Adding upstream version 1.20.14.upstream/1.20.14upstream

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

5 files changed, 3814 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..70fc86b
--- /dev/null
+++ b/src/text/template/parse/lex.go
@@ -0,0 +1,686 @@
+// 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
+	itemBreak    // break keyword
+	itemContinue // continue 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,
+	"break":    itemBreak,
+	"continue": itemContinue,
+	"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 marker
+	rightDelim   string // end of action marker
+	pos          Pos    // current position in the input
+	start        Pos    // start position of this item
+	atEOF        bool   // we have hit the end of input and returned eof
+	parenDepth   int    // nesting depth of ( ) exprs
+	line         int    // 1+number of newlines seen
+	startLine    int    // start line of this item
+	item         item   // item to return to parser
+	insideAction bool   // are we inside an action?
+	options      lexOptions
+}
+
+// lexOptions control behavior of the lexer. All default to false.
+type lexOptions struct {
+	emitComment bool // emit itemComment tokens.
+	breakOK     bool // break keyword allowed
+	continueOK  bool // continue keyword allowed
+}
+
+// next returns the next rune in the input.
+func (l *lexer) next() rune {
+	if int(l.pos) >= len(l.input) {
+		l.atEOF = true
+		return eof
+	}
+	r, w := utf8.DecodeRuneInString(l.input[l.pos:])
+	l.pos += Pos(w)
+	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.
+func (l *lexer) backup() {
+	if !l.atEOF && l.pos > 0 {
+		r, w := utf8.DecodeLastRuneInString(l.input[:l.pos])
+		l.pos -= Pos(w)
+		// Correct newline count.
+		if r == '\n' {
+			l.line--
+		}
+	}
+}
+
+// thisItem returns the item at the current input point with the specified type
+// and advances the input.
+func (l *lexer) thisItem(t itemType) item {
+	i := item{t, l.start, l.input[l.start:l.pos], l.startLine}
+	l.start = l.pos
+	l.startLine = l.line
+	return i
+}
+
+// emit passes the trailing text as an item back to the parser.
+func (l *lexer) emit(t itemType) stateFn {
+	return l.emitItem(l.thisItem(t))
+}
+
+// emitItem passes the specified item to the parser.
+func (l *lexer) emitItem(i item) stateFn {
+	l.item = i
+	return nil
+}
+
+// ignore skips over the pending input before this point.
+// It tracks newlines in the ignored text, so use it only
+// for text that is skipped without calling l.next.
+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 ...any) stateFn {
+	l.item = item{itemError, l.start, fmt.Sprintf(format, args...), l.startLine}
+	l.start = 0
+	l.pos = 0
+	l.input = l.input[:0]
+	return nil
+}
+
+// nextItem returns the next item from the input.
+// Called by the parser, not in the lexing goroutine.
+func (l *lexer) nextItem() item {
+	l.item = item{itemEOF, l.pos, "EOF", l.startLine}
+	state := lexText
+	if l.insideAction {
+		state = lexInsideAction
+	}
+	for {
+		state = state(l)
+		if state == nil {
+			return l.item
+		}
+	}
+}
+
+// lex creates a new scanner for the input string.
+func lex(name, input, left, right string) *lexer {
+	if left == "" {
+		left = leftDelim
+	}
+	if right == "" {
+		right = rightDelim
+	}
+	l := &lexer{
+		name:         name,
+		input:        input,
+		leftDelim:    left,
+		rightDelim:   right,
+		line:         1,
+		startLine:    1,
+		insideAction: false,
+	}
+	return l
+}
+
+// state functions
+
+const (
+	leftDelim    = "{{"
+	rightDelim   = "}}"
+	leftComment  = "/*"
+	rightComment = "*/"
+)
+
+// lexText scans until an opening action delimiter, "{{".
+func lexText(l *lexer) stateFn {
+	if x := strings.Index(l.input[l.pos:], l.leftDelim); x >= 0 {
+		if x > 0 {
+			l.pos += Pos(x)
+			// Do we trim any trailing space?
+			trimLength := Pos(0)
+			delimEnd := l.pos + Pos(len(l.leftDelim))
+			if hasLeftTrimMarker(l.input[delimEnd:]) {
+				trimLength = rightTrimLength(l.input[l.start:l.pos])
+			}
+			l.pos -= trimLength
+			l.line += strings.Count(l.input[l.start:l.pos], "\n")
+			i := l.thisItem(itemText)
+			l.pos += trimLength
+			l.ignore()
+			if len(i.val) > 0 {
+				return l.emitItem(i)
+			}
+		}
+		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")
+		return l.emit(itemText)
+	}
+	return l.emit(itemEOF)
+}
+
+// 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.
+// (The text to be trimmed has already been emitted.)
+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
+	}
+	i := l.thisItem(itemLeftDelim)
+	l.insideAction = true
+	l.pos += afterMarker
+	l.ignore()
+	l.parenDepth = 0
+	return l.emitItem(i)
+}
+
+// lexComment scans a comment. The left comment marker is known to be present.
+func lexComment(l *lexer) stateFn {
+	l.pos += Pos(len(leftComment))
+	x := strings.Index(l.input[l.pos:], rightComment)
+	if x < 0 {
+		return l.errorf("unclosed comment")
+	}
+	l.pos += Pos(x + len(rightComment))
+	delim, trimSpace := l.atRightDelim()
+	if !delim {
+		return l.errorf("comment ends before closing delimiter")
+	}
+	i := l.thisItem(itemComment)
+	if trimSpace {
+		l.pos += trimMarkerLen
+	}
+	l.pos += Pos(len(l.rightDelim))
+	if trimSpace {
+		l.pos += leftTrimLength(l.input[l.pos:])
+	}
+	l.ignore()
+	if l.options.emitComment {
+		return l.emitItem(i)
+	}
+	return lexText
+}
+
+// lexRightDelim scans the right delimiter, which is known to be present, possibly with a trim marker.
+func lexRightDelim(l *lexer) stateFn {
+	_, trimSpace := l.atRightDelim()
+	if trimSpace {
+		l.pos += trimMarkerLen
+		l.ignore()
+	}
+	l.pos += Pos(len(l.rightDelim))
+	i := l.thisItem(itemRightDelim)
+	if trimSpace {
+		l.pos += leftTrimLength(l.input[l.pos:])
+		l.ignore()
+	}
+	l.insideAction = false
+	return l.emitItem(i)
+}
+
+// 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 == '=':
+		return l.emit(itemAssign)
+	case r == ':':
+		if l.next() != '=' {
+			return l.errorf("expected :=")
+		}
+		return l.emit(itemDeclare)
+	case r == '|':
+		return 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.parenDepth++
+		return l.emit(itemLeftParen)
+	case r == ')':
+		l.parenDepth--
+		if l.parenDepth < 0 {
+			return l.errorf("unexpected right paren")
+		}
+		return l.emit(itemRightParen)
+	case r <= unicode.MaxASCII && unicode.IsPrint(r):
+		return l.emit(itemChar)
+	default:
+		return l.errorf("unrecognized character in action: %#U", r)
+	}
+}
+
+// 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.
+		}
+	}
+	return l.emit(itemSpace)
+}
+
+// lexIdentifier scans an alphanumeric.
+func lexIdentifier(l *lexer) stateFn {
+	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:
+				item := key[word]
+				if item == itemBreak && !l.options.breakOK || item == itemContinue && !l.options.continueOK {
+					return l.emit(itemIdentifier)
+				}
+				return l.emit(item)
+			case word[0] == '.':
+				return l.emit(itemField)
+			case word == "true", word == "false":
+				return l.emit(itemBool)
+			default:
+				return l.emit(itemIdentifier)
+			}
+		}
+	}
+}
+
+// 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 -> "$".
+		return l.emit(itemVariable)
+	}
+	return lexFieldOrVariable(l, itemVariable)
+}
+
+// lexFieldOrVariable scans a field or variable: [.$]Alphanumeric.
+// The . or $ has been scanned.
+func lexFieldOrVariable(l *lexer, typ itemType) stateFn {
+	if l.atTerminator() { // Nothing interesting follows -> "." or "$".
+		if typ == itemVariable {
+			return l.emit(itemVariable)
+		}
+		return l.emit(itemDot)
+	}
+	var r rune
+	for {
+		r = l.next()
+		if !isAlphaNumeric(r) {
+			l.backup()
+			break
+		}
+	}
+	if !l.atTerminator() {
+		return l.errorf("bad character %#U", r)
+	}
+	return l.emit(typ)
+}
+
+// atTerminator reports whether the input is at valid termination character to
+// appear after an identifier. Breaks .X.Y into two pieces. Also catches cases
+// like "$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
+	}
+	return strings.HasPrefix(l.input[l.pos:], l.rightDelim)
+}
+
+// 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
+		}
+	}
+	return l.emit(itemCharConstant)
+}
+
+// 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])
+		}
+		return l.emit(itemComplex)
+	}
+	return l.emit(itemNumber)
+}
+
+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
+		}
+	}
+	return l.emit(itemString)
+}
+
+// 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
+		}
+	}
+	return l.emit(itemRawString)
+}
+
+// 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
+}
diff --git a/src/text/template/parse/lex_test.go b/src/text/template/parse/lex_test.go
new file mode 100644
index 0000000..d47f10f
--- /dev/null
+++ b/src/text/template/parse/lex_test.go
@@ -0,0 +1,582 @@
+// 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"
+	"testing"
+)
+
+// Make the types prettyprint.
+var itemName = map[itemType]string{
+	itemError:        "error",
+	itemBool:         "bool",
+	itemChar:         "char",
+	itemCharConstant: "charconst",
+	itemComment:      "comment",
+	itemComplex:      "complex",
+	itemDeclare:      ":=",
+	itemEOF:          "EOF",
+	itemField:        "field",
+	itemIdentifier:   "identifier",
+	itemLeftDelim:    "left delim",
+	itemLeftParen:    "(",
+	itemNumber:       "number",
+	itemPipe:         "pipe",
+	itemRawString:    "raw string",
+	itemRightDelim:   "right delim",
+	itemRightParen:   ")",
+	itemSpace:        "space",
+	itemString:       "string",
+	itemVariable:     "variable",
+
+	// keywords
+	itemDot:      ".",
+	itemBlock:    "block",
+	itemBreak:    "break",
+	itemContinue: "continue",
+	itemDefine:   "define",
+	itemElse:     "else",
+	itemIf:       "if",
+	itemEnd:      "end",
+	itemNil:      "nil",
+	itemRange:    "range",
+	itemTemplate: "template",
+	itemWith:     "with",
+}
+
+func (i itemType) String() string {
+	s := itemName[i]
+	if s == "" {
+		return fmt.Sprintf("item%d", int(i))
+	}
+	return s
+}
+
+type lexTest struct {
+	name  string
+	input string
+	items []item
+}
+
+func mkItem(typ itemType, text string) item {
+	return item{
+		typ: typ,
+		val: text,
+	}
+}
+
+var (
+	tDot        = mkItem(itemDot, ".")
+	tBlock      = mkItem(itemBlock, "block")
+	tEOF        = mkItem(itemEOF, "")
+	tFor        = mkItem(itemIdentifier, "for")
+	tLeft       = mkItem(itemLeftDelim, "{{")
+	tLpar       = mkItem(itemLeftParen, "(")
+	tPipe       = mkItem(itemPipe, "|")
+	tQuote      = mkItem(itemString, `"abc \n\t\" "`)
+	tRange      = mkItem(itemRange, "range")
+	tRight      = mkItem(itemRightDelim, "}}")
+	tRpar       = mkItem(itemRightParen, ")")
+	tSpace      = mkItem(itemSpace, " ")
+	raw         = "`" + `abc\n\t\" ` + "`"
+	rawNL       = "`now is{{\n}}the time`" // Contains newline inside raw quote.
