[Fix] no-duplicates: type import fixer generates valid TypeScript

Fixes #2114, #2130

CHANGELOG.md

@@ -8,6 +8,7 @@ This change log adheres to standards from [Keep a CHANGELOG](http://keepachangel
 
 ### Fixed
 - [`no-duplicates`]: ensure autofix avoids excessive newlines ([#2028], thanks [@ertrzyiks])
+- [`no-duplicates`]: type import fixer now generates valid TypeScript ([#2149])
 - [`extensions`]: avoid crashing on partially typed import/export statements ([#2118], thanks [@ljharb])
 - [`no-extraneous-dependencies`]: add ESM intermediate package.json support] ([#2121], thanks [@paztis])
 
@@ -808,6 +809,7 @@ for info on changes for earlier releases.
 
 [`memo-parser`]: ./memo-parser/README.md
 
+[#2149]: https://github.com/benmosher/eslint-plugin-import/pull/2149
 [#2138]: https://github.com/benmosher/eslint-plugin-import/pull/2138
 [#2121]: https://github.com/benmosher/eslint-plugin-import/pull/2121
 [#2099]: https://github.com/benmosher/eslint-plugin-import/pull/2099

src/rules/no-duplicates.js

@@ -276,13 +276,23 @@ module.exports = {
 
     const imported = new Map();
     const nsImported = new Map();
-    const typesImported = new Map();
+    const defaultTypesImported = new Map();
+    const namedTypesImported = new Map();
+
+    function getImportMap(n) {
+      if (n.importKind === 'type') {
+        return n.specifiers[0].type === 'ImportDefaultSpecifier' ?
+          defaultTypesImported : namedTypesImported;
+      }
+
+      return hasNamespace(n) ? nsImported : imported;
+    }
+
     return {
       'ImportDeclaration': function (n) {
         // resolved path will cover aliased duplicates
         const resolvedPath = resolver(n.source.value);
-        const importMap = n.importKind === 'type' ? typesImported :
-          (hasNamespace(n) ? nsImported : imported);
+        const importMap = getImportMap(n);
 
         if (importMap.has(resolvedPath)) {
           importMap.get(resolvedPath).push(n);
@@ -294,7 +304,8 @@ module.exports = {
       'Program:exit': function () {
         checkImports(imported, context);
         checkImports(nsImported, context);
-        checkImports(typesImported, context);
+        checkImports(defaultTypesImported, context);
+        checkImports(namedTypesImported, context);
       },
     };
   },

tests/src/rules/no-duplicates.js

@@ -437,8 +437,89 @@ context('TypeScript', function() {
             },
             parserConfig,
           ),
+          test(
+            {
+              code: "import type x from './foo'; import type y from './bar'",
+              parser,
+            },
+            parserConfig,
+          ),
+          test(
+            {
+              code: "import type {x} from './foo'; import type {y} from './bar'",
+              parser,
+            },
+            parserConfig,
+          ),
+          test(
+            {
+              code: "import type x from './foo'; import type {y} from './foo'",
+              parser,
+            },
+            parserConfig,
+          ),
+        ],
+        invalid: [
+          test(
+            {
+              code: "import type x from './foo'; import type y from './foo'",
+              parser,
+              errors: [
+                {
+                  line: 1,
+                  column: 20,
+                  message: "'./foo' imported multiple times.",
+                },
+                {
+                  line: 1,
+                  column: 48,
+                  message: "'./foo' imported multiple times.",
+                },
+              ],
+            },
+            parserConfig,
+          ),
+          test(
+            {
+              code: "import type x from './foo'; import type x from './foo'",
+              output: "import type x from './foo'; ",
+              parser,
+              errors: [
+                {
+                  line: 1,
+                  column: 20,
+                  message: "'./foo' imported multiple times.",
+                },
+                {
+                  line: 1,
+                  column: 48,
+                  message: "'./foo' imported multiple times.",
+                },
+              ],
+            },
+            parserConfig,
+          ),
+          test(
+            {
+              code: "import type {x} from './foo'; import type {y} from './foo'",
+              parser,
+              output: `import type {x,y} from './foo'; `,
+              errors: [
+                {
+                  line: 1,
+                  column: 22,
+                  message: "'./foo' imported multiple times.",
+                },
+                {
+                  line: 1,
+                  column: 52,
+                  message: "'./foo' imported multiple times.",
+                },
+              ],
+            },
+            parserConfig,
+          ),
         ],
-        invalid: [],
       });
     });
 });