fix: don't lowercase nesting selector (#4048)

src/language-css/printer-postcss.js

@@ -289,15 +289,22 @@ function genericPrint(path, options, print) {
       return adjustStrings(node.value, options);
     }
     case "selector-tag": {
+      const parentNode = path.getParentNode();
+      const index = parentNode && parentNode.nodes.indexOf(node);
+      const prevNode = index && parentNode.nodes[index - 1];
+
       return concat([
         node.namespace
           ? concat([node.namespace === true ? "" : node.namespace.trim(), "|"])
           : "",
-        adjustNumbers(
-          isHTMLTag(node.value) || isKeyframeAtRuleKeywords(path, node.value)
-            ? node.value.toLowerCase()
-            : node.value
-        )
+        prevNode.type === "selector-nesting"
+          ? node.value
+          : adjustNumbers(
+              isHTMLTag(node.value) ||
+              isKeyframeAtRuleKeywords(path, node.value)
+                ? node.value.toLowerCase()
+                : node.value
+            )
       ]);
     }
     case "selector-id": {

tests/css_case/__snapshots__/jsfmt.spec.js.snap

@@ -273,6 +273,8 @@ a:AFTER {
 }
 
 TABLE {}
+
+.foo { &-KeepSelector {} &-KeepSelector & .KeepClassSelector {} &-100\\.200 {} }
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 // Convention in this test file:
 // - The case should be preserved for things prefixed with "Keep".
@@ -426,6 +428,15 @@ a:after {
 table {
 }
 
+.foo {
+  &-KeepSelector {
+  }
+  &-KeepSelector & .KeepClassSelector {
+  }
+  &-100\\.200 {
+  }
+}
+
 `;
 
 exports[`case.scss 1`] = `
@@ -574,6 +585,8 @@ a:AFTER {
 }
 
 TABLE {}
+
+.foo { &-KeepSelector {} &-KeepSelector & .KeepClassSelector {} &-100\\.200 {} }
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 // Convention in this test file:
 // - The case should be preserved for things prefixed with "Keep".
@@ -725,4 +738,13 @@ a:after {
 table {
 }
 
+.foo {
+  &-KeepSelector {
+  }
+  &-KeepSelector & .KeepClassSelector {
+  }
+  &-100\\.200 {
+  }
+}
+
 `;

tests/css_case/case.less

@@ -140,3 +140,5 @@ a:AFTER {
 }
 
 TABLE {}
+
+.foo { &-KeepSelector {} &-KeepSelector & .KeepClassSelector {} &-100\.200 {} }

tests/css_case/case.scss

@@ -143,3 +143,5 @@ a:AFTER {
 }
 
 TABLE {}
+
+.foo { &-KeepSelector {} &-KeepSelector & .KeepClassSelector {} &-100\.200 {} }