1 files changed, 671 insertions, 0 deletions
diff --git a/src/text/template/parse/lex.go b/src/text/template/parse/lex.go
new file mode 100644
index 0000000..6784071
--- /dev/null
+++ b/src/text/template/parse/lex.go
@@ -0,0 +1,671 @@
+// Copyright 2011 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 parse
+
+import (
+	"fmt"
+	"strings"
+	"unicode"
+	"unicode/utf8"
+)
+
+// item represents a token or text string returned from the scanner.
+type item struct {
+	typ  itemType // The type of this item.
+	pos  Pos      // The starting position, in bytes, of this item in the input string.
+	val  string   // The value of this item.
+	line int      // The line number at the start of this item.
+}
+
+func (i item) String() string {
+	switch {
+	case i.typ == itemEOF:
+		return "EOF"
+	case i.typ == itemError:
+		return i.val
+	case i.typ > itemKeyword:
+		return fmt.Sprintf("<%s>", i.val)
+	case len(i.val) > 10:
+		return fmt.Sprintf("%.10q...", i.val)
+	}
+	return fmt.Sprintf("%q", i.val)
+}
+
+// itemType identifies the type of lex items.
+type itemType int
+
+const (
+	itemError        itemType = iota // error occurred; value is text of error
+	itemBool                         // boolean constant
+	itemChar                         // printable ASCII character; grab bag for comma etc.
+	itemCharConstant                 // character constant
+	itemComment                      // comment text
+	itemComplex                      // complex constant (1+2i); imaginary is just a number
+	itemAssign                       // equals ('=') introducing an assignment
+	itemDeclare                      // colon-equals (':=') introducing a declaration
+	itemEOF
+	itemField      // alphanumeric identifier starting with '.'
+	itemIdentifier // alphanumeric identifier not starting with '.'
+	itemLeftDelim  // left action delimiter
+	itemLeftParen  // '(' inside action
+	itemNumber     // simple number, including imaginary
+	itemPipe       // pipe symbol
+	itemRawString  // raw quoted string (includes quotes)
+	itemRightDelim // right action delimiter
+	itemRightParen // ')' inside action
+	itemSpace      // run of spaces separating arguments
+	itemString     // quoted string (includes quotes)
+	itemText       // plain text
+	itemVariable   // variable starting with '$', such as '$' or  '$1' or '$hello'
+	// Keywords appear after all the rest.
+	itemKeyword  // used only to delimit the keywords
+	itemBlock    // block keyword
+	itemDot      // the cursor, spelled '.'
+	itemDefine   // define keyword
+	itemElse     // else keyword
+	itemEnd      // end keyword
+	itemIf       // if keyword
+	itemNil      // the untyped nil constant, easiest to treat as a keyword
+	itemRange    // range keyword
+	itemTemplate // template keyword
+	itemWith     // with keyword
+)
+
+var key = map[string]itemType{
+	".":        itemDot,
+	"block":    itemBlock,
+	"define":   itemDefine,
+	"else":     itemElse,
+	"end":      itemEnd,
+	"if":       itemIf,
+	"range":    itemRange,
+	"nil":      itemNil,
+	"template": itemTemplate,
+	"with":     itemWith,
+}
+
+const eof = -1
+
+// Trimming spaces.
+// If the action begins "{{- " rather than "{{", then all space/tab/newlines
+// preceding the action are trimmed; conversely if it ends " -}}" the
+// leading spaces are trimmed. This is done entirely in the lexer; the
+// parser never sees it happen. We require an ASCII space (' ', \t, \r, \n)
+// to be present to avoid ambiguity with things like "{{-3}}". It reads
+// better with the space present anyway. For simplicity, only ASCII
+// does the job.
+const (
+	spaceChars    = " \t\r\n"  // These are the space characters defined by Go itself.
+	trimMarker    = '-'        // Attached to left/right delimiter, trims trailing spaces from preceding/following text.
+	trimMarkerLen = Pos(1 + 1) // marker plus space before or after
+)
+
+// stateFn represents the state of the scanner as a function that returns the next state.
+type stateFn func(*lexer) stateFn
+
+// lexer holds the state of the scanner.
+type lexer struct {
+	name        string    // the name of the input; used only for error reports
+	input       string    // the string being scanned
+	leftDelim   string    // start of action
+	rightDelim  string    // end of action
+	emitComment bool      // emit itemComment tokens.
