esbuild/internal/css_parser/css_parser_selector.go

package css_parser

import (
	"fmt"
	"strings"

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

type parseSelectorOpts struct {
	composesContext         *composesContext
	pseudoClassKind         css_ast.PseudoClassKind
	isDeclarationContext    bool
	stopOnCloseParen        bool
	onlyOneComplexSelector  bool
	isForgivingSelectorList bool
	noLeadingCombinator     bool
}

func (p *parser) parseSelectorList(opts parseSelectorOpts) (list []css_ast.ComplexSelector, ok bool) {
	// Potentially parse an empty list for ":is()" and ":where()"
	if opts.isForgivingSelectorList && opts.stopOnCloseParen && p.peek(css_lexer.TCloseParen) {
		ok = true
		return
	}

	// Parse the first selector
	sel, good := p.parseComplexSelector(parseComplexSelectorOpts{
		parseSelectorOpts: opts,
		isFirst:           true,
	})
	if !good {
		return
	}
	list = p.flattenLocalAndGlobalSelectors(list, sel)

	// Parse the remaining selectors
	if opts.onlyOneComplexSelector {
		if t := p.current(); t.Kind == css_lexer.TComma {
			p.prevError = t.Range.Loc
			kind := fmt.Sprintf(":%s(...)", opts.pseudoClassKind.String())
			p.log.AddIDWithNotes(logger.MsgID_CSS_CSSSyntaxError, logger.Warning, &p.tracker, t.Range,
				fmt.Sprintf("Unexpected \",\" inside %q", kind),
				[]logger.MsgData{{Text: fmt.Sprintf("Different CSS tools behave differently in this case, so esbuild doesn't allow it. "+
					"Either remove this comma or split this selector up into multiple comma-separated %q selectors instead.", kind)}})
			return
		}
	} else {
	skip:
		for {
			p.eat(css_lexer.TWhitespace)
			if !p.eat(css_lexer.TComma) {
				break
			}
			p.eat(css_lexer.TWhitespace)
			sel, good := p.parseComplexSelector(parseComplexSelectorOpts{
				parseSelectorOpts: opts,
			})
			if !good {
				return
			}

			// Omit duplicate selectors
			if p.options.minifySyntax {
				for _, existing := range list {
					if sel.Equal(existing, nil) {
						continue skip
					}
				}
			}

			list = p.flattenLocalAndGlobalSelectors(list, sel)
		}
	}

	// Remove the leading ampersand when minifying and it can be implied:
	//
	//   "a { & b {} }" => "a { b {} }"
	//
	// It can't be implied if it's not at the beginning, if there are multiple of
	// them, or if the selector list is inside of a pseudo-class selector:
	//
	//   "a { b & {} }"
	//   "a { & b & {} }"
	//   "a { :has(& b) {} }"
	//
	if p.options.minifySyntax && !opts.stopOnCloseParen {
		for i := 1; i < len(list); i++ {
			if analyzeLeadingAmpersand(list[i], opts.isDeclarationContext) != cannotRemoveLeadingAmpersand {
				list[i].Selectors = list[i].Selectors[1:]
			}
		}

		switch analyzeLeadingAmpersand(list[0], opts.isDeclarationContext) {
		case canAlwaysRemoveLeadingAmpersand:
			list[0].Selectors = list[0].Selectors[1:]

		case canRemoveLeadingAmpersandIfNotFirst:
			for i := 1; i < len(list); i++ {
				if sel := list[i].Selectors[0]; len(sel.NestingSelectorLocs) == 0 && (sel.Combinator.Byte != 0 || sel.TypeSelector == nil) {
					list[0].Selectors = list[0].Selectors[1:]
					list[0], list[i] = list[i], list[0]
					break
				}
			}
		}
	}

	ok = true
	return
}

func mergeCompoundSelectors(target *css_ast.CompoundSelector, source css_ast.CompoundSelector) {
	// ".foo:local(&)" => "&.foo"
	if len(source.NestingSelectorLocs) > 0 && len(target.NestingSelectorLocs) == 0 {
		target.NestingSelectorLocs = source.NestingSelectorLocs
	}

	if source.TypeSelector != nil {
		if target.TypeSelector == nil {
			// ".foo:local(div)" => "div.foo"
			target.TypeSelector = source.TypeSelector
		} else {
			// "div:local(span)" => "div:is(span)"
			//
			// Note: All other implementations of this (Lightning CSS, PostCSS, and
			// Webpack) do something really weird here. They do this instead:
			//
			// "div:local(span)" => "divspan"
			//
			// But that just seems so obviously wrong that I'm not going to do that.
			target.SubclassSelectors = append(target.SubclassSelectors, css_ast.SubclassSelector{
				Range: source.TypeSelector.Range(),
				Data: &css_ast.SSPseudoClassWithSelectorList{
					Kind:      css_ast.PseudoClassIs,
					Selectors: []css_ast.ComplexSelector{{Selectors: []css_ast.CompoundSelector{{TypeSelector: source.TypeSelector}}}},
				},
			})
		}
	}