+	tRawQuote   = mkItem(itemRawString, raw)
+	tRawQuoteNL = mkItem(itemRawString, rawNL)
+)
+
+var lexTests = []lexTest{
+	{"empty", "", []item{tEOF}},
+	{"spaces", " \t\n", []item{mkItem(itemText, " \t\n"), tEOF}},
+	{"text", `now is the time`, []item{mkItem(itemText, "now is the time"), tEOF}},
+	{"text with comment", "hello-{{/* this is a comment */}}-world", []item{
+		mkItem(itemText, "hello-"),
+		mkItem(itemComment, "/* this is a comment */"),
+		mkItem(itemText, "-world"),
+		tEOF,
+	}},
+	{"punctuation", "{{,@% }}", []item{
+		tLeft,
+		mkItem(itemChar, ","),
+		mkItem(itemChar, "@"),
+		mkItem(itemChar, "%"),
+		tSpace,
+		tRight,
+		tEOF,
+	}},
+	{"parens", "{{((3))}}", []item{
+		tLeft,
+		tLpar,
+		tLpar,
+		mkItem(itemNumber, "3"),
+		tRpar,
+		tRpar,
+		tRight,
+		tEOF,
+	}},
+	{"empty action", `{{}}`, []item{tLeft, tRight, tEOF}},
+	{"for", `{{for}}`, []item{tLeft, tFor, tRight, tEOF}},
+	{"block", `{{block "foo" .}}`, []item{
+		tLeft, tBlock, tSpace, mkItem(itemString, `"foo"`), tSpace, tDot, tRight, tEOF,
+	}},
+	{"quote", `{{"abc \n\t\" "}}`, []item{tLeft, tQuote, tRight, tEOF}},
+	{"raw quote", "{{" + raw + "}}", []item{tLeft, tRawQuote, tRight, tEOF}},
+	{"raw quote with newline", "{{" + rawNL + "}}", []item{tLeft, tRawQuoteNL, tRight, tEOF}},
+	{"numbers", "{{1 02 0x14 0X14 -7.2i 1e3 1E3 +1.2e-4 4.2i 1+2i 1_2 0x1.e_fp4 0X1.E_FP4}}", []item{
+		tLeft,
+		mkItem(itemNumber, "1"),
+		tSpace,
+		mkItem(itemNumber, "02"),
+		tSpace,
+		mkItem(itemNumber, "0x14"),
+		tSpace,
+		mkItem(itemNumber, "0X14"),
+		tSpace,
+		mkItem(itemNumber, "-7.2i"),
+		tSpace,
+		mkItem(itemNumber, "1e3"),
+		tSpace,
+		mkItem(itemNumber, "1E3"),
+		tSpace,
+		mkItem(itemNumber, "+1.2e-4"),
+		tSpace,
+		mkItem(itemNumber, "4.2i"),
+		tSpace,
+		mkItem(itemComplex, "1+2i"),
+		tSpace,
+		mkItem(itemNumber, "1_2"),
+		tSpace,
+		mkItem(itemNumber, "0x1.e_fp4"),
+		tSpace,
+		mkItem(itemNumber, "0X1.E_FP4"),
+		tRight,
+		tEOF,
+	}},
+	{"characters", `{{'a' '\n' '\'' '\\' '\u00FF' '\xFF' '本'}}`, []item{
+		tLeft,
+		mkItem(itemCharConstant, `'a'`),
+		tSpace,
+		mkItem(itemCharConstant, `'\n'`),
+		tSpace,
+		mkItem(itemCharConstant, `'\''`),
+		tSpace,
+		mkItem(itemCharConstant, `'\\'`),
+		tSpace,
+		mkItem(itemCharConstant, `'\u00FF'`),
+		tSpace,
+		mkItem(itemCharConstant, `'\xFF'`),
+		tSpace,
+		mkItem(itemCharConstant, `'本'`),
+		tRight,
+		tEOF,
+	}},
+	{"bools", "{{true false}}", []item{
+		tLeft,
+		mkItem(itemBool, "true"),
+		tSpace,
+		mkItem(itemBool, "false"),
+		tRight,
+		tEOF,
+	}},
+	{"dot", "{{.}}", []item{
+		tLeft,
+		tDot,
+		tRight,
+		tEOF,
+	}},
+	{"nil", "{{nil}}", []item{
+		tLeft,
+		mkItem(itemNil, "nil"),
+		tRight,
+		tEOF,
+	}},
+	{"dots", "{{.x . .2 .x.y.z}}", []item{
+		tLeft,
+		mkItem(itemField, ".x"),
+		tSpace,
+		tDot,
+		tSpace,
+		mkItem(itemNumber, ".2"),
+		tSpace,
+		mkItem(itemField, ".x"),
+		mkItem(itemField, ".y"),
+		mkItem(itemField, ".z"),
+		tRight,
+		tEOF,
+	}},
+	{"keywords", "{{range if else end with}}", []item{
+		tLeft,
+		mkItem(itemRange, "range"),
+		tSpace,
+		mkItem(itemIf, "if"),
+		tSpace,
+		mkItem(itemElse, "else"),
+		tSpace,
+		mkItem(itemEnd, "end"),
+		tSpace,
+		mkItem(itemWith, "with"),
+		tRight,
+		tEOF,
+	}},
+	{"variables", "{{$c := printf $ $hello $23 $ $var.Field .Method}}", []item{
+		tLeft,
+		mkItem(itemVariable, "$c"),
+		tSpace,
+		mkItem(itemDeclare, ":="),
+		tSpace,
+		mkItem(itemIdentifier, "printf"),
+		tSpace,
+		mkItem(itemVariable, "$"),
+		tSpace,
+		mkItem(itemVariable, "$hello"),
+		tSpace,
+		mkItem(itemVariable, "$23"),
+		tSpace,
+		mkItem(itemVariable, "$"),
+		tSpace,
+		mkItem(itemVariable, "$var"),
+		mkItem(itemField, ".Field"),
+		tSpace,
+		mkItem(itemField, ".Method"),
+		tRight,
+		tEOF,
+	}},
+	{"variable invocation", "{{$x 23}}", []item{
+		tLeft,
+		mkItem(itemVariable, "$x"),
+		tSpace,
+		mkItem(itemNumber, "23"),
+		tRight,
+		tEOF,
+	}},
+	{"pipeline", `intro {{echo hi 1.2 |noargs|args 1 "hi"}} outro`, []item{
+		mkItem(itemText, "intro "),
+		tLeft,
+		mkItem(itemIdentifier, "echo"),
+		tSpace,
+		mkItem(itemIdentifier, "hi"),
+		tSpace,
+		mkItem(itemNumber, "1.2"),
+		tSpace,
+		tPipe,
+		mkItem(itemIdentifier, "noargs"),
+		tPipe,
+		mkItem(itemIdentifier, "args"),
+		tSpace,
+		mkItem(itemNumber, "1"),
+		tSpace,
+		mkItem(itemString, `"hi"`),
+		tRight,
+		mkItem(itemText, " outro"),
+		tEOF,
+	}},
+	{"declaration", "{{$v := 3}}", []item{
+		tLeft,
+		mkItem(itemVariable, "$v"),
+		tSpace,
+		mkItem(itemDeclare, ":="),
+		tSpace,
+		mkItem(itemNumber, "3"),
+		tRight,
+		tEOF,
+	}},
+	{"2 declarations", "{{$v , $w := 3}}", []item{
+		tLeft,
+		mkItem(itemVariable, "$v"),
+		tSpace,
+		mkItem(itemChar, ","),
+		tSpace,
+		mkItem(itemVariable, "$w"),
+		tSpace,
+		mkItem(itemDeclare, ":="),
+		tSpace,
+		mkItem(itemNumber, "3"),
+		tRight,
+		tEOF,
+	}},
+	{"field of parenthesized expression", "{{(.X).Y}}", []item{
+		tLeft,
+		tLpar,
+		mkItem(itemField, ".X"),
+		tRpar,
+		mkItem(itemField, ".Y"),
+		tRight,
+		tEOF,
+	}},
+	{"trimming spaces before and after", "hello- {{- 3 -}} -world", []item{
+		mkItem(itemText, "hello-"),
+		tLeft,
+		mkItem(itemNumber, "3"),
+		tRight,
+		mkItem(itemText, "-world"),
+		tEOF,
+	}},
+	{"trimming spaces before and after comment", "hello- {{- /* hello */ -}} -world", []item{
+		mkItem(itemText, "hello-"),
+		mkItem(itemComment, "/* hello */"),
+		mkItem(itemText, "-world"),
+		tEOF,
+	}},
+	// errors
+	{"badchar", "#{{\x01}}", []item{
+		mkItem(itemText, "#"),
+		tLeft,
+		mkItem(itemError, "unrecognized character in action: U+0001"),
+	}},
+	{"unclosed action", "{{", []item{
+		tLeft,
+		mkItem(itemError, "unclosed action"),
+	}},
+	{"EOF in action", "{{range", []item{
+		tLeft,
+		tRange,
+		mkItem(itemError, "unclosed action"),
+	}},
+	{"unclosed quote", "{{\"\n\"}}", []item{
+		tLeft,
+		mkItem(itemError, "unterminated quoted string"),
+	}},
+	{"unclosed raw quote", "{{`xx}}", []item{
+		tLeft,
+		mkItem(itemError, "unterminated raw quoted string"),
+	}},
+	{"unclosed char constant", "{{'\n}}", []item{
+		tLeft,
+		mkItem(itemError, "unterminated character constant"),
+	}},
+	{"bad number", "{{3k}}", []item{
+		tLeft,
+		mkItem(itemError, `bad number syntax: "3k"`),
+	}},
+	{"unclosed paren", "{{(3}}", []item{
+		tLeft,
+		tLpar,
+		mkItem(itemNumber, "3"),
+		mkItem(itemError, `unclosed left paren`),
+	}},
+	{"extra right paren", "{{3)}}", []item{
+		tLeft,
+		mkItem(itemNumber, "3"),
+		mkItem(itemError, "unexpected right paren"),
+	}},
+
+	// Fixed bugs
+	// Many elements in an action blew the lookahead until
+	// we made lexInsideAction not loop.
+	{"long pipeline deadlock", "{{|||||}}", []item{
+		tLeft,
+		tPipe,
+		tPipe,
+		tPipe,
+		tPipe,
+		tPipe,
+		tRight,
+		tEOF,
+	}},
+	{"text with bad comment", "hello-{{/*/}}-world", []item{
+		mkItem(itemText, "hello-"),
+		mkItem(itemError, `unclosed comment`),
+	}},
+	{"text with comment close separated from delim", "hello-{{/* */ }}-world", []item{
+		mkItem(itemText, "hello-"),
+		mkItem(itemError, `comment ends before closing delimiter`),
+	}},
+	// This one is an error that we can't catch because it breaks templates with
+	// minimized JavaScript. Should have fixed it before Go 1.1.
+	{"unmatched right delimiter", "hello-{.}}-world", []item{
+		mkItem(itemText, "hello-{.}}-world"),
+		tEOF,
+	}},
+}
+
+// collect gathers the emitted items into a slice.
+func collect(t *lexTest, left, right string) (items []item) {
+	l := lex(t.name, t.input, left, right)
+	l.options = lexOptions{
+		emitComment: true,
+		breakOK:     true,
+		continueOK:  true,
+	}
+	for {
+		item := l.nextItem()
+		items = append(items, item)
+		if item.typ == itemEOF || item.typ == itemError {
+			break
+		}
+	}
+	return
+}
+
+func equal(i1, i2 []item, checkPos bool) bool {
+	if len(i1) != len(i2) {
+		return false
+	}
+	for k := range i1 {
+		if i1[k].typ != i2[k].typ {
+			return false
+		}
+		if i1[k].val != i2[k].val {
+			return false
+		}
+		if checkPos && i1[k].pos != i2[k].pos {
+			return false
+		}
+		if checkPos && i1[k].line != i2[k].line {
+			return false
+		}
+	}
+	return true
+}
+
+func TestLex(t *testing.T) {
+	for _, test := range lexTests {
+		items := collect(&test, "", "")
+		if !equal(items, test.items, false) {
+			t.Errorf("%s: got\n\t%+v\nexpected\n\t%v", test.name, items, test.items)
+			return // TODO
+		}
+		t.Log(test.name, "OK")
+	}
+}
+
+// Some easy cases from above, but with delimiters $$ and @@
+var lexDelimTests = []lexTest{
+	{"punctuation", "$$,@%{{}}@@", []item{
+		tLeftDelim,
+		mkItem(itemChar, ","),
+		mkItem(itemChar, "@"),
+		mkItem(itemChar, "%"),
+		mkItem(itemChar, "{"),
+		mkItem(itemChar, "{"),
+		mkItem(itemChar, "}"),
+		mkItem(itemChar, "}"),
+		tRightDelim,
+		tEOF,
+	}},
+	{"empty action", `$$@@`, []item{tLeftDelim, tRightDelim, tEOF}},
+	{"for", `$$for@@`, []item{tLeftDelim, tFor, tRightDelim, tEOF}},
+	{"quote", `$$"abc \n\t\" "@@`, []item{tLeftDelim, tQuote, tRightDelim, tEOF}},
+	{"raw quote", "$$" + raw + "@@", []item{tLeftDelim, tRawQuote, tRightDelim, tEOF}},
+}
+
+var (
+	tLeftDelim  = mkItem(itemLeftDelim, "$$")
+	tRightDelim = mkItem(itemRightDelim, "@@")
+)
+
+func TestDelims(t *testing.T) {
+	for _, test := range lexDelimTests {
+		items := collect(&test, "$$", "@@")
+		if !equal(items, test.items, false) {
+			t.Errorf("%s: got\n\t%v\nexpected\n\t%v", test.name, items, test.items)
+		}
+	}
+}
+
+func TestDelimsAlphaNumeric(t *testing.T) {
+	test := lexTest{"right delimiter with alphanumeric start", "{{hub .host hub}}", []item{
+		mkItem(itemLeftDelim, "{{hub"),
+		mkItem(itemSpace, " "),
+		mkItem(itemField, ".host"),
+		mkItem(itemSpace, " "),
+		mkItem(itemRightDelim, "hub}}"),
+		tEOF,
+	}}
+	items := collect(&test, "{{hub", "hub}}")
+
+	if !equal(items, test.items, false) {
+		t.Errorf("%s: got\n\t%v\nexpected\n\t%v", test.name, items, test.items)
+	}
+}
+
+func TestDelimsAndMarkers(t *testing.T) {
+	test := lexTest{"delims that look like markers", "{{- .x -}} {{- - .x - -}}", []item{
+		mkItem(itemLeftDelim, "{{- "),
+		mkItem(itemField, ".x"),
+		mkItem(itemRightDelim, " -}}"),
+		mkItem(itemLeftDelim, "{{- "),
+		mkItem(itemField, ".x"),
+		mkItem(itemRightDelim, " -}}"),
+		tEOF,
+	}}
+	items := collect(&test, "{{- ", " -}}")
+
+	if !equal(items, test.items, false) {
+		t.Errorf("%s: got\n\t%v\nexpected\n\t%v", test.name, items, test.items)
+	}
+}
+
+var lexPosTests = []lexTest{
+	{"empty", "", []item{{itemEOF, 0, "", 1}}},
+	{"punctuation", "{{,@%#}}", []item{
+		{itemLeftDelim, 0, "{{", 1},
+		{itemChar, 2, ",", 1},
+		{itemChar, 3, "@", 1},
+		{itemChar, 4, "%", 1},
+		{itemChar, 5, "#", 1},
+		{itemRightDelim, 6, "}}", 1},
+		{itemEOF, 8, "", 1},
+	}},
+	{"sample", "0123{{hello}}xyz", []item{
+		{itemText, 0, "0123", 1},
+		{itemLeftDelim, 4, "{{", 1},
+		{itemIdentifier, 6, "hello", 1},
+		{itemRightDelim, 11, "}}", 1},
+		{itemText, 13, "xyz", 1},
+		{itemEOF, 16, "", 1},
+	}},
+	{"trimafter", "{{x -}}\n{{y}}", []item{
+		{itemLeftDelim, 0, "{{", 1},
+		{itemIdentifier, 2, "x", 1},
+		{itemRightDelim, 5, "}}", 1},
+		{itemLeftDelim, 8, "{{", 2},
+		{itemIdentifier, 10, "y", 2},
+		{itemRightDelim, 11, "}}", 2},
+		{itemEOF, 13, "", 2},
+	}},
+	{"trimbefore", "{{x}}\n{{- y}}", []item{
+		{itemLeftDelim, 0, "{{", 1},
+		{itemIdentifier, 2, "x", 1},
+		{itemRightDelim, 3, "}}", 1},
+		{itemLeftDelim, 6, "{{", 2},
+		{itemIdentifier, 10, "y", 2},
+		{itemRightDelim, 11, "}}", 2},
+		{itemEOF, 13, "", 2},
+	}},
+}
+
+// The other tests don't check position, to make the test cases easier to construct.
+// This one does.
+func TestPos(t *testing.T) {
+	for _, test := range lexPosTests {
+		items := collect(&test, "", "")
+		if !equal(items, test.items, true) {
+			t.Errorf("%s: got\n\t%v\nexpected\n\t%v", test.name, items, test.items)
+			if len(items) == len(test.items) {
+				// Detailed print; avoid item.String() to expose the position value.
+				for i := range items {
+					if !equal(items[i:i+1], test.items[i:i+1], true) {
+						i1 := items[i]
+						i2 := test.items[i]
+						t.Errorf("\t#%d: got {%v %d %q %d} expected {%v %d %q %d}",
+							i, i1.typ, i1.pos, i1.val, i1.line, i2.typ, i2.pos, i2.val, i2.line)
+					}
+				}
+			}
+		}
+	}
+}
+
+// parseLexer is a local version of parse that lets us pass in the lexer instead of building it.
+// We expect an error, so the tree set and funcs list are explicitly nil.
+func (t *Tree) parseLexer(lex *lexer) (tree *Tree, err error) {
+	defer t.recover(&err)
+	t.ParseName = t.Name
+	t.startParse(nil, lex, map[string]*Tree{})
+	t.parse()
+	t.add()
+	t.stopParse()
+	return t, nil
+}
diff --git a/src/text/template/parse/node.go b/src/text/template/parse/node.go
new file mode 100644
index 0000000..4726822
--- /dev/null
+++ b/src/text/template/parse/node.go
@@ -0,0 +1,1008 @@
+// 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.
