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js_lexer.go
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js_lexer.go
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package js_lexer
// The lexer converts a source file to a stream of tokens. Unlike many
// compilers, esbuild does not run the lexer to completion before the parser is
// started. Instead, the lexer is called repeatedly by the parser as the parser
// parses the file. This is because many tokens are context-sensitive and need
// high-level information from the parser. Examples are regular expression
// literals and JSX elements.
//
// For efficiency, the text associated with textual tokens is stored in two
// separate ways depending on the token. Identifiers use UTF-8 encoding which
// allows them to be slices of the input file without allocating extra memory.
// Strings use UTF-16 encoding so they can represent unicode surrogates
// accurately.
import (
"fmt"
"strconv"
"strings"
"unicode"
"unicode/utf16"
"unicode/utf8"
"github.com/evanw/esbuild/internal/js_ast"
"github.com/evanw/esbuild/internal/logger"
)
type T uint
// If you add a new token, remember to add it to "tokenToString" too
const (
TEndOfFile T = iota
TSyntaxError
// "#!/usr/bin/env node"
THashbang
// Literals
TNoSubstitutionTemplateLiteral // Contents are in lexer.StringLiteral ([]uint16)
TNumericLiteral // Contents are in lexer.Number (float64)
TStringLiteral // Contents are in lexer.StringLiteral ([]uint16)
TBigIntegerLiteral // Contents are in lexer.Identifier (string)
// Pseudo-literals
TTemplateHead // Contents are in lexer.StringLiteral ([]uint16)
TTemplateMiddle // Contents are in lexer.StringLiteral ([]uint16)
TTemplateTail // Contents are in lexer.StringLiteral ([]uint16)
// Punctuation
TAmpersand
TAmpersandAmpersand
TAsterisk
TAsteriskAsterisk
TAt
TBar
TBarBar
TCaret
TCloseBrace
TCloseBracket
TCloseParen
TColon
TComma
TDot
TDotDotDot
TEqualsEquals
TEqualsEqualsEquals
TEqualsGreaterThan
TExclamation
TExclamationEquals
TExclamationEqualsEquals
TGreaterThan
TGreaterThanEquals
TGreaterThanGreaterThan
TGreaterThanGreaterThanGreaterThan
TLessThan
TLessThanEquals
TLessThanLessThan
TMinus
TMinusMinus
TOpenBrace
TOpenBracket
TOpenParen
TPercent
TPlus
TPlusPlus
TQuestion
TQuestionDot
TQuestionQuestion
TSemicolon
TSlash
TTilde
// Assignments (keep in sync with IsAssign() below)
TAmpersandAmpersandEquals
TAmpersandEquals
TAsteriskAsteriskEquals
TAsteriskEquals
TBarBarEquals
TBarEquals
TCaretEquals
TEquals
TGreaterThanGreaterThanEquals
TGreaterThanGreaterThanGreaterThanEquals
TLessThanLessThanEquals
TMinusEquals
TPercentEquals
TPlusEquals
TQuestionQuestionEquals
TSlashEquals
// Class-private fields and methods
TPrivateIdentifier
// Identifiers
TIdentifier // Contents are in lexer.Identifier (string)
TEscapedKeyword // A keyword that has been escaped as an identifer
// Reserved words
TBreak
TCase
TCatch
TClass
TConst
TContinue
TDebugger
TDefault
TDelete
TDo
TElse
TEnum
TExport
TExtends
TFalse
TFinally
TFor
TFunction
TIf
TImport
TIn
TInstanceof
TNew
TNull
TReturn
TSuper
TSwitch
TThis
TThrow
TTrue
TTry
TTypeof
TVar
TVoid
TWhile
TWith
)
func (t T) IsAssign() bool {
return t >= TAmpersandAmpersandEquals && t <= TSlashEquals
}
var Keywords = map[string]T{
// Reserved words
"break": TBreak,
