Source: css_parser.go in package github.com/evanw/esbuild/internal/css

package css_parser

import (
	"fmt"
	"strings"

	"github.com/evanw/esbuild/internal/ast"
	"github.com/evanw/esbuild/internal/compat"
	"github.com/evanw/esbuild/internal/css_ast"
	"github.com/evanw/esbuild/internal/css_lexer"
	"github.com/evanw/esbuild/internal/logger"
)

This is mostly a normal CSS parser with one exception: the addition of support for parsing https://drafts.csswg.org/css-nesting-1/.


type parser struct {
	log           logger.Log
	source        logger.Source
	options       Options
	tokens        []css_lexer.Token
	stack         []css_lexer.T
	index         int
	end           int
	prevError     logger.Loc
	importRecords []ast.ImportRecord
}

type Options struct {
	UnsupportedCSSFeatures compat.CSSFeature
	MangleSyntax           bool
	RemoveWhitespace       bool
}

func Parse(log logger.Log, source logger.Source, options Options) css_ast.AST {
	p := parser{
		log:       log,
		source:    source,
		options:   options,
		tokens:    css_lexer.Tokenize(log, source),
		prevError: logger.Loc{Start: -1},
	}
	p.end = len(p.tokens)
	tree := css_ast.AST{}
	tree.Rules = p.parseListOfRules(ruleContext{
		isTopLevel:     true,
		parseSelectors: true,
	})
	tree.ImportRecords = p.importRecords
	p.expect(css_lexer.TEndOfFile)
	return tree
}

func (p *parser) advance() {
	if p.index < p.end {
		p.index++
	}
}

func (p *parser) at(index int) css_lexer.Token {
	if index < p.end {
		return p.tokens[index]
	}
	if p.end < len(p.tokens) {
		return css_lexer.Token{
			Kind:  css_lexer.TEndOfFile,
			Range: logger.Range{Loc: p.tokens[p.end].Range.Loc},
		}
	}
	return css_lexer.Token{
		Kind:  css_lexer.TEndOfFile,
		Range: logger.Range{Loc: logger.Loc{Start: int32(len(p.source.Contents))}},
	}
}

func (p *parser) current() css_lexer.Token {
	return p.at(p.index)
}

func (p *parser) next() css_lexer.Token {
	return p.at(p.index + 1)
}

func (p *parser) raw() string {
	t := p.current()
	return p.source.Contents[t.Range.Loc.Start:t.Range.End()]
}

func (p *parser) decoded() string {
	return p.current().DecodedText(p.source.Contents)
}

func (p *parser) peek(kind css_lexer.T) bool {
	return kind == p.current().Kind
}

func (p *parser) eat(kind css_lexer.T) bool {
	if p.peek(kind) {
		p.advance()
		return true
	}
	return false
}

func (p *parser) expect(kind css_lexer.T) bool {
	if p.eat(kind) {
		return true
	}
	t := p.current()
	var text string

Have a nice error message for forgetting a trailing semicolon

		text = "Expected \";\""
		t = p.at(p.index - 1)
	} else {
		switch t.Kind {
		case css_lexer.TEndOfFile, css_lexer.TWhitespace:
			text = fmt.Sprintf("Expected %s but found %s", kind.String(), t.Kind.String())
			t.Range.Len = 0
		case css_lexer.TBadURL, css_lexer.TBadString:
			text = fmt.Sprintf("Expected %s but found %s", kind.String(), t.Kind.String())
		default:
			text = fmt.Sprintf("Expected %s but found %q", kind.String(), p.raw())
		}
	}
	if t.Range.Loc.Start > p.prevError.Start {
		p.log.AddRangeWarning(&p.source, t.Range, text)
		p.prevError = t.Range.Loc
	}
	return false
}