+	pos         Pos       // current position in the input
+	start       Pos       // start position of this item
+	width       Pos       // width of last rune read from input
+	items       chan item // channel of scanned items
+	parenDepth  int       // nesting depth of ( ) exprs
+	line        int       // 1+number of newlines seen
+	startLine   int       // start line of this item
+}
+
+// next returns the next rune in the input.
+func (l *lexer) next() rune {
+	if int(l.pos) >= len(l.input) {
+		l.width = 0
+		return eof
+	}
+	r, w := utf8.DecodeRuneInString(l.input[l.pos:])
+	l.width = Pos(w)
+	l.pos += l.width
+	if r == '\n' {
+		l.line++
+	}
+	return r
+}
+
+// peek returns but does not consume the next rune in the input.
+func (l *lexer) peek() rune {
+	r := l.next()
+	l.backup()
+	return r
+}
+
+// backup steps back one rune. Can only be called once per call of next.
+func (l *lexer) backup() {
+	l.pos -= l.width
+	// Correct newline count.
+	if l.width == 1 && l.input[l.pos] == '\n' {
+		l.line--
+	}
+}
+
+// emit passes an item back to the client.
+func (l *lexer) emit(t itemType) {
+	l.items <- item{t, l.start, l.input[l.start:l.pos], l.startLine}
+	l.start = l.pos
+	l.startLine = l.line
+}
+
+// ignore skips over the pending input before this point.
+func (l *lexer) ignore() {
+	l.line += strings.Count(l.input[l.start:l.pos], "\n")
+	l.start = l.pos
+	l.startLine = l.line
+}
+
+// accept consumes the next rune if it's from the valid set.
+func (l *lexer) accept(valid string) bool {
+	if strings.ContainsRune(valid, l.next()) {
+		return true
+	}
+	l.backup()
+	return false
+}
+
+// acceptRun consumes a run of runes from the valid set.
+func (l *lexer) acceptRun(valid string) {
+	for strings.ContainsRune(valid, l.next()) {
+	}
+	l.backup()
+}
+
+// errorf returns an error token and terminates the scan by passing
+// back a nil pointer that will be the next state, terminating l.nextItem.
+func (l *lexer) errorf(format string, args ...interface{}) stateFn {
+	l.items <- item{itemError, l.start, fmt.Sprintf(format, args...), l.startLine}
+	return nil
+}
+
+// nextItem returns the next item from the input.
+// Called by the parser, not in the lexing goroutine.
+func (l *lexer) nextItem() item {
+	return <-l.items
+}
+
+// drain drains the output so the lexing goroutine will exit.
+// Called by the parser, not in the lexing goroutine.
+func (l *lexer) drain() {
+	for range l.items {
+	}
+}
+
+// lex creates a new scanner for the input string.
+func lex(name, input, left, right string, emitComment bool) *lexer {
+	if left == "" {
+		left = leftDelim
+	}
+	if right == "" {
+		right = rightDelim
+	}
+	l := &lexer{
+		name:        name,
+		input:       input,
+		leftDelim:   left,
+		rightDelim:  right,
+		emitComment: emitComment,
+		items:       make(chan item),
+		line:        1,
+		startLine:   1,
+	}
+	go l.run()
+	return l
+}
+
+// run runs the state machine for the lexer.
+func (l *lexer) run() {
+	for state := lexText; state != nil; {
+		state = state(l)
+	}
+	close(l.items)
+}
+
+// state functions
+
+const (
+	leftDelim    = "{{"
+	rightDelim   = "}}"
+	leftComment  = "/*"
+	rightComment = "*/"
+)
+
+// lexText scans until an opening action delimiter, "{{".
+func lexText(l *lexer) stateFn {
+	l.width = 0
+	if x := strings.Index(l.input[l.pos:], l.leftDelim); x >= 0 {
+		ldn := Pos(len(l.leftDelim))
+		l.pos += Pos(x)
+		trimLength := Pos(0)
+		if hasLeftTrimMarker(l.input[l.pos+ldn:]) {
+			trimLength = rightTrimLength(l.input[l.start:l.pos])
+		}
+		l.pos -= trimLength
+		if l.pos > l.start {
+			l.line += strings.Count(l.input[l.start:l.pos], "\n")
+			l.emit(itemText)
+		}
+		l.pos += trimLength
+		l.ignore()
+		return lexLeftDelim
+	}
+	l.pos = Pos(len(l.input))
+	// Correctly reached EOF.
