feat: css nesting support (#64)

Author: jantimon

src/index.js

@@ -230,6 +230,11 @@ function localizeNode(rule, mode, localAliasMap) {
 
         break;
       }
+      case "nesting": {
+        if (node.value === "&") {
+          context.hasLocals = true;
+        }
+      }
     }
 
     context.lastWasSpacing = false;

test/index.test.js

@@ -844,6 +844,30 @@ const tests = [
     input: ":global(.a:not(:global .b, :global .c)) {}",
     error: /A :global is not allowed inside of a :global/,
   },
+  {
+    name: "consider & statements as pure",
+    input: ".foo { &:hover { a_value: some-value; } }",
+    options: { mode: "pure" },
+    expected: ":local(.foo) { &:hover { a_value: some-value; } }",
+  },
+  {
+    name: "consider selector & statements as pure",
+    input: ".foo { html &:hover { a_value: some-value; } }",
+    options: { mode: "pure" },
+    expected: ":local(.foo) { html &:hover { a_value: some-value; } }",
+  },
+  {
+    name: "consider selector & statements as pure",
+    input: ".foo { &:global(.bar) { a_value: some-value; } }",
+    options: { mode: "pure" },
+    expected: ":local(.foo) { &.bar { a_value: some-value; } }",
+  },
+  {
+    name: "throw on nested & selectors without a local selector",
+    input: ":global(.foo) { &:hover { a_value: some-value; } }",
+    options: { mode: "pure" },
+    error: /is not pure/,
+  },
   /*
   Bug in postcss-selector-parser
   {