EOF = -(iota + 1)
+	Ident
+	Int
+	Float
+	Char
+	String
+	RawString
+	Comment
+
+	// internal use only
+	skipComment
+)
+
+var tokenString = map[rune]string{
+	EOF:       "EOF",
+	Ident:     "Ident",
+	Int:       "Int",
+	Float:     "Float",
+	Char:      "Char",
+	String:    "String",
+	RawString: "RawString",
+	Comment:   "Comment",
+}
+
+// TokenString returns a printable string for a token or Unicode character.
+func TokenString(tok rune) string {
+	if s, found := tokenString[tok]; found {
+		return s
+	}
+	return fmt.Sprintf("%q", string(tok))
+}
+
+// GoWhitespace is the default value for the Scanner's Whitespace field.
+// Its value selects Go's white space characters.
+const GoWhitespace = 1<<'\t' | 1<<'\n' | 1<<'\r' | 1<<' '
+
+const bufLen = 1024 // at least utf8.UTFMax
+
+// A Scanner implements reading of Unicode characters and tokens from an io.Reader.
+type Scanner struct {
+	// Input
+	src io.Reader
+
+	// Source buffer
+	srcBuf [bufLen + 1]byte // +1 for sentinel for common case of s.next()
+	srcPos int              // reading position (srcBuf index)
+	srcEnd int              // source end (srcBuf index)
+
+	// Source position
+	srcBufOffset int // byte offset of srcBuf[0] in source
+	line         int // line count
+	column       int // character count
+	lastLineLen  int // length of last line in characters (for correct column reporting)
+	lastCharLen  int // length of last character in bytes
+
+	// Token text buffer
+	// Typically, token text is stored completely in srcBuf, but in general
+	// the token text's head may be buffered in tokBuf while the token text's
+	// tail is stored in srcBuf.
+	tokBuf bytes.Buffer // token text head that is not in srcBuf anymore
+	tokPos int          // token text tail position (srcBuf index); valid if >= 0
+	tokEnd int          // token text tail end (srcBuf index)
+
+	// One character look-ahead
+	ch rune // character before current srcPos
+
+	// Error is called for each error encountered. If no Error
+	// function is set, the error is reported to os.Stderr.
+	Error func(s *Scanner, msg string)
+
+	// ErrorCount is incremented by one for each error encountered.
+	ErrorCount int
+
+	// The Mode field controls which tokens are recognized. For instance,
+	// to recognize Ints, set the ScanInts bit in Mode. The field may be
+	// changed at any time.
+	Mode uint
+
+	// The Whitespace field controls which characters are recognized
+	// as white space. To recognize a character ch <= ' ' as white space,
+	// set the ch'th bit in Whitespace (the Scanner's behavior is undefined
+	// for values ch > ' '). The field may be changed at any time.
+	Whitespace uint64
+
+	// IsIdentRune is a predicate controlling the characters accepted
+	// as the ith rune in an identifier. The set of valid characters
+	// must not intersect with the set of white space characters.
+	// If no IsIdentRune function is set, regular Go identifiers are
+	// accepted instead. The field may be changed at any time.
+	IsIdentRune func(ch rune, i int) bool
+
+	// Start position of most recently scanned token; set by Scan.
+	// Calling Init or Next invalidates the position (Line == 0).
+	// The Filename field is always left untouched by the Scanner.
+	// If an error is reported (via Error) and Position is invalid,
+	// the scanner is not inside a token. Call Pos to obtain an error
+	// position in that case, or to obtain the position immediately
+	// after the most recently scanned token.
+	Position
+}
+
+// Init initializes a Scanner with a new source and returns s.
+// Error is set to nil, ErrorCount is set to 0, Mode is set to GoTokens,
+// and Whitespace is set to GoWhitespace.
+func (s *Scanner) Init(src io.Reader) *Scanner {
+	s.src = src
+
+	// initialize source buffer
+	// (the first call to next() will fill it by calling src.Read)
+	s.srcBuf[0] = utf8.RuneSelf // sentinel
+	s.srcPos = 0
+	s.srcEnd = 0
+
+	// initialize source position
+	s.srcBufOffset = 0
+	s.line = 1
+	s.column = 0
+	s.lastLineLen = 0
+	s.lastCharLen = 0
+
+	// initialize token text buffer
+	// (required for first call to next()).
+	s.tokPos = -1
+
+	// initialize one character look-ahead
+	s.ch = -2 // no char read yet, not EOF
+
+	// initialize public fields
+	s.Error = nil
+	s.ErrorCount = 0
+	s.Mode = GoTokens
+	s.Whitespace = GoWhitespace
+	s.Line = 0 // invalidate token position
+
+	return s
+}
+
+// next reads and returns the next Unicode character. It is designed such
+// that only a minimal amount of work needs to be done in the common ASCII
+// case (one test to check for both ASCII and end-of-buffer, and one test
+// to check for newlines).
+func (s *Scanner) next() rune {
+	ch, width := rune(s.srcBuf[s.srcPos]), 1
+
+	if ch >= utf8.RuneSelf {
+		// uncommon case: not ASCII or not enough bytes
+		for s.srcPos+utf8.UTFMax > s.srcEnd && !utf8.FullRune(s.srcBuf[s.srcPos:s.srcEnd]) {
+			// not enough bytes: read some more, but first
+			// save away token text if any
+			if s.tokPos >= 0 {
+				s.tokBuf.Write(s.srcBuf[s.tokPos:s.srcPos])
+				s.tokPos = 0
+				// s.tokEnd is set by Scan()
+			}
+			// move unread bytes to beginning of buffer
+			copy(s.srcBuf[0:], s.srcBuf[s.srcPos:s.srcEnd])
+			s.srcBufOffset += s.srcPos
+			// read more bytes
+			// (an io.Reader must return io.EOF when it reaches
+			// the end of what it is reading - simply returning
+			// n == 0 will make this loop retry forever; but the
+			// error is in the reader implementation in that case)
+			i := s.srcEnd - s.srcPos
+			n, err := s.src.Read(s.srcBuf[i:bufLen])
+			s.srcPos = 0
+			s.srcEnd = i + n
+			s.srcBuf[s.srcEnd] = utf8.RuneSelf // sentinel
+			if err != nil {
+				if err != io.EOF {
+					s.error(err.Error())
+				}
+				if s.srcEnd == 0 {
+					if s.lastCharLen > 0 {
+						// previous character was not EOF
+						s.column++
+					}
+					s.lastCharLen = 0
+					return EOF
+				}
+				// If err == EOF, we won't be getting more
+				// bytes; break to avoid infinite loop. If
+				// err is something else, we don't know if
+				// we can get more bytes; thus also break.
+				break
+			}
+		}
+		// at least one byte
+		ch = rune(s.srcBuf[s.srcPos])
+		if ch >= utf8.RuneSelf {
+			// uncommon case: not ASCII
+			ch, width = utf8.DecodeRune(s.srcBuf[s.srcPos:s.srcEnd])
+			if ch == utf8.RuneError && width == 1 {
+				// advance for correct error position
+				s.srcPos += width
+				s.lastCharLen = width
+				s.column++
+				s.error("invalid UTF-8 encoding")
+				return ch
+			}
+		}
+	}
+
+	// advance
+	s.srcPos += width
+	s.lastCharLen = width
+	s.column++
+
+	// special situations
+	switch ch {
+	case 0:
+		// for compatibility with other tools
+		s.error("invalid character NUL")
+	case '\n':
+		s.line++
+		s.lastLineLen = s.column
+		s.column = 0
+	}
+
+	return ch
+}
+
+// Next reads and returns the next Unicode character.
