feat(eslint-plugin): [no-shadow] exclude external type declaration merging

packages/eslint-plugin/src/rules/no-shadow.ts

@@ -95,10 +95,10 @@ export default util.createRule<Options, MessageIds>({
     }
 
     function isTypeImport(
-      definition: Definition,
+      definition?: Definition,
     ): definition is ImportBindingDefinition {
       return (
-        definition.type === DefinitionType.ImportBinding &&
+        definition?.type === DefinitionType.ImportBinding &&
         definition.parent.importKind === 'type'
       );
     }
@@ -225,6 +225,58 @@ export default util.createRule<Options, MessageIds>({
       );
     }
 
+    function isImportDeclaration(
+      definition:
+        | TSESTree.ImportDeclaration
+        | TSESTree.TSImportEqualsDeclaration,
+    ): definition is TSESTree.ImportDeclaration {
+      return definition.type === AST_NODE_TYPES.ImportDeclaration;
+    }
+
+    function isStringLiteral(
+      node: TSESTree.Node | null,
+    ): node is TSESTree.StringLiteral {
+      return (
+        !!node &&
+        node.type === AST_NODE_TYPES.Literal &&
+        typeof node.value === 'string'
+      );
+    }
+
+    function isExternalModuleDeclarationWithName(
+      scope: TSESLint.Scope.Scope,
+      name: string,
+    ): boolean {
+      return (
+        scope.type === ScopeType.tsModule &&
+        scope.block.type === AST_NODE_TYPES.TSModuleDeclaration &&
+        scope.block.id.type === AST_NODE_TYPES.Literal &&
+        scope.block.id.value === name
+      );
+    }
+
+    function isExternalDeclerationMerging(
+      scope: TSESLint.Scope.Scope,
+      variable: TSESLint.Scope.Variable,
+      shadowed: TSESLint.Scope.Variable,
+    ): boolean {
+      const [firstDefinition] = shadowed.defs;
+      const [secondDefinition] = variable.defs;
+
+      return (
+        isTypeImport(firstDefinition) &&
+        isImportDeclaration(firstDefinition.parent) &&
+        isStringLiteral(firstDefinition.parent.source) &&
+        isExternalModuleDeclarationWithName(
+          scope,
+          firstDefinition.parent.source.value,
+        ) &&
+        secondDefinition.node.type === AST_NODE_TYPES.TSInterfaceDeclaration &&
+        secondDefinition.node.parent?.type ===
+          AST_NODE_TYPES.ExportNamedDeclaration
+      );
+    }
+
     /**
      * Check if variable name is allowed.
      * @param variable The variable to check.
@@ -404,6 +456,10 @@ export default util.createRule<Options, MessageIds>({
           continue;
         }
 
+        if (isExternalDeclerationMerging(scope, variable, shadowed)) {
+          continue;
+        }
+
         const isESLintGlobal = 'writeable' in shadowed;
         if (
           (shadowed.identifiers.length > 0 ||

packages/eslint-plugin/tests/rules/no-shadow.test.ts

@@ -51,6 +51,15 @@ class Foo {
 }
 interface Foo {
   prop2: string;
+}
+    `,
+    `
+import type { Foo } from 'bar';
+
+declare module 'bar' {
+  export interface Foo {
+    x: string;
+  }
 }
     `,
     // type value shadowing
@@ -1442,5 +1451,83 @@ function doThing(foo: number, bar: number) {}
         },
       ],
     },
+    {
+      code: `
+interface Foo {}
+
+declare module 'bar' {
+  export interface Foo {
+    x: string;
+  }
+}
+      `,
+      errors: [
+        {
+          messageId: 'noShadow',
+          data: { name: 'Foo' },
+          type: AST_NODE_TYPES.Identifier,
+          line: 5,
+          column: 20,
+        },
+      ],
+    },
+    {
+      code: `
+import type { Foo } from 'bar';
+
+declare module 'baz' {
+  export interface Foo {
+    x: string;
+  }
+}
+      `,
+      errors: [
+        {
+          messageId: 'noShadow',
+          data: { name: 'Foo' },
+          type: AST_NODE_TYPES.Identifier,
+          line: 5,
+          column: 20,
+        },
+      ],
+    },
+    {
+      code: `
+import type { Foo } from 'bar';
+
+declare module 'bar' {
+  export type Foo = string;
+}
+      `,
+      errors: [
+        {
+          messageId: 'noShadow',
+          data: { name: 'Foo' },
+          type: AST_NODE_TYPES.Identifier,
+          line: 5,
+          column: 15,
+        },
+      ],
+    },
+    {
+      code: `
+import type { Foo } from 'bar';
+
+declare module 'bar' {
+  interface Foo {
+    x: string;
+  }
+}
+      `,
+      errors: [
+        {
+          messageId: 'noShadow',
+          data: { name: 'Foo' },
+          type: AST_NODE_TYPES.Identifier,
+          line: 5,
+          column: 13,
+        },
+      ],
+    },
   ],
 });