func (p *parser) unexpected() {
	if t := p.current(); t.Range.Loc.Start > p.prevError.Start {
		var text string
		switch t.Kind {
		case css_lexer.TEndOfFile, css_lexer.TWhitespace:
			text = fmt.Sprintf("Unexpected %s", t.Kind.String())
			t.Range.Len = 0
		case css_lexer.TBadURL, css_lexer.TBadString:
			text = fmt.Sprintf("Unexpected %s", t.Kind.String())
		default:
			text = fmt.Sprintf("Unexpected %q", p.raw())
		}
		p.log.AddRangeWarning(&p.source, t.Range, text)
		p.prevError = t.Range.Loc
	}
}

type ruleContext struct {
	isTopLevel     bool
	parseSelectors bool
}

func (p *parser) parseListOfRules(context ruleContext) []css_ast.R {
	didWarnAboutCharset := false
	didWarnAboutImport := false
	rules := []css_ast.R{}
	locs := []logger.Loc{}

	for {
		switch p.current().Kind {
		case css_lexer.TEndOfFile, css_lexer.TCloseBrace:
			return rules

		case css_lexer.TWhitespace:
			p.advance()
			continue

		case css_lexer.TAtKeyword:
			first := p.current().Range
			rule := p.parseAtRule(atRuleContext{})

Validate structure

			if context.isTopLevel {
				switch rule.(type) {
				case *css_ast.RAtCharset:
					if !didWarnAboutCharset && len(rules) > 0 {
						p.log.AddRangeWarningWithNotes(&p.source, first, "\"@charset\" must be the first rule in the file",
							[]logger.MsgData{logger.RangeData(&p.source, logger.Range{Loc: locs[len(locs)-1]},
								"This rule cannot come before a \"@charset\" rule")})
						didWarnAboutCharset = true
					}

				case *css_ast.RAtImport:
					if !didWarnAboutImport {
					importLoop:
						for i, before := range rules {
							switch before.(type) {
							case *css_ast.RAtCharset, *css_ast.RAtImport:
							default:
								p.log.AddRangeWarningWithNotes(&p.source, first, "All \"@import\" rules must come first",
									[]logger.MsgData{logger.RangeData(&p.source, logger.Range{Loc: locs[i]},
										"This rule cannot come before an \"@import\" rule")})
								didWarnAboutImport = true
								break importLoop
							}
						}
					}
				}
			}

			rules = append(rules, rule)
			if context.isTopLevel {
				locs = append(locs, first.Loc)
			}
			continue

		case css_lexer.TCDO, css_lexer.TCDC:
			if context.isTopLevel {
				p.advance()
				continue
			}
		}

		if context.isTopLevel {
			locs = append(locs, p.current().Range.Loc)
		}
		if context.parseSelectors {
			rules = append(rules, p.parseSelectorRule())
		} else {
			rules = append(rules, p.parseQualifiedRuleFrom(p.index, false /* isAlreadyInvalid */))
		}
	}
}

func (p *parser) parseListOfDeclarations() (list []css_ast.R) {
	for {
		switch p.current().Kind {
		case css_lexer.TWhitespace, css_lexer.TSemicolon:
			p.advance()

		case css_lexer.TEndOfFile, css_lexer.TCloseBrace:
			p.processDeclarations(list)
			return

		case css_lexer.TAtKeyword:
			list = append(list, p.parseAtRule(atRuleContext{
				isDeclarationList: true,
			}))

Reference: https://drafts.csswg.org/css-nesting-1/

			list = append(list, p.parseSelectorRule())

		default:
			list = append(list, p.parseDeclaration())
		}
	}
}

func (p *parser) parseURLOrString() (string, logger.Range, bool) {
	t := p.current()
	switch t.Kind {
	case css_lexer.TString:
		text := p.decoded()
		p.advance()
		return text, t.Range, true

	case css_lexer.TURL:
		text := p.decoded()
		p.advance()
		return text, t.Range, true

	case css_lexer.TFunction:
		if p.decoded() == "url" {
			p.advance()
			t = p.current()
			text := p.decoded()
			if p.expect(css_lexer.TString) && p.expect(css_lexer.TCloseParen) {
				return text, t.Range, true
			}
		}
	}

	return "", logger.Range{}, false
}

func (p *parser) expectURLOrString() (url string, r logger.Range, ok bool) {
	url, r, ok = p.parseURLOrString()
	if !ok {
		p.expect(css_lexer.TURL)
	}
	return
}

type atRuleKind uint8

const (
	atRuleUnknown atRuleKind = iota
	atRuleDeclarations
	atRuleInheritContext
	atRuleEmpty
)

var specialAtRules = map[string]atRuleKind{
	"font-face": atRuleDeclarations,
	"page":      atRuleDeclarations,