	// ".foo:local(.bar)" => ".foo.bar"
	target.SubclassSelectors = append(target.SubclassSelectors, source.SubclassSelectors...)
}

func containsLocalOrGlobalSelector(sel css_ast.ComplexSelector) bool {
	for _, s := range sel.Selectors {
		for _, ss := range s.SubclassSelectors {
			switch pseudo := ss.Data.(type) {
			case *css_ast.SSPseudoClass:
				if pseudo.Name == "global" || pseudo.Name == "local" {
					return true
				}

			case *css_ast.SSPseudoClassWithSelectorList:
				if pseudo.Kind == css_ast.PseudoClassGlobal || pseudo.Kind == css_ast.PseudoClassLocal {
					return true
				}
			}
		}
	}
	return false
}

// This handles the ":local()" and ":global()" annotations from CSS modules
func (p *parser) flattenLocalAndGlobalSelectors(list []css_ast.ComplexSelector, sel css_ast.ComplexSelector) []css_ast.ComplexSelector {
	// Only do the work to flatten the whole list if there's a ":local" or a ":global"
	if p.options.symbolMode != symbolModeDisabled && containsLocalOrGlobalSelector(sel) {
		var selectors []css_ast.CompoundSelector

		for _, s := range sel.Selectors {
			oldSubclassSelectors := s.SubclassSelectors
			s.SubclassSelectors = make([]css_ast.SubclassSelector, 0, len(oldSubclassSelectors))

			for _, ss := range oldSubclassSelectors {
				switch pseudo := ss.Data.(type) {
				case *css_ast.SSPseudoClass:
					if pseudo.Name == "global" || pseudo.Name == "local" {
						// Remove bare ":global" and ":local" pseudo-classes
						continue
					}

				case *css_ast.SSPseudoClassWithSelectorList:
					if pseudo.Kind == css_ast.PseudoClassGlobal || pseudo.Kind == css_ast.PseudoClassLocal {
						inner := pseudo.Selectors[0].Selectors

						// Replace this pseudo-class with all inner compound selectors.
						// The first inner compound selector is merged with the compound
						// selector before it and the last inner compound selector is
						// merged with the compound selector after it:
						//
						// "div:local(.a .b):hover" => "div.a b:hover"
						//
						// This behavior is really strange since this is not how anything
						// involving pseudo-classes in real CSS works at all. However, all
						// other implementations (Lightning CSS, PostCSS, and Webpack) are
						// consistent with this strange behavior, so we do it too.
						if inner[0].Combinator.Byte == 0 {
							mergeCompoundSelectors(&s, inner[0])
							inner = inner[1:]
						} else {
							// "div:local(+ .foo):hover" => "div + .foo:hover"
						}
						if n := len(inner); n > 0 {
							if !s.IsInvalidBecauseEmpty() {
								// Don't add this selector if it consisted only of a bare ":global" or ":local"
								selectors = append(selectors, s)
							}
							selectors = append(selectors, inner[:n-1]...)
							s = inner[n-1]
						}
						continue
					}
				}

				s.SubclassSelectors = append(s.SubclassSelectors, ss)
			}

			if !s.IsInvalidBecauseEmpty() {
				// Don't add this selector if it consisted only of a bare ":global" or ":local"
				selectors = append(selectors, s)
			}
		}

		if len(selectors) == 0 {
			// Treat a bare ":global" or ":local" as a bare "&" nesting selector
			selectors = append(selectors, css_ast.CompoundSelector{
				NestingSelectorLocs:       []logger.Loc{sel.Selectors[0].Range().Loc},
				WasEmptyFromLocalOrGlobal: true,
			})

