1 files changed, 472 insertions, 0 deletions
diff --git a/src/pkg/template/parse/lex.go b/src/pkg/template/parse/lex.go
new file mode 100644
index 000000000..83ad6c628
--- /dev/null
+++ b/src/pkg/template/parse/lex.go
@@ -0,0 +1,472 @@
+// 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"
+	"utf8"
+)
+
+// item represents a token or text string returned from the scanner.
+type item struct {
+	typ itemType
+	val string
+}
+
+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
+	itemComplex                      // complex constant (1+2i); imaginary is just a number
+	itemColonEquals                  // colon-equals (':=') introducing a declaration
+	itemEOF
+	itemField      // alphanumeric identifier, starting with '.', possibly chained ('.x.y')
+	itemIdentifier // alphanumeric identifier
+	itemLeftDelim  // left action delimiter
+	itemNumber     // simple number, including imaginary
+	itemPipe       // pipe symbol
+	itemRawString  // raw quoted string (includes quotes)
+	itemRightDelim // right action delimiter
+	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
+	itemDot      // the cursor, spelled '.'.
+	itemDefine   // define keyword
+	itemElse     // else keyword
+	itemEnd      // end keyword
+	itemIf       // if keyword
+	itemRange    // range keyword
+	itemTemplate // template keyword
+	itemWith     // with keyword
+)
+
+// Make the types prettyprint.
+var itemName = map[itemType]string{
+	itemError:        "error",
+	itemBool:         "bool",
+	itemChar:         "char",
+	itemCharConstant: "charconst",
+	itemComplex:      "complex",
+	itemColonEquals:  ":=",
+	itemEOF:          "EOF",
+	itemField:        "field",
+	itemIdentifier:   "identifier",
+	itemLeftDelim:    "left delim",
+	itemNumber:       "number",
+	itemPipe:         "pipe",
+	itemRawString:    "raw string",
+	itemRightDelim:   "right delim",
+	itemString:       "string",
+	itemVariable:     "variable",
+	// keywords
+	itemDot:      ".",
+	itemDefine:   "define",
+	itemElse:     "else",
+	itemIf:       "if",
+	itemEnd:      "end",
+	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
+}
+
+var key = map[string]itemType{
+	".":        itemDot,
+	"define":   itemDefine,
+	"else":     itemElse,
+	"end":      itemEnd,
+	"if":       itemIf,
+	"range":    itemRange,
+	"template": itemTemplate,
+	"with":     itemWith,
+}
+
+const eof = -1
+
+// 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.
+	state stateFn   // the next lexing function to enter
+	pos   int       // current position in the input.
+	start int       // start position of this item.
+	width int       // width of last rune read from input.
+	items chan item // channel of scanned items.
+}
+
+// next returns the next rune in the input.
+func (l *lexer) next() (rune int) {
+	if l.pos >= len(l.input) {
+		l.width = 0
+		return eof
+	}
+	rune, l.width = utf8.DecodeRuneInString(l.input[l.pos:])
+	l.pos += l.width
+	return rune
+}
+
+// peek returns but does not consume the next rune in the input.
+func (l *lexer) peek() int {
+	rune := l.next()
+	l.backup()
+	return rune
+}
+
+// backup steps back one rune. Can only be called once per call of next.
+func (l *lexer) backup() {
+	l.pos -= l.width
+}
+
+// emit passes an item back to the client.
+func (l *lexer) emit(t itemType) {
+	l.items <- item{t, l.input[l.start:l.pos]}
+	l.start = l.pos
+}
+
+// ignore skips over the pending input before this point.
+func (l *lexer) ignore() {
+	l.start = l.pos
+}
+
+// accept consumes the next rune if it's from the valid set.
+func (l *lexer) accept(valid string) bool {
+	if strings.IndexRune(valid, l.next()) >= 0 {
+		return true
+	}
+	l.backup()
+	return false
+}
+
+// acceptRun consumes a run of runes from the valid set.
+func (l *lexer) acceptRun(valid string) {
+	for strings.IndexRune(valid, l.next()) >= 0 {
+	}
+	l.backup()
+}
+
+// lineNumber reports which line we're on. Doing it this way
+// means we don't have to worry about peek double counting.
