switch glide to govendor (#43)

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

vendor/github.com/aymerick/raymond/parser/parser.go

@@ -0,0 +1,846 @@
+// Package parser provides a handlebars syntax analyser. It consumes the tokens provided by the lexer to build an AST.
+package parser
+
+import (
+	"fmt"
+	"regexp"
+	"runtime"
+	"strconv"
+
+	"github.com/aymerick/raymond/ast"
+	"github.com/aymerick/raymond/lexer"
+)
+
+// References:
+//   - https://github.com/wycats/handlebars.js/blob/master/src/handlebars.yy
+//   - https://github.com/golang/go/blob/master/src/text/template/parse/parse.go
+
+// parser is a syntax analyzer.
+type parser struct {
+	// Lexer
+	lex *lexer.Lexer
+
+	// Root node
+	root ast.Node
+
+	// Tokens parsed but not consumed yet
+	tokens []*lexer.Token
+
+	// All tokens have been retreieved from lexer
+	lexOver bool
+}
+
+var (
+	rOpenComment  = regexp.MustCompile(`^\{\{~?!-?-?`)
+	rCloseComment = regexp.MustCompile(`-?-?~?\}\}$`)
+	rOpenAmp      = regexp.MustCompile(`^\{\{~?&`)
+)
+
+// new instanciates a new parser
+func new(input string) *parser {
+	return &parser{
+		lex: lexer.Scan(input),
+	}
+}
+
+// Parse analyzes given input and returns the AST root node.
+func Parse(input string) (result *ast.Program, err error) {
+	// recover error
+	defer errRecover(&err)
+
+	parser := new(input)
+
+	// parse
+	result = parser.parseProgram()
+
+	// check last token
+	token := parser.shift()
+	if token.Kind != lexer.TokenEOF {
+		// Parsing ended before EOF
+		errToken(token, "Syntax error")
+	}
+
+	// fix whitespaces
+	processWhitespaces(result)
+
+	// named returned values
+	return
+}
+
+// errRecover recovers parsing panic
+func errRecover(errp *error) {
+	e := recover()
+	if e != nil {
+		switch err := e.(type) {
+		case runtime.Error:
+			panic(e)
+		case error:
+			*errp = err
+		default:
+			panic(e)
+		}
+	}
+}
+
+// errPanic panics
+func errPanic(err error, line int) {
+	panic(fmt.Errorf("Parse error on line %d:\n%s", line, err))
+}
+
+// errNode panics with given node infos
+func errNode(node ast.Node, msg string) {
+	errPanic(fmt.Errorf("%s\nNode: %s", msg, node), node.Location().Line)
+}
+
+// errNode panics with given Token infos
+func errToken(tok *lexer.Token, msg string) {
+	errPanic(fmt.Errorf("%s\nToken: %s", msg, tok), tok.Line)
+}
+
+// errNode panics because of an unexpected Token kind
+func errExpected(expect lexer.TokenKind, tok *lexer.Token) {
+	errPanic(fmt.Errorf("Expecting %s, got: '%s'", expect, tok), tok.Line)
+}
+
+// program : statement*
+func (p *parser) parseProgram() *ast.Program {
+	result := ast.NewProgram(p.next().Pos, p.next().Line)
+
+	for p.isStatement() {
+		result.AddStatement(p.parseStatement())
+	}
+
+	return result
+}
+
+// statement : mustache | block | rawBlock | partial | content | COMMENT
+func (p *parser) parseStatement() ast.Node {
+	var result ast.Node
+
+	tok := p.next()
+
+	switch tok.Kind {
+	case lexer.TokenOpen, lexer.TokenOpenUnescaped:
+		// mustache
+		result = p.parseMustache()
+	case lexer.TokenOpenBlock:
+		// block
+		result = p.parseBlock()
+	case lexer.TokenOpenInverse:
+		// block
+		result = p.parseInverse()
+	case lexer.TokenOpenRawBlock:
+		// rawBlock
+		result = p.parseRawBlock()
+	case lexer.TokenOpenPartial:
+		// partial
+		result = p.parsePartial()
+	case lexer.TokenContent:
+		// content
+		result = p.parseContent()
+	case lexer.TokenComment:
+		// COMMENT
+		result = p.parseComment()
+	}
+
+	return result
+}
+
+// isStatement returns true if next token starts a statement
+func (p *parser) isStatement() bool {
+	if !p.have(1) {
+		return false
+	}
+
+	switch p.next().Kind {
+	case lexer.TokenOpen, lexer.TokenOpenUnescaped, lexer.TokenOpenBlock,
+		lexer.TokenOpenInverse, lexer.TokenOpenRawBlock, lexer.TokenOpenPartial,
+		lexer.TokenContent, lexer.TokenComment:
+		return true
+	}
+
+	return false
+}
+
+// content : CONTENT
+func (p *parser) parseContent() *ast.ContentStatement {
+	// CONTENT
+	tok := p.shift()
+	if tok.Kind != lexer.TokenContent {
+		// @todo This check can be removed if content is optional in a raw block
+		errExpected(lexer.TokenContent, tok)
+	}
+
+	return ast.NewContentStatement(tok.Pos, tok.Line, tok.Val)
+}
+
+// COMMENT
+func (p *parser) parseComment() *ast.CommentStatement {
+	// COMMENT
+	tok := p.shift()
+
+	value := rOpenComment.ReplaceAllString(tok.Val, "")
+	value = rCloseComment.ReplaceAllString(value, "")
+
+	result := ast.NewCommentStatement(tok.Pos, tok.Line, value)
+	result.Strip = ast.NewStripForStr(tok.Val)
+
+	return result
+}
+
+// param* hash?
