fix #1803: panic with invalid "@import" conditions

CHANGELOG.md

@@ -146,6 +146,14 @@ In addition to the breaking changes above, the following changes are also includ
     .example{--some-var: var(--tw-empty, )}/*! Some legal comment */body{background-color:red}
     ```
 
+* Fix panic when printing invalid CSS ([#1803](https://github.com/evanw/esbuild/issues/1803))
+
+    This release fixes a panic caused by a conditional CSS `@import` rule with a URL token. Code like this caused esbuild to enter an unexpected state because the case where tokens in the import condition with associated import records wasn't handled. This case is now handled correctly:
+
+    ```css
+    @import "example.css" url(foo);
+    ```
+
 * Mark `Set` and `Map` with array arguments as pure ([#1791](https://github.com/evanw/esbuild/issues/1791))
 
     This release introduces special behavior for references to the global `Set` and `Map` constructors that marks them as `/* @__PURE__ */` if they are known to not have any side effects. These constructors evaluate the iterator of whatever is passed to them and the iterator could have side effects, so this is only safe if whatever is passed to them is an array, since the array iterator has no side effects.

internal/bundler/bundler_css_test.go

@@ -566,6 +566,21 @@ func TestCSSAtImportConditionsBundleExternal(t *testing.T) {
 	})
 }
 
+func TestCSSAtImportConditionsBundleExternalConditionWithURL(t *testing.T) {
+	css_suite.expectBundled(t, bundled{
+		files: map[string]string{
+			"/entry.css": `
+				@import "https://example.com/foo.css" (foo: url("foo.png")) and (bar: url("bar.png"));
+			`,
+		},
+		entryPaths: []string{"/entry.css"},
+		options: config.Options{
+			Mode:          config.ModeBundle,
+			AbsOutputFile: "/out.css",
+		},
+	})
+}
+
 func TestCSSAtImportConditionsBundle(t *testing.T) {
 	css_suite.expectBundled(t, bundled{
 		files: map[string]string{

internal/bundler/linker.go

@@ -174,8 +174,9 @@ type chunkReprCSS struct {
 }
 
 type externalImportCSS struct {
-	path       logger.Path
-	conditions []css_ast.Token
+	path                   logger.Path
+	conditions             []css_ast.Token
+	conditionImportRecords []ast.ImportRecord
 }
 
 // Returns a log where "log.HasErrors()" only returns true if any errors have
@@ -2822,10 +2823,15 @@ func (c *linkerContext) findImportedFilesInCSSOrder(entryPoints []uint32) (exter
 							external.conditions = append(external.conditions, atImport.ImportConditions)
 						}
 
+						// Clone any import records associated with the condition tokens
+						conditions, conditionImportRecords := css_ast.CloneTokensWithImportRecords(
+							atImport.ImportConditions, repr.AST.ImportRecords, nil, nil)
+
 						externals[record.Path] = external
 						externalOrder = append(externalOrder, externalImportCSS{
-							path:       record.Path,
-							conditions: atImport.ImportConditions,
+							path:                   record.Path,
+							conditions:             conditions,
+							conditionImportRecords: conditionImportRecords,
 						})
 					}
 				}
@@ -4868,9 +4874,12 @@ func (c *linkerContext) generateChunkCSS(chunks []chunkInfo, chunkIndex int, chu
 		// Insert all external "@import" rules at the front. In CSS, all "@import"
 		// rules must come first or the browser will just ignore them.
 		for _, external := range chunkRepr.externalImportsInOrder {
+			var conditions []css_ast.Token
+			conditions, tree.ImportRecords = css_ast.CloneTokensWithImportRecords(
+				external.conditions, external.conditionImportRecords, conditions, tree.ImportRecords)
 			tree.Rules = append(tree.Rules, css_ast.Rule{Data: &css_ast.RAtImport{
 				ImportRecordIndex: uint32(len(tree.ImportRecords)),
-				ImportConditions:  external.conditions,
+				ImportConditions:  conditions,
 			}})
 			tree.ImportRecords = append(tree.ImportRecords, ast.ImportRecord{
 				Kind: ast.ImportAt,

internal/bundler/snapshots/snapshots_css.txt

@@ -93,6 +93,13 @@ TestCSSAtImportConditionsBundleExternal
 
 /* entry.css */
 
+================================================================================
+TestCSSAtImportConditionsBundleExternalConditionWithURL
+---------- /out.css ----------
+@import "https://example.com/foo.css" (foo: url(foo.png)) and (bar: url(bar.png));
+
+/* entry.css */
+
 ================================================================================
 TestCSSAtImportConditionsNoBundle
 ---------- /out.css ----------

internal/css_ast/css_ast.go

@@ -231,6 +231,31 @@ func (t Token) IsAngle() bool {
 	return false
 }
 
+func CloneTokensWithImportRecords(
+	tokensIn []Token, importRecordsIn []ast.ImportRecord,
+	tokensOut []Token, importRecordsOut []ast.ImportRecord,
+) ([]Token, []ast.ImportRecord) {
+	for _, t := range tokensIn {
+		// If this is a URL token, also clone the import record
+		if t.Kind == css_lexer.TURL {
+			importRecordIndex := uint32(len(importRecordsOut))
+			importRecordsOut = append(importRecordsOut, importRecordsIn[t.ImportRecordIndex])
+			t.ImportRecordIndex = importRecordIndex
+		}
+
+		// Also search for URL tokens in this token's children
+		if t.Children != nil {
+			var children []Token
+			children, importRecordsOut = CloneTokensWithImportRecords(*t.Children, importRecordsIn, children, importRecordsOut)
+			t.Children = &children
+		}
+
+		tokensOut = append(tokensOut, t)
+	}
+
+	return tokensOut, importRecordsOut
+}
+
 type Rule struct {
 	Loc  logger.Loc
 	Data R

internal/css_parser/css_parser.go

@@ -647,9 +647,15 @@ func (p *parser) parseAtRule(context atRuleContext) css_ast.Rule {
 		p.eat(css_lexer.TWhitespace)
 		if path, r, ok := p.expectURLOrString(); ok {
 			importConditionsStart := p.index
-			for p.current().Kind != css_lexer.TSemicolon && p.current().Kind != css_lexer.TEndOfFile {
+			for {
+				if kind := p.current().Kind; kind == css_lexer.TSemicolon || kind == css_lexer.TOpenBrace || kind == css_lexer.TEndOfFile {
+					break
+				}
 				p.parseComponentValue()
 			}
+			if p.current().Kind == css_lexer.TOpenBrace {
+				break // Avoid parsing an invalid "@import" rule
+			}
 			importConditions := p.convertTokens(p.tokens[importConditionsStart:p.index])
 			kind := ast.ImportAt
 

internal/css_parser/css_parser_test.go

@@ -836,7 +836,8 @@ func TestAtImport(t *testing.T) {
 <stdin>: warning: Expected ";" but found end of file
 `)
 
-	expectParseError(t, "@import \"foo.css\" {}", "<stdin>: warning: Expected \";\" but found end of file\n")
+	expectParseError(t, "@import \"foo.css\" {}", "<stdin>: warning: Expected \";\"\n")
+	expectPrinted(t, "@import \"foo\"\na { color: red }\nb { color: blue }", "@import \"foo\" a { color: red }\nb {\n  color: blue;\n}\n")
 }
 
 func TestLegalComment(t *testing.T) {