+func (l *lexer) lineNumber() int {
+	return 1 + strings.Count(l.input[:l.pos], "\n")
+}
+
+// error returns an error token and terminates the scan by passing
+// back a nil pointer that will be the next state, terminating l.run.
+func (l *lexer) errorf(format string, args ...interface{}) stateFn {
+	l.items <- item{itemError, fmt.Sprintf(format, args...)}
+	return nil
+}
+
+// nextItem returns the next item from the input.
+func (l *lexer) nextItem() item {
+	for {
+		select {
+		case item := <-l.items:
+			return item
+		default:
+			l.state = l.state(l)
+		}
+	}
+	panic("not reached")
+}
+
+// lex creates a new scanner for the input string.
+func lex(name, input string) *lexer {
+	l := &lexer{
+		name:  name,
+		input: input,
+		state: lexText,
+		items: make(chan item, 2), // Two items of buffering is sufficient for all state functions
+	}
+	return l
+}
+
+// state functions
+
+const (
+	leftDelim    = "{{"
+	rightDelim   = "}}"
+	leftComment  = "{{/*"
+	rightComment = "*/}}"
+)
+
+// lexText scans until an opening action delimiter, "{{".
+func lexText(l *lexer) stateFn {
+	for {
+		if strings.HasPrefix(l.input[l.pos:], leftDelim) {
+			if l.pos > l.start {
+				l.emit(itemText)
+			}
+			return lexLeftDelim
+		}
+		if l.next() == eof {
+			break
+		}
+	}
+	// Correctly reached EOF.
+	if l.pos > l.start {
+		l.emit(itemText)
+	}
+	l.emit(itemEOF)
+	return nil
+}
+
+// lexLeftDelim scans the left delimiter, which is known to be present.
+func lexLeftDelim(l *lexer) stateFn {
+	if strings.HasPrefix(l.input[l.pos:], leftComment) {
+		return lexComment
+	}
+	l.pos += len(leftDelim)
+	l.emit(itemLeftDelim)
+	return lexInsideAction
+}
+
+// lexComment scans a comment. The left comment marker is known to be present.
+func lexComment(l *lexer) stateFn {
+	i := strings.Index(l.input[l.pos:], rightComment)
+	if i < 0 {
+		return l.errorf("unclosed comment")
+	}
+	l.pos += i + len(rightComment)
+	l.ignore()
+	return lexText
+}
+
+// lexRightDelim scans the right delimiter, which is known to be present.
+func lexRightDelim(l *lexer) stateFn {
+	l.pos += len(rightDelim)
+	l.emit(itemRightDelim)
+	return lexText
+}
+
+// lexInsideAction scans the elements inside action delimiters.
+func lexInsideAction(l *lexer) stateFn {
+	// Either number, quoted string, or identifier.
+	// Spaces separate and are ignored.
+	// Pipe symbols separate and are emitted.
+	if strings.HasPrefix(l.input[l.pos:], rightDelim) {
+		return lexRightDelim
+	}
+	switch r := l.next(); {
+	case r == eof || r == '\n':
+		return l.errorf("unclosed action")
+	case isSpace(r):
+		l.ignore()
+	case r == ':':
+		if l.next() != '=' {
+			return l.errorf("expected :=")
+		}
+		l.emit(itemColonEquals)
+	case r == '|':
+		l.emit(itemPipe)
+	case r == '"':
+		return lexQuote
+	case r == '`':
+		return lexRawQuote
+	case r == '$':
+		return lexIdentifier
+	case r == '\'':
+		return lexChar
+	case r == '.':
+		// special look-ahead for ".field" so we don't break l.backup().
+		if l.pos < len(l.input) {
+			r := l.input[l.pos]
+			if r < '0' || '9' < r {
+				return lexIdentifier // itemDot comes from the keyword table.
+			}
+		}
+		fallthrough // '.' can start a number.
+	case r == '+' || r == '-' || ('0' <= r && r <= '9'):
+		l.backup()
+		return lexNumber
+	case isAlphaNumeric(r):
+		l.backup()
+		return lexIdentifier
+	case r <= unicode.MaxASCII && unicode.IsPrint(r):
+		l.emit(itemChar)
+		return lexInsideAction
+	default:
+		return l.errorf("unrecognized character in action: %#U", r)
+	}
+	return lexInsideAction
+}
+
+// lexIdentifier scans an alphanumeric or field.
