From 230e1fcf7ecebb28e364a1fb777ee0c74504f021 Mon Sep 17 00:00:00 2001
From: Brad Zacher <brad.zacher@gmail.com>
Date: Mon, 24 Oct 2022 17:21:09 +1030
Subject: [PATCH] feat(eslint-plugin): [no-unsafe-declaration-merging] switch
 to use scope analysis instead of type information

---
 .../rules/no-unsafe-declaration-merging.ts    | 45 ++++++++++++++-----
 .../no-unsafe-declaration-merging.test.ts     | 16 +++----
 2 files changed, 39 insertions(+), 22 deletions(-)

diff --git a/packages/eslint-plugin/src/rules/no-unsafe-declaration-merging.ts b/packages/eslint-plugin/src/rules/no-unsafe-declaration-merging.ts
index 7982fe5c5f4..89d68db6e67 100644
--- a/packages/eslint-plugin/src/rules/no-unsafe-declaration-merging.ts
+++ b/packages/eslint-plugin/src/rules/no-unsafe-declaration-merging.ts
@@ -1,5 +1,6 @@
+import type { Scope } from '@typescript-eslint/scope-manager';
 import type { TSESTree } from '@typescript-eslint/utils';
-import * as ts from 'typescript';
+import { AST_NODE_TYPES } from '@typescript-eslint/utils';
 
 import * as util from '../util';
 
@@ -10,7 +11,7 @@ export default util.createRule({
     docs: {
       description: 'Disallow unsafe declaration merging',
       recommended: 'strict',
-      requiresTypeChecking: true,
+      requiresTypeChecking: false,
     },
     messages: {
       unsafeMerging:
@@ -20,17 +21,22 @@ export default util.createRule({
   },
   defaultOptions: [],
   create(context) {
-    const parserServices = util.getParserServices(context);
-    const checker = parserServices.program.getTypeChecker();
-
     function checkUnsafeDeclaration(
+      scope: Scope,
       node: TSESTree.Identifier,
-      unsafeKind: ts.SyntaxKind,
+      unsafeKind: AST_NODE_TYPES,
     ): void {
-      const tsNode = parserServices.esTreeNodeToTSNodeMap.get(node);
-      const type = checker.getTypeAtLocation(tsNode);
-      const symbol = type.getSymbol();
-      if (symbol?.declarations?.some(decl => decl.kind === unsafeKind)) {
+      const variable = scope.set.get(node.name);
+      if (!variable) {
+        return;
+      }
+
+      const defs = variable.defs;
+      if (defs.length <= 1) {
+        return;
+      }
+
+      if (defs.some(def => def.node.type === unsafeKind)) {
         context.report({
           node,
           messageId: 'unsafeMerging',
@@ -41,11 +47,26 @@ export default util.createRule({
     return {
       ClassDeclaration(node): void {
         if (node.id) {
-          checkUnsafeDeclaration(node.id, ts.SyntaxKind.InterfaceDeclaration);
+          // by default eslint returns the inner class scope for the ClassDeclaration node
+          // but we want the outer scope within which merged variables will sit
+          const currentScope = context.getScope().upper;
+          if (currentScope == null) {
+            return;
+          }
+
+          checkUnsafeDeclaration(
+            currentScope,
+            node.id,
+            AST_NODE_TYPES.TSInterfaceDeclaration,
+          );
         }
       },
       TSInterfaceDeclaration(node): void {
-        checkUnsafeDeclaration(node.id, ts.SyntaxKind.ClassDeclaration);
+        checkUnsafeDeclaration(
+          context.getScope(),
+          node.id,
+          AST_NODE_TYPES.ClassDeclaration,
+        );
       },
     };
   },
diff --git a/packages/eslint-plugin/tests/rules/no-unsafe-declaration-merging.test.ts b/packages/eslint-plugin/tests/rules/no-unsafe-declaration-merging.test.ts
index e92c1ed36e7..1feabbe8158 100644
--- a/packages/eslint-plugin/tests/rules/no-unsafe-declaration-merging.test.ts
+++ b/packages/eslint-plugin/tests/rules/no-unsafe-declaration-merging.test.ts
@@ -80,23 +80,19 @@ class Foo {}
     },
     {
       code: `
-namespace Foo {
-  export interface Bar {}
-}
-namespace Foo {
-  export class Bar {}
-}
+class Foo {}
+interface Foo {}
       `,
       errors: [
         {
           messageId: 'unsafeMerging',
-          line: 3,
-          column: 20,
+          line: 2,
+          column: 7,
         },
         {
           messageId: 'unsafeMerging',
-          line: 6,
-          column: 16,
+          line: 3,
+          column: 11,
         },
       ],
     },