+// It returns EOF at the end of the source. It reports
+// a read error by calling s.Error, if not nil; otherwise
+// it prints an error message to os.Stderr. Next does not
+// update the Scanner's Position field; use Pos() to
+// get the current position.
+func (s *Scanner) Next() rune {
+	s.tokPos = -1 // don't collect token text
+	s.Line = 0    // invalidate token position
+	ch := s.Peek()
+	if ch != EOF {
+		s.ch = s.next()
+	}
+	return ch
+}
+
+// Peek returns the next Unicode character in the source without advancing
+// the scanner. It returns EOF if the scanner's position is at the last
+// character of the source.
+func (s *Scanner) Peek() rune {
+	if s.ch == -2 {
+		// this code is only run for the very first character
+		s.ch = s.next()
+		if s.ch == '\uFEFF' {
+			s.ch = s.next() // ignore BOM
+		}
+	}
+	return s.ch
+}
+
+func (s *Scanner) error(msg string) {
+	s.tokEnd = s.srcPos - s.lastCharLen // make sure token text is terminated
+	s.ErrorCount++
+	if s.Error != nil {
+		s.Error(s, msg)
+		return
+	}
+	pos := s.Position
+	if !pos.IsValid() {
+		pos = s.Pos()
+	}
+	fmt.Fprintf(os.Stderr, "%s: %s\n", pos, msg)
+}
+
+func (s *Scanner) errorf(format string, args ...interface{}) {
+	s.error(fmt.Sprintf(format, args...))
+}
+
+func (s *Scanner) isIdentRune(ch rune, i int) bool {
+	if s.IsIdentRune != nil {
+		return s.IsIdentRune(ch, i)
+	}
+	return ch == '_' || unicode.IsLetter(ch) || unicode.IsDigit(ch) && i > 0
+}
+
+func (s *Scanner) scanIdentifier() rune {
+	// we know the zero'th rune is OK; start scanning at the next one
+	ch := s.next()
+	for i := 1; s.isIdentRune(ch, i); i++ {
+		ch = s.next()
+	}
+	return ch
+}
+
+func lower(ch rune) rune     { return ('a' - 'A') | ch } // returns lower-case ch iff ch is ASCII letter
+func isDecimal(ch rune) bool { return '0' <= ch && ch <= '9' }
+func isHex(ch rune) bool     { return '0' <= ch && ch <= '9' || 'a' <= lower(ch) && lower(ch) <= 'f' }
+
+// digits accepts the sequence { digit | '_' } starting with ch0.
+// If base <= 10, digits accepts any decimal digit but records
+// the first invalid digit >= base in *invalid if *invalid == 0.
+// digits returns the first rune that is not part of the sequence
+// anymore, and a bitset describing whether the sequence contained
+// digits (bit 0 is set), or separators '_' (bit 1 is set).
+func (s *Scanner) digits(ch0 rune, base int, invalid *rune) (ch rune, digsep int) {
+	ch = ch0
+	if base <= 10 {
+		max := rune('0' + base)
+		for isDecimal(ch) || ch == '_' {
+			ds := 1
+			if ch == '_' {
+				ds = 2
+			} else if ch >= max && *invalid == 0 {
+				*invalid = ch
+			}
+			digsep |= ds
+			ch = s.next()
+		}
+	} else {
+		for isHex(ch) || ch == '_' {
+			ds := 1
+			if ch == '_' {
+				ds = 2
+			}
+			digsep |= ds
+			ch = s.next()
+		}
+	}
+	return
+}
+
+func (s *Scanner) scanNumber(ch rune, seenDot bool) (rune, rune) {
+	base := 10         // number base
+	prefix := rune(0)  // one of 0 (decimal), '0' (0-octal), 'x', 'o', or 'b'
+	digsep := 0        // bit 0: digit present, bit 1: '_' present
+	invalid := rune(0) // invalid digit in literal, or 0
+
+	// integer part
+	var tok rune
+	var ds int
+	if !seenDot {
+		tok = Int
+		if ch == '0' {
+			ch = s.next()
+			switch lower(ch) {
+			case 'x':
+				ch = s.next()
+				base, prefix = 16, 'x'
+			case 'o':
+				ch = s.next()
+				base, prefix = 8, 'o'
+			case 'b':
+				ch = s.next()
+				base, prefix = 2, 'b'
+			default:
+				base, prefix = 8, '0'
+				digsep = 1 // leading 0
+			}
+		}
+		ch, ds = s.digits(ch, base, &invalid)
+		digsep |= ds
+		if ch == '.' && s.Mode&ScanFloats != 0 {
+			ch = s.next()
+			seenDot = true
+		}
+	}
+
+	// fractional part
+	if seenDot {
+		tok = Float
+		if prefix == 'o' || prefix == 'b' {
+			s.error("invalid radix point in " + litname(prefix))
+		}
+		ch, ds = s.digits(ch, base, &invalid)
+		digsep |= ds
+	}
+
+	if digsep&1 == 0 {
+		s.error(litname(prefix) + " has no digits")
+	}
+
+	// exponent
+	if e := lower(ch); (e == 'e' || e == 'p') && s.Mode&ScanFloats != 0 {
+		switch {
+		case e == 'e' && prefix != 0 && prefix != '0':
+			s.errorf("%q exponent requires decimal mantissa", ch)
+		case e == 'p' && prefix != 'x':
+			s.errorf("%q exponent requires hexadecimal mantissa", ch)
+		}
+		ch = s.next()
+		tok = Float
+		if ch == '+' || ch == '-' {
+			ch = s.next()
+		}
+		ch, ds = s.digits(ch, 10, nil)
+		digsep |= ds
+		if ds&1 == 0 {
+			s.error("exponent has no digits")
+		}
+	} else if prefix == 'x' && tok == Float {
+		s.error("hexadecimal mantissa requires a 'p' exponent")
+	}
+
+	if tok == Int && invalid != 0 {
+		s.errorf("invalid digit %q in %s", invalid, litname(prefix))
+	}
+
+	if digsep&2 != 0 {
+		s.tokEnd = s.srcPos - s.lastCharLen // make sure token text is terminated
+		if i := invalidSep(s.TokenText()); i >= 0 {
+			s.error("'_' must separate successive digits")
+		}
+	}
+
+	return tok, ch
+}
+
+func litname(prefix rune) string {
+	switch prefix {
+	default:
+		return "decimal literal"
+	case 'x':
+		return "hexadecimal literal"
+	case 'o', '0':
+		return "octal literal"
+	case 'b':
+		return "binary literal"
+	}
+}
+
+// invalidSep returns the index of the first invalid separator in x, or -1.
+func invalidSep(x string) int {
+	x1 := ' ' // prefix char, we only care if it's 'x'
+	d := '.'  // digit, one of '_', '0' (a digit), or '.' (anything else)
+	i := 0
+
+	// a prefix counts as a digit
+	if len(x) >= 2 && x[0] == '0' {
+		x1 = lower(rune(x[1]))
+		if x1 == 'x' || x1 == 'o' || x1 == 'b' {
+			d = '0'
+			i = 2
+		}
+	}
+
+	// mantissa and exponent
+	for ; i < len(x); i++ {
+		p := d // previous digit
+		d = rune(x[i])
+		switch {
+		case d == '_':
+			if p != '0' {
+				return i
+			}
+		case isDecimal(d) || x1 == 'x' && isHex(d):
+			d = '0'
+		default:
+			if p == '_' {
+				return i - 1
+			}
+			d = '.'
