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lex.go
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694 lines (646 loc) · 17.9 KB
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// 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
rightDelim string // end of action
emitComment bool // emit itemComment tokens.
pos Pos // current position in the input
start Pos // start position of this item
width Pos // width of last rune read from input
items chan item // channel of scanned items
parenDepth int // nesting depth of ( ) exprs
line int // 1+number of newlines seen
startLine int // start line of this item
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.width = 0
return eof
}
r, w := utf8.DecodeRuneInString(l.input[l.pos:])
l.width = Pos(w)
l.pos += l.width
if r == '\n' {
l.line++
}
return r
}
// peek returns but does not consume the next rune in the input.
func (l *lexer) peek() rune {
r := l.next()
l.backup()
return r
}
// backup steps back one rune. Can only be called once per call of next.
func (l *lexer) backup() {
l.pos -= l.width
// Correct newline count.
if l.width == 1 && l.input[l.pos] == '\n' {
l.line--
}
}
// emit passes an item back to the client.
func (l *lexer) emit(t itemType) {
l.items <- item{t, l.start, l.input[l.start:l.pos], l.startLine}
l.start = l.pos
l.startLine = l.line
}
// ignore skips over the pending input before this point.
func (l *lexer) ignore() {
l.line += strings.Count(l.input[l.start:l.pos], "\n")
l.start = l.pos
l.startLine = l.line
}
// accept consumes the next rune if it's from the valid set.
func (l *lexer) accept(valid string) bool {
if strings.ContainsRune(valid, l.next()) {
return true
}
l.backup()
return false
}
// acceptRun consumes a run of runes from the valid set.
func (l *lexer) acceptRun(valid string) {
for strings.ContainsRune(valid, l.next()) {
}
l.backup()
}
// errorf returns an error token and terminates the scan by passing
// back a nil pointer that will be the next state, terminating l.nextItem.
func (l *lexer) errorf(format string, args ...any) stateFn {
l.items <- item{itemError, l.start, fmt.Sprintf(format, args...), l.startLine}
return nil
}
// nextItem returns the next item from the input.
// Called by the parser, not in the lexing goroutine.
func (l *lexer) nextItem() item {
return <-l.items
}
// drain drains the output so the lexing goroutine will exit.
// Called by the parser, not in the lexing goroutine.
func (l *lexer) drain() {
for range l.items {
}
}
// lex creates a new scanner for the input string.
func lex(name, input, left, right string, emitComment bool) *lexer {
if left == "" {
left = leftDelim
}
if right == "" {
right = rightDelim
}
l := &lexer{
name: name,
input: input,
leftDelim: left,
rightDelim: right,
emitComment: emitComment,
items: make(chan item),
line: 1,
startLine: 1,
}
go l.run()
return l
}
// run runs the state machine for the lexer.
func (l *lexer) run() {
for state := lexText; state != nil; {
state = state(l)
}
close(l.items)
}
// state functions
const (
leftDelim = "{{"
rightDelim = "}}"
leftComment = "/*"
rightComment = "*/"
)
// lexText scans until an opening action delimiter, "{{".
func lexText(l *lexer) stateFn {
l.width = 0
if x := strings.Index(l.input[l.pos:], l.leftDelim); x >= 0 {
ldn := Pos(len(l.leftDelim))
l.pos += Pos(x)
trimLength := Pos(0)
if hasLeftTrimMarker(l.input[l.pos+ldn:]) {
trimLength = rightTrimLength(l.input[l.start:l.pos])
}
l.pos -= trimLength
if l.pos > l.start {
l.line += strings.Count(l.input[l.start:l.pos], "\n")
l.emit(itemText)
}
l.pos += trimLength
l.ignore()
return lexLeftDelim
}
l.pos = Pos(len(l.input))
// Correctly reached EOF.
if l.pos > l.start {
l.line += strings.Count(l.input[l.start:l.pos], "\n")
l.emit(itemText)
}
l.emit(itemEOF)
return nil
}
// rightTrimLength returns the length of the spaces at the end of the string.