			// Make sure we report that nesting is present so that it can be lowered
			p.nestingIsPresent = true
		}

		sel.Selectors = selectors
	}

	return append(list, sel)
}

type leadingAmpersand uint8

const (
	cannotRemoveLeadingAmpersand leadingAmpersand = iota
	canAlwaysRemoveLeadingAmpersand
	canRemoveLeadingAmpersandIfNotFirst
)

func analyzeLeadingAmpersand(sel css_ast.ComplexSelector, isDeclarationContext bool) leadingAmpersand {
	if len(sel.Selectors) > 1 {
		if first := sel.Selectors[0]; first.IsSingleAmpersand() {
			second := sel.Selectors[1]
			rest := css_ast.ComplexSelector{Selectors: sel.Selectors[1:]}
			if second.Combinator.Byte == 0 && rest.ContainsNestingCombinator() {
				// ".foo { & &.bar {} }" => ".foo { & &.bar {} }"
				// ".foo { & .bar:not(& .baz) {} }" => ".foo { & .bar:not(& .baz) {} }"

				// The specification says: "If a selector in the <relative-selector-list>
				// does not start with a combinator but does contain the nesting selector,
				// it is interpreted as a non-relative selector." So we don't want to
				// remove the leading "&" here as that would change the meaning to a
				// non-relative selector. See: https://www.w3.org/TR/css-nesting-1/
			} else if second.Combinator.Byte != 0 || second.TypeSelector == nil || !isDeclarationContext {
				// "& + div {}" => "+ div {}"
				// "& div {}" => "div {}"
				// ".foo { & + div {} }" => ".foo { + div {} }"
				// ".foo { & + &.bar {} }" => ".foo { + &.bar {} }"
				// ".foo { & :hover {} }" => ".foo { :hover {} }"
				return canAlwaysRemoveLeadingAmpersand
			} else {
				// ".foo { & div {} }"
				// ".foo { .bar, & div {} }" => ".foo { .bar, div {} }"

				// The first iteration of CSS nesting didn't support an implicit "&" if
				// the selector started with an identifier. This was done to avoid
				// confusion with declarations in the parser, as the parser would
				// otherwise need unbounded lookahead to distinguish between the two.
				// Consider the following:
				//
				//   span {
				//     color:blue;
				//     div:hover span {}
				//   }
				//
				// The "color:blue" is a declaration while "div:hover" is actually a
				// relative selector in a nested style rule. The parser would need to
				// scan to the ";" or "{" to distinguish between the two cases.
				// Generally you want to avoid parsers with unbounded lookahead.
				//
				// However, this edge case is commonly encountered and it's confusing
				// that it doesn't work. So the CSS working group later added unbounded
				// lookahead to fix it: https://github.com/w3c/csswg-drafts/issues/7961.
				//
				// We deliberately don't take advantage of that newest syntax addition
				// here so that our output still works in browsers before that newest
				// syntax addition. We still keep a leading "&" before identifiers.
				return canRemoveLeadingAmpersandIfNotFirst
			}
		}
	} else {
		// "& {}" => "& {}"
	}
	return cannotRemoveLeadingAmpersand
}

type parseComplexSelectorOpts struct {
	parseSelectorOpts
	isFirst bool
}

func (p *parser) parseComplexSelector(opts parseComplexSelectorOpts) (result css_ast.ComplexSelector, ok bool) {
	// This is an extension: https://drafts.csswg.org/css-nesting-1/
	var combinator css_ast.Combinator
	if !opts.noLeadingCombinator {
		combinator = p.parseCombinator()
		if combinator.Byte != 0 {
			p.nestingIsPresent = true
			p.eat(css_lexer.TWhitespace)
		}
	}

	// Parent
	sel, good := p.parseCompoundSelector(parseComplexSelectorOpts{
		parseSelectorOpts: opts.parseSelectorOpts,
		isFirst:           opts.isFirst,
	})
	if !good {
		return
	}
	sel.Combinator = combinator
	result.Selectors = append(result.Selectors, sel)

	stop := css_lexer.TOpenBrace
	if opts.stopOnCloseParen {
		stop = css_lexer.TCloseParen
	}
	for {
		p.eat(css_lexer.TWhitespace)
		if p.peek(css_lexer.TEndOfFile) || p.peek(css_lexer.TComma) || p.peek(stop) {
			break
		}

		// Optional combinator
		combinator := p.parseCombinator()
		if combinator.Byte != 0 {
			p.eat(css_lexer.TWhitespace)
		}