+func (p *parser) parseExpressionParamsHash() ([]ast.Node, *ast.Hash) {
+	var params []ast.Node
+	var hash *ast.Hash
+
+	// params*
+	if p.isParam() {
+		params = p.parseParams()
+	}
+
+	// hash?
+	if p.isHashSegment() {
+		hash = p.parseHash()
+	}
+
+	return params, hash
+}
+
+// helperName param* hash?
+func (p *parser) parseExpression(tok *lexer.Token) *ast.Expression {
+	result := ast.NewExpression(tok.Pos, tok.Line)
+
+	// helperName
+	result.Path = p.parseHelperName()
+
+	// param* hash?
+	result.Params, result.Hash = p.parseExpressionParamsHash()
+
+	return result
+}
+
+// rawBlock : openRawBlock content endRawBlock
+// openRawBlock : OPEN_RAW_BLOCK helperName param* hash? CLOSE_RAW_BLOCK
+// endRawBlock : OPEN_END_RAW_BLOCK helperName CLOSE_RAW_BLOCK
+func (p *parser) parseRawBlock() *ast.BlockStatement {
+	// OPEN_RAW_BLOCK
+	tok := p.shift()
+
+	result := ast.NewBlockStatement(tok.Pos, tok.Line)
+
+	// helperName param* hash?
+	result.Expression = p.parseExpression(tok)
+
+	openName := result.Expression.Canonical()
+
+	// CLOSE_RAW_BLOCK
+	tok = p.shift()
+	if tok.Kind != lexer.TokenCloseRawBlock {
+		errExpected(lexer.TokenCloseRawBlock, tok)
+	}
+
+	// content
+	// @todo Is content mandatory in a raw block ?
+	content := p.parseContent()
+
+	program := ast.NewProgram(tok.Pos, tok.Line)
+	program.AddStatement(content)
+
+	result.Program = program
+
+	// OPEN_END_RAW_BLOCK
+	tok = p.shift()
+	if tok.Kind != lexer.TokenOpenEndRawBlock {
+		// should never happen as it is caught by lexer
+		errExpected(lexer.TokenOpenEndRawBlock, tok)
+	}
+
+	// helperName
+	endID := p.parseHelperName()
+
+	closeName, ok := ast.HelperNameStr(endID)
+	if !ok {
+		errNode(endID, "Erroneous closing expression")
+	}
+
+	if openName != closeName {
+		errNode(endID, fmt.Sprintf("%s doesn't match %s", openName, closeName))
+	}
+
+	// CLOSE_RAW_BLOCK
+	tok = p.shift()
+	if tok.Kind != lexer.TokenCloseRawBlock {
+		errExpected(lexer.TokenCloseRawBlock, tok)
+	}
+
+	return result
+}
+
+// block : openBlock program inverseChain? closeBlock
+func (p *parser) parseBlock() *ast.BlockStatement {
+	// openBlock
+	result, blockParams := p.parseOpenBlock()
+
+	// program
+	program := p.parseProgram()
+	program.BlockParams = blockParams
+	result.Program = program
+
+	// inverseChain?
+	if p.isInverseChain() {
+		result.Inverse = p.parseInverseChain()
+	}
+
+	// closeBlock
+	p.parseCloseBlock(result)
+
+	setBlockInverseStrip(result)
+
+	return result
+}
+
+// setBlockInverseStrip is called when parsing `block` (openBlock | openInverse) and `inverseChain`
+//
+// TODO: This was totally cargo culted ! CHECK THAT !
