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https://github.com/golang/go
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exp/template: lexical scanner for new template package.
An unusual design using slice and a goroutine makes for a compact scanner with very little allocation. R=rsc, r CC=golang-dev, kevlar https://golang.org/cl/4610041
This commit is contained in:
Rob Pike
parent
9ded954a3b
commit
7bc8e90e36
11
src/pkg/exp/template/Makefile
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11
src/pkg/exp/template/Makefile
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# Copyright 2011 The Go Authors. All rights reserved.
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# Use of this source code is governed by a BSD-style
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# license that can be found in the LICENSE file.
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include ../../../Make.inc
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TARG=template
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GOFILES=\
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lex.go\
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include ../../../Make.pkg
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302
src/pkg/exp/template/lex.go
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302
src/pkg/exp/template/lex.go
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// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package template
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import (
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"fmt"
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"strings"
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"unicode"
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"utf8"
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)
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// item represents a token or text string returned from the scanner.
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type item struct {
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typ itemType
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val string
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}
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// itemType identifies the type of lex item.
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type itemType int
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const (
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itemError itemType = iota // error occurred; value is text of error
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itemText // plain text
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itemLeftMeta // left meta-string
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itemRightMeta // right meta-string
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itemPipe // pipe symbol
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itemIdentifier // alphanumeric identifier
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itemNumber // number
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itemRawString // raw quoted string (includes quotes)
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itemString // quoted string (includes quotes)
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itemEOF
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)
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const eof = -1
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// stateFn represents the state of the scanner as a function that returns the next state.
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type stateFn func(*lexer) stateFn
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// lexer holds the state of the scanner.
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type lexer struct {
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name string // the name of the input; used only for error reports.
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input string // the string being scanned.
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pos int // current position in the input.
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start int // start position of this item.
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width int // width of last rune read from input.
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items chan item // channel of scanned items.
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}
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// next returns the next rune in the input.
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func (l *lexer) next() (rune int) {
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if l.pos >= len(l.input) {
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return eof
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}
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rune, l.width = utf8.DecodeRuneInString(l.input[l.pos:])
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l.pos += l.width
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return rune
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}
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// peek returns but does not consume the next rune in the input.
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func (l *lexer) peek() int {
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rune := l.next()
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l.backup()
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return rune
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}
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// backup steps back one rune. Can only be called once per call of next.
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func (l *lexer) backup() {
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l.pos -= l.width
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}
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// emit passes an item back to the client.
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func (l *lexer) emit(t itemType) {
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start := l.start
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l.start = l.pos
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l.items <- item{t, l.input[start:l.pos]}
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}
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// ignore discards whatever input is before this point.
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func (l *lexer) ignore() {
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l.start = l.pos
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}
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// accept consumes the next rune if it's from the valid set.
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func (l *lexer) accept(valid string) bool {
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if strings.IndexRune(valid, l.next()) >= 0 {
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return true
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}
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l.backup()
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return false
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}
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// acceptRun consumes a run of runes from the valid set.
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func (l *lexer) acceptRun(valid string) {
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for strings.IndexRune(valid, l.next()) >= 0 {
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}
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l.backup()
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}
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// lineNumber reports which line we're on. Doing it this way
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// means we don't have to worry about peek double counting.
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func (l *lexer) lineNumber() int {
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return 1 + strings.Count(l.input[:l.pos], "\n")
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}
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// error returns an error token and terminates the scan by passing
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// back a nil pointer that will be the next state, terminating l.run.
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func (l *lexer) error(format string, args ...interface{}) stateFn {
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format = fmt.Sprintf("%s:%d %s", l.name, l.lineNumber(), format)
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l.items <- item{itemError, fmt.Sprintf(format, args...)}
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return nil
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}
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// run lexes the input by execute state functions until nil.
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func (l *lexer) run() {
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for state := lexText; state != nil; {
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state = state(l)
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}
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close(l.items)
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}
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// lex launches a new scanner and returns the channel of items.
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func lex(name, input string) chan item {
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l := &lexer{
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name: name,
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input: input,
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items: make(chan item),
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}
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go l.run()
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return l.items
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}
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// state functions
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const leftMeta = "{{"
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const rightMeta = "}}"
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// lexText scans until a metacharacter
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func lexText(l *lexer) stateFn {
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for {
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if strings.HasPrefix(l.input[l.pos:], leftMeta) {
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if l.pos > l.start {
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l.emit(itemText)
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}
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return lexLeftMeta
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}
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if l.next() == eof {
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break
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}
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}
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// Correctly reached EOF.