"case": TCase,
"catch": TCatch,
"class": TClass,
"const": TConst,
"continue": TContinue,
"debugger": TDebugger,
"default": TDefault,
"delete": TDelete,
"do": TDo,
"else": TElse,
"enum": TEnum,
"export": TExport,
"extends": TExtends,
"false": TFalse,
"finally": TFinally,
"for": TFor,
"function": TFunction,
"if": TIf,
"import": TImport,
"in": TIn,
"instanceof": TInstanceof,
"new": TNew,
"null": TNull,
"return": TReturn,
"super": TSuper,
"switch": TSwitch,
"this": TThis,
"throw": TThrow,
"true": TTrue,
"try": TTry,
"typeof": TTypeof,
"var": TVar,
"void": TVoid,
"while": TWhile,
"with": TWith,
}
var StrictModeReservedWords = map[string]bool{
"implements": true,
"interface": true,
"let": true,
"package": true,
"private": true,
"protected": true,
"public": true,
"static": true,
"yield": true,
}
type json struct {
parse bool
allowComments bool
}
type Lexer struct {
log logger.Log
source logger.Source
current int
start int
end int
ApproximateNewlineCount int
LegacyOctalLoc logger.Loc
PreviousBackslashQuoteInJSX logger.Range
Token T
HasNewlineBefore bool
HasPureCommentBefore bool
PreserveAllCommentsBefore bool
IsLegacyOctalLiteral bool
CommentsToPreserveBefore []js_ast.Comment
AllOriginalComments []js_ast.Comment
codePoint rune
StringLiteral []uint16
Identifier string
JSXFactoryPragmaComment js_ast.Span
JSXFragmentPragmaComment js_ast.Span
SourceMappingURL js_ast.Span
Number float64
rescanCloseBraceAsTemplateToken bool
forGlobalName bool
json json
prevErrorLoc logger.Loc
// The log is disabled during speculative scans that may backtrack
IsLogDisabled bool
}
type LexerPanic struct{}
func NewLexer(log logger.Log, source logger.Source) Lexer {
lexer := Lexer{
log: log,
source: source,
prevErrorLoc: logger.Loc{Start: -1},
}
lexer.step()
lexer.Next()
return lexer
}
func NewLexerGlobalName(log logger.Log, source logger.Source) Lexer {
lexer := Lexer{
log: log,
source: source,
prevErrorLoc: logger.Loc{Start: -1},
forGlobalName: true,
}
lexer.step()
lexer.Next()
return lexer
}
func NewLexerJSON(log logger.Log, source logger.Source, allowComments bool) Lexer {
lexer := Lexer{
log: log,
source: source,
prevErrorLoc: logger.Loc{Start: -1},
json: json{
parse: true,
allowComments: allowComments,
},
}
lexer.step()
lexer.Next()
return lexer
}
func (lexer *Lexer) Loc() logger.Loc {
return logger.Loc{Start: int32(lexer.start)}
}
func (lexer *Lexer) Range() logger.Range {
return logger.Range{Loc: logger.Loc{Start: int32(lexer.start)}, Len: int32(lexer.end - lexer.start)}
}
func (lexer *Lexer) Raw() string {
return lexer.source.Contents[lexer.start:lexer.end]
}
func (lexer *Lexer) RawTemplateContents() string {
var text string
switch lexer.Token {
case TNoSubstitutionTemplateLiteral, TTemplateTail:
// "`x`" or "}x`"
text = lexer.source.Contents[lexer.start+1 : lexer.end-1]
case TTemplateHead, TTemplateMiddle:
// "`x${" or "}x${"
text = lexer.source.Contents[lexer.start+1 : lexer.end-2]
}
if strings.IndexByte(text, '\r') == -1 {
return text
}
// From the specification:
//
// 11.8.6.1 Static Semantics: TV and TRV
//
// TV excludes the code units of LineContinuation while TRV includes
// them. <CR><LF> and <CR> LineTerminatorSequences are normalized to
// <LF> for both TV and TRV. An explicit EscapeSequence is needed to
// include a <CR> or <CR><LF> sequence.
