fix #3046: missing combinator bug with nested css

Author: evanw

CHANGELOG.md

@@ -1,5 +1,46 @@
 # Changelog
 
+## Unreleased
+
+* Fix CSS nesting transform for triple-nested rules that start with a combinator ([#3046](https://github.com/evanw/esbuild/issues/3046))
+
+    This release fixes a bug with esbuild where triple-nested CSS rules that start with a combinator were not transformed correctly for older browsers. Here's an example of such a case before and after this bug fix:
+
+    ```css
+    /* Original input */
+    .a {
+      color: red;
+      > .b {
+        color: green;
+        > .c {
+          color: blue;
+        }
+      }
+    }
+
+    /* Old output (with --target=chrome90) */
+    .a {
+      color: red;
+    }
+    .a > .b {
+      color: green;
+    }
+    .a .b > .c {
+      color: blue;
+    }
+
+    /* New output (with --target=chrome90) */
+    .a {
+      color: red;
+    }
+    .a > .b {
+      color: green;
+    }
+    .a > .b > .c {
+      color: blue;
+    }
+    ```
+
 ## 0.17.15
 
 * Allow keywords as type parameter names in mapped types ([#3033](https://github.com/evanw/esbuild/issues/3033))

internal/css_parser/css_nesting.go

@@ -212,6 +212,9 @@ func substituteAmpersandsInCompoundSelector(sel css_ast.CompoundSelector, replac
 
 		var subclassSelectorPrefix []css_ast.SS
 
+		// Copy over the combinator, if any
+		sel.Combinator = single.Combinator
+
 		// Insert the type selector
 		if single.TypeSelector != nil {
 			if sel.TypeSelector != nil {

internal/css_parser/css_parser_test.go

@@ -883,6 +883,8 @@ func TestNestedSelector(t *testing.T) {
 	expectPrintedLower(t, ".foo { & .bar { color: red } color: blue }", ".foo {\n  color: blue;\n}\n.foo .bar {\n  color: red;\n}\n")
 	expectPrintedLower(t, ".foo { color: blue; & .bar { color: red } zoom: 2 }", ".foo {\n  color: blue;\n  zoom: 2;\n}\n.foo .bar {\n  color: red;\n}\n")
 	expectPrintedLower(t, ".a, .b { .c, .d { color: red } }", ":is(.a, .b) :is(.c, .d) {\n  color: red;\n}\n")
+	expectPrintedLower(t, ".a { color: red; > .b { color: green; > .c { color: blue } } }", ".a {\n  color: red;\n}\n.a > .b {\n  color: green;\n}\n.a > .b > .c {\n  color: blue;\n}\n")
+	expectPrintedLower(t, "> .a { color: red; > .b { color: green; > .c { color: blue } } }", "> .a {\n  color: red;\n}\n> .a > .b {\n  color: green;\n}\n> .a > .b > .c {\n  color: blue;\n}\n")
 	expectPrintedLower(t, ".foo, .bar, .foo:before, .bar:after { &:hover { color: red } }", ":is(.foo, .bar):hover {\n  color: red;\n}\n")
 	expectPrintedLower(t, ".foo, .bar:before { &:hover { color: red } }", ".foo:hover {\n  color: red;\n}\n")
 	expectPrintedLower(t, ".foo, .bar:before { :hover & { color: red } }", ":hover .foo {\n  color: red;\n}\n")