+//
+// cf. prepareBlock() in:
+//   https://github.com/wycats/handlebars.js/blob/master/lib/handlebars/compiler/helper.js
+func setBlockInverseStrip(block *ast.BlockStatement) {
+	if block.Inverse == nil {
+		return
+	}
+
+	if block.Inverse.Chained {
+		b, _ := block.Inverse.Body[0].(*ast.BlockStatement)
+		b.CloseStrip = block.CloseStrip
+	}
+
+	block.InverseStrip = block.Inverse.Strip
+}
+
+// block : openInverse program inverseAndProgram? closeBlock
+func (p *parser) parseInverse() *ast.BlockStatement {
+	// openInverse
+	result, blockParams := p.parseOpenBlock()
+
+	// program
+	program := p.parseProgram()
+
+	program.BlockParams = blockParams
+	result.Inverse = program
+
+	// inverseAndProgram?
+	if p.isInverse() {
+		result.Program = p.parseInverseAndProgram()
+	}
+
+	// closeBlock
+	p.parseCloseBlock(result)
+
+	setBlockInverseStrip(result)
+
+	return result
+}
+
+// helperName param* hash? blockParams?
+func (p *parser) parseOpenBlockExpression(tok *lexer.Token) (*ast.BlockStatement, []string) {
+	var blockParams []string
+
+	result := ast.NewBlockStatement(tok.Pos, tok.Line)
+
+	// helperName param* hash?
+	result.Expression = p.parseExpression(tok)
+
+	// blockParams?
+	if p.isBlockParams() {
+		blockParams = p.parseBlockParams()
+	}
+
+	// named returned values
+	return result, blockParams
+}
+
+// inverseChain : openInverseChain program inverseChain?
+//              | inverseAndProgram
+func (p *parser) parseInverseChain() *ast.Program {
+	if p.isInverse() {
+		// inverseAndProgram
+		return p.parseInverseAndProgram()
+	}
+
+	result := ast.NewProgram(p.next().Pos, p.next().Line)
+
+	// openInverseChain
+	block, blockParams := p.parseOpenBlock()
+
+	// program
+	program := p.parseProgram()
+
+	program.BlockParams = blockParams
+	block.Program = program
+
+	// inverseChain?
+	if p.isInverseChain() {
+		block.Inverse = p.parseInverseChain()
+	}
+
+	setBlockInverseStrip(block)
+
+	result.Chained = true
+	result.AddStatement(block)
+
+	return result
+}
+
+// Returns true if current token starts an inverse chain
+func (p *parser) isInverseChain() bool {
+	return p.isOpenInverseChain() || p.isInverse()
+}
+
+// inverseAndProgram : INVERSE program
+func (p *parser) parseInverseAndProgram() *ast.Program {
+	// INVERSE
+	tok := p.shift()
+
+	// program
+	result := p.parseProgram()
+	result.Strip = ast.NewStripForStr(tok.Val)
+
+	return result
+}
+
+// openBlock : OPEN_BLOCK helperName param* hash? blockParams? CLOSE
+// openInverse : OPEN_INVERSE helperName param* hash? blockParams? CLOSE
+// openInverseChain: OPEN_INVERSE_CHAIN helperName param* hash? blockParams? CLOSE
+func (p *parser) parseOpenBlock() (*ast.BlockStatement, []string) {
+	// OPEN_BLOCK | OPEN_INVERSE | OPEN_INVERSE_CHAIN
+	tok := p.shift()
+
+	// helperName param* hash? blockParams?