+		}
+	}
+	if d == '_' {
+		return len(x) - 1
+	}
+
+	return -1
+}
+
+func digitVal(ch rune) int {
+	switch {
+	case '0' <= ch && ch <= '9':
+		return int(ch - '0')
+	case 'a' <= lower(ch) && lower(ch) <= 'f':
+		return int(lower(ch) - 'a' + 10)
+	}
+	return 16 // larger than any legal digit val
+}
+
+func (s *Scanner) scanDigits(ch rune, base, n int) rune {
+	for n > 0 && digitVal(ch) < base {
+		ch = s.next()
+		n--
+	}
+	if n > 0 {
+		s.error("invalid char escape")
+	}
+	return ch
+}
+
+func (s *Scanner) scanEscape(quote rune) rune {
+	ch := s.next() // read character after '/'
+	switch ch {
+	case 'a', 'b', 'f', 'n', 'r', 't', 'v', '\\', quote:
+		// nothing to do
+		ch = s.next()
+	case '0', '1', '2', '3', '4', '5', '6', '7':
+		ch = s.scanDigits(ch, 8, 3)
+	case 'x':
+		ch = s.scanDigits(s.next(), 16, 2)
+	case 'u':
+		ch = s.scanDigits(s.next(), 16, 4)
+	case 'U':
+		ch = s.scanDigits(s.next(), 16, 8)
+	default:
+		s.error("invalid char escape")
+	}
+	return ch
+}
+
+func (s *Scanner) scanString(quote rune) (n int) {
+	ch := s.next() // read character after quote
+	for ch != quote {
+		if ch == '\n' || ch < 0 {
+			s.error("literal not terminated")
+			return
+		}
+		if ch == '\\' {
+			ch = s.scanEscape(quote)
+		} else {
+			ch = s.next()
+		}
+		n++
+	}
+	return
+}
+
+func (s *Scanner) scanRawString() {
+	ch := s.next() // read character after '`'
+	for ch != '`' {
+		if ch < 0 {
+			s.error("literal not terminated")
+			return
+		}
+		ch = s.next()
+	}
+}
+
+func (s *Scanner) scanChar() {
+	if s.scanString('\'') != 1 {
+		s.error("invalid char literal")
+	}
+}
+
+func (s *Scanner) scanComment(ch rune) rune {
+	// ch == '/' || ch == '*'
+	if ch == '/' {
+		// line comment
+		ch = s.next() // read character after "//"
+		for ch != '\n' && ch >= 0 {
+			ch = s.next()
+		}
+		return ch
+	}
+
+	// general comment
+	ch = s.next() // read character after "/*"
+	for {
+		if ch < 0 {
+			s.error("comment not terminated")
+			break
+		}
+		ch0 := ch
+		ch = s.next()
+		if ch0 == '*' && ch == '/' {
+			ch = s.next()
+			break
+		}
+	}
+	return ch
+}
+
+// Scan reads the next token or Unicode character from source and returns it.
+// It only recognizes tokens t for which the respective Mode bit (1<<-t) is set.
+// It returns EOF at the end of the source. It reports scanner errors (read and
+// token errors) by calling s.Error, if not nil; otherwise it prints an error
+// message to os.Stderr.
+func (s *Scanner) Scan() rune {
+	ch := s.Peek()
+
+	// reset token text position
+	s.tokPos = -1
+	s.Line = 0
+
+redo:
+	// skip white space
+	for s.Whitespace&(1<<uint(ch)) != 0 {
+		ch = s.next()
+	}
+
+	// start collecting token text
+	s.tokBuf.Reset()
+	s.tokPos = s.srcPos - s.lastCharLen
+
+	// set token position
+	// (this is a slightly optimized version of the code in Pos())
+	s.Offset = s.srcBufOffset + s.tokPos
+	if s.column > 0 {
+		// common case: last character was not a '\n'
+		s.Line = s.line
+		s.Column = s.column
+	} else {
+		// last character was a '\n'
+		// (we cannot be at the beginning of the source
+		// since we have called next() at least once)
+		s.Line = s.line - 1
+		s.Column = s.lastLineLen
+	}
+
+	// determine token value
+	tok := ch
+	switch {
+	case s.isIdentRune(ch, 0):
+		if s.Mode&ScanIdents != 0 {
+			tok = Ident
+			ch = s.scanIdentifier()
+		} else {
+			ch = s.next()
+		}
+	case isDecimal(ch):
+		if s.Mode&(ScanInts|ScanFloats) != 0 {
+			tok, ch = s.scanNumber(ch, false)
+		} else {
+			ch = s.next()
+		}
+	default:
+		switch ch {
+		case EOF:
+			break
+		case '"':
+			if s.Mode&ScanStrings != 0 {
+				s.scanString('"')
+				tok = String
+			}
+			ch = s.next()
+		case '\'':
+			if s.Mode&ScanChars != 0 {
+				s.scanChar()
+				tok = Char
+			}
+			ch = s.next()
+		case '.':
+			ch = s.next()
+			if isDecimal(ch) && s.Mode&ScanFloats != 0 {
+				tok, ch = s.scanNumber(ch, true)
+			}
+		case '/':
+			ch = s.next()
+			if (ch == '/' || ch == '*') && s.Mode&ScanComments != 0 {
+				if s.Mode&SkipComments != 0 {
+					s.tokPos = -1 // don't collect token text
+					ch = s.scanComment(ch)
+					goto redo
+				}
+				ch = s.scanComment(ch)
+				tok = Comment
+			}
+		case '`':
+			if s.Mode&ScanRawStrings != 0 {
+				s.scanRawString()
+				tok = RawString
+			}
+			ch = s.next()
+		default:
+			ch = s.next()
+		}
+	}
+
+	// end of token text
+	s.tokEnd = s.srcPos - s.lastCharLen
+
+	s.ch = ch
+	return tok
+}
+
+// Pos returns the position of the character immediately after
+// the character or token returned by the last call to Next or Scan.
+// Use the Scanner's Position field for the start position of the most
+// recently scanned token.
+func (s *Scanner) Pos() (pos Position) {
+	pos.Filename = s.Filename
+	pos.Offset = s.srcBufOffset + s.srcPos - s.lastCharLen
+	switch {
+	case s.column > 0:
+		// common case: last character was not a '\n'
+		pos.Line = s.line
+		pos.Column = s.column
+	case s.lastLineLen > 0:
+		// last character was a '\n'
+		pos.Line = s.line - 1
+		pos.Column = s.lastLineLen
+	default:
+		// at the beginning of the source
+		pos.Line = 1
+		pos.Column = 1
+	}
+	return
+}
+
+// TokenText returns the string corresponding to the most recently scanned token.
+// Valid after calling Scan and in calls of Scanner.Error.
+func (s *Scanner) TokenText() string {
+	if s.tokPos < 0 {
+		// no token text
+		return ""
+	}
+
+	if s.tokEnd < s.tokPos {
+		// if EOF was reached, s.tokEnd is set to -1 (s.srcPos == 0)
+		s.tokEnd = s.tokPos
+	}
+	// s.tokEnd >= s.tokPos
+
+	if s.tokBuf.Len() == 0 {
+		// common case: the entire token text is still in srcBuf
+		return string(s.srcBuf[s.tokPos:s.tokEnd])
+	}
+
+	// part of the token text was saved in tokBuf: save the rest in
+	// tokBuf as well and return its content
+	s.tokBuf.Write(s.srcBuf[s.tokPos:s.tokEnd])
+	s.tokPos = s.tokEnd // ensure idempotency of TokenText() call
+	return s.tokBuf.String()
+}
diff --git a/src/text/scanner/scanner_test.go b/src/text/scanner/scanner_test.go
new file mode 100644
index 0000000..fe39d30
--- /dev/null
+++ b/src/text/scanner/scanner_test.go
@@ -0,0 +1,915 @@
+// Copyright 2009 The Go 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 scanner
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"strings"
+	"testing"
+	"unicode/utf8"
+)
+
+// A StringReader delivers its data one string segment at a time via Read.