func rightTrimLength(s string) Pos {
return Pos(len(s) - len(strings.TrimRight(s, spaceChars)))
}
// atRightDelim reports whether the lexer is at a right delimiter, possibly preceded by a trim marker.
func (l *lexer) atRightDelim() (delim, trimSpaces bool) {
if hasRightTrimMarker(l.input[l.pos:]) && strings.HasPrefix(l.input[l.pos+trimMarkerLen:], l.rightDelim) { // With trim marker.
return true, true
}
if strings.HasPrefix(l.input[l.pos:], l.rightDelim) { // Without trim marker.
return true, false
}
return false, false
}
// leftTrimLength returns the length of the spaces at the beginning of the string.
func leftTrimLength(s string) Pos {
return Pos(len(s) - len(strings.TrimLeft(s, spaceChars)))
}
// lexLeftDelim scans the left delimiter, which is known to be present, possibly with a trim marker.
func lexLeftDelim(l *lexer) stateFn {
l.pos += Pos(len(l.leftDelim))
trimSpace := hasLeftTrimMarker(l.input[l.pos:])
afterMarker := Pos(0)
if trimSpace {
afterMarker = trimMarkerLen
}
if strings.HasPrefix(l.input[l.pos+afterMarker:], leftComment) {
l.pos += afterMarker
l.ignore()
return lexComment
}
l.emit(itemLeftDelim)
l.pos += afterMarker
l.ignore()
l.parenDepth = 0
return lexInsideAction
}
// lexComment scans a comment. The left comment marker is known to be present.
func lexComment(l *lexer) stateFn {
l.pos += Pos(len(leftComment))
i := strings.Index(l.input[l.pos:], rightComment)
if i < 0 {
return l.errorf("unclosed comment")
}
l.pos += Pos(i + len(rightComment))
delim, trimSpace := l.atRightDelim()
if !delim {
return l.errorf("comment ends before closing delimiter")
}
if l.emitComment {
l.emit(itemComment)
}
if trimSpace {
l.pos += trimMarkerLen
}
l.pos += Pos(len(l.rightDelim))
if trimSpace {
l.pos += leftTrimLength(l.input[l.pos:])
}
l.ignore()
return lexText
}
// lexRightDelim scans the right delimiter, which is known to be present, possibly with a trim marker.
func lexRightDelim(l *lexer) stateFn {
trimSpace := hasRightTrimMarker(l.input[l.pos:])
if trimSpace {
l.pos += trimMarkerLen
l.ignore()
}
l.pos += Pos(len(l.rightDelim))
l.emit(itemRightDelim)
if trimSpace {
l.pos += leftTrimLength(l.input[l.pos:])
l.ignore()
}
return lexText
}
// lexInsideAction scans the elements inside action delimiters.
func lexInsideAction(l *lexer) stateFn {
// Either number, quoted string, or identifier.
// Spaces separate arguments; runs of spaces turn into itemSpace.
// Pipe symbols separate and are emitted.
delim, _ := l.atRightDelim()
if delim {
if l.parenDepth == 0 {
return lexRightDelim
}
return l.errorf("unclosed left paren")
}
switch r := l.next(); {
case r == eof:
return l.errorf("unclosed action")
case isSpace(r):
l.backup() // Put space back in case we have " -}}".
return lexSpace
case r == '=':
l.emit(itemAssign)
case r == ':':
if l.next() != '=' {
return l.errorf("expected :=")
}
l.emit(itemDeclare)
case r == '|':
l.emit(itemPipe)
case r == '"':
return lexQuote
case r == '`':
return lexRawQuote
case r == '$':
return lexVariable
case r == '\'':
return lexChar
case r == '.':
// special look-ahead for ".field" so we don't break l.backup().
