Fix an issue with helpers where we re-export the default as a named export

This fixes the issue described here: emberjs/ember.js#16361 (comment)

Author: bantic

lib/transforms/import-declarations.js

@@ -3,8 +3,31 @@ var path_utils = require('../utils/path');
 function transformer(file, api) {
   var j = api.jscodeshift;
 
-  return j(file.source)
-    .find(j.ImportDeclaration)
+  let root = j(file.source);
+
+  let foundHelper;
+
+  root.find(j.ImportDeclaration, {
+    source: { value: '@ember/component/helper' },
+  }).filter(path => {
+    return path.value.specifiers[0].local.name === 'helper';
+  })
+  .forEach(function(path) {
+    foundHelper = true;
+    let specifier = j.importSpecifier(j.identifier('helper'), j.identifier('buildHelper'));                              
+
+    path.value.specifiers[0] = specifier;
+  });
+  
+  if (foundHelper) {
+    root.find(j.CallExpression, {
+      callee: { name: 'helper' }      
+    }).forEach(path => {
+      path.value.callee.name = 'buildHelper';
+    });
+  }
+
+  root.find(j.ImportDeclaration)
     .find(j.Literal)
     .forEach(function(path) {
       var importPath = path.value.value + '.js';
@@ -55,9 +78,9 @@ function transformer(file, api) {
       // remove extension
       newImportPath = newImportPath.slice(0, -targetFileInfo.ext.length);
       j(path).replaceWith(j.literal(newImportPath));
-    })
-    .toSource();
+    });
 
+  return root.toSource();
 }
 
 module.exports = transformer;

test/fixtures/classic-named-exports/input.js

@@ -4,8 +4,8 @@ module.exports = {
     'app.js': 'export default App',
     'router.js': 'export default Router',
     helpers: {
-      'titleize.js': 'export default helper(function() { });',
-      'capitalize.js': 'export default helper(function() { });'
+      'titleize.js': 'import { helper } from \'@ember/component/helper\';\nexport default helper(function() { });',
+      'capitalize.js': 'import { helper } from \'@ember/component/helper\';\nexport default helper(function() { });'
     }
   },
 

test/fixtures/classic-named-exports/output.js

@@ -4,9 +4,9 @@ module.exports = {
     'router.js': 'export default Router',
     ui: {
       components: {
-        'titleize.js': 'export const helper = helper(function() { });',
+        'titleize.js': 'import { helper as buildHelper } from \'@ember/component/helper\';\nexport const helper = buildHelper(function() { });',
         'capitalize': {
-          'helper.js': 'export default helper(function() { });',
+          'helper.js': 'import { helper as buildHelper } from \'@ember/component/helper\';\nexport default buildHelper(function() { });',
           'helper-integration-test.js': '"capitalize helper test"'
         }
       }