+	result, blockParams := p.parseOpenBlockExpression(tok)
+
+	// CLOSE
+	tokClose := p.shift()
+	if tokClose.Kind != lexer.TokenClose {
+		errExpected(lexer.TokenClose, tokClose)
+	}
+
+	result.OpenStrip = ast.NewStrip(tok.Val, tokClose.Val)
+
+	// named returned values
+	return result, blockParams
+}
+
+// closeBlock : OPEN_ENDBLOCK helperName CLOSE
+func (p *parser) parseCloseBlock(block *ast.BlockStatement) {
+	// OPEN_ENDBLOCK
+	tok := p.shift()
+	if tok.Kind != lexer.TokenOpenEndBlock {
+		errExpected(lexer.TokenOpenEndBlock, tok)
+	}
+
+	// helperName
+	endID := p.parseHelperName()
+
+	closeName, ok := ast.HelperNameStr(endID)
+	if !ok {
+		errNode(endID, "Erroneous closing expression")
+	}
+
+	openName := block.Expression.Canonical()
+	if openName != closeName {
+		errNode(endID, fmt.Sprintf("%s doesn't match %s", openName, closeName))
+	}
+
+	// CLOSE
+	tokClose := p.shift()
+	if tokClose.Kind != lexer.TokenClose {
+		errExpected(lexer.TokenClose, tokClose)
+	}
+
+	block.CloseStrip = ast.NewStrip(tok.Val, tokClose.Val)
+}
+
+// mustache : OPEN helperName param* hash? CLOSE
+//          | OPEN_UNESCAPED helperName param* hash? CLOSE_UNESCAPED
+func (p *parser) parseMustache() *ast.MustacheStatement {
+	// OPEN | OPEN_UNESCAPED
+	tok := p.shift()
+
+	closeToken := lexer.TokenClose
+	if tok.Kind == lexer.TokenOpenUnescaped {
+		closeToken = lexer.TokenCloseUnescaped
+	}
+
+	unescaped := false
+	if (tok.Kind == lexer.TokenOpenUnescaped) || (rOpenAmp.MatchString(tok.Val)) {
+		unescaped = true
+	}
+
+	result := ast.NewMustacheStatement(tok.Pos, tok.Line, unescaped)
+
+	// helperName param* hash?
+	result.Expression = p.parseExpression(tok)
+
+	// CLOSE | CLOSE_UNESCAPED
+	tokClose := p.shift()
+	if tokClose.Kind != closeToken {
+		errExpected(closeToken, tokClose)
+	}
+
+	result.Strip = ast.NewStrip(tok.Val, tokClose.Val)
+
+	return result
+}
+
+// partial : OPEN_PARTIAL partialName param* hash? CLOSE
+func (p *parser) parsePartial() *ast.PartialStatement {
+	// OPEN_PARTIAL
+	tok := p.shift()
+
+	result := ast.NewPartialStatement(tok.Pos, tok.Line)
+
+	// partialName
+	result.Name = p.parsePartialName()
+
+	// param* hash?
+	result.Params, result.Hash = p.parseExpressionParamsHash()
+
+	// CLOSE
+	tokClose := p.shift()
+	if tokClose.Kind != lexer.TokenClose {
+		errExpected(lexer.TokenClose, tokClose)
+	}
+
+	result.Strip = ast.NewStrip(tok.Val, tokClose.Val)
+
+	return result
+}
+
+// helperName | sexpr
+func (p *parser) parseHelperNameOrSexpr() ast.Node {
+	if p.isSexpr() {
+		// sexpr
+		return p.parseSexpr()
+	}
+
+	// helperName
+	return p.parseHelperName()
+}
+
+// param : helperName | sexpr
+func (p *parser) parseParam() ast.Node {
+	return p.parseHelperNameOrSexpr()
+}
+
+// Returns true if next tokens represent a `param`
+func (p *parser) isParam() bool {
+	return (p.isSexpr() || p.isHelperName()) && !p.isHashSegment()
+}
+
+// param*
+func (p *parser) parseParams() []ast.Node {
+	var result []ast.Node
+
+	for p.isParam() {
+		result = append(result, p.parseParam())
+	}
+
+	return result
+}
+
+// sexpr : OPEN_SEXPR helperName param* hash? CLOSE_SEXPR
+func (p *parser) parseSexpr() *ast.SubExpression {
+	// OPEN_SEXPR
+	tok := p.shift()
+
+	result := ast.NewSubExpression(tok.Pos, tok.Line)
+
+	// helperName param* hash?