	"document": atRuleInheritContext,
	"media":    atRuleInheritContext,
	"scope":    atRuleInheritContext,
	"supports": atRuleInheritContext,
}

type atRuleContext struct {
	isDeclarationList bool
}

Parse the name

	atToken := p.decoded()
	atRange := p.current().Range
	kind := specialAtRules[atToken]
	p.advance()

Parse the prelude

	preludeStart := p.index
	switch atToken {
	case "charset":
		kind = atRuleEmpty
		p.expect(css_lexer.TWhitespace)
		if p.peek(css_lexer.TString) {
			encoding := p.decoded()
			if encoding != "UTF-8" {
				p.log.AddRangeWarning(&p.source, p.current().Range,
					fmt.Sprintf("\"UTF-8\" will be used instead of unsupported charset %q", encoding))
			}
			p.advance()
			p.expect(css_lexer.TSemicolon)
			return &css_ast.RAtCharset{Encoding: encoding}
		}
		p.expect(css_lexer.TString)

	case "import":
		kind = atRuleEmpty
		p.eat(css_lexer.TWhitespace)
		if path, r, ok := p.expectURLOrString(); ok {
			p.eat(css_lexer.TWhitespace)
			p.expect(css_lexer.TSemicolon)
			importRecordIndex := uint32(len(p.importRecords))
			p.importRecords = append(p.importRecords, ast.ImportRecord{
				Kind:  ast.ImportAt,
				Path:  logger.Path{Text: path},
				Range: r,
			})
			return &css_ast.RAtImport{ImportRecordIndex: importRecordIndex}
		}

	case "keyframes", "-webkit-keyframes", "-moz-keyframes", "-ms-keyframes", "-o-keyframes":
		p.eat(css_lexer.TWhitespace)
		var name string

		if p.peek(css_lexer.TIdent) {
			name = p.decoded()
			p.advance()

Consider string names a syntax error even though they are allowed by the specification and they work in Firefox because they do not work in Chrome or Safari.

			break
		}

		p.eat(css_lexer.TWhitespace)
		if p.expect(css_lexer.TOpenBrace) {
			var blocks []css_ast.KeyframeBlock

		blocks:
			for {
				switch p.current().Kind {
				case css_lexer.TWhitespace:
					p.advance()
					continue

				case css_lexer.TCloseBrace, css_lexer.TEndOfFile:
					break blocks

				case css_lexer.TOpenBrace:
					p.expect(css_lexer.TPercentage)
					p.parseComponentValue()

				default:
					var selectors []string

				selectors:
					for {
						t := p.current()
						switch t.Kind {
						case css_lexer.TWhitespace:
							p.advance()
							continue

						case css_lexer.TOpenBrace, css_lexer.TEndOfFile:
							break selectors

						case css_lexer.TIdent, css_lexer.TPercentage:
							text := p.decoded()
							if t.Kind == css_lexer.TIdent {
								if text == "from" {
									if p.options.MangleSyntax {
										text = "0%" // "0%" is equivalent to but shorter than "from"
									}
								} else if text != "to" {
									p.expect(css_lexer.TPercentage)
								}
							} else if p.options.MangleSyntax && text == "100%" {
								text = "to" // "to" is equivalent to but shorter than "100%"
							}
							selectors = append(selectors, text)
							p.advance()

						default:
							p.expect(css_lexer.TPercentage)
							p.parseComponentValue()
						}