bytes := []byte(text)
end := 0
i := 0
for i < len(bytes) {
c := bytes[i]
i++
if c == '\r' {
// Convert '\r\n' into '\n'
if i < len(bytes) && bytes[i] == '\n' {
i++
}
// Convert '\r' into '\n'
c = '\n'
}
bytes[end] = c
end++
}
return string(bytes[:end])
}
func (lexer *Lexer) IsIdentifierOrKeyword() bool {
return lexer.Token >= TIdentifier
}
func (lexer *Lexer) IsContextualKeyword(text string) bool {
return lexer.Token == TIdentifier && lexer.Raw() == text
}
func (lexer *Lexer) ExpectContextualKeyword(text string) {
if !lexer.IsContextualKeyword(text) {
lexer.ExpectedString(fmt.Sprintf("%q", text))
}
lexer.Next()
}
func (lexer *Lexer) SyntaxError() {
loc := logger.Loc{Start: int32(lexer.end)}
message := "Unexpected end of file"
if lexer.end < len(lexer.source.Contents) {
c, _ := utf8.DecodeRuneInString(lexer.source.Contents[lexer.end:])
if c < 0x20 {
message = fmt.Sprintf("Syntax error \"\\x%02X\"", c)
} else if c >= 0x80 {
message = fmt.Sprintf("Syntax error \"\\u{%x}\"", c)
} else if c != '"' {
message = fmt.Sprintf("Syntax error \"%c\"", c)
} else {
message = "Syntax error '\"'"
}
}
lexer.addError(loc, message)
panic(LexerPanic{})
}
func (lexer *Lexer) ExpectedString(text string) {
found := fmt.Sprintf("%q", lexer.Raw())
if lexer.start == len(lexer.source.Contents) {
found = "end of file"
}
lexer.addRangeError(lexer.Range(), fmt.Sprintf("Expected %s but found %s", text, found))
panic(LexerPanic{})
}
func (lexer *Lexer) Expected(token T) {
if text, ok := tokenToString[token]; ok {
lexer.ExpectedString(text)
} else {
lexer.Unexpected()
}
}
func (lexer *Lexer) Unexpected() {
found := fmt.Sprintf("%q", lexer.Raw())
if lexer.start == len(lexer.source.Contents) {
found = "end of file"
}
lexer.addRangeError(lexer.Range(), fmt.Sprintf("Unexpected %s", found))
panic(LexerPanic{})
}
func (lexer *Lexer) Expect(token T) {
if lexer.Token != token {
lexer.Expected(token)
}
lexer.Next()
}
func (lexer *Lexer) ExpectOrInsertSemicolon() {
if lexer.Token == TSemicolon || (!lexer.HasNewlineBefore &&
lexer.Token != TCloseBrace && lexer.Token != TEndOfFile) {
lexer.Expect(TSemicolon)
}
}
// This parses a single "<" token. If that is the first part of a longer token,
// this function splits off the first "<" and leaves the remainder of the
// current token as another, smaller token. For example, "<<=" becomes "<=".
func (lexer *Lexer) ExpectLessThan(isInsideJSXElement bool) {
switch lexer.Token {
case TLessThan:
if isInsideJSXElement {
lexer.NextInsideJSXElement()
} else {
lexer.Next()
}
case TLessThanEquals:
lexer.Token = TEquals
lexer.start++
lexer.maybeExpandEquals()
case TLessThanLessThan:
lexer.Token = TLessThan
lexer.start++
case TLessThanLessThanEquals:
lexer.Token = TLessThanEquals
lexer.start++
default:
lexer.Expected(TLessThan)
}
}
// This parses a single ">" token. If that is the first part of a longer token,
// this function splits off the first ">" and leaves the remainder of the
// current token as another, smaller token. For example, ">>=" becomes ">=".