		// Child
		sel, good := p.parseCompoundSelector(parseComplexSelectorOpts{
			parseSelectorOpts: opts.parseSelectorOpts,
		})
		if !good {
			return
		}
		sel.Combinator = combinator
		result.Selectors = append(result.Selectors, sel)
	}

	ok = true
	return
}

func (p *parser) nameToken() css_ast.NameToken {
	t := p.current()
	return css_ast.NameToken{
		Kind:  t.Kind,
		Range: t.Range,
		Text:  p.decoded(),
	}
}

func (p *parser) parseCompoundSelector(opts parseComplexSelectorOpts) (sel css_ast.CompoundSelector, ok bool) {
	startLoc := p.current().Range.Loc

	// This is an extension: https://drafts.csswg.org/css-nesting-1/
	hasLeadingNestingSelector := p.peek(css_lexer.TDelimAmpersand)
	if hasLeadingNestingSelector {
		p.nestingIsPresent = true
		sel.NestingSelectorLocs = append(sel.NestingSelectorLocs, startLoc)
		p.advance()
	}

	// Parse the type selector
	typeSelectorLoc := p.current().Range.Loc
	switch p.current().Kind {
	case css_lexer.TDelimBar, css_lexer.TIdent, css_lexer.TDelimAsterisk:
		nsName := css_ast.NamespacedName{}
		if !p.peek(css_lexer.TDelimBar) {
			nsName.Name = p.nameToken()
			p.advance()
		} else {
			// Hack: Create an empty "identifier" to represent this
			nsName.Name.Kind = css_lexer.TIdent
		}
		if p.eat(css_lexer.TDelimBar) {
			if !p.peek(css_lexer.TIdent) && !p.peek(css_lexer.TDelimAsterisk) {
				p.expect(css_lexer.TIdent)
				return
			}
			prefix := nsName.Name
			nsName.NamespacePrefix = &prefix
			nsName.Name = p.nameToken()
			p.advance()
		}
		sel.TypeSelector = &nsName
	}

	// Parse the subclass selectors
subclassSelectors:
	for {
		subclassToken := p.current()

		switch subclassToken.Kind {
		case css_lexer.THash:
			if (subclassToken.Flags & css_lexer.IsID) == 0 {
				break subclassSelectors
			}
			nameLoc := logger.Loc{Start: subclassToken.Range.Loc.Start + 1}
			name := p.decoded()
			sel.SubclassSelectors = append(sel.SubclassSelectors, css_ast.SubclassSelector{
				Range: subclassToken.Range,
				Data: &css_ast.SSHash{
					Name: p.symbolForName(nameLoc, name),
				},
			})
			p.advance()

		case css_lexer.TDelimDot:
			p.advance()
			nameRange := p.current().Range
			name := p.decoded()
			sel.SubclassSelectors = append(sel.SubclassSelectors, css_ast.SubclassSelector{
				Range: logger.Range{Loc: subclassToken.Range.Loc, Len: nameRange.End() - subclassToken.Range.Loc.Start},
				Data: &css_ast.SSClass{
					Name: p.symbolForName(nameRange.Loc, name),
				},
			})
			if !p.expect(css_lexer.TIdent) {
				return
			}

		case css_lexer.TOpenBracket:
			attr, r := p.parseAttributeSelector()
			if r.Len == 0 {
				return
			}
			sel.SubclassSelectors = append(sel.SubclassSelectors, css_ast.SubclassSelector{
				Range: r,
				Data:  &attr,
			})

		case css_lexer.TColon:
			if p.next().Kind == css_lexer.TColon {
				// Special-case the start of the pseudo-element selector section
				for p.peek(css_lexer.TColon) {
					firstColonLoc := p.current().Range.Loc
					isElement := p.next().Kind == css_lexer.TColon
					if isElement {
						p.advance()
					}
					pseudo, r := p.parsePseudoClassSelector(firstColonLoc, isElement)