+
+// Parse nodes.
+
+package parse
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+var textFormat = "%s" // Changed to "%q" in tests for better error messages.
+
+// A Node is an element in the parse tree. The interface is trivial.
+// The interface contains an unexported method so that only
+// types local to this package can satisfy it.
+type Node interface {
+	Type() NodeType
+	String() string
+	// Copy does a deep copy of the Node and all its components.
+	// To avoid type assertions, some XxxNodes also have specialized
+	// CopyXxx methods that return *XxxNode.
+	Copy() Node
+	Position() Pos // byte position of start of node in full original input string
+	// tree returns the containing *Tree.
+	// It is unexported so all implementations of Node are in this package.
+	tree() *Tree
+	// writeTo writes the String output to the builder.
+	writeTo(*strings.Builder)
+}
+
+// NodeType identifies the type of a parse tree node.
+type NodeType int
+
+// Pos represents a byte position in the original input text from which
+// this template was parsed.
+type Pos int
+
+func (p Pos) Position() Pos {
+	return p
+}
+
+// Type returns itself and provides an easy default implementation
+// for embedding in a Node. Embedded in all non-trivial Nodes.
+func (t NodeType) Type() NodeType {
+	return t
+}
+
+const (
+	NodeText       NodeType = iota // Plain text.
+	NodeAction                     // A non-control action such as a field evaluation.
+	NodeBool                       // A boolean constant.
+	NodeChain                      // A sequence of field accesses.
+	NodeCommand                    // An element of a pipeline.
+	NodeDot                        // The cursor, dot.
+	nodeElse                       // An else action. Not added to tree.
+	nodeEnd                        // An end action. Not added to tree.
+	NodeField                      // A field or method name.
+	NodeIdentifier                 // An identifier; always a function name.
+	NodeIf                         // An if action.
+	NodeList                       // A list of Nodes.
+	NodeNil                        // An untyped nil constant.
+	NodeNumber                     // A numerical constant.
+	NodePipe                       // A pipeline of commands.
+	NodeRange                      // A range action.
+	NodeString                     // A string constant.
+	NodeTemplate                   // A template invocation action.
+	NodeVariable                   // A $ variable.
+	NodeWith                       // A with action.
+	NodeComment                    // A comment.
+	NodeBreak                      // A break action.
+	NodeContinue                   // A continue action.
+)
+
+// Nodes.
+
+// ListNode holds a sequence of nodes.
+type ListNode struct {
+	NodeType
+	Pos
+	tr    *Tree
+	Nodes []Node // The element nodes in lexical order.
+}
+
+func (t *Tree) newList(pos Pos) *ListNode {
+	return &ListNode{tr: t, NodeType: NodeList, Pos: pos}
+}
+
+func (l *ListNode) append(n Node) {
+	l.Nodes = append(l.Nodes, n)
+}
+
+func (l *ListNode) tree() *Tree {
+	return l.tr
+}
+
+func (l *ListNode) String() string {
+	var sb strings.Builder
+	l.writeTo(&sb)
+	return sb.String()
+}
+
+func (l *ListNode) writeTo(sb *strings.Builder) {
+	for _, n := range l.Nodes {
+		n.writeTo(sb)
+	}
+}
+
+func (l *ListNode) CopyList() *ListNode {
+	if l == nil {
+		return l
+	}
+	n := l.tr.newList(l.Pos)
+	for _, elem := range l.Nodes {
+		n.append(elem.Copy())
+	}
+	return n
+}
+
+func (l *ListNode) Copy() Node {
+	return l.CopyList()
+}
+
+// TextNode holds plain text.
+type TextNode struct {
+	NodeType
+	Pos
+	tr   *Tree
+	Text []byte // The text; may span newlines.
+}
+
+func (t *Tree) newText(pos Pos, text string) *TextNode {
+	return &TextNode{tr: t, NodeType: NodeText, Pos: pos, Text: []byte(text)}
+}
+
+func (t *TextNode) String() string {
+	return fmt.Sprintf(textFormat, t.Text)
+}
+
+func (t *TextNode) writeTo(sb *strings.Builder) {
+	sb.WriteString(t.String())
+}
+
+func (t *TextNode) tree() *Tree {
+	return t.tr
+}
+
+func (t *TextNode) Copy() Node {
+	return &TextNode{tr: t.tr, NodeType: NodeText, Pos: t.Pos, Text: append([]byte{}, t.Text...)}
+}
+
+// CommentNode holds a comment.
+type CommentNode struct {
+	NodeType
+	Pos
+	tr   *Tree
+	Text string // Comment text.
+}
+
+func (t *Tree) newComment(pos Pos, text string) *CommentNode {
+	return &CommentNode{tr: t, NodeType: NodeComment, Pos: pos, Text: text}
+}
+
+func (c *CommentNode) String() string {
+	var sb strings.Builder
+	c.writeTo(&sb)
+	return sb.String()
+}
+
+func (c *CommentNode) writeTo(sb *strings.Builder) {
+	sb.WriteString("{{")
+	sb.WriteString(c.Text)
+	sb.WriteString("}}")
+}
+
+func (c *CommentNode) tree() *Tree {
+	return c.tr
+}
+
+func (c *CommentNode) Copy() Node {
+	return &CommentNode{tr: c.tr, NodeType: NodeComment, Pos: c.Pos, Text: c.Text}
+}
+
+// PipeNode holds a pipeline with optional declaration
+type PipeNode struct {
+	NodeType
+	Pos
+	tr       *Tree
+	Line     int             // The line number in the input. Deprecated: Kept for compatibility.
+	IsAssign bool            // The variables are being assigned, not declared.
+	Decl     []*VariableNode // Variables in lexical order.
+	Cmds     []*CommandNode  // The commands in lexical order.
+}
+
+func (t *Tree) newPipeline(pos Pos, line int, vars []*VariableNode) *PipeNode {
+	return &PipeNode{tr: t, NodeType: NodePipe, Pos: pos, Line: line, Decl: vars}
+}
+
+func (p *PipeNode) append(command *CommandNode) {
+	p.Cmds = append(p.Cmds, command)
+}
+
+func (p *PipeNode) String() string {
+	var sb strings.Builder
+	p.writeTo(&sb)
+	return sb.String()
+}
+
+func (p *PipeNode) writeTo(sb *strings.Builder) {
+	if len(p.Decl) > 0 {
+		for i, v := range p.Decl {
+			if i > 0 {
+				sb.WriteString(", ")
+			}
+			v.writeTo(sb)
+		}
+		sb.WriteString(" := ")
+	}
+	for i, c := range p.Cmds {
+		if i > 0 {
+			sb.WriteString(" | ")
+		}
+		c.writeTo(sb)
+	}
+}
+
+func (p *PipeNode) tree() *Tree {
+	return p.tr
+}
+
+func (p *PipeNode) CopyPipe() *PipeNode {
+	if p == nil {
+		return p
+	}
+	vars := make([]*VariableNode, len(p.Decl))
+	for i, d := range p.Decl {
+		vars[i] = d.Copy().(*VariableNode)
+	}
+	n := p.tr.newPipeline(p.Pos, p.Line, vars)
+	n.IsAssign = p.IsAssign
+	for _, c := range p.Cmds {
+		n.append(c.Copy().(*CommandNode))
+	}
+	return n
+}
+
+func (p *PipeNode) Copy() Node {
+	return p.CopyPipe()
+}
+
+// ActionNode holds an action (something bounded by delimiters).
+// Control actions have their own nodes; ActionNode represents simple
+// ones such as field evaluations and parenthesized pipelines.
+type ActionNode struct {
+	NodeType
+	Pos
+	tr   *Tree
+	Line int       // The line number in the input. Deprecated: Kept for compatibility.
+	Pipe *PipeNode // The pipeline in the action.
+}
+
+func (t *Tree) newAction(pos Pos, line int, pipe *PipeNode) *ActionNode {
+	return &ActionNode{tr: t, NodeType: NodeAction, Pos: pos, Line: line, Pipe: pipe}
+}
+
+func (a *ActionNode) String() string {
+	var sb strings.Builder
+	a.writeTo(&sb)
+	return sb.String()
+}
+
+func (a *ActionNode) writeTo(sb *strings.Builder) {
+	sb.WriteString("{{")
+	a.Pipe.writeTo(sb)
+	sb.WriteString("}}")
+}
+
+func (a *ActionNode) tree() *Tree {
+	return a.tr
+}
+
+func (a *ActionNode) Copy() Node {
+	return a.tr.newAction(a.Pos, a.Line, a.Pipe.CopyPipe())
+
+}
+
+// CommandNode holds a command (a pipeline inside an evaluating action).
+type CommandNode struct {
+	NodeType
+	Pos
+	tr   *Tree
+	Args []Node // Arguments in lexical order: Identifier, field, or constant.
+}
+
+func (t *Tree) newCommand(pos Pos) *CommandNode {
+	return &CommandNode{tr: t, NodeType: NodeCommand, Pos: pos}
+}
+
+func (c *CommandNode) append(arg Node) {
+	c.Args = append(c.Args, arg)
+}
+
+func (c *CommandNode) String() string {
+	var sb strings.Builder
+	c.writeTo(&sb)
+	return sb.String()
+}
+
+func (c *CommandNode) writeTo(sb *strings.Builder) {
+	for i, arg := range c.Args {
+		if i > 0 {
+			sb.WriteByte(' ')
+		}
+		if arg, ok := arg.(*PipeNode); ok {
+			sb.WriteByte('(')
+			arg.writeTo(sb)
+			sb.WriteByte(')')
+			continue
+		}
+		arg.writeTo(sb)
+	}
+}
+
+func (c *CommandNode) tree() *Tree {
+	return c.tr
+}
+
+func (c *CommandNode) Copy() Node {
+	if c == nil {
+		return c
+	}
+	n := c.tr.newCommand(c.Pos)
+	for _, c := range c.Args {
+		n.append(c.Copy())
+	}
+	return n
+}
+
+// IdentifierNode holds an identifier.
+type IdentifierNode struct {
+	NodeType
+	Pos
+	tr    *Tree
+	Ident string // The identifier's name.
+}
+
+// NewIdentifier returns a new IdentifierNode with the given identifier name.
+func NewIdentifier(ident string) *IdentifierNode {
+	return &IdentifierNode{NodeType: NodeIdentifier, Ident: ident}
+}
+
+// SetPos sets the position. NewIdentifier is a public method so we can't modify its signature.
+// Chained for convenience.
+// TODO: fix one day?
+func (i *IdentifierNode) SetPos(pos Pos) *IdentifierNode {
+	i.Pos = pos
+	return i
+}
+
+// SetTree sets the parent tree for the node. NewIdentifier is a public method so we can't modify its signature.
+// Chained for convenience.
+// TODO: fix one day?
+func (i *IdentifierNode) SetTree(t *Tree) *IdentifierNode {
+	i.tr = t
+	return i
+}
+
+func (i *IdentifierNode) String() string {
+	return i.Ident
+}
+
+func (i *IdentifierNode) writeTo(sb *strings.Builder) {
+	sb.WriteString(i.String())
+}
+
+func (i *IdentifierNode) tree() *Tree {
+	return i.tr
+}
+
+func (i *IdentifierNode) Copy() Node {
+	return NewIdentifier(i.Ident).SetTree(i.tr).SetPos(i.Pos)
+}
+
+// VariableNode holds a list of variable names, possibly with chained field
+// accesses. The dollar sign is part of the (first) name.
+type VariableNode struct {
+	NodeType
+	Pos
+	tr    *Tree
+	Ident []string // Variable name and fields in lexical order.
+}
+
+func (t *Tree) newVariable(pos Pos, ident string) *VariableNode {
+	return &VariableNode{tr: t, NodeType: NodeVariable, Pos: pos, Ident: strings.Split(ident, ".")}
+}
+
+func (v *VariableNode) String() string {
+	var sb strings.Builder
+	v.writeTo(&sb)
+	return sb.String()
+}
+
+func (v *VariableNode) writeTo(sb *strings.Builder) {
+	for i, id := range v.Ident {
+		if i > 0 {
+			sb.WriteByte('.')
+		}
+		sb.WriteString(id)
+	}
+}
+
+func (v *VariableNode) tree() *Tree {
+	return v.tr
+}
+
+func (v *VariableNode) Copy() Node {
+	return &VariableNode{tr: v.tr, NodeType: NodeVariable, Pos: v.Pos, Ident: append([]string{}, v.Ident...)}
+}
+
+// DotNode holds the special identifier '.'.
+type DotNode struct {
+	NodeType
+	Pos
+	tr *Tree
+}
+
+func (t *Tree) newDot(pos Pos) *DotNode {
+	return &DotNode{tr: t, NodeType: NodeDot, Pos: pos}
+}
+
+func (d *DotNode) Type() NodeType {
+	// Override method on embedded NodeType for API compatibility.
+	// TODO: Not really a problem; could change API without effect but
+	// api tool complains.
+	return NodeDot
+}
+
+func (d *DotNode) String() string {
+	return "."
+}
+
+func (d *DotNode) writeTo(sb *strings.Builder) {
+	sb.WriteString(d.String())
+}
+
+func (d *DotNode) tree() *Tree {
+	return d.tr
+}
+
+func (d *DotNode) Copy() Node {
+	return d.tr.newDot(d.Pos)
+}
+
+// NilNode holds the special identifier 'nil' representing an untyped nil constant.
+type NilNode struct {
+	NodeType
+	Pos
+	tr *Tree
+}
+
+func (t *Tree) newNil(pos Pos) *NilNode {
+	return &NilNode{tr: t, NodeType: NodeNil, Pos: pos}
+}
+
+func (n *NilNode) Type() NodeType {
+	// Override method on embedded NodeType for API compatibility.
+	// TODO: Not really a problem; could change API without effect but
+	// api tool complains.
+	return NodeNil
+}
+
+func (n *NilNode) String() string {
+	return "nil"
+}
+
+func (n *NilNode) writeTo(sb *strings.Builder) {
+	sb.WriteString(n.String())
+}
+
+func (n *NilNode) tree() *Tree {
+	return n.tr
+}
+
+func (n *NilNode) Copy() Node {
+	return n.tr.newNil(n.Pos)
+}
+
+// FieldNode holds a field (identifier starting with '.').
+// The names may be chained ('.x.y').
+// The period is dropped from each ident.
+type FieldNode struct {
+	NodeType
+	Pos
+	tr    *Tree
+	Ident []string // The identifiers in lexical order.
+}
+
+func (t *Tree) newField(pos Pos, ident string) *FieldNode {
+	return &FieldNode{tr: t, NodeType: NodeField, Pos: pos, Ident: strings.Split(ident[1:], ".")} // [1:] to drop leading period
+}
+
+func (f *FieldNode) String() string {
+	var sb strings.Builder
+	f.writeTo(&sb)
+	return sb.String()
+}
+
+func (f *FieldNode) writeTo(sb *strings.Builder) {
+	for _, id := range f.Ident {
+		sb.WriteByte('.')
