css: emit mappings for nesting selectors

internal/css_ast/css_ast.go

@@ -640,7 +640,7 @@ func (s ComplexSelector) CloneWithoutLeadingCombinator() ComplexSelector {
 func (sel ComplexSelector) IsRelative() bool {
 	if sel.Selectors[0].Combinator.Byte == 0 {
 		for _, inner := range sel.Selectors {
-			if inner.HasNestingSelector {
+			if inner.HasNestingSelector() {
 				return false
 			}
 			for _, ss := range inner.SubclassSelectors {
@@ -699,7 +699,7 @@ func (a ComplexSelector) Equal(b ComplexSelector, check *CrossFileEqualityCheck)
 
 	for i, ai := range a.Selectors {
 		bi := b.Selectors[i]
-		if ai.HasNestingSelector != bi.HasNestingSelector || ai.Combinator.Byte != bi.Combinator.Byte {
+		if ai.HasNestingSelector() != bi.HasNestingSelector() || ai.Combinator.Byte != bi.Combinator.Byte {
 			return false
 		}
 
@@ -730,12 +730,16 @@ type Combinator struct {
 type CompoundSelector struct {
 	TypeSelector       *NamespacedName
 	SubclassSelectors  []SubclassSelector
-	Combinator         Combinator // Optional, may be 0
-	HasNestingSelector bool       // "&"
+	NestingSelectorLoc ast.Index32 // "&"
+	Combinator         Combinator  // Optional, may be 0
+}
+
+func (sel *CompoundSelector) HasNestingSelector() bool {
+	return sel.NestingSelectorLoc.IsValid()
 }
 
 func (sel CompoundSelector) IsSingleAmpersand() bool {
-	return sel.HasNestingSelector && sel.Combinator.Byte == 0 && sel.TypeSelector == nil && len(sel.SubclassSelectors) == 0
+	return sel.HasNestingSelector() && sel.Combinator.Byte == 0 && sel.TypeSelector == nil && len(sel.SubclassSelectors) == 0
 }
 
 func (sel CompoundSelector) Clone() CompoundSelector {

internal/css_parser/css_nesting.go

@@ -1,6 +1,7 @@
 package css_parser
 
 import (
+	"github.com/evanw/esbuild/internal/ast"
 	"github.com/evanw/esbuild/internal/css_ast"
 )
 
@@ -115,7 +116,7 @@ func lowerNestingInRuleWithContext(rule css_ast.Rule, context *lowerNestingConte
 
 			// Inject the implicit "&" now for simplicity later on
 			if sel.IsRelative() {
-				sel.Selectors = append([]css_ast.CompoundSelector{{HasNestingSelector: true}}, sel.Selectors...)
+				sel.Selectors = append([]css_ast.CompoundSelector{{NestingSelectorLoc: ast.MakeIndex32(uint32(rule.Loc.Start))}}, sel.Selectors...)
 			}
 
 			// Pseudo-elements aren't supported by ":is" (i.e. ":is(div, div::before)"
@@ -143,7 +144,7 @@ func lowerNestingInRuleWithContext(rule css_ast.Rule, context *lowerNestingConte
 			}
 
 			// Are all children of the form "&«something»"?
-			if first := sel.Selectors[0]; !first.HasNestingSelector || first.IsSingleAmpersand() {
+			if first := sel.Selectors[0]; !first.HasNestingSelector() || first.IsSingleAmpersand() {
 				canUseGroupSubSelector = false
 			}
 		}
@@ -152,22 +153,24 @@ func lowerNestingInRuleWithContext(rule css_ast.Rule, context *lowerNestingConte
 		if canUseGroupDescendantCombinator {
 			// "& a, & b {}" => "& :is(a, b) {}"
 			// "& > a, & > b {}" => "& > :is(a, b) {}"
+			nestingSelectorLoc := r.Selectors[0].Selectors[0].NestingSelectorLoc
 			for i := range r.Selectors {
 				sel := &r.Selectors[i]
 				sel.Selectors = sel.Selectors[1:]
 			}
 			merged := multipleComplexSelectorsToSingleComplexSelector(r.Selectors)
-			merged.Selectors = append([]css_ast.CompoundSelector{{HasNestingSelector: true}}, merged.Selectors...)
+			merged.Selectors = append([]css_ast.CompoundSelector{{NestingSelectorLoc: nestingSelectorLoc}}, merged.Selectors...)
 			r.Selectors = []css_ast.ComplexSelector{merged}
 		} else if canUseGroupSubSelector {
 			// "&a, &b {}" => "&:is(a, b) {}"
 			// "> &a, > &b {}" => "> &:is(a, b) {}"
+			nestingSelectorLoc := r.Selectors[0].Selectors[0].NestingSelectorLoc
 			for i := range r.Selectors {
 				sel := &r.Selectors[i]
-				sel.Selectors[0].HasNestingSelector = false
+				sel.Selectors[0].NestingSelectorLoc = ast.Index32{}
 			}
 			merged := multipleComplexSelectorsToSingleComplexSelector(r.Selectors)
-			merged.Selectors[0].HasNestingSelector = true
+			merged.Selectors[0].NestingSelectorLoc = nestingSelectorLoc
 			r.Selectors = []css_ast.ComplexSelector{merged}
 		}
 
