fix comments containg @flow being completely removed from output rather than just the specific directive - fixes #2022

packages/babel/src/transformation/transformers/other/flow.js

@@ -4,6 +4,8 @@ export var metadata = {
   group: "builtin-trailing"
 };
 
+const FLOW_DIRECTIVE = "@flow";
+
 /**
  * [Please add a description.]
  */
@@ -16,8 +18,12 @@ export var visitor = {
 
   Program(node, parent, scope, file) {
     for (var comment of (file.ast.comments: Array)) {
-      if (comment.value.indexOf("@flow") >= 0) {
-        comment._displayed = true;
+      if (comment.value.indexOf(FLOW_DIRECTIVE) >= 0) {
+        // remove flow directive
+        comment.value = comment.value.replace(FLOW_DIRECTIVE, "");
+
+        // remove the comment completely if it only consists of whitespace and/or stars
+        if (!comment.value.replace(/\*/g, "").trim()) comment._displayed = true;
       }
     }
   },

packages/babel/test/fixtures/transformation/flow/strip-directive/actual.js

@@ -6,4 +6,9 @@
  * @flow
  */
 
+/**
+ * @providesModule Foo
+ * @flow
+ */
+
 foo();

packages/babel/test/fixtures/transformation/flow/strip-directive/expected.js

@@ -1 +1,6 @@
+/**
+ * @providesModule Foo
+ * 
+ */
+
 foo();