					// https://www.w3.org/TR/selectors-4/#single-colon-pseudos
					// The four Level 2 pseudo-elements (::before, ::after, ::first-line,
					// and ::first-letter) may, for legacy reasons, be represented using
					// the <pseudo-class-selector> grammar, with only a single ":"
					// character at their start.
					if p.options.minifySyntax && isElement {
						if pseudo, ok := pseudo.(*css_ast.SSPseudoClass); ok && len(pseudo.Args) == 0 {
							switch pseudo.Name {
							case "before", "after", "first-line", "first-letter":
								pseudo.IsElement = false
							}
						}
					}

					sel.SubclassSelectors = append(sel.SubclassSelectors, css_ast.SubclassSelector{
						Range: r,
						Data:  pseudo,
					})
				}
				break subclassSelectors
			}

			pseudo, r := p.parsePseudoClassSelector(subclassToken.Range.Loc, false)
			sel.SubclassSelectors = append(sel.SubclassSelectors, css_ast.SubclassSelector{
				Range: r,
				Data:  pseudo,
			})

		case css_lexer.TDelimAmpersand:
			// This is an extension: https://drafts.csswg.org/css-nesting-1/
			p.nestingIsPresent = true
			sel.NestingSelectorLocs = append(sel.NestingSelectorLocs, subclassToken.Range.Loc)
			p.advance()

		default:
			break subclassSelectors
		}
	}

	// The compound selector must be non-empty
	if sel.IsInvalidBecauseEmpty() {
		p.unexpected()
		return
	}

	// Note: "&div {}" was originally valid, but is now an invalid selector:
	// https://github.com/w3c/csswg-drafts/issues/8662#issuecomment-1514977935.
	// This is because SASS already uses that syntax to mean something very
	// different, so that syntax has been removed to avoid mistakes.
	if hasLeadingNestingSelector && sel.TypeSelector != nil {
		r := logger.Range{Loc: typeSelectorLoc, Len: p.at(p.index-1).Range.End() - typeSelectorLoc.Start}
		text := sel.TypeSelector.Name.Text
		if sel.TypeSelector.NamespacePrefix != nil {
			text = fmt.Sprintf("%s|%s", sel.TypeSelector.NamespacePrefix.Text, text)
		}
		var howToFix string
		suggestion := p.source.TextForRange(r)
		if opts.isFirst {
			suggestion = fmt.Sprintf(":is(%s)", suggestion)
			howToFix = "You can wrap this selector in \":is(...)\" as a workaround. "
		} else {
			r = logger.Range{Loc: startLoc, Len: r.End() - startLoc.Start}
			suggestion += "&"
			howToFix = "You can move the \"&\" to the end of this selector as a workaround. "
		}
		msg := logger.Msg{
			Kind: logger.Warning,
			Data: p.tracker.MsgData(r, fmt.Sprintf("Cannot use type selector %q directly after nesting selector \"&\"", text)),
			Notes: []logger.MsgData{{Text: "CSS nesting syntax does not allow the \"&\" selector to come before a type selector. " +
				howToFix +
				"This restriction exists to avoid problems with SASS nesting, where the same syntax means something very different " +
				"that has no equivalent in real CSS (appending a suffix to the parent selector)."}},
		}
		msg.Data.Location.Suggestion = suggestion
		p.log.AddMsgID(logger.MsgID_CSS_CSSSyntaxError, msg)
		return
	}

	// The type selector must always come first
	switch p.current().Kind {
	case css_lexer.TDelimBar, css_lexer.TIdent, css_lexer.TDelimAsterisk:
		p.unexpected()
		return
	}

	ok = true
	return
}

func (p *parser) parseAttributeSelector() (attr css_ast.SSAttribute, r logger.Range) {
	matchingLoc := p.current().Range.Loc
	p.advance()

	// Parse the namespaced name
	switch p.current().Kind {
	case css_lexer.TDelimBar, css_lexer.TDelimAsterisk:
		// "[|x]"
		// "[*|x]"
		if p.peek(css_lexer.TDelimAsterisk) {
			prefix := p.nameToken()
			p.advance()
			attr.NamespacedName.NamespacePrefix = &prefix
		} else {
			// "[|attr]" is equivalent to "[attr]". From the specification:
			// "In keeping with the Namespaces in the XML recommendation, default
			// namespaces do not apply to attributes, therefore attribute selectors
			// without a namespace component apply only to attributes that have no
			// namespace (equivalent to |attr)."
		}
		if !p.expect(css_lexer.TDelimBar) {
			return
		}
		attr.NamespacedName.Name = p.nameToken()
		if !p.expect(css_lexer.TIdent) {
			return
		}

	default:
		// "[x]"
		// "[x|y]"
		attr.NamespacedName.Name = p.nameToken()
		if !p.expect(css_lexer.TIdent) {
			return
		}
		if p.next().Kind != css_lexer.TDelimEquals && p.eat(css_lexer.TDelimBar) {
			prefix := attr.NamespacedName.Name
			attr.NamespacedName.NamespacePrefix = &prefix
			attr.NamespacedName.Name = p.nameToken()
			if !p.expect(css_lexer.TIdent) {
				return
			}
		}
	}

