no-duplicates: allow duplicate if one is namespace and other not

It is a syntax error to put both namespace and non namespace import on the same line, so allow it.

Fixes #1538

CHANGELOG.md

@@ -9,6 +9,7 @@ This change log adheres to standards from [Keep a CHANGELOG](http://keepachangel
 - [`import/external-module-folders` setting] now correctly works with directories containing modules symlinked from `node_modules` ([#1605], thanks [@skozin])
 - [`extensions`]: for invalid code where `name` does not exist, do not crash ([#1613], thanks [@ljharb])
 - [`extentions`]: Fix scope regex ([#1611], thanks [@yordis])
+- [`no-duplicates`]: allow duplicate imports if one is a namespace and the other not ([#1612], thanks [@sveyret])
 
 ### Changed
 - [`import/external-module-folders` setting] behavior is more strict now: it will only match complete path segments ([#1605], thanks [@skozin])
@@ -644,6 +645,7 @@ for info on changes for earlier releases.
 [`memo-parser`]: ./memo-parser/README.md
 
 [#1613]: https://github.com/benmosher/eslint-plugin-import/issues/1613
+[#1612]: https://github.com/benmosher/eslint-plugin-import/pull/1612
 [#1611]: https://github.com/benmosher/eslint-plugin-import/pull/1611
 [#1605]: https://github.com/benmosher/eslint-plugin-import/pull/1605
 [#1589]: https://github.com/benmosher/eslint-plugin-import/issues/1589
@@ -1081,3 +1083,4 @@ for info on changes for earlier releases.
 [@ivo-stefchev]: https://github.com/ivo-stefchev
 [@skozin]: https://github.com/skozin
 [@yordis]: https://github.com/yordis
+[@sveyret]: https://github.com/sveyret

src/rules/no-duplicates.js

@@ -257,12 +257,14 @@ module.exports = {
     }) : defaultResolver
 
     const imported = new Map()
+    const nsImported = new Map()
     const typesImported = new Map()
     return {
       'ImportDeclaration': function (n) {
         // resolved path will cover aliased duplicates
         const resolvedPath = resolver(n.source.value)
-        const importMap = n.importKind === 'type' ? typesImported : imported
+        const importMap = n.importKind === 'type' ? typesImported :
+          (hasNamespace(n) ? nsImported : imported)
 
         if (importMap.has(resolvedPath)) {
           importMap.get(resolvedPath).push(n)
@@ -273,6 +275,7 @@ module.exports = {
 
       'Program:exit': function () {
         checkImports(imported, context)
+        checkImports(nsImported, context)
         checkImports(typesImported, context)
       },
     }

tests/src/rules/no-duplicates.js

@@ -31,12 +31,20 @@ ruleTester.run('no-duplicates', rule, {
       code: "import x from './bar?optionX'; import y from './bar?optionY';",
       options: [{'considerQueryString': true}],
       settings: { 'import/resolver': 'webpack' },
-     }),
+    }),
     test({
       code: "import x from './foo'; import y from './bar';",
       options: [{'considerQueryString': true}],
       settings: { 'import/resolver': 'webpack' },
-     }),
+    }),
+
+    // #1538: It is impossible to import namespace and other in one line, so allow this.
+    test({
+      code: "import * as ns from './foo'; import {y} from './foo'",
+    }),
+    test({
+      code: "import {y} from './foo'; import * as ns from './foo'",
+    }),
   ],
   invalid: [
     test({
@@ -179,17 +187,24 @@ ruleTester.run('no-duplicates', rule, {
     }),
 
     test({
-      code: "import * as ns from './foo'; import {y} from './foo'",
-      // Autofix bail because first import is a namespace import.
-      output: "import * as ns from './foo'; import {y} from './foo'",
+      code: "import * as ns1 from './foo'; import * as ns2 from './foo'",
+      // Autofix bail because cannot merge namespace imports.
+      output: "import * as ns1 from './foo'; import * as ns2 from './foo'",
+      errors: ['\'./foo\' imported multiple times.', '\'./foo\' imported multiple times.'],
+    }),
+
+    test({
+      code: "import * as ns from './foo'; import {x} from './foo'; import {y} from './foo'",
+      // Autofix could merge some imports, but not the namespace import.
+      output: "import * as ns from './foo'; import {x,y} from './foo'; ",
       errors: ['\'./foo\' imported multiple times.', '\'./foo\' imported multiple times.'],
     }),
 
     test({
       code: "import {x} from './foo'; import * as ns from './foo'; import {y} from './foo'; import './foo'",
       // Autofix could merge some imports, but not the namespace import.
       output: "import {x,y} from './foo'; import * as ns from './foo';  ",
-      errors: ['\'./foo\' imported multiple times.', '\'./foo\' imported multiple times.', '\'./foo\' imported multiple times.', '\'./foo\' imported multiple times.'],
+      errors: ['\'./foo\' imported multiple times.', '\'./foo\' imported multiple times.', '\'./foo\' imported multiple times.'],
     }),
 
     test({