@@ -237,8 +240,8 @@ const (
 )
 
 func substituteAmpersandsInCompoundSelector(sel css_ast.CompoundSelector, replacement css_ast.ComplexSelector, results []css_ast.CompoundSelector, strip leadingCombinatorStrip) []css_ast.CompoundSelector {
-	if sel.HasNestingSelector {
-		sel.HasNestingSelector = false
+	if sel.HasNestingSelector() {
+		sel.NestingSelectorLoc = ast.Index32{}
 
 		// Convert the replacement to a single compound selector
 		var single css_ast.CompoundSelector

internal/css_parser/css_parser.go

@@ -786,7 +786,7 @@ var nonDeprecatedElementsSupportedByIE7 = map[string]bool{
 func isSafeSelectors(complexSelectors []css_ast.ComplexSelector) bool {
 	for _, complex := range complexSelectors {
 		for _, compound := range complex.Selectors {
-			if compound.HasNestingSelector {
+			if compound.HasNestingSelector() {
 				// Bail because this is an extension: https://drafts.csswg.org/css-nesting-1/
 				return false
 			}

internal/css_parser/css_parser_selector.go

@@ -65,7 +65,7 @@ skip:
 
 		case canRemoveLeadingAmpersandIfNotFirst:
 			for i := 1; i < len(list); i++ {
-				if sel := list[i].Selectors[0]; !sel.HasNestingSelector && (sel.Combinator.Byte != 0 || sel.TypeSelector == nil) {
+				if sel := list[i].Selectors[0]; !sel.HasNestingSelector() && (sel.Combinator.Byte != 0 || sel.TypeSelector == nil) {
 					list[0].Selectors = list[0].Selectors[1:]
 					list[0], list[i] = list[i], list[0]
 					break
@@ -85,7 +85,7 @@ func flattenLocalAndGlobalSelectors(list []css_ast.ComplexSelector, sel css_ast.
 	// done separately from the loop below because inlining may produce
 	// multiple complex selectors.
 	if len(sel.Selectors) == 1 {
-		if single := sel.Selectors[0]; !single.HasNestingSelector && single.TypeSelector == nil && len(single.SubclassSelectors) == 1 && single.Combinator.Byte == 0 {
+		if single := sel.Selectors[0]; !single.HasNestingSelector() && single.TypeSelector == nil && len(single.SubclassSelectors) == 1 && single.Combinator.Byte == 0 {
 			if pseudo, ok := single.SubclassSelectors[0].Data.(*css_ast.SSPseudoClassWithSelectorList); ok && (pseudo.Kind == css_ast.PseudoClassGlobal || pseudo.Kind == css_ast.PseudoClassLocal) {
 				// ":local(.a, .b)" => ".a, .b"
 				return append(list, pseudo.Selectors...)
@@ -107,7 +107,7 @@ func flattenLocalAndGlobalSelectors(list []css_ast.ComplexSelector, sel css_ast.
 					// contents can be inlined, then inline it directly. This has to be
 					// done separately from the loop below because inlining may produce
 					// multiple compound selectors.
-					if !s.HasNestingSelector && s.TypeSelector == nil && len(s.SubclassSelectors) == 1 {
+					if !s.HasNestingSelector() && s.TypeSelector == nil && len(s.SubclassSelectors) == 1 {
 						if pseudo, ok := s.SubclassSelectors[0].Data.(*css_ast.SSPseudoClassWithSelectorList); ok &&
 							(pseudo.Kind == css_ast.PseudoClassGlobal || pseudo.Kind == css_ast.PseudoClassLocal) && len(pseudo.Selectors) == 1 {
 							if nested := pseudo.Selectors[0].Selectors; ok && (s.Combinator.Byte == 0 || nested[0].Combinator.Byte == 0) {
@@ -132,9 +132,9 @@ func flattenLocalAndGlobalSelectors(list []css_ast.ComplexSelector, sel css_ast.
 										// ".foo:local(div)" => "div.foo"
 										s.TypeSelector = single.TypeSelector
 									}
-									if single.HasNestingSelector {
+									if single.HasNestingSelector() {
 										// ".foo:local(&)" => "&.foo"
-										s.HasNestingSelector = true
+										s.NestingSelectorLoc = single.NestingSelectorLoc
 									}
 									// ".foo:local(.bar)" => ".foo.bar"
 									subclassSelectors = append(subclassSelectors, single.SubclassSelectors...)
@@ -171,7 +171,7 @@ const (
 func analyzeLeadingAmpersand(sel css_ast.ComplexSelector, isDeclarationContext bool) leadingAmpersand {
 	if len(sel.Selectors) > 1 {
 		if first := sel.Selectors[0]; first.IsSingleAmpersand() {
-			if second := sel.Selectors[1]; second.Combinator.Byte == 0 && second.HasNestingSelector {
+			if second := sel.Selectors[1]; second.Combinator.Byte == 0 && second.HasNestingSelector() {
 				// ".foo { & &.bar {} }" => ".foo { & &.bar {} }"
 			} else if second.Combinator.Byte != 0 || second.TypeSelector == nil || !isDeclarationContext {
 				// "& + div {}" => "+ div {}"
@@ -264,7 +264,7 @@ func (p *parser) parseCompoundSelector(opts parseComplexSelectorOpts) (sel css_a
 	hasLeadingNestingSelector := p.peek(css_lexer.TDelimAmpersand)
 	if hasLeadingNestingSelector {
 		p.reportUseOfNesting(p.current().Range, opts.isDeclarationContext)
-		sel.HasNestingSelector = true
+		sel.NestingSelectorLoc = ast.MakeIndex32(uint32(startLoc.Start))
 		p.advance()
 	}
 