	// Parse the optional matcher operator
	p.eat(css_lexer.TWhitespace)
	if p.eat(css_lexer.TDelimEquals) {
		attr.MatcherOp = "="
	} else {
		switch p.current().Kind {
		case css_lexer.TDelimTilde:
			attr.MatcherOp = "~="
		case css_lexer.TDelimBar:
			attr.MatcherOp = "|="
		case css_lexer.TDelimCaret:
			attr.MatcherOp = "^="
		case css_lexer.TDelimDollar:
			attr.MatcherOp = "$="
		case css_lexer.TDelimAsterisk:
			attr.MatcherOp = "*="
		}
		if attr.MatcherOp != "" {
			p.advance()
			if !p.expect(css_lexer.TDelimEquals) {
				return
			}
		}
	}

	// Parse the optional matcher value
	if attr.MatcherOp != "" {
		p.eat(css_lexer.TWhitespace)
		if !p.peek(css_lexer.TString) && !p.peek(css_lexer.TIdent) {
			p.unexpected()
		}
		attr.MatcherValue = p.decoded()
		p.advance()
		p.eat(css_lexer.TWhitespace)
		if p.peek(css_lexer.TIdent) {
			if modifier := p.decoded(); len(modifier) == 1 {
				if c := modifier[0]; c == 'i' || c == 'I' || c == 's' || c == 'S' {
					attr.MatcherModifier = c
					p.advance()
				}
			}
		}
	}

	closeRange := p.current().Range
	if !p.expectWithMatchingLoc(css_lexer.TCloseBracket, matchingLoc) {
		closeRange.Len = 0
	}
	r = logger.Range{Loc: matchingLoc, Len: closeRange.End() - matchingLoc.Start}
	return
}

func (p *parser) parsePseudoClassSelector(loc logger.Loc, isElement bool) (css_ast.SS, logger.Range) {
	p.advance()

	if p.peek(css_lexer.TFunction) {
		text := p.decoded()
		matchingLoc := logger.Loc{Start: p.current().Range.End() - 1}
		p.advance()

		// Potentially parse a pseudo-class with a selector list
		if !isElement {
			var kind css_ast.PseudoClassKind
			local := p.makeLocalSymbols
			ok := true
			switch text {
			case "global":
				kind = css_ast.PseudoClassGlobal
				if p.options.symbolMode != symbolModeDisabled {
					local = false
				}
			case "has":
				kind = css_ast.PseudoClassHas
			case "is":
				kind = css_ast.PseudoClassIs
			case "local":
				kind = css_ast.PseudoClassLocal
				if p.options.symbolMode != symbolModeDisabled {
					local = true
				}
			case "not":
				kind = css_ast.PseudoClassNot
			case "nth-child":
				kind = css_ast.PseudoClassNthChild
			case "nth-last-child":
				kind = css_ast.PseudoClassNthLastChild
			case "nth-of-type":
				kind = css_ast.PseudoClassNthOfType
			case "nth-last-of-type":
				kind = css_ast.PseudoClassNthLastOfType
			case "where":
				kind = css_ast.PseudoClassWhere
			default:
				ok = false
			}
			if ok {
				old := p.index
				if kind.HasNthIndex() {
					p.eat(css_lexer.TWhitespace)

					// Parse the "An+B" syntax
					if index, ok := p.parseNthIndex(); ok {
						var selectors []css_ast.ComplexSelector

						// Parse the optional "of" clause
						if (kind == css_ast.PseudoClassNthChild || kind == css_ast.PseudoClassNthLastChild) &&
							p.peek(css_lexer.TIdent) && strings.EqualFold(p.decoded(), "of") {
							p.advance()
							p.eat(css_lexer.TWhitespace)

							// Contain the effects of ":local" and ":global"
							oldLocal := p.makeLocalSymbols
							selectors, ok = p.parseSelectorList(parseSelectorOpts{
								stopOnCloseParen:    true,
								noLeadingCombinator: true,
							})
							p.makeLocalSymbols = oldLocal
						}

						// "2n+0" => "2n"
						if p.options.minifySyntax {
							index.Minify()
						}

