--- /dev/null
+// Copyright 2017 Frank Schroeder. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+//
+// Parts of the lexer are from the template/text/parser package
+// For these parts the following applies:
+//
+// 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 of the go 1.2
+// distribution.
+
+package properties
+
+import (
+ "fmt"
+ "strconv"
+ "strings"
+ "unicode/utf8"
+)
+
+// item represents a token or text string returned from the scanner.
+type item struct {
+ typ itemType // The type of this item.
+ pos int // The starting position, in bytes, of this item in the input string.
+ val string // The value of this item.
+}
+
+func (i item) String() string {
+ switch {
+ case i.typ == itemEOF:
+ return "EOF"
+ case i.typ == itemError:
+ return 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
+ itemEOF
+ itemKey // a key
+ itemValue // a value
+ itemComment // a comment
+)
+
+// defines a constant for EOF
+const eof = -1
+
+// permitted whitespace characters space, FF and TAB
+const whitespace = " \f\t"
+
+// 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 {
+ 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
+ lastPos int // position of most recent item returned by nextItem
+ runes []rune // scanned runes for this item
+ items chan item // channel of scanned items
+}
+
+// next returns the next rune in the input.
+func (l *lexer) next() rune {
+ if l.pos >= len(l.input) {
+ l.width = 0
+ return eof
+ }
+ r, w := utf8.DecodeRuneInString(l.input[l.pos:])
+ l.width = w
+ l.pos += l.width
+ return r
+}
+
+// peek returns but does not consume the next rune in the input.
+func (l *lexer) peek() rune {
+ r := l.next()
+ l.backup()
+ return r
+}
+
+// backup steps back one rune. Can only be called once per call of next.
+func (l *lexer) backup() {
+ l.pos -= l.width
+}
+
+// emit passes an item back to the client.
+func (l *lexer) emit(t itemType) {
+ i := item{t, l.start, string(l.runes)}
+ l.items <- i
+ l.start = l.pos
+ l.runes = l.runes[:0]
+}
+
+// ignore skips over the pending input before this point.
+func (l *lexer) ignore() {
+ l.start = l.pos
+}
+
+// appends the rune to the current value
+func (l *lexer) appendRune(r rune) {
+ l.runes = append(l.runes, r)
+}
+
+// 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()
+}
+
+// acceptRunUntil consumes a run of runes up to a terminator.
+func (l *lexer) acceptRunUntil(term rune) {
+ for term != l.next() {
+ }
+ l.backup()
+}
+
+// hasText returns true if the current parsed text is not empty.
+func (l *lexer) isNotEmpty() bool {
+ return l.pos > l.start
+}
+
+// lineNumber reports which line we're on, based on the position of
+// the previous item returned by nextItem. 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.lastPos], "\n")
+}
+
+// errorf returns an error token and terminates the scan by passing
+// back a nil pointer that will be the next state, terminating l.nextItem.
+func (l *lexer) errorf(format string, args ...interface{}) stateFn {
+ l.items <- item{itemError, l.start, fmt.Sprintf(format, args...)}
+ return nil
+}
+
+// nextItem returns the next item from the input.
+func (l *lexer) nextItem() item {
+ i := <-l.items
+ l.lastPos = i.pos
+ return i
+}
+
+// lex creates a new scanner for the input string.
+func lex(input string) *lexer {
+ l := &lexer{
+ input: input,
+ items: make(chan item),
+ runes: make([]rune, 0, 32),
+ }
+ go l.run()
+ return l
+}
+
+// run runs the state machine for the lexer.
+func (l *lexer) run() {
+ for l.state = lexBeforeKey(l); l.state != nil; {
+ l.state = l.state(l)
+ }
+}
+
+// state functions
+
+// lexBeforeKey scans until a key begins.
+func lexBeforeKey(l *lexer) stateFn {
+ switch r := l.next(); {
+ case isEOF(r):
+ l.emit(itemEOF)
+ return nil
+
+ case isEOL(r):
+ l.ignore()
+ return lexBeforeKey
+
+ case isComment(r):
+ return lexComment
+
+ case isWhitespace(r):
+ l.acceptRun(whitespace)
+ l.ignore()
+ return lexKey
+
+ default:
+ l.backup()
+ return lexKey
+ }
+}
+
+// lexComment scans a comment line. The comment character has already been scanned.