+	result.Expression = p.parseExpression(tok)
+
+	// CLOSE_SEXPR
+	tok = p.shift()
+	if tok.Kind != lexer.TokenCloseSexpr {
+		errExpected(lexer.TokenCloseSexpr, tok)
+	}
+
+	return result
+}
+
+// hash : hashSegment+
+func (p *parser) parseHash() *ast.Hash {
+	var pairs []*ast.HashPair
+
+	for p.isHashSegment() {
+		pairs = append(pairs, p.parseHashSegment())
+	}
+
+	firstLoc := pairs[0].Location()
+
+	result := ast.NewHash(firstLoc.Pos, firstLoc.Line)
+	result.Pairs = pairs
+
+	return result
+}
+
+// returns true if next tokens represents a `hashSegment`
+func (p *parser) isHashSegment() bool {
+	return p.have(2) && (p.next().Kind == lexer.TokenID) && (p.nextAt(1).Kind == lexer.TokenEquals)
+}
+
+// hashSegment : ID EQUALS param
+func (p *parser) parseHashSegment() *ast.HashPair {
+	// ID
+	tok := p.shift()
+
+	// EQUALS
+	p.shift()
+
+	// param
+	param := p.parseParam()
+
+	result := ast.NewHashPair(tok.Pos, tok.Line)
+	result.Key = tok.Val
+	result.Val = param
+
+	return result
+}
+
+// blockParams : OPEN_BLOCK_PARAMS ID+ CLOSE_BLOCK_PARAMS
+func (p *parser) parseBlockParams() []string {
+	var result []string
+
+	// OPEN_BLOCK_PARAMS
+	tok := p.shift()
+
+	// ID+
+	for p.isID() {
+		result = append(result, p.shift().Val)
+	}
+
+	if len(result) == 0 {
+		errExpected(lexer.TokenID, p.next())
+	}
+
+	// CLOSE_BLOCK_PARAMS
+	tok = p.shift()
+	if tok.Kind != lexer.TokenCloseBlockParams {
+		errExpected(lexer.TokenCloseBlockParams, tok)
+	}
+
+	return result
+}
+
+// helperName : path | dataName | STRING | NUMBER | BOOLEAN | UNDEFINED | NULL
+func (p *parser) parseHelperName() ast.Node {
+	var result ast.Node
+
+	tok := p.next()
+
+	switch tok.Kind {
+	case lexer.TokenBoolean:
+		// BOOLEAN
+		p.shift()
+		result = ast.NewBooleanLiteral(tok.Pos, tok.Line, (tok.Val == "true"), tok.Val)
+	case lexer.TokenNumber:
+		// NUMBER
+		p.shift()
+
+		val, isInt := parseNumber(tok)
+		result = ast.NewNumberLiteral(tok.Pos, tok.Line, val, isInt, tok.Val)
+	case lexer.TokenString:
+		// STRING
+		p.shift()
+		result = ast.NewStringLiteral(tok.Pos, tok.Line, tok.Val)
+	case lexer.TokenData:
+		// dataName
+		result = p.parseDataName()
+	default:
+		// path
+		result = p.parsePath(false)
+	}
+
+	return result
+}
+
+// parseNumber parses a number
+func parseNumber(tok *lexer.Token) (result float64, isInt bool) {
+	var valInt int
+	var err error
+
+	valInt, err = strconv.Atoi(tok.Val)
+	if err == nil {
+		isInt = true
+
+		result = float64(valInt)
+	} else {
+		isInt = false
+
+		result, err = strconv.ParseFloat(tok.Val, 64)
+		if err != nil {
+			errToken(tok, fmt.Sprintf("Failed to parse number: %s", tok.Val))
+		}
+	}
+
+	// named returned values
+	return
+}
+
+// Returns true if next tokens represent a `helperName`
+func (p *parser) isHelperName() bool {
+	switch p.next().Kind {
+	case lexer.TokenBoolean, lexer.TokenNumber, lexer.TokenString, lexer.TokenData, lexer.TokenID:
+		return true
+	}
+
+	return false
+}
+
+// partialName : helperName | sexpr
+func (p *parser) parsePartialName() ast.Node {
+	return p.parseHelperNameOrSexpr()
+}
+
+// dataName : DATA pathSegments
+func (p *parser) parseDataName() *ast.PathExpression {
+	// DATA
+	p.shift()
+
+	// pathSegments
+	return p.parsePath(true)
+}
+
+// path : pathSegments
+// pathSegments : pathSegments SEP ID
+//              | ID
+func (p *parser) parsePath(data bool) *ast.PathExpression {
+	var tok *lexer.Token
+
+	// ID
+	tok = p.shift()
+	if tok.Kind != lexer.TokenID {
+		errExpected(lexer.TokenID, tok)
+	}
+
+	result := ast.NewPathExpression(tok.Pos, tok.Line, data)
+	result.Part(tok.Val)
+
+	for p.isPathSep() {
+		// SEP
+		tok = p.shift()
+		result.Sep(tok.Val)
+
+		// ID
+		tok = p.shift()
+		if tok.Kind != lexer.TokenID {