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if l.pos > l.start {
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l.emit(itemText)
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}
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l.emit(itemEOF)
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return nil
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}
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// leftMeta scans the left "metacharacter", which is known to be present.
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func lexLeftMeta(l *lexer) stateFn {
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l.pos += len(leftMeta)
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l.emit(itemLeftMeta)
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return lexInsideAction
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}
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// rightMeta scans the right "metacharacter", which is known to be present.
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func lexRightMeta(l *lexer) stateFn {
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l.pos += len(rightMeta)
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l.emit(itemRightMeta)
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return lexText
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}
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// lexInsideAction scans the elements inside "metacharacters".
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func lexInsideAction(l *lexer) stateFn {
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// Either number, quoted string, or identifier.
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// Spaces separate and are ignored.
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// Pipe symbols separate and are emitted.
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for {
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if strings.HasPrefix(l.input[l.pos:], rightMeta) {
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return lexRightMeta
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}
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switch r := l.next(); {
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case r == eof || r == '\n':
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return l.error("unclosed action")
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case isSpace(r):
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l.ignore()
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case r == '|':
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l.emit(itemPipe)
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case r == '"':
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return lexQuote
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case r == '`':
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return lexRawQuote
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case r == '+' || r == '-' || r == '.' || ('0' <= r && r <= '9'):
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l.backup()
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return lexNumber
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case isAlphaNumeric(r):
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l.backup()
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return lexIdentifier
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default:
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return l.error("unrecognized character in action: %#U", r)
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}
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}
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return nil
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}
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// lexIdentifier scans an alphanumeric.
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func lexIdentifier(l *lexer) stateFn {
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Loop:
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for {
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switch r := l.next(); {
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case isAlphaNumeric(r):
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// absorb
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default:
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l.backup()
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l.emit(itemIdentifier)
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break Loop
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}
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}
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return lexInsideAction
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}
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// lexNumber scans a number: decimal, octal, hex, float, or imaginary. This
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// isn't a perfect number scanner - for instance it accepts "." and "0x0.2"
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// and "089" - but when it's wrong the input is invalid and the parser (via
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// strconv) will notice.
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// TODO: without expressions you can do imaginary but not complex.
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func lexNumber(l *lexer) stateFn {
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// Optional leading sign.
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l.accept("+-")
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// Is it hex?
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digits := "0123456789"
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if l.accept("0") && l.accept("xX") {
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digits = "0123456789abcdefABCDEF"
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}
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l.acceptRun(digits)
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if l.accept(".") {
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l.acceptRun(digits)
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}
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if l.accept("eE") {
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l.accept("+-")
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l.acceptRun("0123456789")
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}
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// Is it imaginary?
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l.accept("i")
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// Next thing mustn't be alphanumeric.
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if isAlphaNumeric(l.peek()) {
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l.next()
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return l.error("bad number syntax: %q", l.input[l.start:l.pos])
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}
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l.emit(itemNumber)
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return lexInsideAction
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}
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// lexQuote scans a quoted string.
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func lexQuote(l *lexer) stateFn {
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Loop:
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for {
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switch l.next() {
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case '\\':
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if r := l.next(); r != eof && r != '\n' {
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break
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}
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fallthrough
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case eof, '\n':
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return l.error("unterminated quoted string")
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case '"':
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break Loop
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}
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}
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l.emit(itemString)
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return lexInsideAction
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}
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// lexRawQuote scans a raw quoted string.
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func lexRawQuote(l *lexer) stateFn {
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Loop:
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for {
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switch l.next() {
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case eof, '\n':
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return l.error("unterminated raw quoted string")
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case '`':
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break Loop
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}
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}
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l.emit(itemRawString)
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return lexInsideAction
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}
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// isSpace reports whether r is a space character.
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func isSpace(r int) bool {
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switch r {
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case ' ', '\t', '\n', '\r':
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return true
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}
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return false
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}
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// isAlphaNumeric reports whether r is an alphabetic, digit, or underscore.
