Add "decoratorsBeforeExport" option to @babel/generator (#7948)

* Add "decoratorsBeforeExport" option to @babel/generator

* Docs

packages/babel-generator/src/generators/classes.js

@@ -2,8 +2,9 @@ import * as t from "@babel/types";
 
 export function ClassDeclaration(node: Object, parent: Object) {
   if (
-    !t.isExportDefaultDeclaration(parent) &&
-    !t.isExportNamedDeclaration(parent)
+    !this.format.decoratorsBeforeExport ||
+    (!t.isExportDefaultDeclaration(parent) &&
+      !t.isExportNamedDeclaration(parent))
   ) {
     this.printJoin(node.decorators, node);
   }

packages/babel-generator/src/generators/modules.js

@@ -57,7 +57,10 @@ export function ExportAllDeclaration(node: Object) {
 }
 
 export function ExportNamedDeclaration(node: Object) {
-  if (t.isClassDeclaration(node.declaration)) {
+  if (
+    this.format.decoratorsBeforeExport &&
+    t.isClassDeclaration(node.declaration)
+  ) {
     this.printJoin(node.declaration.decorators, node);
   }
 
@@ -67,7 +70,10 @@ export function ExportNamedDeclaration(node: Object) {
 }
 
 export function ExportDefaultDeclaration(node: Object) {
-  if (t.isClassDeclaration(node.declaration)) {
+  if (
+    this.format.decoratorsBeforeExport &&
+    t.isClassDeclaration(node.declaration)
+  ) {
     this.printJoin(node.declaration.decorators, node);
   }
 

packages/babel-generator/src/index.js

@@ -52,6 +52,10 @@ function normalizeOptions(code, opts): Format {
       style: "  ",
       base: 0,
     },
+    decoratorsBeforeExport:
+      opts.decoratorsBeforeExport === undefined
+        ? true
+        : opts.decoratorsBeforeExport,
   };
 
   if (format.minified) {

packages/babel-generator/src/printer.js

@@ -25,6 +25,7 @@ export type Format = {
     style: string,
     base: number,
   },
+  decoratorsBeforeExport: boolean,
 };
 
 export default class Printer {