+type StringReader struct {
+	data []string
+	step int
+}
+
+func (r *StringReader) Read(p []byte) (n int, err error) {
+	if r.step < len(r.data) {
+		s := r.data[r.step]
+		n = copy(p, s)
+		r.step++
+	} else {
+		err = io.EOF
+	}
+	return
+}
+
+func readRuneSegments(t *testing.T, segments []string) {
+	got := ""
+	want := strings.Join(segments, "")
+	s := new(Scanner).Init(&StringReader{data: segments})
+	for {
+		ch := s.Next()
+		if ch == EOF {
+			break
+		}
+		got += string(ch)
+	}
+	if got != want {
+		t.Errorf("segments=%v got=%s want=%s", segments, got, want)
+	}
+}
+
+var segmentList = [][]string{
+	{},
+	{""},
+	{"日", "本語"},
+	{"\u65e5", "\u672c", "\u8a9e"},
+	{"\U000065e5", " ", "\U0000672c", "\U00008a9e"},
+	{"\xe6", "\x97\xa5\xe6", "\x9c\xac\xe8\xaa\x9e"},
+	{"Hello", ", ", "World", "!"},
+	{"Hello", ", ", "", "World", "!"},
+}
+
+func TestNext(t *testing.T) {
+	for _, s := range segmentList {
+		readRuneSegments(t, s)
+	}
+}
+
+type token struct {
+	tok  rune
+	text string
+}
+
+var f100 = "ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"
+
+var tokenList = []token{
+	{Comment, "// line comments"},
+	{Comment, "//"},
+	{Comment, "////"},
+	{Comment, "// comment"},
+	{Comment, "// /* comment */"},
+	{Comment, "// // comment //"},
+	{Comment, "//" + f100},
+
+	{Comment, "// general comments"},
+	{Comment, "/**/"},
+	{Comment, "/***/"},
+	{Comment, "/* comment */"},
+	{Comment, "/* // comment */"},
+	{Comment, "/* /* comment */"},
+	{Comment, "/*\n comment\n*/"},
+	{Comment, "/*" + f100 + "*/"},
+
+	{Comment, "// identifiers"},
+	{Ident, "a"},
+	{Ident, "a0"},
+	{Ident, "foobar"},
+	{Ident, "abc123"},
+	{Ident, "LGTM"},
+	{Ident, "_"},
+	{Ident, "_abc123"},
+	{Ident, "abc123_"},
+	{Ident, "_abc_123_"},
+	{Ident, "_äöü"},
+	{Ident, "_本"},
+	{Ident, "äöü"},
+	{Ident, "本"},
+	{Ident, "a۰۱۸"},
+	{Ident, "foo६४"},
+	{Ident, "bar９８７６"},
+	{Ident, f100},
+
+	{Comment, "// decimal ints"},
+	{Int, "0"},
+	{Int, "1"},
+	{Int, "9"},
+	{Int, "42"},
+	{Int, "1234567890"},
+
+	{Comment, "// octal ints"},
+	{Int, "00"},
+	{Int, "01"},
+	{Int, "07"},
+	{Int, "042"},
+	{Int, "01234567"},
+
+	{Comment, "// hexadecimal ints"},
+	{Int, "0x0"},
+	{Int, "0x1"},
+	{Int, "0xf"},
+	{Int, "0x42"},
+	{Int, "0x123456789abcDEF"},
+	{Int, "0x" + f100},
+	{Int, "0X0"},
+	{Int, "0X1"},
+	{Int, "0XF"},
+	{Int, "0X42"},
+	{Int, "0X123456789abcDEF"},
+	{Int, "0X" + f100},
+
+	{Comment, "// floats"},
+	{Float, "0."},
+	{Float, "1."},
+	{Float, "42."},
+	{Float, "01234567890."},
+	{Float, ".0"},
+	{Float, ".1"},
+	{Float, ".42"},
+	{Float, ".0123456789"},
+	{Float, "0.0"},
+	{Float, "1.0"},
+	{Float, "42.0"},
+	{Float, "01234567890.0"},
+	{Float, "0e0"},
+	{Float, "1e0"},
+	{Float, "42e0"},
+	{Float, "01234567890e0"},
+	{Float, "0E0"},
+	{Float, "1E0"},
+	{Float, "42E0"},
+	{Float, "01234567890E0"},
+	{Float, "0e+10"},
+	{Float, "1e-10"},
+	{Float, "42e+10"},
+	{Float, "01234567890e-10"},
+	{Float, "0E+10"},
+	{Float, "1E-10"},
+	{Float, "42E+10"},
+	{Float, "01234567890E-10"},
+
+	{Comment, "// chars"},
+	{Char, `' '`},
+	{Char, `'a'`},
+	{Char, `'本'`},
+	{Char, `'\a'`},
+	{Char, `'\b'`},
+	{Char, `'\f'`},
+	{Char, `'\n'`},
+	{Char, `'\r'`},
+	{Char, `'\t'`},
+	{Char, `'\v'`},
+	{Char, `'\''`},
+	{Char, `'\000'`},
+	{Char, `'\777'`},
+	{Char, `'\x00'`},
+	{Char, `'\xff'`},
+	{Char, `'\u0000'`},
+	{Char, `'\ufA16'`},
+	{Char, `'\U00000000'`},
+	{Char, `'\U0000ffAB'`},
+
+	{Comment, "// strings"},
+	{String, `" "`},
+	{String, `"a"`},
+	{String, `"本"`},
+	{String, `"\a"`},
+	{String, `"\b"`},
+	{String, `"\f"`},
+	{String, `"\n"`},
+	{String, `"\r"`},
+	{String, `"\t"`},
+	{String, `"\v"`},
+	{String, `"\""`},
+	{String, `"\000"`},
+	{String, `"\777"`},
+	{String, `"\x00"`},
+	{String, `"\xff"`},
+	{String, `"\u0000"`},
+	{String, `"\ufA16"`},
+	{String, `"\U00000000"`},
+	{String, `"\U0000ffAB"`},
+	{String, `"` + f100 + `"`},
+
+	{Comment, "// raw strings"},
+	{RawString, "``"},
+	{RawString, "`\\`"},
+	{RawString, "`" + "\n\n/* foobar */\n\n" + "`"},
+	{RawString, "`" + f100 + "`"},
+
+	{Comment, "// individual characters"},
+	// NUL character is not allowed
+	{'\x01', "\x01"},
+	{' ' - 1, string(' ' - 1)},
+	{'+', "+"},
+	{'/', "/"},
+	{'.', "."},
+	{'~', "~"},
+	{'(', "("},
+}
+
+func makeSource(pattern string) *bytes.Buffer {
+	var buf bytes.Buffer
+	for _, k := range tokenList {
+		fmt.Fprintf(&buf, pattern, k.text)
+	}
+	return &buf
+}
+
+func checkTok(t *testing.T, s *Scanner, line int, got, want rune, text string) {