						p.eat(css_lexer.TWhitespace)
						if t.Kind != css_lexer.TComma && !p.peek(css_lexer.TOpenBrace) {
							p.expect(css_lexer.TComma)
						}
					}

					if p.expect(css_lexer.TOpenBrace) {
						rules := p.parseListOfDeclarations()
						p.expect(css_lexer.TCloseBrace)
						blocks = append(blocks, css_ast.KeyframeBlock{
							Selectors: selectors,
							Rules:     rules,
						})
					}
				}
			}

			p.expect(css_lexer.TCloseBrace)
			return &css_ast.RAtKeyframes{
				AtToken: atToken,
				Name:    name,
				Blocks:  blocks,
			}
		}

Warn about unsupported at-rules since they will be passed through unmodified and may be part of a CSS preprocessor syntax that should have been compiled away but wasn't. The list of supported at-rules that esbuild draws from is here: https://developer.mozilla.org/en-US/docs/Web/CSS/At-rule. Deprecated and Firefox-only at-rules have been removed.

		if kind == atRuleUnknown {

CSS namespaces are a weird feature that appears to only really be useful for styling XML. And the world has moved on from XHTML to HTML5 so pretty much no one uses CSS namespaces anymore. They are also complicated to support in a bundler because CSS namespaces are file-scoped, which means: * Default namespaces can be different in different files, in which case some default namespaces would have to be converted to prefixed namespaces to avoid collisions. * Prefixed namespaces from different files can use the same name, in which case some prefixed namespaces would need to be renamed to avoid collisions. Instead of implementing all of that for an extremely obscure feature, CSS namespaces are just explicitly not supported.

				p.log.AddRangeWarning(&p.source, atRange, "\"@namespace\" rules are not supported")
			} else {
				p.log.AddRangeWarning(&p.source, atRange, fmt.Sprintf("%q is not a known rule name", "@"+atToken))
			}
		}
	}

Parse an unknown prelude

prelude:
	for {
		switch p.current().Kind {
		case css_lexer.TOpenBrace, css_lexer.TEndOfFile:
			break prelude

		case css_lexer.TSemicolon, css_lexer.TCloseBrace:
			prelude := p.convertTokens(p.tokens[preludeStart:p.index])

Report an error for rules that should have blocks

			if kind != atRuleEmpty && kind != atRuleUnknown {
				p.expect(css_lexer.TOpenBrace)
				p.eat(css_lexer.TSemicolon)
				return &css_ast.RUnknownAt{AtToken: atToken, Prelude: prelude}
			}

Otherwise, parse an unknown at rule

			p.expect(css_lexer.TSemicolon)
			return &css_ast.RUnknownAt{AtToken: atToken, Prelude: prelude}

		default:
			p.parseComponentValue()
		}
	}
	prelude := p.convertTokens(p.tokens[preludeStart:p.index])
	blockStart := p.index

	switch kind {

Report an error for rules that shouldn't have blocks

		p.expect(css_lexer.TSemicolon)
		p.parseBlock(css_lexer.TOpenBrace, css_lexer.TCloseBrace)
		block := p.convertTokens(p.tokens[blockStart:p.index])
		return &css_ast.RUnknownAt{AtToken: atToken, Prelude: prelude, Block: block}

Parse known rules whose blocks consist of whatever the current context is

		p.advance()
		rules := p.parseListOfDeclarations()
		p.expect(css_lexer.TCloseBrace)
		return &css_ast.RKnownAt{AtToken: atToken, Prelude: prelude, Rules: rules}

Parse known rules whose blocks consist of whatever the current context is

		p.advance()
		var rules []css_ast.R
		if context.isDeclarationList {
			rules = p.parseListOfDeclarations()
		} else {
			rules = p.parseListOfRules(ruleContext{
				parseSelectors: true,
			})
		}
		p.expect(css_lexer.TCloseBrace)
		return &css_ast.RKnownAt{AtToken: atToken, Prelude: prelude, Rules: rules}