+	if l.pos > l.start {
+		l.line += strings.Count(l.input[l.start:l.pos], "\n")
+		l.emit(itemText)
+	}
+	l.emit(itemEOF)
+	return nil
+}
+
+// rightTrimLength returns the length of the spaces at the end of the string.
+func rightTrimLength(s string) Pos {
+	return Pos(len(s) - len(strings.TrimRight(s, spaceChars)))
+}
+
+// atRightDelim reports whether the lexer is at a right delimiter, possibly preceded by a trim marker.
+func (l *lexer) atRightDelim() (delim, trimSpaces bool) {
+	if hasRightTrimMarker(l.input[l.pos:]) && strings.HasPrefix(l.input[l.pos+trimMarkerLen:], l.rightDelim) { // With trim marker.
+		return true, true
+	}
+	if strings.HasPrefix(l.input[l.pos:], l.rightDelim) { // Without trim marker.
+		return true, false
+	}
+	return false, false
+}
+
+// leftTrimLength returns the length of the spaces at the beginning of the string.
+func leftTrimLength(s string) Pos {
+	return Pos(len(s) - len(strings.TrimLeft(s, spaceChars)))
+}
+
+// lexLeftDelim scans the left delimiter, which is known to be present, possibly with a trim marker.
+func lexLeftDelim(l *lexer) stateFn {
+	l.pos += Pos(len(l.leftDelim))
+	trimSpace := hasLeftTrimMarker(l.input[l.pos:])
+	afterMarker := Pos(0)
+	if trimSpace {
+		afterMarker = trimMarkerLen
+	}
+	if strings.HasPrefix(l.input[l.pos+afterMarker:], leftComment) {
+		l.pos += afterMarker
+		l.ignore()
+		return lexComment
+	}
+	l.emit(itemLeftDelim)
+	l.pos += afterMarker
+	l.ignore()
+	l.parenDepth = 0
+	return lexInsideAction
+}
+
+// lexComment scans a comment. The left comment marker is known to be present.
+func lexComment(l *lexer) stateFn {
+	l.pos += Pos(len(leftComment))
+	i := strings.Index(l.input[l.pos:], rightComment)
+	if i < 0 {
+		return l.errorf("unclosed comment")
+	}
+	l.pos += Pos(i + len(rightComment))
+	delim, trimSpace := l.atRightDelim()
+	if !delim {
+		return l.errorf("comment ends before closing delimiter")
+	}
+	if l.emitComment {
+		l.emit(itemComment)
+	}
+	if trimSpace {
+		l.pos += trimMarkerLen
+	}
+	l.pos += Pos(len(l.rightDelim))
+	if trimSpace {
+		l.pos += leftTrimLength(l.input[l.pos:])
+	}
+	l.ignore()
+	return lexText
+}
+
+// lexRightDelim scans the right delimiter, which is known to be present, possibly with a trim marker.
+func lexRightDelim(l *lexer) stateFn {
+	trimSpace := hasRightTrimMarker(l.input[l.pos:])
+	if trimSpace {
+		l.pos += trimMarkerLen
+		l.ignore()
+	}
+	l.pos += Pos(len(l.rightDelim))
+	l.emit(itemRightDelim)
+	if trimSpace {
+		l.pos += leftTrimLength(l.input[l.pos:])
+		l.ignore()
+	}
+	return lexText
+}
+
+// lexInsideAction scans the elements inside action delimiters.
+func lexInsideAction(l *lexer) stateFn {
+	// Either number, quoted string, or identifier.
+	// Spaces separate arguments; runs of spaces turn into itemSpace.
+	// Pipe symbols separate and are emitted.
+	delim, _ := l.atRightDelim()
+	if delim {
+		if l.parenDepth == 0 {
+			return lexRightDelim
+		}
+		return l.errorf("unclosed left paren")
+	}
+	switch r := l.next(); {
+	case r == eof:
+		return l.errorf("unclosed action")
+	case isSpace(r):
+		l.backup() // Put space back in case we have " -}}".
+		return lexSpace
+	case r == '=':
+		l.emit(itemAssign)
+	case r == ':':
+		if l.next() != '=' {
+			return l.errorf("expected :=")
+		}
+		l.emit(itemDeclare)
+	case r == '|':
+		l.emit(itemPipe)
+	case r == '"':
+		return lexQuote
+	case r == '`':
+		return lexRawQuote
+	case r == '$':
+		return lexVariable
+	case r == '\'':
+		return lexChar
+	case r == '.':
+		// special look-ahead for ".field" so we don't break l.backup().
