[fix] no-duplicates: fix fixer on cases with default import

Author: golopot

Diff for: CHANGELOG.md

@@ -8,6 +8,7 @@ This change log adheres to standards from [Keep a CHANGELOG](http://keepachangel
 ### Fixed
 - [`order`]: fix `isExternalModule` detect on windows ([#1651], thanks [@fisker])
 - [`order`]: recognize ".." as a "parent" path ([#1658], thanks [@golopot])
+- [`no-duplicates`]: fix fixer on cases with default import ([#1666], thanks [@golopot])
 
 ## [2.20.1] - 2020-02-01
 ### Fixed
@@ -655,6 +656,7 @@ for info on changes for earlier releases.
 
 [`memo-parser`]: ./memo-parser/README.md
 
+[#1666]: https://github.com/benmosher/eslint-plugin-import/pull/1666
 [#1658]: https://github.com/benmosher/eslint-plugin-import/pull/1658
 [#1651]: https://github.com/benmosher/eslint-plugin-import/pull/1651
 [#1635]: https://github.com/benmosher/eslint-plugin-import/issues/1635

Diff for: src/rules/no-duplicates.js

@@ -136,8 +136,13 @@ function getFix(first, rest, sourceCode) {
         fixes.push(fixer.insertTextBefore(closeBrace, specifiersText))
       }
     } else if (!shouldAddDefault && openBrace == null && shouldAddSpecifiers) {
-      // `import './foo'` → `import {...} from './foo'`
-      fixes.push(fixer.insertTextAfter(firstToken, ` {${specifiersText}} from`))
+      if (first.specifiers.length === 0) {
+        // `import './foo'` → `import {...} from './foo'`
+        fixes.push(fixer.insertTextAfter(firstToken, ` {${specifiersText}} from`))
+      } else {
+        // `import def from './foo'` → `import def, {...} from './foo'`
+        fixes.push(fixer.insertTextAfter(first.specifiers[0], `, {${specifiersText}}`))
+      }
     } else if (!shouldAddDefault && openBrace != null && closeBrace != null) {
       // `import {...} './foo'` → `import {..., ...} from './foo'`
       fixes.push(fixer.insertTextBefore(closeBrace, specifiersText))

Diff for: tests/src/rules/no-duplicates.js

@@ -168,6 +168,12 @@ ruleTester.run('no-duplicates', rule, {
       errors: ['\'./foo\' imported multiple times.', '\'./foo\' imported multiple times.'],
     }),
 
+    test({
+      code: "import def from './foo'; import {x} from './foo'",
+      output: "import def, {x} from './foo'; ",
+      errors: ['\'./foo\' imported multiple times.', '\'./foo\' imported multiple times.'],
+    }),
+
     test({
       code: "import {x} from './foo'; import def from './foo'",
       output: "import def, {x} from './foo'; ",