css empty rule removal should happen in parser

internal/bundler/linker.go

@@ -4181,7 +4181,6 @@ 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_parser/css_parser.go

@@ -158,10 +158,11 @@ func (p *parser) parseListOfRules(context ruleContext) []css_ast.R {
 	rules := []css_ast.R{}
 	locs := []logger.Loc{}
 
+loop:
 	for {
 		switch p.current().Kind {
 		case css_lexer.TEndOfFile, css_lexer.TCloseBrace:
-			return rules
+			break loop
 
 		case css_lexer.TWhitespace:
 			p.advance()
@@ -222,6 +223,11 @@ func (p *parser) parseListOfRules(context ruleContext) []css_ast.R {
 			rules = append(rules, p.parseQualifiedRuleFrom(p.index, false /* isAlreadyInvalid */))
 		}
 	}
+
+	if p.options.MangleSyntax {
+		rules = removeEmptyRules(rules)
+	}
+	return rules
 }
 
 func (p *parser) parseListOfDeclarations() (list []css_ast.R) {
@@ -232,6 +238,9 @@ func (p *parser) parseListOfDeclarations() (list []css_ast.R) {
 
 		case css_lexer.TEndOfFile, css_lexer.TCloseBrace:
 			p.processDeclarations(list)
+			if p.options.MangleSyntax {
+				list = removeEmptyRules(list)
+			}
 			return
 
 		case css_lexer.TAtKeyword:
@@ -249,6 +258,32 @@ func (p *parser) parseListOfDeclarations() (list []css_ast.R) {
 	}
 }
 
+func removeEmptyRules(rules []css_ast.R) []css_ast.R {
+	end := 0
+	for _, rule := range rules {
+		switch r := rule.(type) {
+		case *css_ast.RAtKeyframes:
+			if len(r.Blocks) == 0 {
+				continue
+			}
+
+		case *css_ast.RKnownAt:
+			if len(r.Rules) == 0 {
+				continue
+			}
+
+		case *css_ast.RSelector:
+			if len(r.Rules) == 0 {
+				continue
+			}
+		}
+
+		rules[end] = rule
+		end++
+	}
+	return rules[:end]
+}
+
 func (p *parser) parseURLOrString() (string, logger.Range, bool) {
 	t := p.current()
 	switch t.Kind {
@@ -460,10 +495,14 @@ func (p *parser) parseAtRule(context atRuleContext) css_ast.R {
 					if p.expect(css_lexer.TOpenBrace) {
 						rules := p.parseListOfDeclarations()
 						p.expect(css_lexer.TCloseBrace)
-						blocks = append(blocks, css_ast.KeyframeBlock{
-							Selectors: selectors,
-							Rules:     rules,
-						})
+
+						// "@keyframes { from {} to { color: red } }" => "@keyframes { to { color: red } }"
+						if !p.options.MangleSyntax || len(rules) > 0 {
+							blocks = append(blocks, css_ast.KeyframeBlock{
+								Selectors: selectors,
+								Rules:     rules,
+							})
+						}
 					}
 				}
 			}

internal/css_parser/css_parser_test.go

@@ -50,7 +50,9 @@ func expectPrintedCommon(t *testing.T, name string, contents string, expected st
 			}
 		}
 		assertEqual(t, text, "")
-		css := css_printer.Print(tree, css_printer.Options{})
+		css := css_printer.Print(tree, css_printer.Options{
+			RemoveWhitespace: options.RemoveWhitespace,
+		})
 		assertEqual(t, string(css), expected)
 	})
 }
@@ -82,6 +84,14 @@ func expectPrintedLowerMangle(t *testing.T, contents string, expected string) {
 	})
 }
 
+func expectPrintedMangleMinify(t *testing.T, contents string, expected string) {
+	t.Helper()
+	expectPrintedCommon(t, contents+" [mangle, minify]", contents, expected, config.Options{
+		MangleSyntax:     true,
+		RemoveWhitespace: true,
+	})
+}
+
 func TestEscapes(t *testing.T) {
 	// TIdent
 	expectPrinted(t, "a { value: id\\65nt }", "a {\n  value: ident;\n}\n")
@@ -839,3 +849,30 @@ func TestAtRuleValidation(t *testing.T) {
 		"<stdin>: warning: All \"@import\" rules must come first\n"+
 			"<stdin>: note: This rule cannot come before an \"@import\" rule\n")
 }
+
+func TestEmptyRule(t *testing.T) {
+	expectPrinted(t, "div {}", "div {\n}\n")
+	expectPrinted(t, "@media screen {}", "@media screen {\n}\n")
+	expectPrinted(t, "@page { @top-left {} }", "@page {\n  @top-left {\n  }\n}\n")
+	expectPrinted(t, "@keyframes test { from {} to {} }", "@keyframes test {\n  from {\n  }\n  to {\n  }\n}\n")
+
+	expectPrintedMangle(t, "div {}", "")
+	expectPrintedMangle(t, "@media screen {}", "")
+	expectPrintedMangle(t, "@page { @top-left {} }", "")
+	expectPrintedMangle(t, "@keyframes test { from {} to {} }", "")
+
+	expectPrinted(t, "$invalid {}", "$invalid {\n}\n")
+	expectPrinted(t, "@page { color: red; @top-left {} }", "@page {\n  color: red;\n  @top-left {\n  }\n}\n")
+	expectPrinted(t, "@keyframes test { from {} to { color: red } }", "@keyframes test {\n  from {\n  }\n  to {\n    color: red;\n  }\n}\n")
+	expectPrinted(t, "@keyframes test { from { color: red } to {} }", "@keyframes test {\n  from {\n    color: red;\n  }\n  to {\n  }\n}\n")
+
+	expectPrintedMangle(t, "$invalid {}", "$invalid {\n}\n")
+	expectPrintedMangle(t, "@page { color: red; @top-left {} }", "@page {\n  color: red;\n}\n")
+	expectPrintedMangle(t, "@keyframes test { from {} to { color: red } }", "@keyframes test {\n  to {\n    color: red;\n  }\n}\n")
+	expectPrintedMangle(t, "@keyframes test { from { color: red } to {} }", "@keyframes test {\n  0% {\n    color: red;\n  }\n}\n")
+
+	expectPrintedMangleMinify(t, "$invalid {}", "$invalid{}")
+	expectPrintedMangleMinify(t, "@page { color: red; @top-left {} }", "@page{color:red}")
+	expectPrintedMangleMinify(t, "@keyframes test { from {} to { color: red } }", "@keyframes test{to{color:red}}")
+	expectPrintedMangleMinify(t, "@keyframes test { from { color: red } to {} }", "@keyframes test{0%{color:red}}")
+}