func (lexer *Lexer) ExpectGreaterThan(isInsideJSXElement bool) {
switch lexer.Token {
case TGreaterThan:
if isInsideJSXElement {
lexer.NextInsideJSXElement()
} else {
lexer.Next()
}
case TGreaterThanEquals:
lexer.Token = TEquals
lexer.start++
lexer.maybeExpandEquals()
case TGreaterThanGreaterThan:
lexer.Token = TGreaterThan
lexer.start++
case TGreaterThanGreaterThanEquals:
lexer.Token = TGreaterThanEquals
lexer.start++
case TGreaterThanGreaterThanGreaterThan:
lexer.Token = TGreaterThanGreaterThan
lexer.start++
case TGreaterThanGreaterThanGreaterThanEquals:
lexer.Token = TGreaterThanGreaterThanEquals
lexer.start++
default:
lexer.Expected(TGreaterThan)
}
}
func (lexer *Lexer) maybeExpandEquals() {
switch lexer.codePoint {
case '>':
// "=" + ">" = "=>"
lexer.Token = TEqualsGreaterThan
lexer.step()
case '=':
// "=" + "=" = "=="
lexer.Token = TEqualsEquals
lexer.step()
if lexer.Token == '=' {
// "=" + "==" = "==="
lexer.Token = TEqualsEqualsEquals
lexer.step()
}
}
}
func IsIdentifier(text string) bool {
if len(text) == 0 {
return false
}
for i, codePoint := range text {
if i == 0 {
if !IsIdentifierStart(codePoint) {
return false
}
} else {
if !IsIdentifierContinue(codePoint) {
return false
}
}
}
return true
}
func ForceValidIdentifier(text string) string {
if IsIdentifier(text) {
return text
}
sb := strings.Builder{}
// Identifier start
c, width := utf8.DecodeRuneInString(text)
text = text[width:]
if IsIdentifierStart(c) {
sb.WriteRune(c)
} else {
sb.WriteRune('_')
}
// Identifier continue
for text != "" {
c, width := utf8.DecodeRuneInString(text)
text = text[width:]
if IsIdentifierContinue(c) {
sb.WriteRune(c)
} else {
sb.WriteRune('_')
}
}
return sb.String()
}
// This does "IsIdentifier(UTF16ToString(text))" without any allocations
func IsIdentifierUTF16(text []uint16) bool {
n := len(text)
if n == 0 {
return false
}
for i := 0; i < n; i++ {
isStart := i == 0
r1 := rune(text[i])
if r1 >= 0xD800 && r1 <= 0xDBFF && i+1 < n {
if r2 := rune(text[i+1]); r2 >= 0xDC00 && r2 <= 0xDFFF {
r1 = (r1 << 10) + r2 + (0x10000 - (0xD800 << 10) - 0xDC00)
i++
}
}
if isStart {
if !IsIdentifierStart(r1) {
return false
}
} else {
if !IsIdentifierContinue(r1) {
return false
}
}
}
return true
}
func IsIdentifierStart(codePoint rune) bool {
switch codePoint {
case '_', '$',
'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z':
return true
}
// All ASCII identifier start code points are listed above
if codePoint < 0x7F {
return false
}
return unicode.Is(idStart, codePoint)
}
func IsIdentifierContinue(codePoint rune) bool {
switch codePoint {
case '_', '$', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z':
return true
}
// All ASCII identifier start code points are listed above
if codePoint < 0x7F {
return false
}
// ZWNJ and ZWJ are allowed in identifiers
if codePoint == 0x200C || codePoint == 0x200D {
return true
}
return unicode.Is(idContinue, codePoint)
}
// See the "White Space Code Points" table in the ECMAScript standard
func IsWhitespace(codePoint rune) bool {
switch codePoint {
case
'\u0009', // character tabulation
'\u000B', // line tabulation
'\u000C', // form feed
'\u0020', // space
'\u00A0', // no-break space
// Unicode "Space_Separator" code points
'\u1680', // ogham space mark
'\u2000', // en quad
'\u2001', // em quad