+			errExpected(lexer.TokenID, tok)
+		}
+
+		result.Part(tok.Val)
+
+		if len(result.Parts) > 0 {
+			switch tok.Val {
+			case "..", ".", "this":
+				errToken(tok, "Invalid path: "+result.Original)
+			}
+		}
+	}
+
+	return result
+}
+
+// Ensures there is token to parse at given index
+func (p *parser) ensure(index int) {
+	if p.lexOver {
+		// nothing more to grab
+		return
+	}
+
+	nb := index + 1
+
+	for len(p.tokens) < nb {
+		// fetch next token
+		tok := p.lex.NextToken()
+
+		// queue it
+		p.tokens = append(p.tokens, &tok)
+
+		if (tok.Kind == lexer.TokenEOF) || (tok.Kind == lexer.TokenError) {
+			p.lexOver = true
+			break
+		}
+	}
+}
+
+// have returns true is there are a list given number of tokens to consume left
+func (p *parser) have(nb int) bool {
+	p.ensure(nb - 1)
+
+	return len(p.tokens) >= nb
+}
+
+// nextAt returns next token at given index, without consuming it
+func (p *parser) nextAt(index int) *lexer.Token {
+	p.ensure(index)
+
+	return p.tokens[index]
+}
+
+// next returns next token without consuming it
+func (p *parser) next() *lexer.Token {
+	return p.nextAt(0)
+}
+
+// shift returns next token and remove it from the tokens buffer
+//
+// Panics if next token is `TokenError`
+func (p *parser) shift() *lexer.Token {
+	var result *lexer.Token
+
+	p.ensure(0)
+
+	result, p.tokens = p.tokens[0], p.tokens[1:]
+
+	// check error token
+	if result.Kind == lexer.TokenError {
+		errToken(result, "Lexer error")
+	}
+
+	return result
+}
+
+// isToken returns true if next token is of given type
+func (p *parser) isToken(kind lexer.TokenKind) bool {
+	return p.have(1) && p.next().Kind == kind
+}
+
+// isSexpr returns true if next token starts a sexpr
+func (p *parser) isSexpr() bool {
+	return p.isToken(lexer.TokenOpenSexpr)
+}
+
+// isPathSep returns true if next token is a path separator
+func (p *parser) isPathSep() bool {
+	return p.isToken(lexer.TokenSep)
+}
+
+// isID returns true if next token is an ID
+func (p *parser) isID() bool {
+	return p.isToken(lexer.TokenID)
+}
+
+// isBlockParams returns true if next token starts a block params
+func (p *parser) isBlockParams() bool {
+	return p.isToken(lexer.TokenOpenBlockParams)
+}
+
+// isInverse returns true if next token starts an INVERSE sequence
+func (p *parser) isInverse() bool {
+	return p.isToken(lexer.TokenInverse)
+}
+
+// isOpenInverseChain returns true if next token is OPEN_INVERSE_CHAIN
+func (p *parser) isOpenInverseChain() bool {
+	return p.isToken(lexer.TokenOpenInverseChain)
+}

vendor/github.com/aymerick/raymond/parser/whitespace.go

@@ -0,0 +1,360 @@
+package parser
+
+import (
+	"regexp"
+
+	"github.com/aymerick/raymond/ast"
+)
+
+// whitespaceVisitor walks through the AST to perform whitespace control
+//
+// The logic was shamelessly borrowed from:
+//   https://github.com/wycats/handlebars.js/blob/master/lib/handlebars/compiler/whitespace-control.js
+type whitespaceVisitor struct {
+	isRootSeen bool
+}
+
+var (
+	rTrimLeft         = regexp.MustCompile(`^[ \t]*\r?\n?`)
+	rTrimLeftMultiple = regexp.MustCompile(`^\s+`)
+
+	rTrimRight         = regexp.MustCompile(`[ \t]+$`)
+	rTrimRightMultiple = regexp.MustCompile(`\s+$`)
+
+	rPrevWhitespace      = regexp.MustCompile(`\r?\n\s*?$`)
+	rPrevWhitespaceStart = regexp.MustCompile(`(^|\r?\n)\s*?$`)
+
+	rNextWhitespace    = regexp.MustCompile(`^\s*?\r?\n`)
+	rNextWhitespaceEnd = regexp.MustCompile(`^\s*?(\r?\n|$)`)
+
+	rPartialIndent = regexp.MustCompile(`([ \t]+$)`)
+)
+
+// newWhitespaceVisitor instanciates a new whitespaceVisitor
+func newWhitespaceVisitor() *whitespaceVisitor {
+	return &whitespaceVisitor{}
+}
+
+// processWhitespaces performs whitespace control on given AST
+//
+// WARNING: It must be called only once on AST.