+	if got != want {
+		t.Fatalf("tok = %s, want %s for %q", TokenString(got), TokenString(want), text)
+	}
+	if s.Line != line {
+		t.Errorf("line = %d, want %d for %q", s.Line, line, text)
+	}
+	stext := s.TokenText()
+	if stext != text {
+		t.Errorf("text = %q, want %q", stext, text)
+	} else {
+		// check idempotency of TokenText() call
+		stext = s.TokenText()
+		if stext != text {
+			t.Errorf("text = %q, want %q (idempotency check)", stext, text)
+		}
+	}
+}
+
+func checkTokErr(t *testing.T, s *Scanner, line int, want rune, text string) {
+	prevCount := s.ErrorCount
+	checkTok(t, s, line, s.Scan(), want, text)
+	if s.ErrorCount != prevCount+1 {
+		t.Fatalf("want error for %q", text)
+	}
+}
+
+func countNewlines(s string) int {
+	n := 0
+	for _, ch := range s {
+		if ch == '\n' {
+			n++
+		}
+	}
+	return n
+}
+
+func testScan(t *testing.T, mode uint) {
+	s := new(Scanner).Init(makeSource(" \t%s\n"))
+	s.Mode = mode
+	tok := s.Scan()
+	line := 1
+	for _, k := range tokenList {
+		if mode&SkipComments == 0 || k.tok != Comment {
+			checkTok(t, s, line, tok, k.tok, k.text)
+			tok = s.Scan()
+		}
+		line += countNewlines(k.text) + 1 // each token is on a new line
+	}
+	checkTok(t, s, line, tok, EOF, "")
+}
+
+func TestScan(t *testing.T) {
+	testScan(t, GoTokens)
+	testScan(t, GoTokens&^SkipComments)
+}
+
+func TestInvalidExponent(t *testing.T) {
+	const src = "1.5e 1.5E 1e+ 1e- 1.5z"
+	s := new(Scanner).Init(strings.NewReader(src))
+	s.Error = func(s *Scanner, msg string) {
+		const want = "exponent has no digits"
+		if msg != want {
+			t.Errorf("%s: got error %q; want %q", s.TokenText(), msg, want)
+		}
+	}
+	checkTokErr(t, s, 1, Float, "1.5e")
+	checkTokErr(t, s, 1, Float, "1.5E")
+	checkTokErr(t, s, 1, Float, "1e+")
+	checkTokErr(t, s, 1, Float, "1e-")
+	checkTok(t, s, 1, s.Scan(), Float, "1.5")
+	checkTok(t, s, 1, s.Scan(), Ident, "z")
+	checkTok(t, s, 1, s.Scan(), EOF, "")
+	if s.ErrorCount != 4 {
+		t.Errorf("%d errors, want 4", s.ErrorCount)
+	}
+}
+
+func TestPosition(t *testing.T) {
+	src := makeSource("\t\t\t\t%s\n")
+	s := new(Scanner).Init(src)
+	s.Mode = GoTokens &^ SkipComments
+	s.Scan()
+	pos := Position{"", 4, 1, 5}
+	for _, k := range tokenList {
+		if s.Offset != pos.Offset {
+			t.Errorf("offset = %d, want %d for %q", s.Offset, pos.Offset, k.text)
+		}
+		if s.Line != pos.Line {
+			t.Errorf("line = %d, want %d for %q", s.Line, pos.Line, k.text)
+		}
+		if s.Column != pos.Column {
+			t.Errorf("column = %d, want %d for %q", s.Column, pos.Column, k.text)
+		}
+		pos.Offset += 4 + len(k.text) + 1     // 4 tabs + token bytes + newline
+		pos.Line += countNewlines(k.text) + 1 // each token is on a new line
+		s.Scan()
+	}
+	// make sure there were no token-internal errors reported by scanner
+	if s.ErrorCount != 0 {
+		t.Errorf("%d errors", s.ErrorCount)
+	}
+}
+
+func TestScanZeroMode(t *testing.T) {
+	src := makeSource("%s\n")
+	str := src.String()
+	s := new(Scanner).Init(src)
+	s.Mode = 0       // don't recognize any token classes
+	s.Whitespace = 0 // don't skip any whitespace
+	tok := s.Scan()
+	for i, ch := range str {
+		if tok != ch {
+			t.Fatalf("%d. tok = %s, want %s", i, TokenString(tok), TokenString(ch))
+		}
+		tok = s.Scan()
+	}
+	if tok != EOF {
+		t.Fatalf("tok = %s, want EOF", TokenString(tok))
+	}
+	if s.ErrorCount != 0 {
+		t.Errorf("%d errors", s.ErrorCount)
+	}
+}
+
+func testScanSelectedMode(t *testing.T, mode uint, class rune) {
+	src := makeSource("%s\n")
+	s := new(Scanner).Init(src)
+	s.Mode = mode
+	tok := s.Scan()
+	for tok != EOF {
+		if tok < 0 && tok != class {
+			t.Fatalf("tok = %s, want %s", TokenString(tok), TokenString(class))
+		}
+		tok = s.Scan()
+	}
+	if s.ErrorCount != 0 {
+		t.Errorf("%d errors", s.ErrorCount)
+	}
+}
+
+func TestScanSelectedMask(t *testing.T) {
+	testScanSelectedMode(t, 0, 0)
+	testScanSelectedMode(t, ScanIdents, Ident)
+	// Don't test ScanInts and ScanNumbers since some parts of
+	// the floats in the source look like (invalid) octal ints
+	// and ScanNumbers may return either Int or Float.
+	testScanSelectedMode(t, ScanChars, Char)
+	testScanSelectedMode(t, ScanStrings, String)
+	testScanSelectedMode(t, SkipComments, 0)
+	testScanSelectedMode(t, ScanComments, Comment)
+}
+
+func TestScanCustomIdent(t *testing.T) {
+	const src = "faab12345 a12b123 a12 3b"
+	s := new(Scanner).Init(strings.NewReader(src))
+	// ident = ( 'a' | 'b' ) { digit } .
+	// digit = '0' .. '3' .