Otherwise, parse an unknown rule

		p.parseBlock(css_lexer.TOpenBrace, css_lexer.TCloseBrace)
		block, _ := p.convertTokensHelper(p.tokens[blockStart:p.index], css_lexer.TEndOfFile, convertTokensOpts{allowImports: true})
		return &css_ast.RUnknownAt{AtToken: atToken, Prelude: prelude, Block: block}
	}
}

func (p *parser) convertTokens(tokens []css_lexer.Token) []css_ast.Token {
	result, _ := p.convertTokensHelper(tokens, css_lexer.TEndOfFile, convertTokensOpts{})
	return result
}

type convertTokensOpts struct {
	allowImports       bool
	verbatimWhitespace bool
}

func (p *parser) convertTokensHelper(tokens []css_lexer.Token, close css_lexer.T, opts convertTokensOpts) ([]css_ast.Token, []css_lexer.Token) {
	var result []css_ast.Token
	var nextWhitespace css_ast.WhitespaceFlags

loop:
	for len(tokens) > 0 {
		t := tokens[0]
		tokens = tokens[1:]
		if t.Kind == close {
			break loop
		}
		token := css_ast.Token{
			Kind:       t.Kind,
			Text:       t.DecodedText(p.source.Contents),
			Whitespace: nextWhitespace,
		}
		nextWhitespace = 0

		switch t.Kind {
		case css_lexer.TWhitespace:
			if last := len(result) - 1; last >= 0 {
				result[last].Whitespace |= css_ast.WhitespaceAfter
			}
			nextWhitespace = css_ast.WhitespaceBefore
			continue

		case css_lexer.TNumber:
			if p.options.MangleSyntax {
				if text, ok := mangleNumber(token.Text); ok {
					token.Text = text
				}
			}

		case css_lexer.TPercentage:
			if p.options.MangleSyntax {
				if text, ok := mangleNumber(token.PercentValue()); ok {
					token.Text = text + "%"
				}
			}

		case css_lexer.TDimension:
			token.UnitOffset = t.UnitOffset

			if p.options.MangleSyntax {
				if text, ok := mangleNumber(token.DimensionValue()); ok {
					token.Text = text + token.DimensionUnit()
					token.UnitOffset = uint16(len(text))
				}
			}

		case css_lexer.TURL:
			token.ImportRecordIndex = uint32(len(p.importRecords))
			p.importRecords = append(p.importRecords, ast.ImportRecord{
				Kind:     ast.ImportURL,
				Path:     logger.Path{Text: token.Text},
				Range:    t.Range,
				IsUnused: !opts.allowImports,
			})
			token.Text = ""

		case css_lexer.TFunction:
			var nested []css_ast.Token
			original := tokens
			nestedOpts := opts

CSS variables require verbatim whitespace for correctness

				nestedOpts.verbatimWhitespace = true
			}
			nested, tokens = p.convertTokensHelper(tokens, css_lexer.TCloseParen, nestedOpts)
			token.Children = &nested

Treat a URL function call with a string just like a URL token

			if token.Text == "url" && len(nested) == 1 && nested[0].Kind == css_lexer.TString {
				token.Kind = css_lexer.TURL
				token.Text = ""
				token.Children = nil
				token.ImportRecordIndex = uint32(len(p.importRecords))
				p.importRecords = append(p.importRecords, ast.ImportRecord{
					Kind:     ast.ImportURL,
					Path:     logger.Path{Text: nested[0].Text},
					Range:    original[0].Range,
					IsUnused: !opts.allowImports,
				})
			}

		case css_lexer.TOpenParen:
			var nested []css_ast.Token
			nested, tokens = p.convertTokensHelper(tokens, css_lexer.TCloseParen, opts)
			token.Children = &nested

		case css_lexer.TOpenBrace:
			var nested []css_ast.Token
			nested, tokens = p.convertTokensHelper(tokens, css_lexer.TCloseBrace, opts)