+		sb.WriteString(id)
+	}
+}
+
+func (f *FieldNode) tree() *Tree {
+	return f.tr
+}
+
+func (f *FieldNode) Copy() Node {
+	return &FieldNode{tr: f.tr, NodeType: NodeField, Pos: f.Pos, Ident: append([]string{}, f.Ident...)}
+}
+
+// ChainNode holds a term followed by a chain of field accesses (identifier starting with '.').
+// The names may be chained ('.x.y').
+// The periods are dropped from each ident.
+type ChainNode struct {
+	NodeType
+	Pos
+	tr    *Tree
+	Node  Node
+	Field []string // The identifiers in lexical order.
+}
+
+func (t *Tree) newChain(pos Pos, node Node) *ChainNode {
+	return &ChainNode{tr: t, NodeType: NodeChain, Pos: pos, Node: node}
+}
+
+// Add adds the named field (which should start with a period) to the end of the chain.
+func (c *ChainNode) Add(field string) {
+	if len(field) == 0 || field[0] != '.' {
+		panic("no dot in field")
+	}
+	field = field[1:] // Remove leading dot.
+	if field == "" {
+		panic("empty field")
+	}
+	c.Field = append(c.Field, field)
+}
+
+func (c *ChainNode) String() string {
+	var sb strings.Builder
+	c.writeTo(&sb)
+	return sb.String()
+}
+
+func (c *ChainNode) writeTo(sb *strings.Builder) {
+	if _, ok := c.Node.(*PipeNode); ok {
+		sb.WriteByte('(')
+		c.Node.writeTo(sb)
+		sb.WriteByte(')')
+	} else {
+		c.Node.writeTo(sb)
+	}
+	for _, field := range c.Field {
+		sb.WriteByte('.')
+		sb.WriteString(field)
+	}
+}
+
+func (c *ChainNode) tree() *Tree {
+	return c.tr
+}
+
+func (c *ChainNode) Copy() Node {
+	return &ChainNode{tr: c.tr, NodeType: NodeChain, Pos: c.Pos, Node: c.Node, Field: append([]string{}, c.Field...)}
+}
+
+// BoolNode holds a boolean constant.
+type BoolNode struct {
+	NodeType
+	Pos
+	tr   *Tree
+	True bool // The value of the boolean constant.
+}
+
+func (t *Tree) newBool(pos Pos, true bool) *BoolNode {
+	return &BoolNode{tr: t, NodeType: NodeBool, Pos: pos, True: true}
+}
+
+func (b *BoolNode) String() string {
+	if b.True {
+		return "true"
+	}
+	return "false"
+}
+
+func (b *BoolNode) writeTo(sb *strings.Builder) {
+	sb.WriteString(b.String())
+}
+
+func (b *BoolNode) tree() *Tree {
+	return b.tr
+}
+
+func (b *BoolNode) Copy() Node {
+	return b.tr.newBool(b.Pos, b.True)
+}
+
+// NumberNode holds a number: signed or unsigned integer, float, or complex.
+// The value is parsed and stored under all the types that can represent the value.
+// This simulates in a small amount of code the behavior of Go's ideal constants.
+type NumberNode struct {
+	NodeType
+	Pos
+	tr         *Tree
+	IsInt      bool       // Number has an integral value.
+	IsUint     bool       // Number has an unsigned integral value.
+	IsFloat    bool       // Number has a floating-point value.
+	IsComplex  bool       // Number is complex.
+	Int64      int64      // The signed integer value.
+	Uint64     uint64     // The unsigned integer value.
+	Float64    float64    // The floating-point value.
+	Complex128 complex128 // The complex value.
+	Text       string     // The original textual representation from the input.
+}
+
+func (t *Tree) newNumber(pos Pos, text string, typ itemType) (*NumberNode, error) {
+	n := &NumberNode{tr: t, NodeType: NodeNumber, Pos: pos, Text: text}
+	switch typ {
+	case itemCharConstant:
+		rune, _, tail, err := strconv.UnquoteChar(text[1:], text[0])
+		if err != nil {
+			return nil, err
+		}
+		if tail != "'" {
+			return nil, fmt.Errorf("malformed character constant: %s", text)
+		}
+		n.Int64 = int64(rune)
+		n.IsInt = true
+		n.Uint64 = uint64(rune)
+		n.IsUint = true
+		n.Float64 = float64(rune) // odd but those are the rules.
+		n.IsFloat = true
+		return n, nil
+	case itemComplex:
+		// fmt.Sscan can parse the pair, so let it do the work.
+		if _, err := fmt.Sscan(text, &n.Complex128); err != nil {
+			return nil, err
+		}
+		n.IsComplex = true
+		n.simplifyComplex()
+		return n, nil
+	}
+	// Imaginary constants can only be complex unless they are zero.
+	if len(text) > 0 && text[len(text)-1] == 'i' {
+		f, err := strconv.ParseFloat(text[:len(text)-1], 64)
+		if err == nil {
+			n.IsComplex = true
+			n.Complex128 = complex(0, f)
+			n.simplifyComplex()
+			return n, nil
+		}
+	}
+	// Do integer test first so we get 0x123 etc.
+	u, err := strconv.ParseUint(text, 0, 64) // will fail for -0; fixed below.
+	if err == nil {
+		n.IsUint = true
+		n.Uint64 = u
+	}
+	i, err := strconv.ParseInt(text, 0, 64)
+	if err == nil {
+		n.IsInt = true
+		n.Int64 = i
+		if i == 0 {
+			n.IsUint = true // in case of -0.
+			n.Uint64 = u
+		}
+	}
+	// If an integer extraction succeeded, promote the float.
+	if n.IsInt {
+		n.IsFloat = true
+		n.Float64 = float64(n.Int64)
+	} else if n.IsUint {
+		n.IsFloat = true
+		n.Float64 = float64(n.Uint64)
+	} else {
+		f, err := strconv.ParseFloat(text, 64)
+		if err == nil {
+			// If we parsed it as a float but it looks like an integer,
+			// it's a huge number too large to fit in an int. Reject it.
+			if !strings.ContainsAny(text, ".eEpP") {
+				return nil, fmt.Errorf("integer overflow: %q", text)
+			}
+			n.IsFloat = true
+			n.Float64 = f
+			// If a floating-point extraction succeeded, extract the int if needed.
+			if !n.IsInt && float64(int64(f)) == f {
+				n.IsInt = true
+				n.Int64 = int64(f)
+			}
+			if !n.IsUint && float64(uint64(f)) == f {
+				n.IsUint = true
+				n.Uint64 = uint64(f)
+			}
+		}
+	}
+	if !n.IsInt && !n.IsUint && !n.IsFloat {
+		return nil, fmt.Errorf("illegal number syntax: %q", text)
+	}
+	return n, nil
+}
+
+// simplifyComplex pulls out any other types that are represented by the complex number.
+// These all require that the imaginary part be zero.
+func (n *NumberNode) simplifyComplex() {
+	n.IsFloat = imag(n.Complex128) == 0
+	if n.IsFloat {
+		n.Float64 = real(n.Complex128)
+		n.IsInt = float64(int64(n.Float64)) == n.Float64
+		if n.IsInt {
+			n.Int64 = int64(n.Float64)
+		}
+		n.IsUint = float64(uint64(n.Float64)) == n.Float64
+		if n.IsUint {
+			n.Uint64 = uint64(n.Float64)
+		}
+	}
+}
+
+func (n *NumberNode) String() string {
+	return n.Text
+}
+
+func (n *NumberNode) writeTo(sb *strings.Builder) {
+	sb.WriteString(n.String())
+}
+
+func (n *NumberNode) tree() *Tree {
+	return n.tr
+}
+
+func (n *NumberNode) Copy() Node {
+	nn := new(NumberNode)
+	*nn = *n // Easy, fast, correct.
+	return nn
+}
+
+// StringNode holds a string constant. The value has been "unquoted".
+type StringNode struct {
+	NodeType
+	Pos
+	tr     *Tree
+	Quoted string // The original text of the string, with quotes.
+	Text   string // The string, after quote processing.
+}
+
+func (t *Tree) newString(pos Pos, orig, text string) *StringNode {
+	return &StringNode{tr: t, NodeType: NodeString, Pos: pos, Quoted: orig, Text: text}
+}
+
+func (s *StringNode) String() string {
+	return s.Quoted
+}
+
+func (s *StringNode) writeTo(sb *strings.Builder) {
+	sb.WriteString(s.String())
+}
+
+func (s *StringNode) tree() *Tree {
+	return s.tr
+}
+
+func (s *StringNode) Copy() Node {
+	return s.tr.newString(s.Pos, s.Quoted, s.Text)
+}
+
+// endNode represents an {{end}} action.
+// It does not appear in the final parse tree.
+type endNode struct {
+	NodeType
+	Pos
+	tr *Tree
+}
+
+func (t *Tree) newEnd(pos Pos) *endNode {
+	return &endNode{tr: t, NodeType: nodeEnd, Pos: pos}
+}
+
+func (e *endNode) String() string {
+	return "{{end}}"
+}
+
+func (e *endNode) writeTo(sb *strings.Builder) {
+	sb.WriteString(e.String())
+}
+
+func (e *endNode) tree() *Tree {
+	return e.tr
+}
+
+func (e *endNode) Copy() Node {
+	return e.tr.newEnd(e.Pos)
+}
+
+// elseNode represents an {{else}} action. Does not appear in the final tree.
+type elseNode struct {
+	NodeType
+	Pos
+	tr   *Tree
+	Line int // The line number in the input. Deprecated: Kept for compatibility.
+}
+
+func (t *Tree) newElse(pos Pos, line int) *elseNode {
+	return &elseNode{tr: t, NodeType: nodeElse, Pos: pos, Line: line}
+}
+
+func (e *elseNode) Type() NodeType {
+	return nodeElse
+}
+
+func (e *elseNode) String() string {
+	return "{{else}}"
+}
+
+func (e *elseNode) writeTo(sb *strings.Builder) {
+	sb.WriteString(e.String())
+}
+
+func (e *elseNode) tree() *Tree {
+	return e.tr
+}
+
+func (e *elseNode) Copy() Node {
+	return e.tr.newElse(e.Pos, e.Line)
+}
+
+// BranchNode is the common representation of if, range, and with.
+type BranchNode struct {
+	NodeType
+	Pos
+	tr       *Tree
+	Line     int       // The line number in the input. Deprecated: Kept for compatibility.
+	Pipe     *PipeNode // The pipeline to be evaluated.
+	List     *ListNode // What to execute if the value is non-empty.
+	ElseList *ListNode // What to execute if the value is empty (nil if absent).
+}
+
+func (b *BranchNode) String() string {
+	var sb strings.Builder
+	b.writeTo(&sb)
+	return sb.String()
+}
+
+func (b *BranchNode) writeTo(sb *strings.Builder) {
+	name := ""
+	switch b.NodeType {
+	case NodeIf:
+		name = "if"
+	case NodeRange:
+		name = "range"
+	case NodeWith:
+		name = "with"
+	default:
+		panic("unknown branch type")
+	}
+	sb.WriteString("{{")
+	sb.WriteString(name)
+	sb.WriteByte(' ')
+	b.Pipe.writeTo(sb)
+	sb.WriteString("}}")
+	b.List.writeTo(sb)
+	if b.ElseList != nil {
+		sb.WriteString("{{else}}")
+		b.ElseList.writeTo(sb)
+	}
+	sb.WriteString("{{end}}")
+}
+
+func (b *BranchNode) tree() *Tree {
+	return b.tr
+}
+
+func (b *BranchNode) Copy() Node {
+	switch b.NodeType {
+	case NodeIf:
+		return b.tr.newIf(b.Pos, b.Line, b.Pipe, b.List, b.ElseList)
+	case NodeRange:
+		return b.tr.newRange(b.Pos, b.Line, b.Pipe, b.List, b.ElseList)
+	case NodeWith:
+		return b.tr.newWith(b.Pos, b.Line, b.Pipe, b.List, b.ElseList)
+	default:
+		panic("unknown branch type")
+	}
+}
+
+// IfNode represents an {{if}} action and its commands.
+type IfNode struct {
+	BranchNode
+}
+
+func (t *Tree) newIf(pos Pos, line int, pipe *PipeNode, list, elseList *ListNode) *IfNode {
+	return &IfNode{BranchNode{tr: t, NodeType: NodeIf, Pos: pos, Line: line, Pipe: pipe, List: list, ElseList: elseList}}
+}
+
+func (i *IfNode) Copy() Node {
+	return i.tr.newIf(i.Pos, i.Line, i.Pipe.CopyPipe(), i.List.CopyList(), i.ElseList.CopyList())
+}
+
+// BreakNode represents a {{break}} action.
+type BreakNode struct {
+	tr *Tree
+	NodeType
+	Pos
+	Line int
+}
+
+func (t *Tree) newBreak(pos Pos, line int) *BreakNode {
+	return &BreakNode{tr: t, NodeType: NodeBreak, Pos: pos, Line: line}
+}
+
+func (b *BreakNode) Copy() Node                  { return b.tr.newBreak(b.Pos, b.Line) }
+func (b *BreakNode) String() string              { return "{{break}}" }
+func (b *BreakNode) tree() *Tree                 { return b.tr }
+func (b *BreakNode) writeTo(sb *strings.Builder) { sb.WriteString("{{break}}") }
+
+// ContinueNode represents a {{continue}} action.
+type ContinueNode struct {
+	tr *Tree
+	NodeType
+	Pos
+	Line int
+}
+
+func (t *Tree) newContinue(pos Pos, line int) *ContinueNode {
+	return &ContinueNode{tr: t, NodeType: NodeContinue, Pos: pos, Line: line}
+}
+
+func (c *ContinueNode) Copy() Node                  { return c.tr.newContinue(c.Pos, c.Line) }
+func (c *ContinueNode) String() string              { return "{{continue}}" }
+func (c *ContinueNode) tree() *Tree                 { return c.tr }
+func (c *ContinueNode) writeTo(sb *strings.Builder) { sb.WriteString("{{continue}}") }
+
+// RangeNode represents a {{range}} action and its commands.
+type RangeNode struct {
+	BranchNode
+}
+
+func (t *Tree) newRange(pos Pos, line int, pipe *PipeNode, list, elseList *ListNode) *RangeNode {
+	return &RangeNode{BranchNode{tr: t, NodeType: NodeRange, Pos: pos, Line: line, Pipe: pipe, List: list, ElseList: elseList}}
+}
+
+func (r *RangeNode) Copy() Node {
+	return r.tr.newRange(r.Pos, r.Line, r.Pipe.CopyPipe(), r.List.CopyList(), r.ElseList.CopyList())
+}
+
+// WithNode represents a {{with}} action and its commands.