+		if l.pos < Pos(len(l.input)) {
+			r := l.input[l.pos]
+			if r < '0' || '9' < r {
+				return lexField
+			}
+		}
+		fallthrough // '.' can start a number.
+	case r == '+' || r == '-' || ('0' <= r && r <= '9'):
+		l.backup()
+		return lexNumber
+	case isAlphaNumeric(r):
+		l.backup()
+		return lexIdentifier
+	case r == '(':
+		l.emit(itemLeftParen)
+		l.parenDepth++
+	case r == ')':
+		l.emit(itemRightParen)
+		l.parenDepth--
+		if l.parenDepth < 0 {
+			return l.errorf("unexpected right paren %#U", r)
+		}
+	case r <= unicode.MaxASCII && unicode.IsPrint(r):
+		l.emit(itemChar)
+	default:
+		return l.errorf("unrecognized character in action: %#U", r)
+	}
+	return lexInsideAction
+}
+
+// lexSpace scans a run of space characters.
+// We have not consumed the first space, which is known to be present.
+// Take care if there is a trim-marked right delimiter, which starts with a space.
+func lexSpace(l *lexer) stateFn {
+	var r rune
+	var numSpaces int
+	for {
+		r = l.peek()
+		if !isSpace(r) {
+			break
+		}
+		l.next()
+		numSpaces++
+	}
+	// Be careful about a trim-marked closing delimiter, which has a minus
+	// after a space. We know there is a space, so check for the '-' that might follow.
+	if hasRightTrimMarker(l.input[l.pos-1:]) && strings.HasPrefix(l.input[l.pos-1+trimMarkerLen:], l.rightDelim) {
+		l.backup() // Before the space.
+		if numSpaces == 1 {
+			return lexRightDelim // On the delim, so go right to that.
+		}
+	}
+	l.emit(itemSpace)
+	return lexInsideAction
+}
+
+// lexIdentifier scans an alphanumeric.
+func lexIdentifier(l *lexer) stateFn {
+Loop:
+	for {
+		switch r := l.next(); {
+		case isAlphaNumeric(r):
+			// absorb.
+		default:
+			l.backup()
+			word := l.input[l.start:l.pos]
+			if !l.atTerminator() {
+				return l.errorf("bad character %#U", r)
+			}
+			switch {
+			case key[word] > itemKeyword:
+				l.emit(key[word])
+			case word[0] == '.':
+				l.emit(itemField)
+			case word == "true", word == "false":
+				l.emit(itemBool)
+			default:
+				l.emit(itemIdentifier)
+			}
+			break Loop
+		}
+	}
+	return lexInsideAction
+}
+
+// lexField scans a field: .Alphanumeric.
+// The . has been scanned.
+func lexField(l *lexer) stateFn {
+	return lexFieldOrVariable(l, itemField)
+}
+
+// lexVariable scans a Variable: $Alphanumeric.
+// The $ has been scanned.
+func lexVariable(l *lexer) stateFn {
+	if l.atTerminator() { // Nothing interesting follows -> "$".
+		l.emit(itemVariable)
+		return lexInsideAction
+	}
+	return lexFieldOrVariable(l, itemVariable)
+}
+
+// lexVariable scans a field or variable: [.$]Alphanumeric.
+// The . or $ has been scanned.
+func lexFieldOrVariable(l *lexer, typ itemType) stateFn {
+	if l.atTerminator() { // Nothing interesting follows -> "." or "$".
+		if typ == itemVariable {
+			l.emit(itemVariable)
+		} else {
+			l.emit(itemDot)
+		}
+		return lexInsideAction
+	}
+	var r rune
+	for {
+		r = l.next()
+		if !isAlphaNumeric(r) {
+			l.backup()
+			break
+		}
+	}
+	if !l.atTerminator() {
+		return l.errorf("bad character %#U", r)
+	}
+	l.emit(typ)
+	return lexInsideAction
+}
+
+// atTerminator reports whether the input is at valid termination character to
+// appear after an identifier. Breaks .X.Y into two pieces. Also catches cases
+// like "$x+2" not being acceptable without a space, in case we decide one
+// day to implement arithmetic.