Pretty-printing: insert leading and trailing whitespace when not minifying

			if !opts.verbatimWhitespace && !p.options.RemoveWhitespace && len(nested) > 0 {
				nested[0].Whitespace |= css_ast.WhitespaceBefore
				nested[len(nested)-1].Whitespace |= css_ast.WhitespaceAfter
			}

			token.Children = &nested

		case css_lexer.TOpenBracket:
			var nested []css_ast.Token
			nested, tokens = p.convertTokensHelper(tokens, css_lexer.TCloseBracket, opts)
			token.Children = &nested
		}

		result = append(result, token)
	}

	if !opts.verbatimWhitespace {
		for i := range result {
			token := &result[i]

Always remove leading and trailing whitespace

			if i == 0 {
				token.Whitespace &= ^css_ast.WhitespaceBefore
			}
			if i+1 == len(result) {
				token.Whitespace &= ^css_ast.WhitespaceAfter
			}

			switch token.Kind {

Assume that whitespace can always be removed before a comma

				token.Whitespace &= ^css_ast.WhitespaceBefore
				if i > 0 {
					result[i-1].Whitespace &= ^css_ast.WhitespaceAfter
				}

Assume whitespace can always be added after a comma

				if p.options.RemoveWhitespace {
					token.Whitespace &= ^css_ast.WhitespaceAfter
					if i+1 < len(result) {
						result[i+1].Whitespace &= ^css_ast.WhitespaceBefore
					}
				} else {
					token.Whitespace |= css_ast.WhitespaceAfter
					if i+1 < len(result) {
						result[i+1].Whitespace |= css_ast.WhitespaceBefore
					}
				}
			}
		}
	}

Insert an explicit whitespace token if we're in verbatim mode and all tokens were whitespace. In this case there is no token to attach the whitespace before/after flags so this is the only way to represent this. This is the only case where this function generates an explicit whitespace token. It represents whitespace as flags in all other cases.

	if opts.verbatimWhitespace && len(result) == 0 && nextWhitespace == css_ast.WhitespaceBefore {
		result = append(result, css_ast.Token{
			Kind: css_lexer.TWhitespace,
		})
	}

	return result, tokens
}

func mangleNumber(t string) (string, bool) {
	original := t

Remove trailing zeros

		for len(t) > 0 && t[len(t)-1] == '0' {
			t = t[:len(t)-1]
		}

Remove the decimal point if it's unnecessary

		if dot+1 == len(t) {
			t = t[:dot]
			if t == "" || t == "+" || t == "-" {
				t += "0"
			}

Remove a leading zero

			if len(t) >= 3 && t[0] == '0' && t[1] == '.' && t[2] >= '0' && t[2] <= '9' {
				t = t[1:]
			} else if len(t) >= 4 && (t[0] == '+' || t[0] == '-') && t[1] == '0' && t[2] == '.' && t[3] >= '0' && t[3] <= '9' {
				t = t[0:1] + t[2:]
			}
		}
	}

	return t, t != original
}

func (p *parser) parseSelectorRule() css_ast.R {
	preludeStart := p.index

Try parsing the prelude as a selector list

	if list, ok := p.parseSelectorList(); ok {
		rule := css_ast.RSelector{Selectors: list}
		if p.expect(css_lexer.TOpenBrace) {
			rule.Rules = p.parseListOfDeclarations()
			p.expect(css_lexer.TCloseBrace)
			return &rule
		}
	}

Otherwise, parse a generic qualified rule

	return p.parseQualifiedRuleFrom(preludeStart, true /* isAlreadyInvalid */)
}

func (p *parser) parseQualifiedRuleFrom(preludeStart int, isAlreadyInvalid bool) *css_ast.RQualified {
loop:
	for {
		switch p.current().Kind {
		case css_lexer.TOpenBrace, css_lexer.TEndOfFile:
			break loop