+	// with a maximum length of 4
+	s.IsIdentRune = func(ch rune, i int) bool {
+		return i == 0 && (ch == 'a' || ch == 'b') || 0 < i && i < 4 && '0' <= ch && ch <= '3'
+	}
+	checkTok(t, s, 1, s.Scan(), 'f', "f")
+	checkTok(t, s, 1, s.Scan(), Ident, "a")
+	checkTok(t, s, 1, s.Scan(), Ident, "a")
+	checkTok(t, s, 1, s.Scan(), Ident, "b123")
+	checkTok(t, s, 1, s.Scan(), Int, "45")
+	checkTok(t, s, 1, s.Scan(), Ident, "a12")
+	checkTok(t, s, 1, s.Scan(), Ident, "b123")
+	checkTok(t, s, 1, s.Scan(), Ident, "a12")
+	checkTok(t, s, 1, s.Scan(), Int, "3")
+	checkTok(t, s, 1, s.Scan(), Ident, "b")
+	checkTok(t, s, 1, s.Scan(), EOF, "")
+}
+
+func TestScanNext(t *testing.T) {
+	const BOM = '\uFEFF'
+	BOMs := string(BOM)
+	s := new(Scanner).Init(strings.NewReader(BOMs + "if a == bcd /* com" + BOMs + "ment */ {\n\ta += c\n}" + BOMs + "// line comment ending in eof"))
+	checkTok(t, s, 1, s.Scan(), Ident, "if") // the first BOM is ignored
+	checkTok(t, s, 1, s.Scan(), Ident, "a")
+	checkTok(t, s, 1, s.Scan(), '=', "=")
+	checkTok(t, s, 0, s.Next(), '=', "")
+	checkTok(t, s, 0, s.Next(), ' ', "")
+	checkTok(t, s, 0, s.Next(), 'b', "")
+	checkTok(t, s, 1, s.Scan(), Ident, "cd")
+	checkTok(t, s, 1, s.Scan(), '{', "{")
+	checkTok(t, s, 2, s.Scan(), Ident, "a")
+	checkTok(t, s, 2, s.Scan(), '+', "+")
+	checkTok(t, s, 0, s.Next(), '=', "")
+	checkTok(t, s, 2, s.Scan(), Ident, "c")
+	checkTok(t, s, 3, s.Scan(), '}', "}")
+	checkTok(t, s, 3, s.Scan(), BOM, BOMs)
+	checkTok(t, s, 3, s.Scan(), -1, "")
+	if s.ErrorCount != 0 {
+		t.Errorf("%d errors", s.ErrorCount)
+	}
+}
+
+func TestScanWhitespace(t *testing.T) {
+	var buf bytes.Buffer
+	var ws uint64
+	// start at 1, NUL character is not allowed
+	for ch := byte(1); ch < ' '; ch++ {
+		buf.WriteByte(ch)
+		ws |= 1 << ch
+	}
+	const orig = 'x'
+	buf.WriteByte(orig)
+
+	s := new(Scanner).Init(&buf)
+	s.Mode = 0
+	s.Whitespace = ws
+	tok := s.Scan()
+	if tok != orig {
+		t.Errorf("tok = %s, want %s", TokenString(tok), TokenString(orig))
+	}
+}
+
+func testError(t *testing.T, src, pos, msg string, tok rune) {
+	s := new(Scanner).Init(strings.NewReader(src))
+	errorCalled := false
+	s.Error = func(s *Scanner, m string) {
+		if !errorCalled {
+			// only look at first error
+			if p := s.Pos().String(); p != pos {
+				t.Errorf("pos = %q, want %q for %q", p, pos, src)
+			}
+			if m != msg {
+				t.Errorf("msg = %q, want %q for %q", m, msg, src)
+			}
+			errorCalled = true
+		}
+	}
+	tk := s.Scan()
+	if tk != tok {
+		t.Errorf("tok = %s, want %s for %q", TokenString(tk), TokenString(tok), src)
+	}
+	if !errorCalled {
+		t.Errorf("error handler not called for %q", src)
+	}
+	if s.ErrorCount == 0 {
+		t.Errorf("count = %d, want > 0 for %q", s.ErrorCount, src)
+	}
+}
+
+func TestError(t *testing.T) {
+	testError(t, "\x00", "<input>:1:1", "invalid character NUL", 0)
+	testError(t, "\x80", "<input>:1:1", "invalid UTF-8 encoding", utf8.RuneError)
+	testError(t, "\xff", "<input>:1:1", "invalid UTF-8 encoding", utf8.RuneError)
+
+	testError(t, "a\x00", "<input>:1:2", "invalid character NUL", Ident)
+	testError(t, "ab\x80", "<input>:1:3", "invalid UTF-8 encoding", Ident)
+	testError(t, "abc\xff", "<input>:1:4", "invalid UTF-8 encoding", Ident)
+
+	testError(t, `"a`+"\x00", "<input>:1:3", "invalid character NUL", String)
+	testError(t, `"ab`+"\x80", "<input>:1:4", "invalid UTF-8 encoding", String)
+	testError(t, `"abc`+"\xff", "<input>:1:5", "invalid UTF-8 encoding", String)
+
+	testError(t, "`a"+"\x00", "<input>:1:3", "invalid character NUL", RawString)
+	testError(t, "`ab"+"\x80", "<input>:1:4", "invalid UTF-8 encoding", RawString)
+	testError(t, "`abc"+"\xff", "<input>:1:5", "invalid UTF-8 encoding", RawString)
+
+	testError(t, `'\"'`, "<input>:1:3", "invalid char escape", Char)
+	testError(t, `"\'"`, "<input>:1:3", "invalid char escape", String)
+
+	testError(t, `01238`, "<input>:1:6", "invalid digit '8' in octal literal", Int)
+	testError(t, `01238123`, "<input>:1:9", "invalid digit '8' in octal literal", Int)
+	testError(t, `0x`, "<input>:1:3", "hexadecimal literal has no digits", Int)
+	testError(t, `0xg`, "<input>:1:3", "hexadecimal literal has no digits", Int)
+	testError(t, `'aa'`, "<input>:1:4", "invalid char literal", Char)
+	testError(t, `1.5e`, "<input>:1:5", "exponent has no digits", Float)
+	testError(t, `1.5E`, "<input>:1:5", "exponent has no digits", Float)
+	testError(t, `1.5e+`, "<input>:1:6", "exponent has no digits", Float)
+	testError(t, `1.5e-`, "<input>:1:6", "exponent has no digits", Float)
+
+	testError(t, `'`, "<input>:1:2", "literal not terminated", Char)
+	testError(t, `'`+"\n", "<input>:1:2", "literal not terminated", Char)
+	testError(t, `"abc`, "<input>:1:5", "literal not terminated", String)
+	testError(t, `"abc`+"\n", "<input>:1:5", "literal not terminated", String)
+	testError(t, "`abc\n", "<input>:2:1", "literal not terminated", RawString)
+	testError(t, `/*/`, "<input>:1:4", "comment not terminated", EOF)
+}
+
+// An errReader returns (0, err) where err is not io.EOF.