						// Match the closing ")"
						if ok {
							closeRange := p.current().Range
							if !p.expectWithMatchingLoc(css_lexer.TCloseParen, matchingLoc) {
								closeRange.Len = 0
							}
							return &css_ast.SSPseudoClassWithSelectorList{Kind: kind, Selectors: selectors, Index: index},
								logger.Range{Loc: loc, Len: closeRange.End() - loc.Start}
						}
					}
				} else {
					p.eat(css_lexer.TWhitespace)

					// ":local" forces local names and ":global" forces global names
					oldLocal := p.makeLocalSymbols
					p.makeLocalSymbols = local
					selectors, ok := p.parseSelectorList(parseSelectorOpts{
						pseudoClassKind:         kind,
						stopOnCloseParen:        true,
						onlyOneComplexSelector:  kind == css_ast.PseudoClassGlobal || kind == css_ast.PseudoClassLocal,
						isForgivingSelectorList: kind == css_ast.PseudoClassIs || kind == css_ast.PseudoClassWhere,
					})
					p.makeLocalSymbols = oldLocal

					// Match the closing ")"
					if ok {
						closeRange := p.current().Range
						if !p.expectWithMatchingLoc(css_lexer.TCloseParen, matchingLoc) {
							closeRange.Len = 0
						}
						return &css_ast.SSPseudoClassWithSelectorList{Kind: kind, Selectors: selectors},
							logger.Range{Loc: loc, Len: closeRange.End() - loc.Start}
					}
				}
				p.index = old
			}
		}

		args := p.convertTokens(p.parseAnyValue())
		closeRange := p.current().Range
		if !p.expectWithMatchingLoc(css_lexer.TCloseParen, matchingLoc) {
			closeRange.Len = 0
		}
		return &css_ast.SSPseudoClass{IsElement: isElement, Name: text, Args: args},
			logger.Range{Loc: loc, Len: closeRange.End() - loc.Start}
	}

	nameRange := p.current().Range
	name := p.decoded()
	sel := css_ast.SSPseudoClass{IsElement: isElement}
	if p.expect(css_lexer.TIdent) {
		sel.Name = name

		// ":local .local_name :global .global_name {}"
		// ":local { .local_name { :global { .global_name {} } }"
		if p.options.symbolMode != symbolModeDisabled {
			switch name {
			case "local":
				p.makeLocalSymbols = true
			case "global":
				p.makeLocalSymbols = false
			}
		}
	} else {
		nameRange.Len = 0
	}
	return &sel, logger.Range{Loc: loc, Len: nameRange.End() - loc.Start}
}

func (p *parser) parseAnyValue() []css_lexer.Token {
	// Reference: https://drafts.csswg.org/css-syntax-3/#typedef-declaration-value

	p.stack = p.stack[:0] // Reuse allocated memory
	start := p.index

loop:
	for {
		switch p.current().Kind {
		case css_lexer.TCloseParen, css_lexer.TCloseBracket, css_lexer.TCloseBrace:
			last := len(p.stack) - 1
			if last < 0 || !p.peek(p.stack[last]) {
				break loop
			}
			p.stack = p.stack[:last]

		case css_lexer.TSemicolon, css_lexer.TDelimExclamation:
			if len(p.stack) == 0 {
				break loop
			}

		case css_lexer.TOpenParen, css_lexer.TFunction:
			p.stack = append(p.stack, css_lexer.TCloseParen)

		case css_lexer.TOpenBracket:
			p.stack = append(p.stack, css_lexer.TCloseBracket)

		case css_lexer.TOpenBrace:
			p.stack = append(p.stack, css_lexer.TCloseBrace)

		case css_lexer.TEndOfFile:
			break loop
		}

		p.advance()
	}

	tokens := p.tokens[start:p.index]
	if len(tokens) == 0 {
		p.unexpected()
	}
	return tokens
}

func (p *parser) parseCombinator() css_ast.Combinator {
	t := p.current()

	switch t.Kind {
	case css_lexer.TDelimGreaterThan:
		p.advance()
		return css_ast.Combinator{Loc: t.Range.Loc, Byte: '>'}

	case css_lexer.TDelimPlus:
		p.advance()
		return css_ast.Combinator{Loc: t.Range.Loc, Byte: '+'}

	case css_lexer.TDelimTilde:
		p.advance()
		return css_ast.Combinator{Loc: t.Range.Loc, Byte: '~'}

	default:
		return css_ast.Combinator{}
	}
}

func parseInteger(text string) (string, bool) {
	n := len(text)
	if n == 0 {
		return "", false
	}