Error recovery if the block is omitted (likely some CSS meta-syntax)

			if !isAlreadyInvalid {
				p.expect(css_lexer.TOpenBrace)
			}
			prelude := p.convertTokens(p.tokens[preludeStart:p.index])
			p.advance()
			return &css_ast.RQualified{Prelude: prelude}

		default:
			p.parseComponentValue()
		}
	}

	rule := css_ast.RQualified{
		Prelude: p.convertTokens(p.tokens[preludeStart:p.index]),
	}

	if p.eat(css_lexer.TOpenBrace) {
		rule.Rules = p.parseListOfDeclarations()
		p.expect(css_lexer.TCloseBrace)
	} else if !isAlreadyInvalid {
		p.expect(css_lexer.TOpenBrace)
	}

	return &rule
}

Parse the key

	keyStart := p.index
	ok := false
	if p.expect(css_lexer.TIdent) {
		p.eat(css_lexer.TWhitespace)
		if p.expect(css_lexer.TColon) {
			ok = true
		}
	}

Parse the value

	valueStart := p.index
stop:
	for {
		switch p.current().Kind {
		case css_lexer.TEndOfFile, css_lexer.TSemicolon, css_lexer.TCloseBrace:
			break stop

Error recovery if there is an unexpected block (likely some CSS meta-syntax)

			p.parseComponentValue()
			p.eat(css_lexer.TWhitespace)
			if ok && !p.peek(css_lexer.TSemicolon) {
				p.expect(css_lexer.TSemicolon)
			}
			break stop

		default:
			p.parseComponentValue()
		}
	}

Stop now if this is not a valid declaration

	if !ok {
		return &css_ast.RBadDeclaration{
			Tokens: p.convertTokens(p.tokens[keyStart:p.index]),
		}
	}

	keyToken := p.tokens[keyStart]
	keyText := keyToken.DecodedText(p.source.Contents)
	value := p.tokens[valueStart:p.index]
	verbatimWhitespace := strings.HasPrefix(keyText, "--")

Remove trailing "!important"

	important := false
	i := len(value) - 1
	if i >= 0 && value[i].Kind == css_lexer.TWhitespace {
		i--
	}
	if i >= 0 && value[i].Kind == css_lexer.TIdent && strings.EqualFold(value[i].DecodedText(p.source.Contents), "important") {
		i--
		if i >= 0 && value[i].Kind == css_lexer.TWhitespace {
			i--
		}
		if i >= 0 && value[i].Kind == css_lexer.TDelimExclamation {
			value = value[:i]
			important = true
		}
	}

	result, _ := p.convertTokensHelper(value, css_lexer.TEndOfFile, convertTokensOpts{
		allowImports: true,

CSS variables require verbatim whitespace for correctness

		verbatimWhitespace: verbatimWhitespace,
	})

Insert or remove whitespace before the first token

	if !verbatimWhitespace && len(result) > 0 {
		if p.options.RemoveWhitespace {
			result[0].Whitespace &= ^css_ast.WhitespaceBefore
		} else {
			result[0].Whitespace |= css_ast.WhitespaceBefore
		}
	}

	return &css_ast.RDeclaration{
		Key:       css_ast.KnownDeclarations[keyText],
		KeyText:   keyText,
		KeyRange:  keyToken.Range,
		Value:     result,
		Important: important,
	}
}

func (p *parser) parseComponentValue() {
	switch p.current().Kind {
	case css_lexer.TFunction:
		p.parseBlock(css_lexer.TFunction, css_lexer.TCloseParen)

	case css_lexer.TOpenParen:
		p.parseBlock(css_lexer.TOpenParen, css_lexer.TCloseParen)

	case css_lexer.TOpenBrace:
		p.parseBlock(css_lexer.TOpenBrace, css_lexer.TCloseBrace)

	case css_lexer.TOpenBracket:
		p.parseBlock(css_lexer.TOpenBracket, css_lexer.TCloseBracket)

	case css_lexer.TEndOfFile:
		p.unexpected()

	default:
		p.advance()
	}
}

func (p *parser) parseBlock(open css_lexer.T, close css_lexer.T) {
	if p.expect(open) {
		for !p.eat(close) {
			if p.peek(css_lexer.TEndOfFile) {
				p.expect(close)
				return
			}

			p.parseComponentValue()
		}
	}