extensions: add the checkTypeImports option

Author: phryneas

docs/rules/extensions.md

@@ -56,6 +56,8 @@ For example, `["error", "never", { "svg": "always" }]` would require that all ex
 In that case, if you still want to specify extensions, you can do so inside the **pattern** property.
 Default value of `ignorePackages` is `false`.
 
+By default, `import type` and `export type` style imports/exports are ignored. If you want to check them as well, you can set the `checkTypeImports` option to `true`.
+
 ### Exception
 
 When disallowing the use of certain extensions this rule makes an exception and allows the use of extension when the file would not be resolvable without extension.
@@ -167,6 +169,14 @@ import express from 'express';
 import foo from '@/foo';
 ```
 
+The following patterns are considered problems when the option "checkTypeImports" is set to `true`:
+
+```js
+import type { Foo } from './foo';
+
+export type { Foo } from './foo';
+```
+
 ## When Not To Use It
 
 If you are not concerned about a consistent usage of file extension.

src/rules/extensions.js

@@ -14,6 +14,7 @@ const properties = {
   type: 'object',
   properties: {
     pattern: patternProperties,
+    checkTypeImports: { type: 'boolean' },
     ignorePackages: { type: 'boolean' },
   },
 };
@@ -35,7 +36,7 @@ function buildProperties(context) {
     }
 
     // If this is not the new structure, transfer all props to result.pattern
-    if (obj.pattern === undefined && obj.ignorePackages === undefined) {
+    if (obj.pattern === undefined && obj.ignorePackages === undefined && obj.checkTypeImports === undefined) {
       Object.assign(result.pattern, obj);
       return;
     }
@@ -49,6 +50,10 @@ function buildProperties(context) {
     if (obj.ignorePackages !== undefined) {
       result.ignorePackages = obj.ignorePackages;
     }
+
+    if (obj.checkTypeImports !== undefined) {
+      result.checkTypeImports = obj.checkTypeImports;
+    }
   });
 
   if (result.defaultConfig === 'ignorePackages') {
@@ -167,7 +172,7 @@ module.exports = {
 
       if (!extension || !importPath.endsWith(`.${extension}`)) {
         // ignore type-only imports and exports
-        if (node.importKind === 'type' || node.exportKind === 'type') { return; }
+        if (props.checkTypeImports !== true && (node.importKind === 'type' || node.exportKind === 'type')) { return; }
         const extensionRequired = isUseOfExtensionRequired(extension, isPackage);
         const extensionForbidden = isUseOfExtensionForbidden(extension);
         if (extensionRequired && !extensionForbidden) {

tests/src/rules/extensions.js

@@ -640,6 +640,24 @@ describe('TypeScript', () => {
             ],
             parser,
           }),
+          test({
+            code: 'import type T from "./typescript-declare";',
+            errors: ['Missing file extension for "./typescript-declare"'],
+            options: [
+              'always',
+              { ts: 'never', tsx: 'never', js: 'never', jsx: 'never', checkTypeImports: true },
+            ],
+            parser,
+          }),
+          test({
+            code: 'export type { MyType } from "./typescript-declare";',
+            errors: ['Missing file extension for "./typescript-declare"'],
+            options: [
+              'always',
+              { ts: 'never', tsx: 'never', js: 'never', jsx: 'never', checkTypeImports: true },
+            ],
+            parser,
+          }),
         ],
       });
     });