	// Trim leading zeros
	start := 0
	for start < n && text[start] == '0' {
		start++
	}

	// Make sure remaining characters are digits
	if start == n {
		return "0", true
	}
	for i := start; i < n; i++ {
		if c := text[i]; c < '0' || c > '9' {
			return "", false
		}
	}
	return text[start:], true
}

func (p *parser) parseNthIndex() (css_ast.NthIndex, bool) {
	type sign uint8
	const (
		none sign = iota
		negative
		positive
	)

	// Reference: https://drafts.csswg.org/css-syntax-3/#anb-microsyntax
	t0 := p.current()
	text0 := p.decoded()

	// Handle "even" and "odd"
	if t0.Kind == css_lexer.TIdent && (text0 == "even" || text0 == "odd") {
		p.advance()
		p.eat(css_lexer.TWhitespace)
		return css_ast.NthIndex{B: text0}, true
	}

	// Handle a single number
	if t0.Kind == css_lexer.TNumber {
		bNeg := false
		if strings.HasPrefix(text0, "-") {
			bNeg = true
			text0 = text0[1:]
		} else {
			text0 = strings.TrimPrefix(text0, "+")
		}
		if b, ok := parseInteger(text0); ok {
			if bNeg {
				b = "-" + b
			}
			p.advance()
			p.eat(css_lexer.TWhitespace)
			return css_ast.NthIndex{B: b}, true
		}
		p.unexpected()
		return css_ast.NthIndex{}, false
	}

	aSign := none
	if p.eat(css_lexer.TDelimPlus) {
		aSign = positive
		t0 = p.current()
		text0 = p.decoded()
	}

	// Everything from here must be able to contain an "n"
	if t0.Kind != css_lexer.TIdent && t0.Kind != css_lexer.TDimension {
		p.unexpected()
		return css_ast.NthIndex{}, false
	}

	// Check for a leading sign
	if aSign == none {
		if strings.HasPrefix(text0, "-") {
			aSign = negative
			text0 = text0[1:]
		} else {
			text0 = strings.TrimPrefix(text0, "+")
		}
	}

	// The string must contain an "n"
	n := strings.IndexByte(text0, 'n')
	if n < 0 {
		p.unexpected()
		return css_ast.NthIndex{}, false
	}

	// Parse the number before the "n"
	var a string
	if n == 0 {
		if aSign == negative {
			a = "-1"
		} else {
			a = "1"
		}
	} else if aInt, ok := parseInteger(text0[:n]); ok {
		if aSign == negative {
			aInt = "-" + aInt
		}
		a = aInt
	} else {
		p.unexpected()
		return css_ast.NthIndex{}, false
	}
	text0 = text0[n+1:]

	// Parse the stuff after the "n"
	bSign := none
	if strings.HasPrefix(text0, "-") {
		text0 = text0[1:]
		if b, ok := parseInteger(text0); ok {
			p.advance()
			p.eat(css_lexer.TWhitespace)
			return css_ast.NthIndex{A: a, B: "-" + b}, true
		}
		bSign = negative
	}
	if text0 != "" {
		p.unexpected()
		return css_ast.NthIndex{}, false
	}
	p.advance()
	p.eat(css_lexer.TWhitespace)

	// Parse an optional sign delimiter
	if bSign == none {
		if p.eat(css_lexer.TDelimMinus) {
			bSign = negative
			p.eat(css_lexer.TWhitespace)
		} else if p.eat(css_lexer.TDelimPlus) {
			bSign = positive
			p.eat(css_lexer.TWhitespace)
		}
	}

	// Parse an optional trailing number
	t1 := p.current()
	text1 := p.decoded()
	if t1.Kind == css_lexer.TNumber {
		if bSign == none {
			if strings.HasPrefix(text1, "-") {
				bSign = negative
				text1 = text1[1:]
			} else if strings.HasPrefix(text1, "+") {
				text1 = text1[1:]
			}
		}
		if b, ok := parseInteger(text1); ok {
			if bSign == negative {
				b = "-" + b
			}
			p.advance()
			p.eat(css_lexer.TWhitespace)
			return css_ast.NthIndex{A: a, B: b}, true
		}
	}

	// If there is a trailing sign, then there must also be a trailing number
	if bSign != none {
		p.expect(css_lexer.TNumber)
		return css_ast.NthIndex{}, false
	}

	return css_ast.NthIndex{A: a}, true
}