+type WithNode struct {
+	BranchNode
+}
+
+func (t *Tree) newWith(pos Pos, line int, pipe *PipeNode, list, elseList *ListNode) *WithNode {
+	return &WithNode{BranchNode{tr: t, NodeType: NodeWith, Pos: pos, Line: line, Pipe: pipe, List: list, ElseList: elseList}}
+}
+
+func (w *WithNode) Copy() Node {
+	return w.tr.newWith(w.Pos, w.Line, w.Pipe.CopyPipe(), w.List.CopyList(), w.ElseList.CopyList())
+}
+
+// TemplateNode represents a {{template}} action.
+type TemplateNode struct {
+	NodeType
+	Pos
+	tr   *Tree
+	Line int       // The line number in the input. Deprecated: Kept for compatibility.
+	Name string    // The name of the template (unquoted).
+	Pipe *PipeNode // The command to evaluate as dot for the template.
+}
+
+func (t *Tree) newTemplate(pos Pos, line int, name string, pipe *PipeNode) *TemplateNode {
+	return &TemplateNode{tr: t, NodeType: NodeTemplate, Pos: pos, Line: line, Name: name, Pipe: pipe}
+}
+
+func (t *TemplateNode) String() string {
+	var sb strings.Builder
+	t.writeTo(&sb)
+	return sb.String()
+}
+
+func (t *TemplateNode) writeTo(sb *strings.Builder) {
+	sb.WriteString("{{template ")
+	sb.WriteString(strconv.Quote(t.Name))
+	if t.Pipe != nil {
+		sb.WriteByte(' ')
+		t.Pipe.writeTo(sb)
+	}
+	sb.WriteString("}}")
+}
+
+func (t *TemplateNode) tree() *Tree {
+	return t.tr
+}
+
+func (t *TemplateNode) Copy() Node {
+	return t.tr.newTemplate(t.Pos, t.Line, t.Name, t.Pipe.CopyPipe())
+}
diff --git a/src/text/template/parse/parse.go b/src/text/template/parse/parse.go
new file mode 100644
index 0000000..d43d533
--- /dev/null
+++ b/src/text/template/parse/parse.go
@@ -0,0 +1,827 @@
+// 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 builds parse trees for templates as defined by text/template
+// and html/template. Clients should use those packages to construct templates
+// rather than this one, which provides shared internal data structures not
+// intended for general use.
+package parse
+
+import (
+	"bytes"
+	"fmt"
+	"runtime"
+	"strconv"
+	"strings"
+)
+
+// Tree is the representation of a single parsed template.
+type Tree struct {
+	Name      string    // name of the template represented by the tree.
+	ParseName string    // name of the top-level template during parsing, for error messages.
+	Root      *ListNode // top-level root of the tree.
+	Mode      Mode      // parsing mode.
+	text      string    // text parsed to create the template (or its parent)
+	// Parsing only; cleared after parse.
+	funcs      []map[string]any
+	lex        *lexer
+	token      [3]item // three-token lookahead for parser.
+	peekCount  int
+	vars       []string // variables defined at the moment.
+	treeSet    map[string]*Tree
+	actionLine int // line of left delim starting action
+	rangeDepth int
+}
+
+// A mode value is a set of flags (or 0). Modes control parser behavior.
+type Mode uint
+
+const (
+	ParseComments Mode = 1 << iota // parse comments and add them to AST
+	SkipFuncCheck                  // do not check that functions are defined
+)
+
+// Copy returns a copy of the Tree. Any parsing state is discarded.
+func (t *Tree) Copy() *Tree {
+	if t == nil {
+		return nil
+	}
+	return &Tree{
+		Name:      t.Name,
+		ParseName: t.ParseName,
+		Root:      t.Root.CopyList(),
+		text:      t.text,
+	}
+}
+
+// Parse returns a map from template name to parse.Tree, created by parsing the
+// templates described in the argument string. The top-level template will be
+// given the specified name. If an error is encountered, parsing stops and an
+// empty map is returned with the error.
+func Parse(name, text, leftDelim, rightDelim string, funcs ...map[string]any) (map[string]*Tree, error) {
+	treeSet := make(map[string]*Tree)
+	t := New(name)
+	t.text = text
+	_, err := t.Parse(text, leftDelim, rightDelim, treeSet, funcs...)
+	return treeSet, err
+}
+
+// next returns the next token.
+func (t *Tree) next() item {
+	if t.peekCount > 0 {
+		t.peekCount--
+	} else {
+		t.token[0] = t.lex.nextItem()
+	}
+	return t.token[t.peekCount]
+}
+
+// backup backs the input stream up one token.
+func (t *Tree) backup() {
+	t.peekCount++
+}
+
+// backup2 backs the input stream up two tokens.
+// The zeroth token is already there.
+func (t *Tree) backup2(t1 item) {
+	t.token[1] = t1
+	t.peekCount = 2
+}
+
+// backup3 backs the input stream up three tokens
+// The zeroth token is already there.
+func (t *Tree) backup3(t2, t1 item) { // Reverse order: we're pushing back.
+	t.token[1] = t1
+	t.token[2] = t2
+	t.peekCount = 3
+}
+
+// peek returns but does not consume the next token.
+func (t *Tree) peek() item {
+	if t.peekCount > 0 {
+		return t.token[t.peekCount-1]
+	}
+	t.peekCount = 1
+	t.token[0] = t.lex.nextItem()
+	return t.token[0]
+}
+
+// nextNonSpace returns the next non-space token.
+func (t *Tree) nextNonSpace() (token item) {
+	for {
+		token = t.next()
+		if token.typ != itemSpace {
+			break
+		}
+	}
+	return token
+}
+
+// peekNonSpace returns but does not consume the next non-space token.
+func (t *Tree) peekNonSpace() item {
+	token := t.nextNonSpace()
+	t.backup()
+	return token
+}
+
+// Parsing.
+
+// New allocates a new parse tree with the given name.
+func New(name string, funcs ...map[string]any) *Tree {
+	return &Tree{
+		Name:  name,
+		funcs: funcs,
+	}
+}
+
+// ErrorContext returns a textual representation of the location of the node in the input text.
+// The receiver is only used when the node does not have a pointer to the tree inside,
+// which can occur in old code.
+func (t *Tree) ErrorContext(n Node) (location, context string) {
+	pos := int(n.Position())
+	tree := n.tree()
+	if tree == nil {
+		tree = t
+	}
+	text := tree.text[:pos]
+	byteNum := strings.LastIndex(text, "\n")
+	if byteNum == -1 {
+		byteNum = pos // On first line.
+	} else {
+		byteNum++ // After the newline.
+		byteNum = pos - byteNum
+	}
+	lineNum := 1 + strings.Count(text, "\n")
+	context = n.String()
+	return fmt.Sprintf("%s:%d:%d", tree.ParseName, lineNum, byteNum), context
+}
+
+// errorf formats the error and terminates processing.
+func (t *Tree) errorf(format string, args ...any) {
+	t.Root = nil
+	format = fmt.Sprintf("template: %s:%d: %s", t.ParseName, t.token[0].line, format)
+	panic(fmt.Errorf(format, args...))
+}
+
+// error terminates processing.
+func (t *Tree) error(err error) {
+	t.errorf("%s", err)
+}
+
+// expect consumes the next token and guarantees it has the required type.
+func (t *Tree) expect(expected itemType, context string) item {
+	token := t.nextNonSpace()
+	if token.typ != expected {
+		t.unexpected(token, context)
+	}
+	return token
+}
+
+// expectOneOf consumes the next token and guarantees it has one of the required types.
+func (t *Tree) expectOneOf(expected1, expected2 itemType, context string) item {
+	token := t.nextNonSpace()
+	if token.typ != expected1 && token.typ != expected2 {
+		t.unexpected(token, context)
+	}
+	return token
+}
+
+// unexpected complains about the token and terminates processing.
+func (t *Tree) unexpected(token item, context string) {
+	if token.typ == itemError {
+		extra := ""
+		if t.actionLine != 0 && t.actionLine != token.line {
+			extra = fmt.Sprintf(" in action started at %s:%d", t.ParseName, t.actionLine)
+			if strings.HasSuffix(token.val, " action") {
+				extra = extra[len(" in action"):] // avoid "action in action"
+			}
+		}
+		t.errorf("%s%s", token, extra)
+	}
+	t.errorf("unexpected %s in %s", token, context)
+}
+
+// recover is the handler that turns panics into returns from the top level of Parse.
+func (t *Tree) recover(errp *error) {
+	e := recover()
+	if e != nil {
+		if _, ok := e.(runtime.Error); ok {
+			panic(e)
+		}
+		if t != nil {
+			t.stopParse()
+		}
+		*errp = e.(error)
+	}
+}
+
+// startParse initializes the parser, using the lexer.
+func (t *Tree) startParse(funcs []map[string]any, lex *lexer, treeSet map[string]*Tree) {
+	t.Root = nil
+	t.lex = lex
+	t.vars = []string{"$"}
+	t.funcs = funcs
+	t.treeSet = treeSet
+	lex.options = lexOptions{
+		emitComment: t.Mode&ParseComments != 0,
+		breakOK:     !t.hasFunction("break"),
+		continueOK:  !t.hasFunction("continue"),
+	}
+}
+
+// stopParse terminates parsing.
+func (t *Tree) stopParse() {
+	t.lex = nil
+	t.vars = nil
+	t.funcs = nil
+	t.treeSet = nil
+}
+
+// Parse parses the template definition string to construct a representation of
+// the template for execution. If either action delimiter string is empty, the
+// default ("{{" or "}}") is used. Embedded template definitions are added to
+// the treeSet map.
+func (t *Tree) Parse(text, leftDelim, rightDelim string, treeSet map[string]*Tree, funcs ...map[string]any) (tree *Tree, err error) {
+	defer t.recover(&err)
+	t.ParseName = t.Name
+	lexer := lex(t.Name, text, leftDelim, rightDelim)
+	t.startParse(funcs, lexer, treeSet)
+	t.text = text
+	t.parse()
+	t.add()
+	t.stopParse()
+	return t, nil
+}
+
+// add adds tree to t.treeSet.
+func (t *Tree) add() {
+	tree := t.treeSet[t.Name]
+	if tree == nil || IsEmptyTree(tree.Root) {
+		t.treeSet[t.Name] = t
+		return
+	}
+	if !IsEmptyTree(t.Root) {
+		t.errorf("template: multiple definition of template %q", t.Name)
+	}
+}
+
+// IsEmptyTree reports whether this tree (node) is empty of everything but space or comments.
+func IsEmptyTree(n Node) bool {
+	switch n := n.(type) {
+	case nil:
+		return true
+	case *ActionNode:
+	case *CommentNode:
+		return true
+	case *IfNode:
+	case *ListNode:
+		for _, node := range n.Nodes {
+			if !IsEmptyTree(node) {
+				return false
+			}
+		}
+		return true
+	case *RangeNode:
+	case *TemplateNode:
+	case *TextNode:
+		return len(bytes.TrimSpace(n.Text)) == 0
+	case *WithNode:
+	default:
+		panic("unknown node: " + n.String())
+	}
+	return false
+}
+
+// parse is the top-level parser for a template, essentially the same
+// as itemList except it also parses {{define}} actions.
+// It runs to EOF.
+func (t *Tree) parse() {
+	t.Root = t.newList(t.peek().pos)
+	for t.peek().typ != itemEOF {
+		if t.peek().typ == itemLeftDelim {
+			delim := t.next()
+			if t.nextNonSpace().typ == itemDefine {
+				newT := New("definition") // name will be updated once we know it.
+				newT.text = t.text
+				newT.Mode = t.Mode
+				newT.ParseName = t.ParseName
+				newT.startParse(t.funcs, t.lex, t.treeSet)
+				newT.parseDefinition()
+				continue
+			}
+			t.backup2(delim)
+		}
+		switch n := t.textOrAction(); n.Type() {
+		case nodeEnd, nodeElse:
+			t.errorf("unexpected %s", n)
+		default:
+			t.Root.append(n)
+		}
+	}
+}
+
+// parseDefinition parses a {{define}} ...  {{end}} template definition and
+// installs the definition in t.treeSet. The "define" keyword has already
+// been scanned.
+func (t *Tree) parseDefinition() {
+	const context = "define clause"
+	name := t.expectOneOf(itemString, itemRawString, context)
+	var err error
+	t.Name, err = strconv.Unquote(name.val)
+	if err != nil {
+		t.error(err)
+	}
+	t.expect(itemRightDelim, context)
+	var end Node
+	t.Root, end = t.itemList()
+	if end.Type() != nodeEnd {
+		t.errorf("unexpected %s in %s", end, context)
+	}
+	t.add()
+	t.stopParse()
+}
+
+// itemList:
+//
+//	textOrAction*
+//
+// Terminates at {{end}} or {{else}}, returned separately.
+func (t *Tree) itemList() (list *ListNode, next Node) {
+	list = t.newList(t.peekNonSpace().pos)
+	for t.peekNonSpace().typ != itemEOF {
+		n := t.textOrAction()
+		switch n.Type() {
+		case nodeEnd, nodeElse:
+			return list, n
+		}
+		list.append(n)
+	}
+	t.errorf("unexpected EOF")
+	return
+}
+
+// textOrAction:
+//
+//	text | comment | action
+func (t *Tree) textOrAction() Node {
+	switch token := t.nextNonSpace(); token.typ {
+	case itemText:
+		return t.newText(token.pos, token.val)
+	case itemLeftDelim:
+		t.actionLine = token.line
+		defer t.clearActionLine()
+		return t.action()
+	case itemComment:
+		return t.newComment(token.pos, token.val)
+	default:
+		t.unexpected(token, "input")
+	}
+	return nil
+}
+
+func (t *Tree) clearActionLine() {
+	t.actionLine = 0
+}
+
+// Action:
+//
+//	control
+//	command ("|" command)*
+//
+// Left delim is past. Now get actions.
+// First word could be a keyword such as range.
+func (t *Tree) action() (n Node) {
+	switch token := t.nextNonSpace(); token.typ {
+	case itemBlock:
+		return t.blockControl()
+	case itemBreak:
+		return t.breakControl(token.pos, token.line)
+	case itemContinue:
+		return t.continueControl(token.pos, token.line)
+	case itemElse:
+		return t.elseControl()
+	case itemEnd:
+		return t.endControl()
+	case itemIf:
+		return t.ifControl()
+	case itemRange:
+		return t.rangeControl()
+	case itemTemplate:
+		return t.templateControl()
+	case itemWith:
+		return t.withControl()
+	}
+	t.backup()
+	token := t.peek()
+	// Do not pop variables; they persist until "end".
+	return t.newAction(token.pos, token.line, t.pipeline("command", itemRightDelim))
+}
+
+// Break:
+//
+//	{{break}}
+//
+// Break keyword is past.
+func (t *Tree) breakControl(pos Pos, line int) Node {
+	if token := t.nextNonSpace(); token.typ != itemRightDelim {
+		t.unexpected(token, "{{break}}")
+	}
+	if t.rangeDepth == 0 {
+		t.errorf("{{break}} outside {{range}}")
+	}
+	return t.newBreak(pos, line)
+}
+
+// Continue:
+//
+//	{{continue}}
+//
+// Continue keyword is past.