'\u2002', // en space
'\u2003', // em space
'\u2004', // three-per-em space
'\u2005', // four-per-em space
'\u2006', // six-per-em space
'\u2007', // figure space
'\u2008', // punctuation space
'\u2009', // thin space
'\u200A', // hair space
'\u202F', // narrow no-break space
'\u205F', // medium mathematical space
'\u3000', // ideographic space
'\uFEFF': // zero width non-breaking space
return true
default:
return false
}
}
func RangeOfIdentifier(source logger.Source, loc logger.Loc) logger.Range {
text := source.Contents[loc.Start:]
if len(text) == 0 {
return logger.Range{Loc: loc, Len: 0}
}
i := 0
c, _ := utf8.DecodeRuneInString(text[i:])
// Handle private names
if c == '#' {
i++
c, _ = utf8.DecodeRuneInString(text[i:])
}
if IsIdentifierStart(c) || c == '\\' {
// Search for the end of the identifier
for i < len(text) {
c2, width2 := utf8.DecodeRuneInString(text[i:])
if c2 == '\\' {
i += width2
// Skip over bracketed unicode escapes such as "\u{10000}"
if i+2 < len(text) && text[i] == 'u' && text[i+1] == '{' {
i += 2
for i < len(text) {
if text[i] == '}' {
i++
break
}
i++
}
}
} else if !IsIdentifierContinue(c2) {
return logger.Range{Loc: loc, Len: int32(i)}
} else {
i += width2
}
}
}
// When minifying, this identifier may have originally been a string
return source.RangeOfString(loc)
}
func (lexer *Lexer) ExpectJSXElementChild(token T) {
if lexer.Token != token {
lexer.Expected(token)
}
lexer.NextJSXElementChild()
}
func (lexer *Lexer) NextJSXElementChild() {
lexer.HasNewlineBefore = false
originalStart := lexer.end
for {
lexer.start = lexer.end
lexer.Token = 0
switch lexer.codePoint {
case -1: // This indicates the end of the file
lexer.Token = TEndOfFile
case '{':
lexer.step()
lexer.Token = TOpenBrace
case '<':
lexer.step()
lexer.Token = TLessThan
default:
needsFixing := false
stringLiteral:
for {
switch lexer.codePoint {
case -1:
// Reaching the end of the file without a closing element is an error
lexer.SyntaxError()
case '&', '\r', '\n', '\u2028', '\u2029':
// This needs fixing if it has an entity or if it's a multi-line string
needsFixing = true
lexer.step()
case '{', '<':
// Stop when the string ends
break stringLiteral
default:
// Non-ASCII strings need the slow path
if lexer.codePoint >= 0x80 {
needsFixing = true
}
lexer.step()
}
}
lexer.Token = TStringLiteral
text := lexer.source.Contents[originalStart:lexer.end]
if needsFixing {
// Slow path
lexer.StringLiteral = fixWhitespaceAndDecodeJSXEntities(text)
// Skip this token if it turned out to be empty after trimming
if len(lexer.StringLiteral) == 0 {
lexer.HasNewlineBefore = true
continue
}
} else {
// Fast path
n := len(text)
copy := make([]uint16, n)
for i := 0; i < n; i++ {
copy[i] = uint16(text[i])
}
lexer.StringLiteral = copy
}
}
break
}
}
func (lexer *Lexer) ExpectInsideJSXElement(token T) {
if lexer.Token != token {
lexer.Expected(token)
}
lexer.NextInsideJSXElement()
}
func (lexer *Lexer) NextInsideJSXElement() {
lexer.HasNewlineBefore = false
for {
lexer.start = lexer.end
lexer.Token = 0
switch lexer.codePoint {
case -1: // This indicates the end of the file
lexer.Token = TEndOfFile
case '\r', '\n', '\u2028', '\u2029':
lexer.step()
lexer.HasNewlineBefore = true
continue
case '\t', ' ':
lexer.step()
continue
case '.':
lexer.step()
lexer.Token = TDot
case '=':