+type errReader struct{}
+
+func (errReader) Read(b []byte) (int, error) {
+	return 0, io.ErrNoProgress // some error that is not io.EOF
+}
+
+func TestIOError(t *testing.T) {
+	s := new(Scanner).Init(errReader{})
+	errorCalled := false
+	s.Error = func(s *Scanner, msg string) {
+		if !errorCalled {
+			if want := io.ErrNoProgress.Error(); msg != want {
+				t.Errorf("msg = %q, want %q", msg, want)
+			}
+			errorCalled = true
+		}
+	}
+	tok := s.Scan()
+	if tok != EOF {
+		t.Errorf("tok = %s, want EOF", TokenString(tok))
+	}
+	if !errorCalled {
+		t.Errorf("error handler not called")
+	}
+}
+
+func checkPos(t *testing.T, got, want Position) {
+	if got.Offset != want.Offset || got.Line != want.Line || got.Column != want.Column {
+		t.Errorf("got offset, line, column = %d, %d, %d; want %d, %d, %d",
+			got.Offset, got.Line, got.Column, want.Offset, want.Line, want.Column)
+	}
+}
+
+func checkNextPos(t *testing.T, s *Scanner, offset, line, column int, char rune) {
+	if ch := s.Next(); ch != char {
+		t.Errorf("ch = %s, want %s", TokenString(ch), TokenString(char))
+	}
+	want := Position{Offset: offset, Line: line, Column: column}
+	checkPos(t, s.Pos(), want)
+}
+
+func checkScanPos(t *testing.T, s *Scanner, offset, line, column int, char rune) {
+	want := Position{Offset: offset, Line: line, Column: column}
+	checkPos(t, s.Pos(), want)
+	if ch := s.Scan(); ch != char {
+		t.Errorf("ch = %s, want %s", TokenString(ch), TokenString(char))
+		if string(ch) != s.TokenText() {
+			t.Errorf("tok = %q, want %q", s.TokenText(), string(ch))
+		}
+	}
+	checkPos(t, s.Position, want)
+}
+
+func TestPos(t *testing.T) {
+	// corner case: empty source
+	s := new(Scanner).Init(strings.NewReader(""))
+	checkPos(t, s.Pos(), Position{Offset: 0, Line: 1, Column: 1})
+	s.Peek() // peek doesn't affect the position
+	checkPos(t, s.Pos(), Position{Offset: 0, Line: 1, Column: 1})
+
+	// corner case: source with only a newline
+	s = new(Scanner).Init(strings.NewReader("\n"))
+	checkPos(t, s.Pos(), Position{Offset: 0, Line: 1, Column: 1})
+	checkNextPos(t, s, 1, 2, 1, '\n')
+	// after EOF position doesn't change
+	for i := 10; i > 0; i-- {
+		checkScanPos(t, s, 1, 2, 1, EOF)
+	}
+	if s.ErrorCount != 0 {
+		t.Errorf("%d errors", s.ErrorCount)
+	}
+
+	// corner case: source with only a single character
+	s = new(Scanner).Init(strings.NewReader("本"))
+	checkPos(t, s.Pos(), Position{Offset: 0, Line: 1, Column: 1})
+	checkNextPos(t, s, 3, 1, 2, '本')
+	// after EOF position doesn't change
+	for i := 10; i > 0; i-- {
+		checkScanPos(t, s, 3, 1, 2, EOF)
+	}
+	if s.ErrorCount != 0 {
+		t.Errorf("%d errors", s.ErrorCount)
+	}
+
+	// positions after calling Next
+	s = new(Scanner).Init(strings.NewReader("  foo६४  \n\n本語\n"))
+	checkNextPos(t, s, 1, 1, 2, ' ')
+	s.Peek() // peek doesn't affect the position
+	checkNextPos(t, s, 2, 1, 3, ' ')
+	checkNextPos(t, s, 3, 1, 4, 'f')
+	checkNextPos(t, s, 4, 1, 5, 'o')
+	checkNextPos(t, s, 5, 1, 6, 'o')
+	checkNextPos(t, s, 8, 1, 7, '६')
+	checkNextPos(t, s, 11, 1, 8, '४')
+	checkNextPos(t, s, 12, 1, 9, ' ')
+	checkNextPos(t, s, 13, 1, 10, ' ')
+	checkNextPos(t, s, 14, 2, 1, '\n')
+	checkNextPos(t, s, 15, 3, 1, '\n')
+	checkNextPos(t, s, 18, 3, 2, '本')
+	checkNextPos(t, s, 21, 3, 3, '語')
+	checkNextPos(t, s, 22, 4, 1, '\n')
+	// after EOF position doesn't change
+	for i := 10; i > 0; i-- {
+		checkScanPos(t, s, 22, 4, 1, EOF)
+	}
+	if s.ErrorCount != 0 {
+		t.Errorf("%d errors", s.ErrorCount)
+	}
+
+	// positions after calling Scan
+	s = new(Scanner).Init(strings.NewReader("abc\n本語\n\nx"))
+	s.Mode = 0
+	s.Whitespace = 0
+	checkScanPos(t, s, 0, 1, 1, 'a')
+	s.Peek() // peek doesn't affect the position
+	checkScanPos(t, s, 1, 1, 2, 'b')
+	checkScanPos(t, s, 2, 1, 3, 'c')
+	checkScanPos(t, s, 3, 1, 4, '\n')
+	checkScanPos(t, s, 4, 2, 1, '本')
+	checkScanPos(t, s, 7, 2, 2, '語')
+	checkScanPos(t, s, 10, 2, 3, '\n')
+	checkScanPos(t, s, 11, 3, 1, '\n')
+	checkScanPos(t, s, 12, 4, 1, 'x')
+	// after EOF position doesn't change
+	for i := 10; i > 0; i-- {
+		checkScanPos(t, s, 13, 4, 2, EOF)
+	}
+	if s.ErrorCount != 0 {
+		t.Errorf("%d errors", s.ErrorCount)
+	}
+}
+
+type countReader int
+
+func (r *countReader) Read([]byte) (int, error) {
+	*r++
+	return 0, io.EOF
+}
+
+func TestNextEOFHandling(t *testing.T) {
+	var r countReader
+
+	// corner case: empty source
+	s := new(Scanner).Init(&r)
+
+	tok := s.Next()
+	if tok != EOF {
+		t.Error("1) EOF not reported")
+	}
+
+	tok = s.Peek()
+	if tok != EOF {
+		t.Error("2) EOF not reported")
+	}
+
+	if r != 1 {
+		t.Errorf("scanner called Read %d times, not once", r)
+	}
+}
+
+func TestScanEOFHandling(t *testing.T) {
+	var r countReader
+
+	// corner case: empty source
+	s := new(Scanner).Init(&r)
+
+	tok := s.Scan()
+	if tok != EOF {
+		t.Error("1) EOF not reported")
+	}
+
+	tok = s.Peek()
+	if tok != EOF {
+		t.Error("2) EOF not reported")
+	}
+
+	if r != 1 {
+		t.Errorf("scanner called Read %d times, not once", r)
+	}
+}
+
+func TestIssue29723(t *testing.T) {
+	s := new(Scanner).Init(strings.NewReader(`x "`))
+	s.Error = func(s *Scanner, _ string) {
+		got := s.TokenText() // this call shouldn't panic
+		const want = `"`
+		if got != want {
+			t.Errorf("got %q; want %q", got, want)
+		}
+	}
+	for r := s.Scan(); r != EOF; r = s.Scan() {
+	}
+}
+
+func TestNumbers(t *testing.T) {
+	for _, test := range []struct {
+		tok              rune
+		src, tokens, err string
+	}{
+		// binaries
+		{Int, "0b0", "0b0", ""},
+		{Int, "0b1010", "0b1010", ""},
+		{Int, "0B1110", "0B1110", ""},
+
+		{Int, "0b", "0b", "binary literal has no digits"},
+		{Int, "0b0190", "0b0190", "invalid digit '9' in binary literal"},
+		{Int, "0b01a0", "0b01 a0", ""}, // only accept 0-9
+
+		// binary floats (invalid)
+		{Float, "0b.", "0b.", "invalid radix point in binary literal"},
+		{Float, "0b.1", "0b.1", "invalid radix point in binary literal"},
+		{Float, "0b1.0", "0b1.0", "invalid radix point in binary literal"},
+		{Float, "0b1e10", "0b1e10", "'e' exponent requires decimal mantissa"},