+func (t *Tree) continueControl(pos Pos, line int) Node {
+	if token := t.nextNonSpace(); token.typ != itemRightDelim {
+		t.unexpected(token, "{{continue}}")
+	}
+	if t.rangeDepth == 0 {
+		t.errorf("{{continue}} outside {{range}}")
+	}
+	return t.newContinue(pos, line)
+}
+
+// Pipeline:
+//
+//	declarations? command ('|' command)*
+func (t *Tree) pipeline(context string, end itemType) (pipe *PipeNode) {
+	token := t.peekNonSpace()
+	pipe = t.newPipeline(token.pos, token.line, nil)
+	// Are there declarations or assignments?
+decls:
+	if v := t.peekNonSpace(); v.typ == itemVariable {
+		t.next()
+		// Since space is a token, we need 3-token look-ahead here in the worst case:
+		// in "$x foo" we need to read "foo" (as opposed to ":=") to know that $x is an
+		// argument variable rather than a declaration. So remember the token
+		// adjacent to the variable so we can push it back if necessary.
+		tokenAfterVariable := t.peek()
+		next := t.peekNonSpace()
+		switch {
+		case next.typ == itemAssign, next.typ == itemDeclare:
+			pipe.IsAssign = next.typ == itemAssign
+			t.nextNonSpace()
+			pipe.Decl = append(pipe.Decl, t.newVariable(v.pos, v.val))
+			t.vars = append(t.vars, v.val)
+		case next.typ == itemChar && next.val == ",":
+			t.nextNonSpace()
+			pipe.Decl = append(pipe.Decl, t.newVariable(v.pos, v.val))
+			t.vars = append(t.vars, v.val)
+			if context == "range" && len(pipe.Decl) < 2 {
+				switch t.peekNonSpace().typ {
+				case itemVariable, itemRightDelim, itemRightParen:
+					// second initialized variable in a range pipeline
+					goto decls
+				default:
+					t.errorf("range can only initialize variables")
+				}
+			}
+			t.errorf("too many declarations in %s", context)
+		case tokenAfterVariable.typ == itemSpace:
+			t.backup3(v, tokenAfterVariable)
+		default:
+			t.backup2(v)
+		}
+	}
+	for {
+		switch token := t.nextNonSpace(); token.typ {
+		case end:
+			// At this point, the pipeline is complete
+			t.checkPipeline(pipe, context)
+			return
+		case itemBool, itemCharConstant, itemComplex, itemDot, itemField, itemIdentifier,
+			itemNumber, itemNil, itemRawString, itemString, itemVariable, itemLeftParen:
+			t.backup()
+			pipe.append(t.command())
+		default:
+			t.unexpected(token, context)
+		}
+	}
+}
+
+func (t *Tree) checkPipeline(pipe *PipeNode, context string) {
+	// Reject empty pipelines
+	if len(pipe.Cmds) == 0 {
+		t.errorf("missing value for %s", context)
+	}
+	// Only the first command of a pipeline can start with a non executable operand
+	for i, c := range pipe.Cmds[1:] {
+		switch c.Args[0].Type() {
+		case NodeBool, NodeDot, NodeNil, NodeNumber, NodeString:
+			// With A|B|C, pipeline stage 2 is B
+			t.errorf("non executable command in pipeline stage %d", i+2)
+		}
+	}
+}
+
+func (t *Tree) parseControl(allowElseIf bool, context string) (pos Pos, line int, pipe *PipeNode, list, elseList *ListNode) {
+	defer t.popVars(len(t.vars))
+	pipe = t.pipeline(context, itemRightDelim)
+	if context == "range" {
+		t.rangeDepth++
+	}
+	var next Node
+	list, next = t.itemList()
+	if context == "range" {
+		t.rangeDepth--
+	}
+	switch next.Type() {
+	case nodeEnd: //done
+	case nodeElse:
+		if allowElseIf {
+			// Special case for "else if". If the "else" is followed immediately by an "if",
+			// the elseControl will have left the "if" token pending. Treat
+			//	{{if a}}_{{else if b}}_{{end}}
+			// as
+			//	{{if a}}_{{else}}{{if b}}_{{end}}{{end}}.
+			// To do this, parse the if as usual and stop at it {{end}}; the subsequent{{end}}
+			// is assumed. This technique works even for long if-else-if chains.
+			// TODO: Should we allow else-if in with and range?
+			if t.peek().typ == itemIf {
+				t.next() // Consume the "if" token.
+				elseList = t.newList(next.Position())
+				elseList.append(t.ifControl())
+				// Do not consume the next item - only one {{end}} required.
+				break
+			}
+		}
+		elseList, next = t.itemList()
+		if next.Type() != nodeEnd {
+			t.errorf("expected end; found %s", next)
+		}
+	}
+	return pipe.Position(), pipe.Line, pipe, list, elseList
+}
+
+// If:
+//
+//	{{if pipeline}} itemList {{end}}
+//	{{if pipeline}} itemList {{else}} itemList {{end}}
+//
+// If keyword is past.
+func (t *Tree) ifControl() Node {
+	return t.newIf(t.parseControl(true, "if"))
+}
+
+// Range:
+//
+//	{{range pipeline}} itemList {{end}}
+//	{{range pipeline}} itemList {{else}} itemList {{end}}
+//
+// Range keyword is past.
+func (t *Tree) rangeControl() Node {
+	r := t.newRange(t.parseControl(false, "range"))
+	return r
+}
+
+// With:
+//
+//	{{with pipeline}} itemList {{end}}
+//	{{with pipeline}} itemList {{else}} itemList {{end}}
+//
+// If keyword is past.
+func (t *Tree) withControl() Node {
+	return t.newWith(t.parseControl(false, "with"))
+}
+
+// End:
+//
+//	{{end}}
+//
+// End keyword is past.
+func (t *Tree) endControl() Node {
+	return t.newEnd(t.expect(itemRightDelim, "end").pos)
+}
+
+// Else:
+//
+//	{{else}}
+//
+// Else keyword is past.
+func (t *Tree) elseControl() Node {
+	// Special case for "else if".
+	peek := t.peekNonSpace()
+	if peek.typ == itemIf {
+		// We see "{{else if ... " but in effect rewrite it to {{else}}{{if ... ".
+		return t.newElse(peek.pos, peek.line)
+	}
+	token := t.expect(itemRightDelim, "else")
+	return t.newElse(token.pos, token.line)
+}
+
+// Block:
+//
+//	{{block stringValue pipeline}}
+//
+// Block keyword is past.
+// The name must be something that can evaluate to a string.
+// The pipeline is mandatory.
+func (t *Tree) blockControl() Node {
+	const context = "block clause"
+
+	token := t.nextNonSpace()
+	name := t.parseTemplateName(token, context)
+	pipe := t.pipeline(context, itemRightDelim)
+
+	block := New(name) // name will be updated once we know it.
+	block.text = t.text
+	block.Mode = t.Mode
+	block.ParseName = t.ParseName
+	block.startParse(t.funcs, t.lex, t.treeSet)
+	var end Node
+	block.Root, end = block.itemList()
+	if end.Type() != nodeEnd {
+		t.errorf("unexpected %s in %s", end, context)
+	}
+	block.add()
+	block.stopParse()
+
+	return t.newTemplate(token.pos, token.line, name, pipe)
+}
+
+// Template:
+//
+//	{{template stringValue pipeline}}
+//
+// Template keyword is past. The name must be something that can evaluate
+// to a string.
+func (t *Tree) templateControl() Node {
+	const context = "template clause"
+	token := t.nextNonSpace()
+	name := t.parseTemplateName(token, context)
+	var pipe *PipeNode
+	if t.nextNonSpace().typ != itemRightDelim {
+		t.backup()
+		// Do not pop variables; they persist until "end".
+		pipe = t.pipeline(context, itemRightDelim)
+	}
+	return t.newTemplate(token.pos, token.line, name, pipe)
+}
+
+func (t *Tree) parseTemplateName(token item, context string) (name string) {
+	switch token.typ {
+	case itemString, itemRawString:
+		s, err := strconv.Unquote(token.val)
+		if err != nil {
+			t.error(err)
+		}
+		name = s
+	default:
+		t.unexpected(token, context)
+	}
+	return
+}
+
+// command:
+//
+//	operand (space operand)*
+//
+// space-separated arguments up to a pipeline character or right delimiter.
+// we consume the pipe character but leave the right delim to terminate the action.
+func (t *Tree) command() *CommandNode {
+	cmd := t.newCommand(t.peekNonSpace().pos)
+	for {
+		t.peekNonSpace() // skip leading spaces.
+		operand := t.operand()
+		if operand != nil {
+			cmd.append(operand)
+		}
+		switch token := t.next(); token.typ {
+		case itemSpace:
+			continue
+		case itemRightDelim, itemRightParen:
+			t.backup()
+		case itemPipe:
+			// nothing here; break loop below
+		default:
+			t.unexpected(token, "operand")
+		}
+		break
+	}
+	if len(cmd.Args) == 0 {
+		t.errorf("empty command")
+	}
+	return cmd
+}
+
+// operand:
+//
+//	term .Field*
+//
+// An operand is a space-separated component of a command,
+// a term possibly followed by field accesses.
+// A nil return means the next item is not an operand.
+func (t *Tree) operand() Node {
+	node := t.term()
+	if node == nil {
+		return nil
+	}
+	if t.peek().typ == itemField {
+		chain := t.newChain(t.peek().pos, node)
+		for t.peek().typ == itemField {
+			chain.Add(t.next().val)
+		}
+		// Compatibility with original API: If the term is of type NodeField
+		// or NodeVariable, just put more fields on the original.
+		// Otherwise, keep the Chain node.
+		// Obvious parsing errors involving literal values are detected here.
+		// More complex error cases will have to be handled at execution time.
+		switch node.Type() {
+		case NodeField:
+			node = t.newField(chain.Position(), chain.String())
+		case NodeVariable:
+			node = t.newVariable(chain.Position(), chain.String())
+		case NodeBool, NodeString, NodeNumber, NodeNil, NodeDot:
+			t.errorf("unexpected . after term %q", node.String())
+		default:
+			node = chain
+		}
+	}
+	return node
+}
+
+// term:
+//
+//	literal (number, string, nil, boolean)
+//	function (identifier)
+//	.
+//	.Field
+//	$
+//	'(' pipeline ')'
+//
+// A term is a simple "expression".
+// A nil return means the next item is not a term.
+func (t *Tree) term() Node {
+	switch token := t.nextNonSpace(); token.typ {
+	case itemIdentifier:
+		checkFunc := t.Mode&SkipFuncCheck == 0
+		if checkFunc && !t.hasFunction(token.val) {
+			t.errorf("function %q not defined", token.val)
+		}
+		return NewIdentifier(token.val).SetTree(t).SetPos(token.pos)
+	case itemDot:
+		return t.newDot(token.pos)
+	case itemNil:
+		return t.newNil(token.pos)
+	case itemVariable:
+		return t.useVar(token.pos, token.val)
+	case itemField:
+		return t.newField(token.pos, token.val)
+	case itemBool:
+		return t.newBool(token.pos, token.val == "true")
+	case itemCharConstant, itemComplex, itemNumber:
+		number, err := t.newNumber(token.pos, token.val, token.typ)
+		if err != nil {
+			t.error(err)
+		}
+		return number
+	case itemLeftParen:
+		return t.pipeline("parenthesized pipeline", itemRightParen)
+	case itemString, itemRawString:
+		s, err := strconv.Unquote(token.val)
+		if err != nil {
+			t.error(err)
+		}
+		return t.newString(token.pos, token.val, s)
+	}
+	t.backup()
+	return nil
+}
+
+// hasFunction reports if a function name exists in the Tree's maps.
+func (t *Tree) hasFunction(name string) bool {
+	for _, funcMap := range t.funcs {
+		if funcMap == nil {
+			continue
+		}
+		if funcMap[name] != nil {
+			return true
+		}
+	}
+	return false
+}
+
+// popVars trims the variable list to the specified length
+func (t *Tree) popVars(n int) {
+	t.vars = t.vars[:n]
+}
+
+// useVar returns a node for a variable reference. It errors if the
+// variable is not defined.
+func (t *Tree) useVar(pos Pos, name string) Node {
+	v := t.newVariable(pos, name)
+	for _, varName := range t.vars {
+		if varName == v.Ident[0] {
+			return v
+		}
+	}
+	t.errorf("undefined variable %q", v.Ident[0])
+	return nil
+}
diff --git a/src/text/template/parse/parse_test.go b/src/text/template/parse/parse_test.go
new file mode 100644
index 0000000..59e0a17
--- /dev/null
+++ b/src/text/template/parse/parse_test.go
@@ -0,0 +1,711 @@
+// 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 (
+	"flag"
+	"fmt"
+	"strings"
+	"testing"
+)
+
+var debug = flag.Bool("debug", false, "show the errors produced by the main tests")
+
+type numberTest struct {
+	text      string
+	isInt     bool
+	isUint    bool
+	isFloat   bool
+	isComplex bool
+	int64
+	uint64
+	float64
+	complex128
+}
+
+var numberTests = []numberTest{
+	// basics
+	{"0", true, true, true, false, 0, 0, 0, 0},
+	{"-0", true, true, true, false, 0, 0, 0, 0}, // check that -0 is a uint.
+	{"73", true, true, true, false, 73, 73, 73, 0},
+	{"7_3", true, true, true, false, 73, 73, 73, 0},
+	{"0b10_010_01", true, true, true, false, 73, 73, 73, 0},
+	{"0B10_010_01", true, true, true, false, 73, 73, 73, 0},
+	{"073", true, true, true, false, 073, 073, 073, 0},
+	{"0o73", true, true, true, false, 073, 073, 073, 0},
+	{"0O73", true, true, true, false, 073, 073, 073, 0},
+	{"0x73", true, true, true, false, 0x73, 0x73, 0x73, 0},
+	{"0X73", true, true, true, false, 0x73, 0x73, 0x73, 0},
+	{"0x7_3", true, true, true, false, 0x73, 0x73, 0x73, 0},
+	{"-73", true, false, true, false, -73, 0, -73, 0},
+	{"+73", true, false, true, false, 73, 0, 73, 0},
+	{"100", true, true, true, false, 100, 100, 100, 0},
+	{"1e9", true, true, true, false, 1e9, 1e9, 1e9, 0},
+	{"-1e9", true, false, true, false, -1e9, 0, -1e9, 0},
+	{"-1.2", false, false, true, false, 0, 0, -1.2, 0},
+	{"1e19", false, true, true, false, 0, 1e19, 1e19, 0},
+	{"1e1_9", false, true, true, false, 0, 1e19, 1e19, 0},
+	{"1E19", false, true, true, false, 0, 1e19, 1e19, 0},
+	{"-1e19", false, false, true, false, 0, 0, -1e19, 0},
+	{"0x_1p4", true, true, true, false, 16, 16, 16, 0},
+	{"0X_1P4", true, true, true, false, 16, 16, 16, 0},
+	{"0x_1p-4", false, false, true, false, 0, 0, 1 / 16., 0},
+	{"4i", false, false, false, true, 0, 0, 0, 4i},
+	{"-1.2+4.2i", false, false, false, true, 0, 0, 0, -1.2 + 4.2i},
+	{"073i", false, false, false, true, 0, 0, 0, 73i}, // not octal!