+func processWhitespaces(node ast.Node) {
+	node.Accept(newWhitespaceVisitor())
+}
+
+func omitRightFirst(body []ast.Node, multiple bool) {
+	omitRight(body, -1, multiple)
+}
+
+func omitRight(body []ast.Node, i int, multiple bool) {
+	if i+1 >= len(body) {
+		return
+	}
+
+	current := body[i+1]
+
+	node, ok := current.(*ast.ContentStatement)
+	if !ok {
+		return
+	}
+
+	if !multiple && node.RightStripped {
+		return
+	}
+
+	original := node.Value
+
+	r := rTrimLeft
+	if multiple {
+		r = rTrimLeftMultiple
+	}
+
+	node.Value = r.ReplaceAllString(node.Value, "")
+
+	node.RightStripped = (original != node.Value)
+}
+
+func omitLeftLast(body []ast.Node, multiple bool) {
+	omitLeft(body, len(body), multiple)
+}
+
+func omitLeft(body []ast.Node, i int, multiple bool) bool {
+	if i-1 < 0 {
+		return false
+	}
+
+	current := body[i-1]
+
+	node, ok := current.(*ast.ContentStatement)
+	if !ok {
+		return false
+	}
+
+	if !multiple && node.LeftStripped {
+		return false
+	}
+
+	original := node.Value
+
+	r := rTrimRight
+	if multiple {
+		r = rTrimRightMultiple
+	}
+
+	node.Value = r.ReplaceAllString(node.Value, "")
+
+	node.LeftStripped = (original != node.Value)
+
+	return node.LeftStripped
+}
+
+func isPrevWhitespace(body []ast.Node) bool {
+	return isPrevWhitespaceProgram(body, len(body), false)
+}
+
+func isPrevWhitespaceProgram(body []ast.Node, i int, isRoot bool) bool {
+	if i < 1 {
+		return isRoot
+	}
+
+	prev := body[i-1]
+
+	if node, ok := prev.(*ast.ContentStatement); ok {
+		if (node.Value == "") && node.RightStripped {
+			// already stripped, so it may be an empty string not catched by regexp
+			return true
+		}
+
+		r := rPrevWhitespaceStart
+		if (i > 1) || !isRoot {
+			r = rPrevWhitespace
+		}
+
+		return r.MatchString(node.Value)
+	}
+
+	return false
+}
+
+func isNextWhitespace(body []ast.Node) bool {
+	return isNextWhitespaceProgram(body, -1, false)
+}
+
+func isNextWhitespaceProgram(body []ast.Node, i int, isRoot bool) bool {
+	if i+1 >= len(body) {
+		return isRoot
+	}
+
+	next := body[i+1]
+
+	if node, ok := next.(*ast.ContentStatement); ok {
+		if (node.Value == "") && node.LeftStripped {
+			// already stripped, so it may be an empty string not catched by regexp
+			return true
+		}
+
+		r := rNextWhitespaceEnd
+		if (i+2 > len(body)) || !isRoot {
+			r = rNextWhitespace
+		}
+
+		return r.MatchString(node.Value)
+	}
+
+	return false
+}
+
+//
+// Visitor interface
+//
+
+func (v *whitespaceVisitor) VisitProgram(program *ast.Program) interface{} {
+	isRoot := !v.isRootSeen
+	v.isRootSeen = true
+
+	body := program.Body
+	for i, current := range body {
+		strip, _ := current.Accept(v).(*ast.Strip)
+		if strip == nil {
+			continue
+		}
+
+		_isPrevWhitespace := isPrevWhitespaceProgram(body, i, isRoot)
+		_isNextWhitespace := isNextWhitespaceProgram(body, i, isRoot)
+
+		openStandalone := strip.OpenStandalone && _isPrevWhitespace
+		closeStandalone := strip.CloseStandalone && _isNextWhitespace
+		inlineStandalone := strip.InlineStandalone && _isPrevWhitespace && _isNextWhitespace
+
+		if strip.Close {
+			omitRight(body, i, true)
+		}
+
+		if strip.Open && (i > 0) {
+			omitLeft(body, i, true)
+		}
+
+		if inlineStandalone {
+			omitRight(body, i, false)
+
+			if omitLeft(body, i, false) {
+				// If we are on a standalone node, save the indent info for partials
+				if partial, ok := current.(*ast.PartialStatement); ok {
+					// Pull out the whitespace from the final line
+					if i > 0 {
+						if prevContent, ok := body[i-1].(*ast.ContentStatement); ok {
+							partial.Indent = rPartialIndent.FindString(prevContent.Original)
+						}
+					}
+				}
+			}
+		}
+
+		if b, ok := current.(*ast.BlockStatement); ok {
+			if openStandalone {
+				prog := b.Program
+				if prog == nil {
+					prog = b.Inverse