+func (l *lexer) atTerminator() bool {
+	r := l.peek()
+	if isSpace(r) {
+		return true
+	}
+	switch r {
+	case eof, '.', ',', '|', ':', ')', '(':
+		return true
+	}
+	// Does r start the delimiter? This can be ambiguous (with delim=="//", $x/2 will
+	// succeed but should fail) but only in extremely rare cases caused by willfully
+	// bad choice of delimiter.
+	if rd, _ := utf8.DecodeRuneInString(l.rightDelim); rd == r {
+		return true
+	}
+	return false
+}
+
+// lexChar scans a character constant. The initial quote is already
+// scanned. Syntax checking is done by the parser.
+func lexChar(l *lexer) stateFn {
+Loop:
+	for {
+		switch l.next() {
+		case '\\':
+			if r := l.next(); r != eof && r != '\n' {
+				break
+			}
+			fallthrough
+		case eof, '\n':
+			return l.errorf("unterminated character constant")
+		case '\'':
+			break Loop
+		}
+	}
+	l.emit(itemCharConstant)
+	return lexInsideAction
+}
+
+// lexNumber scans a number: decimal, octal, hex, float, or imaginary. This
+// isn't a perfect number scanner - for instance it accepts "." and "0x0.2"
+// and "089" - but when it's wrong the input is invalid and the parser (via
+// strconv) will notice.
+func lexNumber(l *lexer) stateFn {
+	if !l.scanNumber() {
+		return l.errorf("bad number syntax: %q", l.input[l.start:l.pos])
+	}
+	if sign := l.peek(); sign == '+' || sign == '-' {
+		// Complex: 1+2i. No spaces, must end in 'i'.
+		if !l.scanNumber() || l.input[l.pos-1] != 'i' {
+			return l.errorf("bad number syntax: %q", l.input[l.start:l.pos])
+		}
+		l.emit(itemComplex)
+	} else {
+		l.emit(itemNumber)
+	}
+	return lexInsideAction
+}
+
+func (l *lexer) scanNumber() bool {
+	// Optional leading sign.
+	l.accept("+-")
+	// Is it hex?
+	digits := "0123456789_"
+	if l.accept("0") {
+		// Note: Leading 0 does not mean octal in floats.
+		if l.accept("xX") {
+			digits = "0123456789abcdefABCDEF_"
+		} else if l.accept("oO") {
+			digits = "01234567_"
+		} else if l.accept("bB") {
+			digits = "01_"
+		}
+	}
+	l.acceptRun(digits)
+	if l.accept(".") {
+		l.acceptRun(digits)
+	}
+	if len(digits) == 10+1 && l.accept("eE") {
+		l.accept("+-")
+		l.acceptRun("0123456789_")
+	}
+	if len(digits) == 16+6+1 && l.accept("pP") {
+		l.accept("+-")
+		l.acceptRun("0123456789_")
+	}
+	// Is it imaginary?
+	l.accept("i")
+	// Next thing mustn't be alphanumeric.
+	if isAlphaNumeric(l.peek()) {
+		l.next()
+		return false
+	}
+	return true
+}
+
+// lexQuote scans a quoted string.
+func lexQuote(l *lexer) stateFn {
+Loop:
+	for {
+		switch l.next() {
+		case '\\':
+			if r := l.next(); r != eof && r != '\n' {
+				break
+			}
+			fallthrough
+		case eof, '\n':
+			return l.errorf("unterminated quoted string")
+		case '"':
+			break Loop
+		}
+	}
+	l.emit(itemString)
+	return lexInsideAction
+}
+
+// lexRawQuote scans a raw quoted string.
+func lexRawQuote(l *lexer) stateFn {
+Loop:
+	for {
+		switch l.next() {
+		case eof:
+			return l.errorf("unterminated raw quoted string")
+		case '`':
+			break Loop
+		}
+	}
+	l.emit(itemRawString)
+	return lexInsideAction
+}
+
+// isSpace reports whether r is a space character.
+func isSpace(r rune) bool {
+	return r == ' ' || r == '\t' || r == '\r' || r == '\n'
+}
+
+// isAlphaNumeric reports whether r is an alphabetic, digit, or underscore.
+func isAlphaNumeric(r rune) bool {
+	return r == '_' || unicode.IsLetter(r) || unicode.IsDigit(r)
+}
+
+func hasLeftTrimMarker(s string) bool {
+	return len(s) >= 2 && s[0] == trimMarker && isSpace(rune(s[1]))
+}
+
+func hasRightTrimMarker(s string) bool {
+	return len(s) >= 2 && isSpace(rune(s[0])) && s[1] == trimMarker
+}