if l.pos < Pos(len(l.input)) {
r := l.input[l.pos]
if r < '0' || '9' < r {
return lexField
}
}
fallthrough // '.' can start a number.
case r == '+' || r == '-' || ('0' <= r && r <= '9'):
l.backup()
return lexNumber
case isAlphaNumeric(r):
l.backup()
return lexIdentifier
case r == '(':
l.emit(itemLeftParen)
l.parenDepth++
case r == ')':
l.emit(itemRightParen)
l.parenDepth--
if l.parenDepth < 0 {
return l.errorf("unexpected right paren %#U", r)
}
case r <= unicode.MaxASCII && unicode.IsPrint(r):
l.emit(itemChar)
default:
return l.errorf("unrecognized character in action: %#U", r)
}
return lexInsideAction
}
// lexSpace scans a run of space characters.
// We have not consumed the first space, which is known to be present.
// Take care if there is a trim-marked right delimiter, which starts with a space.
func lexSpace(l *lexer) stateFn {
var r rune
var numSpaces int
for {
r = l.peek()
if !isSpace(r) {
break
}
l.next()
numSpaces++
}
// Be careful about a trim-marked closing delimiter, which has a minus
// after a space. We know there is a space, so check for the '-' that might follow.
if hasRightTrimMarker(l.input[l.pos-1:]) && strings.HasPrefix(l.input[l.pos-1+trimMarkerLen:], l.rightDelim) {
l.backup() // Before the space.
if numSpaces == 1 {
return lexRightDelim // On the delim, so go right to that.
}
}
l.emit(itemSpace)
return lexInsideAction
}
// lexIdentifier scans an alphanumeric.
func lexIdentifier(l *lexer) stateFn {
Loop:
for {
switch r := l.next(); {
case isAlphaNumeric(r):
// absorb.
default:
l.backup()
word := l.input[l.start:l.pos]
if !l.atTerminator() {
return l.errorf("bad character %#U", r)
}
switch {
case key[word] > itemKeyword:
item := key[word]
if item == itemBreak && !l.breakOK || item == itemContinue && !l.continueOK {
l.emit(itemIdentifier)
} else {
l.emit(item)
}
case word[0] == '.':
l.emit(itemField)
case word == "true", word == "false":
l.emit(itemBool)
default:
l.emit(itemIdentifier)
}
break Loop
}
}
return lexInsideAction
}
// lexField scans a field: .Alphanumeric.
// The . has been scanned.
func lexField(l *lexer) stateFn {
return lexFieldOrVariable(l, itemField)
}
// lexVariable scans a Variable: $Alphanumeric.
// The $ has been scanned.
func lexVariable(l *lexer) stateFn {
if l.atTerminator() { // Nothing interesting follows -> "$".
l.emit(itemVariable)
return lexInsideAction
}
return lexFieldOrVariable(l, itemVariable)
}
// lexVariable scans a field or variable: [.$]Alphanumeric.
// The . or $ has been scanned.
func lexFieldOrVariable(l *lexer, typ itemType) stateFn {
if l.atTerminator() { // Nothing interesting follows -> "." or "$".
if typ == itemVariable {
l.emit(itemVariable)
} else {
l.emit(itemDot)
}
return lexInsideAction
}
var r rune
for {
r = l.next()
if !isAlphaNumeric(r) {
l.backup()
break
}
}
if !l.atTerminator() {
return l.errorf("bad character %#U", r)
}
l.emit(typ)
return lexInsideAction
}
// atTerminator reports whether the input is at valid termination character to
// appear after an identifier. Breaks .X.Y into two pieces. Also catches cases
// like "$x+2" not being acceptable without a space, in case we decide one
// day to implement arithmetic.
func (l *lexer) atTerminator() bool {
r := l.peek()
if isSpace(r) {
return true
}
switch r {
case eof, '.', ',', '|', ':', ')', '(':
return true
}
// Are we at a right delimiter? TODO: This is harder than it should be
// because lookahead is only one rune.
