css: parser separates layers pre/post @import

internal/css_ast/css_ast.go

@@ -35,9 +35,12 @@ type AST struct {
 	GlobalScope          map[string]ast.LocRef
 	Composes             map[ast.Ref]*Composes
 
-	// This contains all layer names in the file. It can be used to replace the
-	// layer-related side effects of importing this file.
-	Layers [][]string
+	// These contain all layer names in the file. It can be used to replace the
+	// layer-related side effects of importing this file. They are split into two
+	// groups (those before and after "@import" rules) so that the linker can put
+	// them in the right places.
+	LayersPreImport  [][]string
+	LayersPostImport [][]string
 }
 
 type Composes struct {

internal/css_parser/css_parser.go

@@ -31,7 +31,8 @@ type parser struct {
 	nestingWarnings   map[logger.Loc]struct{}
 	tracker           logger.LineColumnTracker
 	enclosingAtMedia  [][]css_ast.Token
-	layers            [][]string
+	layersPreImport   [][]string
+	layersPostImport  [][]string
 	enclosingLayer    []string
 	anonLayerCount    int
 	index             int
@@ -42,6 +43,7 @@ type parser struct {
 	options           Options
 	nestingIsPresent  bool
 	makeLocalSymbols  bool
+	hasSeenAtImport   bool
 }
 
 type Options struct {
@@ -153,7 +155,8 @@ func Parse(log logger.Log, source logger.Source, options Options) css_ast.AST {
 		LocalScope:           p.localScope,
 		GlobalScope:          p.globalScope,
 		Composes:             p.composes,
-		Layers:               p.layers,
+		LayersPreImport:      p.layersPreImport,
+		LayersPostImport:     p.layersPostImport,
 	}
 }
 
@@ -359,7 +362,7 @@ func (p *parser) recordAtLayerRule(layers [][]string) {
 			clone := make([]string, 0, len(p.enclosingLayer)+len(layer))
 			layer = append(append(clone, p.enclosingLayer...), layer...)
 		}
-		p.layers = append(p.layers, layer)
+		p.layersPostImport = append(p.layersPostImport, layer)
 	}
 }
 
@@ -1248,6 +1251,14 @@ abortRuleParser:
 					Path:  logger.Path{Text: path},
 					Range: r,
 				})
+
+				// Fill in the pre-import layers once we see the first "@import"
+				if !p.hasSeenAtImport {
+					p.hasSeenAtImport = true
+					p.layersPreImport = p.layersPostImport
+					p.layersPostImport = nil
+				}
+
 				return css_ast.Rule{Loc: atRange.Loc, Data: &css_ast.RAtImport{
 					ImportRecordIndex: importRecordIndex,
 					ImportConditions:  importConditions,

internal/linker/linker.go

@@ -3496,7 +3496,8 @@ func (c *linkerContext) findImportedFilesInCSSOrder(entryPoints []uint32) (exter
 
 				// Remove this redundant entry either if it has no named layers
 				// or if it's wrapped in an anonymous layer without a name
-				hasNamedLayers := len(c.graph.Files[order.sourceIndex].InputFile.Repr.(*graph.CSSRepr).AST.Layers) > 0
+				tree := c.graph.Files[order.sourceIndex].InputFile.Repr.(*graph.CSSRepr).AST
+				hasNamedLayers := len(tree.LayersPreImport) > 0 || len(tree.LayersPostImport) > 0
 				hasAnonymousLayer := false
 				for _, conditions := range order.conditions {
 					if len(conditions.Layers) == 1 {
@@ -5891,9 +5892,17 @@ func (c *linkerContext) generateChunkCSS(chunkIndex int, chunkWaitGroup *sync.Wa
 				}
 				rules = append(rules, rule)
 			}
-		} else if len(ast.Layers) > 0 {
+		} else if pre, post := len(ast.LayersPreImport), len(ast.LayersPostImport); pre > 0 || post > 0 {
 			// Only include "@layer" information for redundant import order entries
-			rules = []css_ast.Rule{{Data: &css_ast.RAtLayer{Names: ast.Layers}}}
+			var layers [][]string
+			if pre == 0 {
+				layers = ast.LayersPostImport
+			} else if post == 0 {
+				layers = ast.LayersPreImport
+			} else {
+				layers = append(append(make([][]string, 0, pre+post), ast.LayersPreImport...), ast.LayersPostImport...)
+			}
+			rules = []css_ast.Rule{{Data: &css_ast.RAtLayer{Names: layers}}}
 		}
 
 		for i := len(entry.conditions) - 1; i >= 0; i-- {