@@ -296,12 +296,14 @@ func (p *parser) parseCompoundSelector(opts parseComplexSelectorOpts) (sel css_a
 	// Parse the subclass selectors
 subclassSelectors:
 	for {
-		switch p.current().Kind {
+		subclassToken := p.current()
+
+		switch subclassToken.Kind {
 		case css_lexer.THash:
-			if (p.current().Flags & css_lexer.IsID) == 0 {
+			if (subclassToken.Flags & css_lexer.IsID) == 0 {
 				break subclassSelectors
 			}
-			nameLoc := logger.Loc{Start: p.current().Range.Loc.Start + 1}
+			nameLoc := logger.Loc{Start: subclassToken.Range.Loc.Start + 1}
 			name := p.decoded()
 			sel.SubclassSelectors = append(sel.SubclassSelectors, css_ast.SubclassSelector{
 				Data: &css_ast.SSHash{
@@ -368,8 +370,8 @@ subclassSelectors:
 
 		case css_lexer.TDelimAmpersand:
 			// This is an extension: https://drafts.csswg.org/css-nesting-1/
-			p.reportUseOfNesting(p.current().Range, sel.HasNestingSelector)
-			sel.HasNestingSelector = true
+			p.reportUseOfNesting(subclassToken.Range, sel.HasNestingSelector())
+			sel.NestingSelectorLoc = ast.MakeIndex32(uint32(subclassToken.Range.Loc.Start))
 			p.advance()
 
 		default:
@@ -378,7 +380,7 @@ subclassSelectors:
 	}
 
 	// The compound selector must be non-empty
-	if !sel.HasNestingSelector && sel.TypeSelector == nil && len(sel.SubclassSelectors) == 0 {
+	if !sel.HasNestingSelector() && sel.TypeSelector == nil && len(sel.SubclassSelectors) == 0 {
 		p.unexpected()
 		return
 	}

internal/css_printer/css_printer.go

@@ -449,7 +449,11 @@ func (p *printer) printCompoundSelector(sel css_ast.CompoundSelector, isFirst bo
 		p.printNamespacedName(*sel.TypeSelector, whitespace)
 	}
 
-	if sel.HasNestingSelector {
+	if sel.HasNestingSelector() {
+		if p.options.AddSourceMappings {
+			p.builder.AddSourceMapping(logger.Loc{Start: int32(sel.NestingSelectorLoc.GetIndex())}, "", p.css)
+		}
+
 		p.print("&")
 	}