[Fix] no-duplicates: Ignore duplicate modules in different TypeScript module declarations

Without this the `import/no-duplicates` rule reports imports of the same
module inside different module declarations in the same file. It even
autofixed them, which break the code.

Closes #2273

Author: remcohaszing

Diff for: CHANGELOG.md

@@ -13,6 +13,7 @@ This change log adheres to standards from [Keep a CHANGELOG](https://keepachange
 
 ### Fixed
 - [`default`]: `typescript-eslint-parser`: avoid a crash on exporting as namespace (thanks [@ljharb])
+- [`no-duplicates:`]: ignore duplicate modules in different TypeScript module declarations ([#2378], thanks [@remcohaszing])
 
 ### Changed
 - [Tests] `no-nodejs-modules`: add tests for node protocol URL ([#2367], thanks [@sosukesuzuki])

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

@@ -274,17 +274,23 @@ module.exports = {
       return defaultResolver(parts[1]) + '?' + parts[2];
     }) : defaultResolver;
 
-    const imported = new Map();
-    const nsImported = new Map();
-    const defaultTypesImported = new Map();
-    const namedTypesImported = new Map();
+    const moduleMaps = new Map();
 
     function getImportMap(n) {
+      if (!moduleMaps.has(n.parent)) {
+        moduleMaps.set(n.parent, {
+          imported: new Map(),
+          nsImported: new Map(),
+          defaultTypesImported: new Map(),
+          namedTypesImported: new Map(),
+        });
+      }
+      const map = moduleMaps.get(n.parent);
       if (n.importKind === 'type') {
-        return n.specifiers.length > 0 && n.specifiers[0].type === 'ImportDefaultSpecifier' ? defaultTypesImported : namedTypesImported;
+        return n.specifiers.length > 0 && n.specifiers[0].type === 'ImportDefaultSpecifier' ? map.defaultTypesImported : map.namedTypesImported;
       }
 
-      return hasNamespace(n) ? nsImported : imported;
+      return hasNamespace(n) ? map.nsImported : map.imported;
     }
 
     return {
@@ -301,10 +307,12 @@ module.exports = {
       },
 
       'Program:exit': function () {
-        checkImports(imported, context);
-        checkImports(nsImported, context);
-        checkImports(defaultTypesImported, context);
-        checkImports(namedTypesImported, context);
+        for (const map of moduleMaps.values()) {
+          checkImports(map.imported, context);
+          checkImports(map.nsImported, context);
+          checkImports(map.defaultTypesImported, context);
+          checkImports(map.namedTypesImported, context);
+        }
       },
     };
   },

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

@@ -454,6 +454,20 @@ context('TypeScript', function () {
             `,
             ...parserConfig,
           }),
+          test({
+            code: `
+              import type { Identifier } from 'module';
+
+              declare module 'module2' {
+                import type { Identifier } from 'module';
+              }
+
+              declare module 'module3' {
+                import type { Identifier } from 'module';
+              }
+            `,
+            ...parserConfig,
+          }),
         ],
         invalid: [
           test({