+func lexComment(l *lexer) stateFn {
+ l.acceptRun(whitespace)
+ l.ignore()
+ for {
+ switch r := l.next(); {
+ case isEOF(r):
+ l.ignore()
+ l.emit(itemEOF)
+ return nil
+ case isEOL(r):
+ l.emit(itemComment)
+ return lexBeforeKey
+ default:
+ l.appendRune(r)
+ }
+ }
+}
+
+// lexKey scans the key up to a delimiter
+func lexKey(l *lexer) stateFn {
+ var r rune
+
+Loop:
+ for {
+ switch r = l.next(); {
+
+ case isEscape(r):
+ err := l.scanEscapeSequence()
+ if err != nil {
+ return l.errorf(err.Error())
+ }
+
+ case isEndOfKey(r):
+ l.backup()
+ break Loop
+
+ case isEOF(r):
+ break Loop
+
+ default:
+ l.appendRune(r)
+ }
+ }
+
+ if len(l.runes) > 0 {
+ l.emit(itemKey)
+ }
+
+ if isEOF(r) {
+ l.emit(itemEOF)
+ return nil
+ }
+
+ return lexBeforeValue
+}
+
+// lexBeforeValue scans the delimiter between key and value.
+// Leading and trailing whitespace is ignored.
+// We expect to be just after the key.
+func lexBeforeValue(l *lexer) stateFn {
+ l.acceptRun(whitespace)
+ l.accept(":=")
+ l.acceptRun(whitespace)
+ l.ignore()
+ return lexValue
+}
+
+// lexValue scans text until the end of the line. We expect to be just after the delimiter.
+func lexValue(l *lexer) stateFn {
+ for {
+ switch r := l.next(); {
+ case isEscape(r):
+ if isEOL(l.peek()) {
+ l.next()
+ l.acceptRun(whitespace)
+ } else {
+ err := l.scanEscapeSequence()
+ if err != nil {
+ return l.errorf(err.Error())
+ }
+ }
+
+ case isEOL(r):
+ l.emit(itemValue)
+ l.ignore()
+ return lexBeforeKey
+
+ case isEOF(r):
+ l.emit(itemValue)
+ l.emit(itemEOF)
+ return nil
+
+ default:
+ l.appendRune(r)
+ }
+ }
+}
+
+// scanEscapeSequence scans either one of the escaped characters
+// or a unicode literal. We expect to be after the escape character.
+func (l *lexer) scanEscapeSequence() error {
+ switch r := l.next(); {
+
+ case isEscapedCharacter(r):
+ l.appendRune(decodeEscapedCharacter(r))
+ return nil
+
+ case atUnicodeLiteral(r):
+ return l.scanUnicodeLiteral()
+
+ case isEOF(r):
+ return fmt.Errorf("premature EOF")
+
+ // silently drop the escape character and append the rune as is
+ default:
+ l.appendRune(r)
+ return nil
+ }
+}
+
+// scans a unicode literal in the form \uXXXX. We expect to be after the \u.
+func (l *lexer) scanUnicodeLiteral() error {
+ // scan the digits
+ d := make([]rune, 4)
+ for i := 0; i < 4; i++ {
+ d[i] = l.next()
+ if d[i] == eof || !strings.ContainsRune("0123456789abcdefABCDEF", d[i]) {
+ return fmt.Errorf("invalid unicode literal")
+ }
+ }
+
+ // decode the digits into a rune
+ r, err := strconv.ParseInt(string(d), 16, 0)
+ if err != nil {
+ return err
+ }
+
+ l.appendRune(rune(r))
+ return nil
+}
+
+// decodeEscapedCharacter returns the unescaped rune. We expect to be after the escape character.
+func decodeEscapedCharacter(r rune) rune {
+ switch r {
+ case 'f':
+ return '\f'
+ case 'n':
+ return '\n'
+ case 'r':
+ return '\r'
+ case 't':
+ return '\t'
+ default:
+ return r
+ }
+}
+
+// atUnicodeLiteral reports whether we are at a unicode literal.
+// The escape character has already been consumed.
+func atUnicodeLiteral(r rune) bool {
+ return r == 'u'
+}
+
+// isComment reports whether we are at the start of a comment.
+func isComment(r rune) bool {
+ return r == '#' || r == '!'
+}
+
+// isEndOfKey reports whether the rune terminates the current key.
+func isEndOfKey(r rune) bool {
+ return strings.ContainsRune(" \f\t\r\n:=", r)
+}
+
+// isEOF reports whether we are at EOF.
+func isEOF(r rune) bool {
+ return r == eof
+}
+
+// isEOL reports whether we are at a new line character.
+func isEOL(r rune) bool {
+ return r == '\n' || r == '\r'
+}
+
+// isEscape reports whether the rune is the escape character which
+// prefixes unicode literals and other escaped characters.
+func isEscape(r rune) bool {
+ return r == '\\'
+}
+
+// isEscapedCharacter reports whether we are at one of the characters that need escaping.
+// The escape character has already been consumed.
+func isEscapedCharacter(r rune) bool {
+ return strings.ContainsRune(" :=fnrt", r)
+}
+
+// isWhitespace reports whether the rune is a whitespace character.
+func isWhitespace(r rune) bool {
+ return strings.ContainsRune(whitespace, r)
+}
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