internal/css_printer/css_printer.go

@@ -19,7 +19,6 @@ type printer struct {
 }
 
 type Options struct {
-	MangleSyntax     bool
 	RemoveWhitespace bool
 	ASCIIOnly        bool
 }
@@ -78,11 +77,6 @@ func (p *printer) printRule(rule css_ast.R, indent int32, omitTrailingSemicolon
 		}
 		indent++
 		for _, block := range r.Blocks {
-			// "@keyframes { from {} to { color: red } }" => "@keyframes { to { color: red } }"
-			if p.options.MangleSyntax && len(block.Rules) == 0 {
-				continue
-			}
-
 			if !p.options.RemoveWhitespace {
 				p.printIndent(indent)
 			}
@@ -111,16 +105,6 @@ func (p *printer) printRule(rule css_ast.R, indent int32, omitTrailingSemicolon
 		p.print("}")
 
 	case *css_ast.RKnownAt:
-		// "@font-face {}" => ""
-		// "@page {}" => ""
-		// "@document {}" => ""
-		// "@media {}" => ""
-		// "@scope {}" => ""
-		// "@supports {}" => ""
-		if p.options.MangleSyntax && len(r.Rules) == 0 {
-			return
-		}
-
 		p.print("@")
 		whitespace := mayNeedWhitespaceAfter
 		if len(r.Prelude) == 0 {
@@ -157,11 +141,6 @@ func (p *printer) printRule(rule css_ast.R, indent int32, omitTrailingSemicolon
 		}
 
 	case *css_ast.RSelector:
-		// "a {}" => ""
-		if p.options.MangleSyntax && len(r.Rules) == 0 {
-			return
-		}
-
 		p.printComplexSelectors(r.Selectors, indent)
 		if !p.options.RemoveWhitespace {
 			p.print(" ")

internal/css_printer/css_printer_test.go

@@ -48,13 +48,6 @@ func expectPrintedMinify(t *testing.T, contents string, expected string) {
 	})
 }
 
-func expectPrintedMangle(t *testing.T, contents string, expected string) {
-	t.Helper()
-	expectPrintedCommon(t, contents+" [mangled]", contents, expected, Options{
-		MangleSyntax: true,
-	})
-}
-
 func expectPrintedASCII(t *testing.T, contents string, expected string) {
 	t.Helper()
 	expectPrintedCommon(t, contents+" [ascii]", contents, expected, Options{
@@ -399,23 +392,3 @@ 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, "$invalid {}", "$invalid {\n}\n")
-	expectPrinted(t, "@media screen {}", "@media screen {\n}\n")
-	expectPrinted(t, "@keyframes test { from {} to { color: red } }", "@keyframes test {\n  from {\n  }\n  to {\n    color: red;\n  }\n}\n")
-	expectPrinted(t, "@keyframes test { from { color: red } to {} }", "@keyframes test {\n  from {\n    color: red;\n  }\n  to {\n  }\n}\n")
-
-	expectPrintedMinify(t, "div {}", "div{}")
-	expectPrintedMinify(t, "$invalid {}", "$invalid{}")
-	expectPrintedMinify(t, "@media screen {}", "@media screen{}")
-	expectPrintedMinify(t, "@keyframes test { from {} to { color: red } }", "@keyframes test{from{}to{color:red}}")
-	expectPrintedMinify(t, "@keyframes test { from { color: red } to {} }", "@keyframes test{from{color:red}to{}}")
-
-	expectPrintedMangle(t, "div {}", "")
-	expectPrintedMangle(t, "$invalid {}", "$invalid {\n}\n")
-	expectPrintedMangle(t, "@media screen {}", "")
-	expectPrintedMangle(t, "@keyframes test { from {} to { color: red } }", "@keyframes test {\n  to {\n    color: red;\n  }\n}\n")
-	expectPrintedMangle(t, "@keyframes test { from { color: red } to {} }", "@keyframes test {\n  from {\n    color: red;\n  }\n}\n")
-}