+		{Float, "0b1P-1", "0b1P-1", "'P' exponent requires hexadecimal mantissa"},
+
+		// octals
+		{Int, "0o0", "0o0", ""},
+		{Int, "0o1234", "0o1234", ""},
+		{Int, "0O1234", "0O1234", ""},
+
+		{Int, "0o", "0o", "octal literal has no digits"},
+		{Int, "0o8123", "0o8123", "invalid digit '8' in octal literal"},
+		{Int, "0o1293", "0o1293", "invalid digit '9' in octal literal"},
+		{Int, "0o12a3", "0o12 a3", ""}, // only accept 0-9
+
+		// octal floats (invalid)
+		{Float, "0o.", "0o.", "invalid radix point in octal literal"},
+		{Float, "0o.2", "0o.2", "invalid radix point in octal literal"},
+		{Float, "0o1.2", "0o1.2", "invalid radix point in octal literal"},
+		{Float, "0o1E+2", "0o1E+2", "'E' exponent requires decimal mantissa"},
+		{Float, "0o1p10", "0o1p10", "'p' exponent requires hexadecimal mantissa"},
+
+		// 0-octals
+		{Int, "0", "0", ""},
+		{Int, "0123", "0123", ""},
+
+		{Int, "08123", "08123", "invalid digit '8' in octal literal"},
+		{Int, "01293", "01293", "invalid digit '9' in octal literal"},
+		{Int, "0F.", "0 F .", ""}, // only accept 0-9
+		{Int, "0123F.", "0123 F .", ""},
+		{Int, "0123456x", "0123456 x", ""},
+
+		// decimals
+		{Int, "1", "1", ""},
+		{Int, "1234", "1234", ""},
+
+		{Int, "1f", "1 f", ""}, // only accept 0-9
+
+		// decimal floats
+		{Float, "0.", "0.", ""},
+		{Float, "123.", "123.", ""},
+		{Float, "0123.", "0123.", ""},
+
+		{Float, ".0", ".0", ""},
+		{Float, ".123", ".123", ""},
+		{Float, ".0123", ".0123", ""},
+
+		{Float, "0.0", "0.0", ""},
+		{Float, "123.123", "123.123", ""},
+		{Float, "0123.0123", "0123.0123", ""},
+
+		{Float, "0e0", "0e0", ""},
+		{Float, "123e+0", "123e+0", ""},
+		{Float, "0123E-1", "0123E-1", ""},
+
+		{Float, "0.e+1", "0.e+1", ""},
+		{Float, "123.E-10", "123.E-10", ""},
+		{Float, "0123.e123", "0123.e123", ""},
+
+		{Float, ".0e-1", ".0e-1", ""},
+		{Float, ".123E+10", ".123E+10", ""},
+		{Float, ".0123E123", ".0123E123", ""},
+
+		{Float, "0.0e1", "0.0e1", ""},
+		{Float, "123.123E-10", "123.123E-10", ""},
+		{Float, "0123.0123e+456", "0123.0123e+456", ""},
+
+		{Float, "0e", "0e", "exponent has no digits"},
+		{Float, "0E+", "0E+", "exponent has no digits"},
+		{Float, "1e+f", "1e+ f", "exponent has no digits"},
+		{Float, "0p0", "0p0", "'p' exponent requires hexadecimal mantissa"},
+		{Float, "1.0P-1", "1.0P-1", "'P' exponent requires hexadecimal mantissa"},
+
+		// hexadecimals
+		{Int, "0x0", "0x0", ""},
+		{Int, "0x1234", "0x1234", ""},
+		{Int, "0xcafef00d", "0xcafef00d", ""},
+		{Int, "0XCAFEF00D", "0XCAFEF00D", ""},
+
+		{Int, "0x", "0x", "hexadecimal literal has no digits"},
+		{Int, "0x1g", "0x1 g", ""},
+
+		// hexadecimal floats
+		{Float, "0x0p0", "0x0p0", ""},
+		{Float, "0x12efp-123", "0x12efp-123", ""},
+		{Float, "0xABCD.p+0", "0xABCD.p+0", ""},
+		{Float, "0x.0189P-0", "0x.0189P-0", ""},
+		{Float, "0x1.ffffp+1023", "0x1.ffffp+1023", ""},
+
+		{Float, "0x.", "0x.", "hexadecimal literal has no digits"},
+		{Float, "0x0.", "0x0.", "hexadecimal mantissa requires a 'p' exponent"},
+		{Float, "0x.0", "0x.0", "hexadecimal mantissa requires a 'p' exponent"},
+		{Float, "0x1.1", "0x1.1", "hexadecimal mantissa requires a 'p' exponent"},
+		{Float, "0x1.1e0", "0x1.1e0", "hexadecimal mantissa requires a 'p' exponent"},
+		{Float, "0x1.2gp1a", "0x1.2 gp1a", "hexadecimal mantissa requires a 'p' exponent"},
+		{Float, "0x0p", "0x0p", "exponent has no digits"},
+		{Float, "0xeP-", "0xeP-", "exponent has no digits"},
+		{Float, "0x1234PAB", "0x1234P AB", "exponent has no digits"},
+		{Float, "0x1.2p1a", "0x1.2p1 a", ""},
+
+		// separators
+		{Int, "0b_1000_0001", "0b_1000_0001", ""},
+		{Int, "0o_600", "0o_600", ""},
+		{Int, "0_466", "0_466", ""},
+		{Int, "1_000", "1_000", ""},
+		{Float, "1_000.000_1", "1_000.000_1", ""},
+		{Int, "0x_f00d", "0x_f00d", ""},
+		{Float, "0x_f00d.0p1_2", "0x_f00d.0p1_2", ""},
+
+		{Int, "0b__1000", "0b__1000", "'_' must separate successive digits"},
+		{Int, "0o60___0", "0o60___0", "'_' must separate successive digits"},
+		{Int, "0466_", "0466_", "'_' must separate successive digits"},
+		{Float, "1_.", "1_.", "'_' must separate successive digits"},
+		{Float, "0._1", "0._1", "'_' must separate successive digits"},
+		{Float, "2.7_e0", "2.7_e0", "'_' must separate successive digits"},
+		{Int, "0x___0", "0x___0", "'_' must separate successive digits"},
+		{Float, "0x1.0_p0", "0x1.0_p0", "'_' must separate successive digits"},
+	} {
+		s := new(Scanner).Init(strings.NewReader(test.src))
+		var err string
+		s.Error = func(s *Scanner, msg string) {
+			if err == "" {
+				err = msg
+			}
+		}
+
+		for i, want := range strings.Split(test.tokens, " ") {
+			err = ""
+			tok := s.Scan()
+			lit := s.TokenText()
+			if i == 0 {
+				if tok != test.tok {
+					t.Errorf("%q: got token %s; want %s", test.src, TokenString(tok), TokenString(test.tok))
+				}
+				if err != test.err {
+					t.Errorf("%q: got error %q; want %q", test.src, err, test.err)
+				}
+			}
+			if lit != want {
+				t.Errorf("%q: got literal %q (%s); want %s", test.src, lit, TokenString(tok), want)
+			}
+		}
+
+		// make sure we read all
+		if tok := s.Scan(); tok != EOF {
+			t.Errorf("%q: got %s; want EOF", test.src, TokenString(tok))
+		}
+	}
+}
+
+func TestIssue30320(t *testing.T) {
+	for _, test := range []struct {
+		in, want string
+		mode     uint
+	}{
+		{"foo01.bar31.xx-0-1-1-0", "01 31 0 1 1 0", ScanInts},
+		{"foo0/12/0/5.67", "0 12 0 5 67", ScanInts},
+		{"xxx1e0yyy", "1 0", ScanInts},
+		{"1_2", "1_2", ScanInts},
+		{"xxx1.0yyy2e3ee", "1 0 2 3", ScanInts},
+		{"xxx1.0yyy2e3ee", "1.0 2e3", ScanFloats},
+	} {
+		got := extractInts(test.in, test.mode)
+		if got != test.want {
+			t.Errorf("%q: got %q; want %q", test.in, got, test.want)
+		}
+	}
+}
+
+func extractInts(t string, mode uint) (res string) {
+	var s Scanner
+	s.Init(strings.NewReader(t))
+	s.Mode = mode
+	for {
+		switch tok := s.Scan(); tok {
+		case Int, Float:
+			if len(res) > 0 {
+				res += " "
+			}
+			res += s.TokenText()
+		case EOF:
+			return
+		}
+	}
+}