rightDelim := l.rightDelim
defer func(pos Pos, line int) {
l.pos = pos
l.line = line
}(l.pos, l.line)
for len(rightDelim) > 0 {
rNext := l.next()
if rNext == eof {
return false
}
rDelim, size := utf8.DecodeRuneInString(rightDelim)
if rNext != rDelim {
return false
}
rightDelim = rightDelim[size:]
}
return true
}
// lexChar scans a character constant. The initial quote is already
// scanned. Syntax checking is done by the parser.
func lexChar(l *lexer) stateFn {
Loop:
for {
switch l.next() {
case '\\':
if r := l.next(); r != eof && r != '\n' {
break
}
fallthrough
case eof, '\n':
return l.errorf("unterminated character constant")
case '\'':
break Loop
}
}
l.emit(itemCharConstant)
return lexInsideAction
}
// lexNumber scans a number: decimal, octal, hex, float, or imaginary. This
// isn't a perfect number scanner - for instance it accepts "." and "0x0.2"
// and "089" - but when it's wrong the input is invalid and the parser (via
// strconv) will notice.
func lexNumber(l *lexer) stateFn {
if !l.scanNumber() {
return l.errorf("bad number syntax: %q", l.input[l.start:l.pos])
}
if sign := l.peek(); sign == '+' || sign == '-' {
// Complex: 1+2i. No spaces, must end in 'i'.
if !l.scanNumber() || l.input[l.pos-1] != 'i' {
return l.errorf("bad number syntax: %q", l.input[l.start:l.pos])
}
l.emit(itemComplex)
} else {
l.emit(itemNumber)
}
return lexInsideAction
}
func (l *lexer) scanNumber() bool {
// Optional leading sign.
l.accept("+-")
// Is it hex?
digits := "0123456789_"
if l.accept("0") {
// Note: Leading 0 does not mean octal in floats.
if l.accept("xX") {
digits = "0123456789abcdefABCDEF_"
} else if l.accept("oO") {
digits = "01234567_"
} else if l.accept("bB") {
digits = "01_"
}
}
l.acceptRun(digits)
if l.accept(".") {
l.acceptRun(digits)
}
if len(digits) == 10+1 && l.accept("eE") {
l.accept("+-")
l.acceptRun("0123456789_")
}
if len(digits) == 16+6+1 && l.accept("pP") {
l.accept("+-")
l.acceptRun("0123456789_")
}
// Is it imaginary?
l.accept("i")
// Next thing mustn't be alphanumeric.
if isAlphaNumeric(l.peek()) {
l.next()
return false
}
return true
}
// lexQuote scans a quoted string.
func lexQuote(l *lexer) stateFn {
Loop:
for {
switch l.next() {
case '\\':
if r := l.next(); r != eof && r != '\n' {
break
}
fallthrough
case eof, '\n':
return l.errorf("unterminated quoted string")
case '"':
break Loop
}
}
l.emit(itemString)
return lexInsideAction
}
// lexRawQuote scans a raw quoted string.
func lexRawQuote(l *lexer) stateFn {
Loop:
for {
switch l.next() {
case eof:
return l.errorf("unterminated raw quoted string")
case '`':
break Loop
}
}
l.emit(itemRawString)
return lexInsideAction
}
// isSpace reports whether r is a space character.
func isSpace(r rune) bool {
return r == ' ' || r == '\t' || r == '\r' || r == '\n'
}
// isAlphaNumeric reports whether r is an alphabetic, digit, or underscore.
func isAlphaNumeric(r rune) bool {
return r == '_' || unicode.IsLetter(r) || unicode.IsDigit(r)
}
func hasLeftTrimMarker(s string) bool {
return len(s) >= 2 && s[0] == trimMarker && isSpace(rune(s[1]))
}
func hasRightTrimMarker(s string) bool {
return len(s) >= 2 && isSpace(rune(s[0])) && s[1] == trimMarker
}