Transform class static block (#12143)

Co-authored-by: Nicolò Ribaudo <nicolo.ribaudo@gmail.com>
Co-authored-by: Brian Ng <bng412@gmail.com>

packages/babel-plugin-proposal-class-static-block/src/index.js

@@ -0,0 +1,61 @@
+import { declare } from "@babel/helper-plugin-utils";
+import syntaxClassStaticBlock from "@babel/plugin-syntax-class-static-block";
+
+/**
+ * Generate a uid that is not in `denyList`
+ *
+ * @param {*} scope
+ * @param {Set<string>} a deny list that the generated uid should avoid
+ * @returns
+ */
+function generateUid(scope, denyList: Set<string>) {
+  const name = "";
+  let uid;
+  let i = 1;
+  do {
+    uid = scope._generateUid(name, i);
+    i++;
+  } while (denyList.has(uid));
+  return uid;
+}
+
+export default declare(({ types: t, template, assertVersion }) => {
+  // todo: change to ^7.12.0 when it is published
+  assertVersion("^7.11.6");
+
+  return {
+    name: "proposal-class-static-block",
+    inherits: syntaxClassStaticBlock,
+    visitor: {
+      Class(path: NodePath<Class>) {
+        const { scope } = path;
+        const classBody = path.get("body");
+        const privateNames = new Set();
+        let staticBlockPath;
+        for (const path of classBody.get("body")) {
+          if (path.isPrivate()) {
+            privateNames.add(path.get("key.id").node.name);
+          } else if (path.isStaticBlock()) {
+            staticBlockPath = path;
+          }
+        }
+        if (!staticBlockPath) {
+          return;
+        }
+        const staticBlockRef = t.privateName(
+          t.identifier(generateUid(scope, privateNames)),
+        );
+        classBody.pushContainer(
+          "body",
+          t.classPrivateProperty(
+            staticBlockRef,
+            template.expression.ast`(() => { ${staticBlockPath.node.body} })()`,
+            [],
+            /* static */ true,
+          ),
+        );
+        staticBlockPath.remove();
+      },
+    },
+  };
+});