+				}
+
+				omitRightFirst(prog.Body, false)
+
+				// Strip out the previous content node if it's whitespace only
+				omitLeft(body, i, false)
+			}
+
+			if closeStandalone {
+				prog := b.Inverse
+				if prog == nil {
+					prog = b.Program
+				}
+
+				// Always strip the next node
+				omitRight(body, i, false)
+
+				omitLeftLast(prog.Body, false)
+			}
+
+		}
+	}
+
+	return nil
+}
+
+func (v *whitespaceVisitor) VisitBlock(block *ast.BlockStatement) interface{} {
+	if block.Program != nil {
+		block.Program.Accept(v)
+	}
+
+	if block.Inverse != nil {
+		block.Inverse.Accept(v)
+	}
+
+	program := block.Program
+	inverse := block.Inverse
+
+	if program == nil {
+		program = inverse
+		inverse = nil
+	}
+
+	firstInverse := inverse
+	lastInverse := inverse
+
+	if (inverse != nil) && inverse.Chained {
+		b, _ := inverse.Body[0].(*ast.BlockStatement)
+		firstInverse = b.Program
+
+		for lastInverse.Chained {
+			b, _ := lastInverse.Body[len(lastInverse.Body)-1].(*ast.BlockStatement)
+			lastInverse = b.Program
+		}
+	}
+
+	closeProg := firstInverse
+	if closeProg == nil {
+		closeProg = program
+	}
+
+	strip := &ast.Strip{
+		Open:  (block.OpenStrip != nil) && block.OpenStrip.Open,
+		Close: (block.CloseStrip != nil) && block.CloseStrip.Close,
+
+		OpenStandalone:  isNextWhitespace(program.Body),
+		CloseStandalone: isPrevWhitespace(closeProg.Body),
+	}
+
+	if (block.OpenStrip != nil) && block.OpenStrip.Close {
+		omitRightFirst(program.Body, true)
+	}
+
+	if inverse != nil {
+		if block.InverseStrip != nil {
+			inverseStrip := block.InverseStrip
+
+			if inverseStrip.Open {
+				omitLeftLast(program.Body, true)
+			}
+
+			if inverseStrip.Close {
+				omitRightFirst(firstInverse.Body, true)
+			}
+		}
+
+		if (block.CloseStrip != nil) && block.CloseStrip.Open {
+			omitLeftLast(lastInverse.Body, true)
+		}
+
+		// Find standalone else statements
+		if isPrevWhitespace(program.Body) && isNextWhitespace(firstInverse.Body) {
+			omitLeftLast(program.Body, false)
+
+			omitRightFirst(firstInverse.Body, false)
+		}
+	} else if (block.CloseStrip != nil) && block.CloseStrip.Open {
+		omitLeftLast(program.Body, true)
+	}
+
+	return strip
+}
+
+func (v *whitespaceVisitor) VisitMustache(mustache *ast.MustacheStatement) interface{} {
+	return mustache.Strip
+}
+
+func _inlineStandalone(strip *ast.Strip) interface{} {
+	return &ast.Strip{
+		Open:             strip.Open,
+		Close:            strip.Close,
+		InlineStandalone: true,
+	}
+}
+
+func (v *whitespaceVisitor) VisitPartial(node *ast.PartialStatement) interface{} {
+	strip := node.Strip
+	if strip == nil {
+		strip = &ast.Strip{}
+	}
+
+	return _inlineStandalone(strip)
+}
+
+func (v *whitespaceVisitor) VisitComment(node *ast.CommentStatement) interface{} {
+	strip := node.Strip
+	if strip == nil {
+		strip = &ast.Strip{}
+	}
+
+	return _inlineStandalone(strip)
+}
+
+// NOOP
+func (v *whitespaceVisitor) VisitContent(node *ast.ContentStatement) interface{}    { return nil }
+func (v *whitespaceVisitor) VisitExpression(node *ast.Expression) interface{}       { return nil }
+func (v *whitespaceVisitor) VisitSubExpression(node *ast.SubExpression) interface{} { return nil }
+func (v *whitespaceVisitor) VisitPath(node *ast.PathExpression) interface{}         { return nil }
+func (v *whitespaceVisitor) VisitString(node *ast.StringLiteral) interface{}        { return nil }
+func (v *whitespaceVisitor) VisitBoolean(node *ast.BooleanLiteral) interface{}      { return nil }
+func (v *whitespaceVisitor) VisitNumber(node *ast.NumberLiteral) interface{}        { return nil }
+func (v *whitespaceVisitor) VisitHash(node *ast.Hash) interface{}                   { return nil }
+func (v *whitespaceVisitor) VisitHashPair(node *ast.HashPair) interface{}           { return nil }