+	// complex with 0 imaginary are float (and maybe integer)
+	{"0i", true, true, true, true, 0, 0, 0, 0},
+	{"-1.2+0i", false, false, true, true, 0, 0, -1.2, -1.2},
+	{"-12+0i", true, false, true, true, -12, 0, -12, -12},
+	{"13+0i", true, true, true, true, 13, 13, 13, 13},
+	// funny bases
+	{"0123", true, true, true, false, 0123, 0123, 0123, 0},
+	{"-0x0", true, true, true, false, 0, 0, 0, 0},
+	{"0xdeadbeef", true, true, true, false, 0xdeadbeef, 0xdeadbeef, 0xdeadbeef, 0},
+	// character constants
+	{`'a'`, true, true, true, false, 'a', 'a', 'a', 0},
+	{`'\n'`, true, true, true, false, '\n', '\n', '\n', 0},
+	{`'\\'`, true, true, true, false, '\\', '\\', '\\', 0},
+	{`'\''`, true, true, true, false, '\'', '\'', '\'', 0},
+	{`'\xFF'`, true, true, true, false, 0xFF, 0xFF, 0xFF, 0},
+	{`'パ'`, true, true, true, false, 0x30d1, 0x30d1, 0x30d1, 0},
+	{`'\u30d1'`, true, true, true, false, 0x30d1, 0x30d1, 0x30d1, 0},
+	{`'\U000030d1'`, true, true, true, false, 0x30d1, 0x30d1, 0x30d1, 0},
+	// some broken syntax
+	{text: "+-2"},
+	{text: "0x123."},
+	{text: "1e."},
+	{text: "0xi."},
+	{text: "1+2."},
+	{text: "'x"},
+	{text: "'xx'"},
+	{text: "'433937734937734969526500969526500'"}, // Integer too large - issue 10634.
+	// Issue 8622 - 0xe parsed as floating point. Very embarrassing.
+	{"0xef", true, true, true, false, 0xef, 0xef, 0xef, 0},
+}
+
+func TestNumberParse(t *testing.T) {
+	for _, test := range numberTests {
+		// If fmt.Sscan thinks it's complex, it's complex. We can't trust the output
+		// because imaginary comes out as a number.
+		var c complex128
+		typ := itemNumber
+		var tree *Tree
+		if test.text[0] == '\'' {
+			typ = itemCharConstant
+		} else {
+			_, err := fmt.Sscan(test.text, &c)
+			if err == nil {
+				typ = itemComplex
+			}
+		}
+		n, err := tree.newNumber(0, test.text, typ)
+		ok := test.isInt || test.isUint || test.isFloat || test.isComplex
+		if ok && err != nil {
+			t.Errorf("unexpected error for %q: %s", test.text, err)
+			continue
+		}
+		if !ok && err == nil {
+			t.Errorf("expected error for %q", test.text)
+			continue
+		}
+		if !ok {
+			if *debug {
+				fmt.Printf("%s\n\t%s\n", test.text, err)
+			}
+			continue
+		}
+		if n.IsComplex != test.isComplex {
+			t.Errorf("complex incorrect for %q; should be %t", test.text, test.isComplex)
+		}
+		if test.isInt {
+			if !n.IsInt {
+				t.Errorf("expected integer for %q", test.text)
+			}
+			if n.Int64 != test.int64 {
+				t.Errorf("int64 for %q should be %d Is %d", test.text, test.int64, n.Int64)
+			}
+		} else if n.IsInt {
+			t.Errorf("did not expect integer for %q", test.text)
+		}
+		if test.isUint {
+			if !n.IsUint {
+				t.Errorf("expected unsigned integer for %q", test.text)
+			}
+			if n.Uint64 != test.uint64 {
+				t.Errorf("uint64 for %q should be %d Is %d", test.text, test.uint64, n.Uint64)
+			}
+		} else if n.IsUint {
+			t.Errorf("did not expect unsigned integer for %q", test.text)
+		}
+		if test.isFloat {
+			if !n.IsFloat {
+				t.Errorf("expected float for %q", test.text)
+			}
+			if n.Float64 != test.float64 {
+				t.Errorf("float64 for %q should be %g Is %g", test.text, test.float64, n.Float64)
+			}
+		} else if n.IsFloat {
+			t.Errorf("did not expect float for %q", test.text)
+		}
+		if test.isComplex {
+			if !n.IsComplex {
+				t.Errorf("expected complex for %q", test.text)
+			}
+			if n.Complex128 != test.complex128 {
+				t.Errorf("complex128 for %q should be %g Is %g", test.text, test.complex128, n.Complex128)
+			}
+		} else if n.IsComplex {
+			t.Errorf("did not expect complex for %q", test.text)
+		}
+	}
+}
+
+type parseTest struct {
+	name   string
+	input  string
+	ok     bool
+	result string // what the user would see in an error message.
+}
+
+const (
+	noError  = true
+	hasError = false
+)
+
+var parseTests = []parseTest{
+	{"empty", "", noError,
+		``},
+	{"comment", "{{/*\n\n\n*/}}", noError,
+		``},
+	{"spaces", " \t\n", noError,
+		`" \t\n"`},
+	{"text", "some text", noError,
+		`"some text"`},
+	{"emptyAction", "{{}}", hasError,
+		`{{}}`},
+	{"field", "{{.X}}", noError,
+		`{{.X}}`},
+	{"simple command", "{{printf}}", noError,
+		`{{printf}}`},
+	{"$ invocation", "{{$}}", noError,
+		"{{$}}"},
+	{"variable invocation", "{{with $x := 3}}{{$x 23}}{{end}}", noError,
+		"{{with $x := 3}}{{$x 23}}{{end}}"},
+	{"variable with fields", "{{$.I}}", noError,
+		"{{$.I}}"},
+	{"multi-word command", "{{printf `%d` 23}}", noError,
+		"{{printf `%d` 23}}"},
+	{"pipeline", "{{.X|.Y}}", noError,
+		`{{.X | .Y}}`},
+	{"pipeline with decl", "{{$x := .X|.Y}}", noError,
+		`{{$x := .X | .Y}}`},
+	{"nested pipeline", "{{.X (.Y .Z) (.A | .B .C) (.E)}}", noError,
+		`{{.X (.Y .Z) (.A | .B .C) (.E)}}`},
+	{"field applied to parentheses", "{{(.Y .Z).Field}}", noError,
+		`{{(.Y .Z).Field}}`},
+	{"simple if", "{{if .X}}hello{{end}}", noError,
+		`{{if .X}}"hello"{{end}}`},
+	{"if with else", "{{if .X}}true{{else}}false{{end}}", noError,
+		`{{if .X}}"true"{{else}}"false"{{end}}`},
+	{"if with else if", "{{if .X}}true{{else if .Y}}false{{end}}", noError,
+		`{{if .X}}"true"{{else}}{{if .Y}}"false"{{end}}{{end}}`},
+	{"if else chain", "+{{if .X}}X{{else if .Y}}Y{{else if .Z}}Z{{end}}+", noError,
+		`"+"{{if .X}}"X"{{else}}{{if .Y}}"Y"{{else}}{{if .Z}}"Z"{{end}}{{end}}{{end}}"+"`},
+	{"simple range", "{{range .X}}hello{{end}}", noError,
+		`{{range .X}}"hello"{{end}}`},
+	{"chained field range", "{{range .X.Y.Z}}hello{{end}}", noError,
+		`{{range .X.Y.Z}}"hello"{{end}}`},
+	{"nested range", "{{range .X}}hello{{range .Y}}goodbye{{end}}{{end}}", noError,
+		`{{range .X}}"hello"{{range .Y}}"goodbye"{{end}}{{end}}`},
+	{"range with else", "{{range .X}}true{{else}}false{{end}}", noError,
+		`{{range .X}}"true"{{else}}"false"{{end}}`},
+	{"range over pipeline", "{{range .X|.M}}true{{else}}false{{end}}", noError,
+		`{{range .X | .M}}"true"{{else}}"false"{{end}}`},
+	{"range []int", "{{range .SI}}{{.}}{{end}}", noError,
+		`{{range .SI}}{{.}}{{end}}`},
+	{"range 1 var", "{{range $x := .SI}}{{.}}{{end}}", noError,
+		`{{range $x := .SI}}{{.}}{{end}}`},
+	{"range 2 vars", "{{range $x, $y := .SI}}{{.}}{{end}}", noError,
+		`{{range $x, $y := .SI}}{{.}}{{end}}`},
+	{"range with break", "{{range .SI}}{{.}}{{break}}{{end}}", noError,
+		`{{range .SI}}{{.}}{{break}}{{end}}`},
+	{"range with continue", "{{range .SI}}{{.}}{{continue}}{{end}}", noError,
+		`{{range .SI}}{{.}}{{continue}}{{end}}`},
+	{"constants", "{{range .SI 1 -3.2i true false 'a' nil}}{{end}}", noError,
+		`{{range .SI 1 -3.2i true false 'a' nil}}{{end}}`},
+	{"template", "{{template `x`}}", noError,
+		`{{template "x"}}`},
+	{"template with arg", "{{template `x` .Y}}", noError,
+		`{{template "x" .Y}}`},
+	{"with", "{{with .X}}hello{{end}}", noError,
+		`{{with .X}}"hello"{{end}}`},
+	{"with with else", "{{with .X}}hello{{else}}goodbye{{end}}", noError,
+		`{{with .X}}"hello"{{else}}"goodbye"{{end}}`},
+	// Trimming spaces.
+	{"trim left", "x \r\n\t{{- 3}}", noError, `"x"{{3}}`},
+	{"trim right", "{{3 -}}\n\n\ty", noError, `{{3}}"y"`},
+	{"trim left and right", "x \r\n\t{{- 3 -}}\n\n\ty", noError, `"x"{{3}}"y"`},
+	{"trim with extra spaces", "x\n{{-  3   -}}\ny", noError, `"x"{{3}}"y"`},
+	{"comment trim left", "x \r\n\t{{- /* hi */}}", noError, `"x"`},
+	{"comment trim right", "{{/* hi */ -}}\n\n\ty", noError, `"y"`},
+	{"comment trim left and right", "x \r\n\t{{- /* */ -}}\n\n\ty", noError, `"x""y"`},
+	{"block definition", `{{block "foo" .}}hello{{end}}`, noError,
+		`{{template "foo" .}}`},
+
+	{"newline in assignment", "{{ $x \n := \n 1 \n }}", noError, "{{$x := 1}}"},
+	{"newline in empty action", "{{\n}}", hasError, "{{\n}}"},
+	{"newline in pipeline", "{{\n\"x\"\n|\nprintf\n}}", noError, `{{"x" | printf}}`},
+	{"newline in comment", "{{/*\nhello\n*/}}", noError, ""},
+	{"newline in comment", "{{-\n/*\nhello\n*/\n-}}", noError, ""},
+	{"spaces around continue", "{{range .SI}}{{.}}{{ continue }}{{end}}", noError,
+		`{{range .SI}}{{.}}{{continue}}{{end}}`},
+	{"spaces around break", "{{range .SI}}{{.}}{{ break }}{{end}}", noError,
+		`{{range .SI}}{{.}}{{break}}{{end}}`},
+
+	// Errors.
+	{"unclosed action", "hello{{range", hasError, ""},
+	{"unmatched end", "{{end}}", hasError, ""},
+	{"unmatched else", "{{else}}", hasError, ""},
+	{"unmatched else after if", "{{if .X}}hello{{end}}{{else}}", hasError, ""},
+	{"multiple else", "{{if .X}}1{{else}}2{{else}}3{{end}}", hasError, ""},
+	{"missing end", "hello{{range .x}}", hasError, ""},
+	{"missing end after else", "hello{{range .x}}{{else}}", hasError, ""},
+	{"undefined function", "hello{{undefined}}", hasError, ""},
+	{"undefined variable", "{{$x}}", hasError, ""},
+	{"variable undefined after end", "{{with $x := 4}}{{end}}{{$x}}", hasError, ""},
+	{"variable undefined in template", "{{template $v}}", hasError, ""},
+	{"declare with field", "{{with $x.Y := 4}}{{end}}", hasError, ""},
+	{"template with field ref", "{{template .X}}", hasError, ""},
+	{"template with var", "{{template $v}}", hasError, ""},
+	{"invalid punctuation", "{{printf 3, 4}}", hasError, ""},
+	{"multidecl outside range", "{{with $v, $u := 3}}{{end}}", hasError, ""},
+	{"too many decls in range", "{{range $u, $v, $w := 3}}{{end}}", hasError, ""},
+	{"dot applied to parentheses", "{{printf (printf .).}}", hasError, ""},
+	{"adjacent args", "{{printf 3`x`}}", hasError, ""},
+	{"adjacent args with .", "{{printf `x`.}}", hasError, ""},
+	{"extra end after if", "{{if .X}}a{{else if .Y}}b{{end}}{{end}}", hasError, ""},
+	{"break outside range", "{{range .}}{{end}} {{break}}", hasError, ""},
+	{"continue outside range", "{{range .}}{{end}} {{continue}}", hasError, ""},
+	{"break in range else", "{{range .}}{{else}}{{break}}{{end}}", hasError, ""},
+	{"continue in range else", "{{range .}}{{else}}{{continue}}{{end}}", hasError, ""},
+	// Other kinds of assignments and operators aren't available yet.
+	{"bug0a", "{{$x := 0}}{{$x}}", noError, "{{$x := 0}}{{$x}}"},
+	{"bug0b", "{{$x += 1}}{{$x}}", hasError, ""},
+	{"bug0c", "{{$x ! 2}}{{$x}}", hasError, ""},
+	{"bug0d", "{{$x % 3}}{{$x}}", hasError, ""},
+	// Check the parse fails for := rather than comma.
+	{"bug0e", "{{range $x := $y := 3}}{{end}}", hasError, ""},
+	// Another bug: variable read must ignore following punctuation.
+	{"bug1a", "{{$x:=.}}{{$x!2}}", hasError, ""},                     // ! is just illegal here.
+	{"bug1b", "{{$x:=.}}{{$x+2}}", hasError, ""},                     // $x+2 should not parse as ($x) (+2).
+	{"bug1c", "{{$x:=.}}{{$x +2}}", noError, "{{$x := .}}{{$x +2}}"}, // It's OK with a space.
