[New] no-duplicates: support inline type import with inlineTypeImport option

Author: snewcomer

CHANGELOG.md

@@ -19,6 +19,7 @@ This change log adheres to standards from [Keep a CHANGELOG](https://keepachange
 - Add [`no-empty-named-blocks`] rule ([#2568], thanks [@guilhermelimak])
 - [`prefer-default-export`]: add "target" option ([#2602], thanks [@azyzz228])
 - [`no-absolute-path`]: add fixer ([#2613], thanks [@adipascu])
+- [`no-duplicates`]: support inline type import with `inlineTypeImport` option ([#2475], thanks [@snewcomer])
 
 ### Fixed
 - [`order`]: move nested imports closer to main import entry ([#2396], thanks [@pri1311])
@@ -1045,6 +1046,7 @@ for info on changes for earlier releases.
 [#2506]: https://github.com/import-js/eslint-plugin-import/pull/2506
 [#2503]: https://github.com/import-js/eslint-plugin-import/pull/2503
 [#2490]: https://github.com/import-js/eslint-plugin-import/pull/2490
+[#2475]: https://github.com/import-js/eslint-plugin-import/pull/2475
 [#2473]: https://github.com/import-js/eslint-plugin-import/pull/2473
 [#2466]: https://github.com/import-js/eslint-plugin-import/pull/2466
 [#2459]: https://github.com/import-js/eslint-plugin-import/pull/2459
@@ -1760,6 +1762,7 @@ for info on changes for earlier releases.
 [@singles]: https://github.com/singles
 [@skozin]: https://github.com/skozin
 [@skyrpex]: https://github.com/skyrpex
+[@snewcomer]: https://github.com/snewcomer
 [@sompylasar]: https://github.com/sompylasar
 [@soryy708]: https://github.com/soryy708
 [@sosukesuzuki]: https://github.com/sosukesuzuki

docs/rules/no-duplicates.md

@@ -67,6 +67,33 @@ import SomeDefaultClass from './mod?minify'
 import * from './mod.js?minify'
 ```
 
+### Inline Type imports
+
+TypeScript 4.5 introduced a new [feature](https://devblogs.microsoft.com/typescript/announcing-typescript-4-5/#type-on-import-names) that allows mixing of named value and type imports. In order to support fixing to an inline type import when duplicate imports are detected, `prefer-inline` can be set to true.
+
+Config:
+
+```json
+"import/no-duplicates": ["error", {"prefer-inline": true}]
+```
+
+<!--tabs-->
+
+❌ Invalid `["error", "prefer-inline"]`
+
+```js
+import { AValue, type AType } from './mama-mia'
+import type { BType } from './mama-mia'
+```
+
+✅ Valid with `["error", "prefer-inline"]`
+
+```js
+import { AValue, type AType, type BType } from './mama-mia'
+```
+
+<!--tabs-->
+
 ## When Not To Use It
 
 If the core ESLint version is good enough (i.e. you're _not_ using Flow and you _are_ using [`import/extensions`](./extensions.md)), keep it and don't use this.

src/rules/no-duplicates.js

@@ -1,13 +1,15 @@
 import resolve from 'eslint-module-utils/resolve';
 import docsUrl from '../docsUrl';
+import semver from 'semver';
+import typescriptPkg from 'typescript/package.json';
 
 function checkImports(imported, context) {
   for (const [module, nodes] of imported.entries()) {
     if (nodes.length > 1) {
       const message = `'${module}' imported multiple times.`;
       const [first, ...rest] = nodes;
       const sourceCode = context.getSourceCode();
-      const fix = getFix(first, rest, sourceCode);
+      const fix = getFix(first, rest, sourceCode, context);
 
       context.report({
         node: first.source,
@@ -25,7 +27,7 @@ function checkImports(imported, context) {
   }
 }
 
-function getFix(first, rest, sourceCode) {
+function getFix(first, rest, sourceCode, context) {
   // Sorry ESLint <= 3 users, no autofix for you. Autofixing duplicate imports
   // requires multiple `fixer.whatever()` calls in the `fix`: We both need to
   // update the first one, and remove the rest. Support for multiple
@@ -108,10 +110,19 @@ function getFix(first, rest, sourceCode) {
 
     const [specifiersText] = specifiers.reduce(
       ([result, needsComma], specifier) => {
+        const isTypeSpecifier = specifier.importNode.importKind === 'type';
+
+        const preferInline = context.options[0] && context.options[0]['prefer-inline'];
+        // a user might set prefer-inline but not have a supporting TypeScript version.  Flow does not support inline types so this should fail in that case as well.
+        if (preferInline && !semver.satisfies(typescriptPkg.version, '>= 4.5')) {
+          throw new Error('Your version of TypeScript does not support inline type imports.');
+        }
+
+        const insertText = `${preferInline && isTypeSpecifier ? 'type ' : ''}${specifier.text}`;
         return [
           needsComma && !specifier.isEmpty
-            ? `${result},${specifier.text}`
-            : `${result}${specifier.text}`,
+            ? `${result},${insertText}`
+            : `${result}${insertText}`,
           specifier.isEmpty ? needsComma : true,
         ];
       },
@@ -257,6 +268,9 @@ module.exports = {
           considerQueryString: {
             type: 'boolean',
           },
+          'prefer-inline': {
+            type: 'boolean',
+          },
         },
         additionalProperties: false,
       },
@@ -291,6 +305,9 @@ module.exports = {
       if (n.importKind === 'type') {
         return n.specifiers.length > 0 && n.specifiers[0].type === 'ImportDefaultSpecifier' ? map.defaultTypesImported : map.namedTypesImported;
       }
+      if (n.specifiers.some((spec) => spec.importKind === 'type')) {
+        return map.namedTypesImported;
+      }
 
       return hasNamespace(n) ? map.nsImported : map.imported;
     }