+func lexIdentifier(l *lexer) stateFn {
+Loop:
+	for {
+		switch r := l.next(); {
+		case isAlphaNumeric(r):
+			// absorb.
+		case r == '.' && (l.input[l.start] == '.' || l.input[l.start] == '$'):
+			// field chaining; absorb into one token.
+		default:
+			l.backup()
+			word := l.input[l.start:l.pos]
+			switch {
+			case key[word] > itemKeyword:
+				l.emit(key[word])
+			case word[0] == '.':
+				l.emit(itemField)
+			case word[0] == '$':
+				l.emit(itemVariable)
+			case word == "true", word == "false":
+				l.emit(itemBool)
+			default:
+				l.emit(itemIdentifier)
+			}
+			break Loop
+		}
+	}
+	return lexInsideAction
+}
+
+// lexChar scans a character constant. The initial quote is already
+// scanned.  Syntax checking is done by the parse.
+func lexChar(l *lexer) stateFn {
+Loop:
+	for {
+		switch l.next() {
+		case '\\':
+			if r := l.next(); r != eof && r != '\n' {
+				break
+			}
+			fallthrough
+		case eof, '\n':
+			return l.errorf("unterminated character constant")
+		case '\'':
+			break Loop
+		}
+	}
+	l.emit(itemCharConstant)
+	return lexInsideAction
+}
+
+// lexNumber scans a number: decimal, octal, hex, float, or imaginary.  This
+// isn't a perfect number scanner - for instance it accepts "." and "0x0.2"
+// and "089" - but when it's wrong the input is invalid and the parser (via
+// strconv) will notice.
+func lexNumber(l *lexer) stateFn {
+	if !l.scanNumber() {
+		return l.errorf("bad number syntax: %q", l.input[l.start:l.pos])
+	}
+	if sign := l.peek(); sign == '+' || sign == '-' {
+		// Complex: 1+2i.  No spaces, must end in 'i'.
+		if !l.scanNumber() || l.input[l.pos-1] != 'i' {
+			return l.errorf("bad number syntax: %q", l.input[l.start:l.pos])
+		}
+		l.emit(itemComplex)
+	} else {
+		l.emit(itemNumber)
+	}
+	return lexInsideAction
+}
+
+func (l *lexer) scanNumber() bool {
+	// Optional leading sign.
+	l.accept("+-")
+	// Is it hex?
+	digits := "0123456789"
+	if l.accept("0") && l.accept("xX") {
+		digits = "0123456789abcdefABCDEF"
+	}
+	l.acceptRun(digits)
+	if l.accept(".") {
+		l.acceptRun(digits)
+	}
+	if l.accept("eE") {
+		l.accept("+-")
+		l.acceptRun("0123456789")
+	}
+	// Is it imaginary?
+	l.accept("i")
+	// Next thing mustn't be alphanumeric.
+	if isAlphaNumeric(l.peek()) {
+		l.next()
+		return false
+	}
+	return true
+}
+
+// lexQuote scans a quoted string.
+func lexQuote(l *lexer) stateFn {
+Loop:
+	for {
+		switch l.next() {
+		case '\\':
+			if r := l.next(); r != eof && r != '\n' {
+				break
+			}
+			fallthrough
+		case eof, '\n':
+			return l.errorf("unterminated quoted string")
+		case '"':
+			break Loop
+		}
+	}
+	l.emit(itemString)
+	return lexInsideAction
+}
+
+// lexRawQuote scans a raw quoted string.
+func lexRawQuote(l *lexer) stateFn {
+Loop:
+	for {
+		switch l.next() {
+		case eof, '\n':
+			return l.errorf("unterminated raw quoted string")
+		case '`':
+			break Loop
+		}
+	}
+	l.emit(itemRawString)
+	return lexInsideAction
+}
+
+// isSpace reports whether r is a space character.
+func isSpace(r int) bool {
+	switch r {
+	case ' ', '\t', '\n', '\r':
+		return true
+	}
+	return false
+}
+
+// isAlphaNumeric reports whether r is an alphabetic, digit, or underscore.
+func isAlphaNumeric(r int) bool {
+	return r == '_' || unicode.IsLetter(r) || unicode.IsDigit(r)
+}