+	// dot following a literal value
+	{"dot after integer", "{{1.E}}", hasError, ""},
+	{"dot after float", "{{0.1.E}}", hasError, ""},
+	{"dot after boolean", "{{true.E}}", hasError, ""},
+	{"dot after char", "{{'a'.any}}", hasError, ""},
+	{"dot after string", `{{"hello".guys}}`, hasError, ""},
+	{"dot after dot", "{{..E}}", hasError, ""},
+	{"dot after nil", "{{nil.E}}", hasError, ""},
+	// Wrong pipeline
+	{"wrong pipeline dot", "{{12|.}}", hasError, ""},
+	{"wrong pipeline number", "{{.|12|printf}}", hasError, ""},
+	{"wrong pipeline string", "{{.|printf|\"error\"}}", hasError, ""},
+	{"wrong pipeline char", "{{12|printf|'e'}}", hasError, ""},
+	{"wrong pipeline boolean", "{{.|true}}", hasError, ""},
+	{"wrong pipeline nil", "{{'c'|nil}}", hasError, ""},
+	{"empty pipeline", `{{printf "%d" ( ) }}`, hasError, ""},
+	// Missing pipeline in block
+	{"block definition", `{{block "foo"}}hello{{end}}`, hasError, ""},
+}
+
+var builtins = map[string]any{
+	"printf":   fmt.Sprintf,
+	"contains": strings.Contains,
+}
+
+func testParse(doCopy bool, t *testing.T) {
+	textFormat = "%q"
+	defer func() { textFormat = "%s" }()
+	for _, test := range parseTests {
+		tmpl, err := New(test.name).Parse(test.input, "", "", make(map[string]*Tree), builtins)
+		switch {
+		case err == nil && !test.ok:
+			t.Errorf("%q: expected error; got none", test.name)
+			continue
+		case err != nil && test.ok:
+			t.Errorf("%q: unexpected error: %v", test.name, err)
+			continue
+		case err != nil && !test.ok:
+			// expected error, got one
+			if *debug {
+				fmt.Printf("%s: %s\n\t%s\n", test.name, test.input, err)
+			}
+			continue
+		}
+		var result string
+		if doCopy {
+			result = tmpl.Root.Copy().String()
+		} else {
+			result = tmpl.Root.String()
+		}
+		if result != test.result {
+			t.Errorf("%s=(%q): got\n\t%v\nexpected\n\t%v", test.name, test.input, result, test.result)
+		}
+	}
+}
+
+func TestParse(t *testing.T) {
+	testParse(false, t)
+}
+
+// Same as TestParse, but we copy the node first
+func TestParseCopy(t *testing.T) {
+	testParse(true, t)
+}
+
+func TestParseWithComments(t *testing.T) {
+	textFormat = "%q"
+	defer func() { textFormat = "%s" }()
+	tests := [...]parseTest{
+		{"comment", "{{/*\n\n\n*/}}", noError, "{{/*\n\n\n*/}}"},
+		{"comment trim left", "x \r\n\t{{- /* hi */}}", noError, `"x"{{/* hi */}}`},
+		{"comment trim right", "{{/* hi */ -}}\n\n\ty", noError, `{{/* hi */}}"y"`},
+		{"comment trim left and right", "x \r\n\t{{- /* */ -}}\n\n\ty", noError, `"x"{{/* */}}"y"`},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			tr := New(test.name)
+			tr.Mode = ParseComments
+			tmpl, err := tr.Parse(test.input, "", "", make(map[string]*Tree))
+			if err != nil {
+				t.Errorf("%q: expected error; got none", test.name)
+			}
+			if result := tmpl.Root.String(); result != test.result {
+				t.Errorf("%s=(%q): got\n\t%v\nexpected\n\t%v", test.name, test.input, result, test.result)
+			}
+		})
+	}
+}
+
+func TestKeywordsAndFuncs(t *testing.T) {
+	// Check collisions between functions and new keywords like 'break'. When a
+	// break function is provided, the parser should treat 'break' as a function,
+	// not a keyword.
+	textFormat = "%q"
+	defer func() { textFormat = "%s" }()
+
+	inp := `{{range .X}}{{break 20}}{{end}}`
+	{
+		// 'break' is a defined function, don't treat it as a keyword: it should
+		// accept an argument successfully.
+		var funcsWithKeywordFunc = map[string]any{
+			"break": func(in any) any { return in },
+		}
+		tmpl, err := New("").Parse(inp, "", "", make(map[string]*Tree), funcsWithKeywordFunc)
+		if err != nil || tmpl == nil {
+			t.Errorf("with break func: unexpected error: %v", err)
+		}
+	}
+
+	{
+		// No function called 'break'; treat it as a keyword. Results in a parse
+		// error.
+		tmpl, err := New("").Parse(inp, "", "", make(map[string]*Tree), make(map[string]any))
+		if err == nil || tmpl != nil {
+			t.Errorf("without break func: expected error; got none")
+		}
+	}
+}
+
+func TestSkipFuncCheck(t *testing.T) {
+	oldTextFormat := textFormat
+	textFormat = "%q"
+	defer func() { textFormat = oldTextFormat }()
+	tr := New("skip func check")
+	tr.Mode = SkipFuncCheck
+	tmpl, err := tr.Parse("{{fn 1 2}}", "", "", make(map[string]*Tree))
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	expected := "{{fn 1 2}}"
+	if result := tmpl.Root.String(); result != expected {
+		t.Errorf("got\n\t%v\nexpected\n\t%v", result, expected)
+	}
+}
+
+type isEmptyTest struct {
+	name  string
+	input string
+	empty bool
+}
+
+var isEmptyTests = []isEmptyTest{
+	{"empty", ``, true},
+	{"nonempty", `hello`, false},
+	{"spaces only", " \t\n \t\n", true},
+	{"comment only", "{{/* comment */}}", true},
+	{"definition", `{{define "x"}}something{{end}}`, true},
+	{"definitions and space", "{{define `x`}}something{{end}}\n\n{{define `y`}}something{{end}}\n\n", true},
+	{"definitions and text", "{{define `x`}}something{{end}}\nx\n{{define `y`}}something{{end}}\ny\n", false},
+	{"definition and action", "{{define `x`}}something{{end}}{{if 3}}foo{{end}}", false},
+}
+
+func TestIsEmpty(t *testing.T) {
+	if !IsEmptyTree(nil) {
+		t.Errorf("nil tree is not empty")
+	}
+	for _, test := range isEmptyTests {
+		tree, err := New("root").Parse(test.input, "", "", make(map[string]*Tree), nil)
+		if err != nil {
+			t.Errorf("%q: unexpected error: %v", test.name, err)
+			continue
+		}
+		if empty := IsEmptyTree(tree.Root); empty != test.empty {
+			t.Errorf("%q: expected %t got %t", test.name, test.empty, empty)
+		}
+	}
+}
+
+func TestErrorContextWithTreeCopy(t *testing.T) {
+	tree, err := New("root").Parse("{{if true}}{{end}}", "", "", make(map[string]*Tree), nil)
+	if err != nil {
+		t.Fatalf("unexpected tree parse failure: %v", err)
+	}
+	treeCopy := tree.Copy()
+	wantLocation, wantContext := tree.ErrorContext(tree.Root.Nodes[0])
+	gotLocation, gotContext := treeCopy.ErrorContext(treeCopy.Root.Nodes[0])
+	if wantLocation != gotLocation {
+		t.Errorf("wrong error location want %q got %q", wantLocation, gotLocation)
+	}
+	if wantContext != gotContext {
+		t.Errorf("wrong error location want %q got %q", wantContext, gotContext)
+	}
+}
+
+// All failures, and the result is a string that must appear in the error message.
+var errorTests = []parseTest{
+	// Check line numbers are accurate.
+	{"unclosed1",
+		"line1\n{{",
+		hasError, `unclosed1:2: unclosed action`},
+	{"unclosed2",
+		"line1\n{{define `x`}}line2\n{{",
+		hasError, `unclosed2:3: unclosed action`},
+	{"unclosed3",
+		"line1\n{{\"x\"\n\"y\"\n",
+		hasError, `unclosed3:4: unclosed action started at unclosed3:2`},
+	{"unclosed4",
+		"{{\n\n\n\n\n",
+		hasError, `unclosed4:6: unclosed action started at unclosed4:1`},
+	{"var1",
+		"line1\n{{\nx\n}}",
+		hasError, `var1:3: function "x" not defined`},
+	// Specific errors.
+	{"function",
+		"{{foo}}",
+		hasError, `function "foo" not defined`},
+	{"comment1",
+		"{{/*}}",
+		hasError, `comment1:1: unclosed comment`},
+	{"comment2",
+		"{{/*\nhello\n}}",
+		hasError, `comment2:1: unclosed comment`},
+	{"lparen",
+		"{{.X (1 2 3}}",
+		hasError, `unclosed left paren`},
+	{"rparen",
+		"{{.X 1 2 3 ) }}",
+		hasError, "unexpected right paren"},
+	{"rparen2",
+		"{{(.X 1 2 3",
+		hasError, `unclosed action`},
+	{"space",
+		"{{`x`3}}",
+		hasError, `in operand`},
+	{"idchar",
+		"{{a#}}",
+		hasError, `'#'`},
+	{"charconst",
+		"{{'a}}",
+		hasError, `unterminated character constant`},
+	{"stringconst",
+		`{{"a}}`,
+		hasError, `unterminated quoted string`},
+	{"rawstringconst",
+		"{{`a}}",
+		hasError, `unterminated raw quoted string`},
+	{"number",
+		"{{0xi}}",
+		hasError, `number syntax`},
+	{"multidefine",
+		"{{define `a`}}a{{end}}{{define `a`}}b{{end}}",
+		hasError, `multiple definition of template`},
+	{"eof",
+		"{{range .X}}",
+		hasError, `unexpected EOF`},
+	{"variable",
+		// Declare $x so it's defined, to avoid that error, and then check we don't parse a declaration.
+		"{{$x := 23}}{{with $x.y := 3}}{{$x 23}}{{end}}",
+		hasError, `unexpected ":="`},
+	{"multidecl",
+		"{{$a,$b,$c := 23}}",
+		hasError, `too many declarations`},
+	{"undefvar",
+		"{{$a}}",
+		hasError, `undefined variable`},
+	{"wrongdot",
+		"{{true.any}}",
+		hasError, `unexpected . after term`},
+	{"wrongpipeline",
+		"{{12|false}}",
+		hasError, `non executable command in pipeline`},
+	{"emptypipeline",
+		`{{ ( ) }}`,
+		hasError, `missing value for parenthesized pipeline`},
+	{"multilinerawstring",
+		"{{ $v := `\n` }} {{",
+		hasError, `multilinerawstring:2: unclosed action`},
+	{"rangeundefvar",
+		"{{range $k}}{{end}}",
+		hasError, `undefined variable`},
+	{"rangeundefvars",
+		"{{range $k, $v}}{{end}}",
+		hasError, `undefined variable`},
+	{"rangemissingvalue1",
+		"{{range $k,}}{{end}}",
+		hasError, `missing value for range`},
+	{"rangemissingvalue2",
+		"{{range $k, $v := }}{{end}}",
+		hasError, `missing value for range`},
+	{"rangenotvariable1",
+		"{{range $k, .}}{{end}}",
+		hasError, `range can only initialize variables`},
+	{"rangenotvariable2",
+		"{{range $k, 123 := .}}{{end}}",
+		hasError, `range can only initialize variables`},
+}
+
+func TestErrors(t *testing.T) {
+	for _, test := range errorTests {
+		t.Run(test.name, func(t *testing.T) {
+			_, err := New(test.name).Parse(test.input, "", "", make(map[string]*Tree))
+			if err == nil {
+				t.Fatalf("expected error %q, got nil", test.result)
+			}
+			if !strings.Contains(err.Error(), test.result) {
+				t.Fatalf("error %q does not contain %q", err, test.result)
+			}
+		})
+	}
+}
+
+func TestBlock(t *testing.T) {
+	const (
+		input = `a{{block "inner" .}}bar{{.}}baz{{end}}b`
+		outer = `a{{template "inner" .}}b`
+		inner = `bar{{.}}baz`
+	)
+	treeSet := make(map[string]*Tree)
+	tmpl, err := New("outer").Parse(input, "", "", treeSet, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if g, w := tmpl.Root.String(), outer; g != w {
+		t.Errorf("outer template = %q, want %q", g, w)
+	}
+	inTmpl := treeSet["inner"]
+	if inTmpl == nil {
+		t.Fatal("block did not define template")
+	}
+	if g, w := inTmpl.Root.String(), inner; g != w {
+		t.Errorf("inner template = %q, want %q", g, w)
+	}
+}
+
+func TestLineNum(t *testing.T) {
+	// const count = 100
+	const count = 3
+	text := strings.Repeat("{{printf 1234}}\n", count)
+	tree, err := New("bench").Parse(text, "", "", make(map[string]*Tree), builtins)
+	if err != nil {
+		t.Fatal(err)
+	}
+	// Check the line numbers. Each line is an action containing a template, followed by text.
+	// That's two nodes per line.
+	nodes := tree.Root.Nodes
+	for i := 0; i < len(nodes); i += 2 {
+		line := 1 + i/2
+		// Action first.
+		action := nodes[i].(*ActionNode)
+		if action.Line != line {
+			t.Errorf("line %d: action is line %d", line, action.Line)
+		}
+		pipe := action.Pipe
+		if pipe.Line != line {
+			t.Errorf("line %d: pipe is line %d", line, pipe.Line)
+		}
+	}
+}
+
+func BenchmarkParseLarge(b *testing.B) {
+	text := strings.Repeat("{{1234}}\n", 10000)
+	for i := 0; i < b.N; i++ {
+		_, err := New("bench").Parse(text, "", "", make(map[string]*Tree), builtins)
+		if err != nil {
+			b.Fatal(err)
+		}
+	}
+}
+
+var sinkv, sinkl string
+
+func BenchmarkVariableString(b *testing.B) {
+	v := &VariableNode{
+		Ident: []string{"$", "A", "BB", "CCC", "THIS_IS_THE_VARIABLE_BEING_PROCESSED"},
+	}
+	b.ResetTimer()
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		sinkv = v.String()
+	}
+	if sinkv == "" {
+		b.Fatal("Benchmark was not run")
+	}
+}
+
+func BenchmarkListString(b *testing.B) {
+	text := `
+{{(printf .Field1.Field2.Field3).Value}}
+{{$x := (printf .Field1.Field2.Field3).Value}}
+{{$y := (printf $x.Field1.Field2.Field3).Value}}
+{{$z := $y.Field1.Field2.Field3}}
+{{if contains $y $z}}
+	{{printf "%q" $y}}
+{{else}}
+	{{printf "%q" $x}}
+{{end}}
+{{with $z.Field1 | contains "boring"}}
+	{{printf "%q" . | printf "%s"}}
+{{else}}
+	{{printf "%d %d %d" 11 11 11}}
+	{{printf "%d %d %s" 22 22 $x.Field1.Field2.Field3 | printf "%s"}}
+	{{printf "%v" (contains $z.Field1.Field2 $y)}}
+{{end}}
+`
+	tree, err := New("bench").Parse(text, "", "", make(map[string]*Tree), builtins)
+	if err != nil {
+		b.Fatal(err)
+	}
+	b.ResetTimer()
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		sinkl = tree.Root.String()
+	}
+	if sinkl == "" {
+		b.Fatal("Benchmark was not run")
+	}
+}