Fix: css empty rulesets should be removed

internal/bundler/linker.go

@@ -4088,6 +4088,7 @@ func (repr *chunkReprCSS) generate(c *linkerContext, chunk *chunkInfo) func(gene
 			ast.Rules = rules
 
 			compileResult.printedCSS = css_printer.Print(ast, css_printer.Options{
+				MangleSyntax:     c.options.MangleSyntax,
 				RemoveWhitespace: c.options.RemoveWhitespace,
 				ASCIIOnly:        c.options.ASCIIOnly,
 			})

internal/css_printer/css_printer.go

@@ -19,6 +19,7 @@ type printer struct {
 }
 
 type Options struct {
+	MangleSyntax     bool
 	RemoveWhitespace bool
 	ASCIIOnly        bool
 }
@@ -89,6 +90,10 @@ func (p *printer) printRule(rule css_ast.R, indent int, omitTrailingSemicolon bo
 		}
 		indent++
 		for _, block := range r.Blocks {
+			if p.MangleSyntax && len(block.Rules) == 0 {
+				continue
+			}
+
 			if !p.RemoveWhitespace {
 				p.printIndent(indent)
 			}
@@ -117,6 +122,9 @@ func (p *printer) printRule(rule css_ast.R, indent int, omitTrailingSemicolon bo
 		p.print("}")
 
 	case *css_ast.RKnownAt:
+		if p.MangleSyntax && len(r.Rules) == 0 {
+			return
+		}
 		p.print("@")
 		whitespace := mayNeedWhitespaceAfter
 		if len(r.Prelude) == 0 {
@@ -153,13 +161,21 @@ func (p *printer) printRule(rule css_ast.R, indent int, omitTrailingSemicolon bo
 		}
 
 	case *css_ast.RSelector:
+		if p.MangleSyntax && len(r.Rules) == 0 {
+			return
+		}
+
 		p.printComplexSelectors(r.Selectors, indent)
 		if !p.RemoveWhitespace {
 			p.print(" ")
 		}
 		p.printRuleBlock(r.Rules, indent)
 
 	case *css_ast.RQualified:
+		if p.MangleSyntax && len(r.Rules) == 0 {
+			return
+		}
+
 		hasWhitespaceAfter := p.printTokens(r.Prelude)
 		if !hasWhitespaceAfter && !p.RemoveWhitespace {
 			p.print(" ")

internal/css_printer/css_printer_test.go

@@ -48,6 +48,13 @@ func expectPrintedMinify(t *testing.T, contents string, expected string) {
 	})
 }
 
+func expectPrinteMangleSyntax(t *testing.T, contents string, expected string) {
+	t.Helper()
+	expectPrintedCommon(t, contents+" [minified]", contents, expected, Options{
+		MangleSyntax: true,
+	})
+}
+
 func expectPrintedASCII(t *testing.T, contents string, expected string) {
 	t.Helper()
 	expectPrintedCommon(t, contents+" [ascii]", contents, expected, Options{
@@ -399,3 +406,19 @@ func TestASCII(t *testing.T) {
 	// This character should always be escaped
 	expectPrinted(t, ".\\FEFF:after { content: '\uFEFF' }", ".\\feff:after {\n  content: \"\\feff\";\n}\n")
 }
+
+func TestEmptyRule(t *testing.T) {
+	expectPrinted(t, "div {}", "div {\n}\n")
+	expectPrinted(t, ".a {}", ".a {\n}\n")
+	expectPrinted(t, ".a {}.b { color: red;}", ".a {\n}\n.b {\n  color: red;\n}\n")
+	expectPrinted(t, "@media (prefers-reduced-motion: no-preference) {\n}", "@media (prefers-reduced-motion: no-preference) {\n}\n")
+	expectPrinted(t, "@keyframes test {\n  from {}\n  to {\n  color: red;\n}\n}", "@keyframes test {\n  from {\n  }\n  to {\n    color: red;\n  }\n}\n")
+
+	expectPrintedMinify(t, "p:hover {}", "p:hover{}")
+	expectPrintedMinify(t, ".a {}\n.b {\n  color: red;\n}", ".a{}.b{color:red}")
+	expectPrintedMinify(t, "@keyframes mini {\n  from {}\n  to {\n  color: red;\n}\n}", "@keyframes mini{from{}to{color:red}}")
+
+	expectPrinteMangleSyntax(t, "a:hover {}", "")
+	expectPrinteMangleSyntax(t, ".a {}\n.b {\n  color: red;\n}", ".b {\n  color: red;\n}\n")
+	expectPrinteMangleSyntax(t, "@keyframes test {\n  from {}\n  to {\n  color: red;\n}\n}", "@keyframes test {\n  to {\n    color: red;\n  }\n}\n")
+}