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func isAlphaNumeric(r int) bool {
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return r == '_' || unicode.IsLetter(r) || unicode.IsDigit(r)
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}
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126
src/pkg/exp/template/lex_test.go
Normal file
126
src/pkg/exp/template/lex_test.go
Normal file
@ -0,0 +1,126 @@
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// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package template
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import (
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"fmt"
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"reflect"
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"testing"
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)
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// Make the types prettyprint.
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var itemName = map[itemType]string{
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itemError: "Error",
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itemText: "Text",
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itemLeftMeta: "LeftMeta",
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itemRightMeta: "RightMeta",
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itemPipe: "Pipe",
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itemIdentifier: "Identifier",
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itemNumber: "Number",
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itemRawString: "RawString",
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itemString: "String",
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itemEOF: "EOF",
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}
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func (i itemType) String() string {
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s := itemName[i]
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if s == "" {
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return fmt.Sprintf("item%d", int(i))
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}
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return s
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}
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type lexTest struct {
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name string
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input string
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items []item
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}
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var (
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tEOF = item{itemEOF, ""}
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tLeft = item{itemLeftMeta, "{{"}
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tRight = item{itemRightMeta, "}}"}
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tPipe = item{itemPipe, "|"}
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tFor = item{itemIdentifier, "for"}
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tQuote = item{itemString, `"abc \n\t\" "`}
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raw = "`" + `abc\n\t\" ` + "`"
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tRawQuote = item{itemRawString, raw}
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)
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var lexTests = []lexTest{
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{"empty", "", []item{tEOF}},
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{"spaces", " \t\n", []item{{itemText, " \t\n"}, tEOF}},
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{"text", `now is the time`, []item{{itemText, "now is the time"}, tEOF}},
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{"empty action", `{{}}`, []item{tLeft, tRight, tEOF}},
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{"for", `{{for }}`, []item{tLeft, tFor, tRight, tEOF}},
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{"quote", `{{"abc \n\t\" "}}`, []item{tLeft, tQuote, tRight, tEOF}},
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{"raw quote", "{{" + raw + "}}", []item{tLeft, tRawQuote, tRight, tEOF}},
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{"numbers", "{{1 02 0x14 -7.2i 1e3 +1.2e-4}}", []item{
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tLeft,
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{itemNumber, "1"},
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{itemNumber, "02"},
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{itemNumber, "0x14"},
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{itemNumber, "-7.2i"},
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{itemNumber, "1e3"},
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{itemNumber, "+1.2e-4"},
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tRight,
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tEOF,
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}},
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{"pipeline", `intro {{echo hi 1.2 |noargs|args 1 "hi"}} outro`, []item{
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{itemText, "intro "},
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tLeft,
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{itemIdentifier, "echo"},
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{itemIdentifier, "hi"},
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{itemNumber, "1.2"},
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tPipe,
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{itemIdentifier, "noargs"},
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tPipe,
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{itemIdentifier, "args"},
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{itemNumber, "1"},
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{itemString, `"hi"`},
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tRight,
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{itemText, " outro"},
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tEOF,
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}},
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// errors
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{"badchar", "#{{#}}", []item{
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{itemText, "#"},
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tLeft,
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{itemError, "badchar:1 unrecognized character in action: U+0023 '#'"},
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}},
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{"unclosed action", "{{\n}}", []item{
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tLeft,
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{itemError, "unclosed action:2 unclosed action"},
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}},
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{"unclosed quote", "{{\"\n\"}}", []item{
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tLeft,
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{itemError, "unclosed quote:2 unterminated quoted string"},
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}},
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{"unclosed raw quote", "{{`xx\n`}}", []item{
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tLeft,
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{itemError, "unclosed raw quote:2 unterminated raw quoted string"},
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}},
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{"bad number", "{{3k}}", []item{
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tLeft,
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{itemError, `bad number:1 bad number syntax: "3k"`},
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}},
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}
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// collect gathers the emitted items into a slice.
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func collect(t *lexTest) (items []item) {
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for i := range lex(t.name, t.input) {
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items = append(items, i)
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}
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return
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}
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func TestLex(t *testing.T) {
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for _, test := range lexTests {
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items := collect(&test)
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if !reflect.DeepEqual(items, test.items) {
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t.Errorf("%s: got\n\t%v; expected\n\t%v", test.name, items, test.items)
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}
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}
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}
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