Added babel-helper-split-export-declaration (#7313)

packages/babel-helper-split-export-declaration/src/index.js

@@ -0,0 +1,76 @@
+import * as t from "@babel/types";
+
+export default function splitExportDeclaration(exportDeclaration) {
+  if (!exportDeclaration.isExportDeclaration()) {
+    throw new Error("Only export declarations can be splitted.");
+  }
+
+  // build specifiers that point back to this export declaration
+  const isDefault = exportDeclaration.isExportDefaultDeclaration();
+  const declaration = exportDeclaration.get("declaration");
+  const isClassDeclaration = declaration.isClassDeclaration();
+
+  if (isDefault) {
+    const standaloneDeclaration =
+      declaration.isFunctionDeclaration() || isClassDeclaration;
+
+    const scope = declaration.isScope()
+      ? declaration.scope.parent
+      : declaration.scope;
+
+    let id = declaration.node.id;
+    let needBindingRegistration = false;
+
+    if (!id) {
+      needBindingRegistration = true;
+
+      id = scope.generateUidIdentifier("default");
+
+      if (
+        standaloneDeclaration ||
+        declaration.isFunctionExpression() ||
+        declaration.isClassExpression()
+      ) {
+        declaration.node.id = t.cloneNode(id);
+      }
+    }
+
+    const updatedDeclaration = standaloneDeclaration
+      ? declaration
+      : t.variableDeclaration("var", [
+          t.variableDeclarator(t.cloneNode(id), declaration.node),
+        ]);
+
+    const updatedExportDeclaration = t.exportNamedDeclaration(null, [
+      t.exportSpecifier(t.cloneNode(id), t.identifier("default")),
+    ]);
+
+    exportDeclaration.insertAfter(updatedExportDeclaration);
+    exportDeclaration.replaceWith(updatedDeclaration);
+
+    if (needBindingRegistration) {
+      scope.registerBinding(
+        isClassDeclaration ? "let" : "var",
+        exportDeclaration,
+      );
+    }
+
+    return exportDeclaration;
+  }
+
+  if (exportDeclaration.get("specifiers").length > 0) {
+    throw new Error("It doesn't make sense to split exported specifiers.");
+  }
+
+  const bindingIdentifiers = declaration.getOuterBindingIdentifiers();
+
+  const specifiers = Object.keys(bindingIdentifiers).map(name => {
+    return t.exportSpecifier(t.identifier(name), t.identifier(name));
+  });
+
+  const aliasDeclar = t.exportNamedDeclaration(null, specifiers);
+
+  exportDeclaration.insertAfter(aliasDeclar);
+  exportDeclaration.replaceWith(declaration.node);
+  return exportDeclaration;
+}