lexer.step()
lexer.Token = TEquals
case '{':
lexer.step()
lexer.Token = TOpenBrace
case '}':
lexer.step()
lexer.Token = TCloseBrace
case '<':
lexer.step()
lexer.Token = TLessThan
case '>':
lexer.step()
lexer.Token = TGreaterThan
case '/':
// '/' or '//' or '/* ... */'
lexer.step()
switch lexer.codePoint {
case '/':
singleLineComment:
for {
lexer.step()
switch lexer.codePoint {
case '\r', '\n', '\u2028', '\u2029':
break singleLineComment
case -1: // This indicates the end of the file
break singleLineComment
}
}
continue
case '*':
lexer.step()
startRange := lexer.Range()
multiLineComment:
for {
switch lexer.codePoint {
case '*':
lexer.step()
if lexer.codePoint == '/' {
lexer.step()
break multiLineComment
}
case '\r', '\n', '\u2028', '\u2029':
lexer.step()
lexer.HasNewlineBefore = true
case -1: // This indicates the end of the file
lexer.start = lexer.end
lexer.addErrorWithNotes(lexer.Loc(), "Expected \"*/\" to terminate multi-line comment",
[]logger.MsgData{logger.RangeData(&lexer.source, startRange, "The multi-line comment starts here")})
panic(LexerPanic{})
default:
lexer.step()
}
}
continue
default:
lexer.Token = TSlash
}
case '\'', '"':
var backslash logger.Range
quote := lexer.codePoint
needsDecode := false
lexer.step()
stringLiteral:
for {
switch lexer.codePoint {
case -1: // This indicates the end of the file
lexer.SyntaxError()
case '&':
needsDecode = true
lexer.step()
case '\\':
backslash = logger.Range{Loc: logger.Loc{Start: int32(lexer.end)}, Len: 1}
lexer.step()
continue
case quote:
if backslash.Len > 0 {
backslash.Len++
lexer.PreviousBackslashQuoteInJSX = backslash
}
lexer.step()
break stringLiteral
default:
// Non-ASCII strings need the slow path
if lexer.codePoint >= 0x80 {
needsDecode = true
}
lexer.step()
}
backslash = logger.Range{}
}
lexer.Token = TStringLiteral
text := lexer.source.Contents[lexer.start+1 : lexer.end-1]
if needsDecode {
// Slow path
lexer.StringLiteral = decodeJSXEntities([]uint16{}, text)
} else {
// Fast path
n := len(text)
copy := make([]uint16, n)
for i := 0; i < n; i++ {
copy[i] = uint16(text[i])
}
lexer.StringLiteral = copy
}
default:
// Check for unusual whitespace characters
if IsWhitespace(lexer.codePoint) {
lexer.step()
continue
}
if IsIdentifierStart(lexer.codePoint) {
lexer.step()
for IsIdentifierContinue(lexer.codePoint) || lexer.codePoint == '-' {
lexer.step()
}
// Parse JSX namespaces. These are not supported by React or TypeScript
// but someone using JSX syntax in more obscure ways may find a use for
// them. A namespaced name is just always turned into a string so you
// can't use this feature to reference JavaScript identifiers.
if lexer.codePoint == ':' {
lexer.step()
if IsIdentifierStart(lexer.codePoint) {
lexer.step()
for IsIdentifierContinue(lexer.codePoint) || lexer.codePoint == '-' {
lexer.step()
}
} else {
lexer.addError(logger.Loc{Start: lexer.Range().End()},
fmt.Sprintf("Expected identifier after %q in namespaced JSX name", lexer.Raw()))
}
}
lexer.Identifier = lexer.Raw()
lexer.Token = TIdentifier
break
}
lexer.end = lexer.current
lexer.Token = TSyntaxError
}
return
}
}
func (lexer *Lexer) Next() {
lexer.HasNewlineBefore = lexer.end == 0
lexer.HasPureCommentBefore = false
lexer.CommentsToPreserveBefore = nil
for {
lexer.start = lexer.end
lexer.Token = 0