fixes after landing css change

CHANGELOG.md

@@ -32,6 +32,10 @@
 
     The parser previously allowed this for regular functions but not for async or generator functions. Now with this release, this behavior is also allowed for these special kinds of functions too.
 
+* Remove empty CSS rules when minifying ([#851](https://github.com/evanw/esbuild/pull/851))
+
+    Empty rules with no content such as `div {}` are now removed when CSS is minified. This change was contributed by [@susiwen8](https://github.com/susiwen8).
+
 ## 0.8.49
 
 * Work around a problem with `pnpm` and `NODE_PATH` ([#816](https://github.com/evanw/esbuild/issues/816))

internal/css_printer/css_printer.go

@@ -90,6 +90,7 @@ func (p *printer) printRule(rule css_ast.R, indent int, omitTrailingSemicolon bo
 		}
 		indent++
 		for _, block := range r.Blocks {
+			// "@keyframes { from {} to { color: red } }" => "@keyframes { to { color: red } }"
 			if p.MangleSyntax && len(block.Rules) == 0 {
 				continue
 			}
@@ -122,9 +123,16 @@ func (p *printer) printRule(rule css_ast.R, indent int, omitTrailingSemicolon bo
 		p.print("}")
 
 	case *css_ast.RKnownAt:
+		// "@font-face {}" => ""
+		// "@page {}" => ""
+		// "@document {}" => ""
+		// "@media {}" => ""
+		// "@scope {}" => ""
+		// "@supports {}" => ""
 		if p.MangleSyntax && len(r.Rules) == 0 {
 			return
 		}
+
 		p.print("@")
 		whitespace := mayNeedWhitespaceAfter
 		if len(r.Prelude) == 0 {
@@ -161,6 +169,7 @@ func (p *printer) printRule(rule css_ast.R, indent int, omitTrailingSemicolon bo
 		}
 
 	case *css_ast.RSelector:
+		// "a {}" => ""
 		if p.MangleSyntax && len(r.Rules) == 0 {
 			return
 		}
@@ -172,10 +181,6 @@ func (p *printer) printRule(rule css_ast.R, indent int, omitTrailingSemicolon bo
 		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

@@ -48,9 +48,9 @@ func expectPrintedMinify(t *testing.T, contents string, expected string) {
 	})
 }
 
-func expectPrinteMangleSyntax(t *testing.T, contents string, expected string) {
+func expectPrintedMangle(t *testing.T, contents string, expected string) {
 	t.Helper()
-	expectPrintedCommon(t, contents+" [minified]", contents, expected, Options{
+	expectPrintedCommon(t, contents+" [mangled]", contents, expected, Options{
 		MangleSyntax: true,
 	})
 }
@@ -409,16 +409,20 @@ func TestASCII(t *testing.T) {
 
 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")
+	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")
 }