typescript-eslint · JoshuaKGoldberg · Dec 16, 2025 · Dec 1, 2025 · Dec 1, 2025 · Dec 1, 2025
diff --git a/packages/eslint-plugin/src/rules/method-signature-style.ts b/packages/eslint-plugin/src/rules/method-signature-style.ts
@@ -4,6 +4,7 @@ import { AST_NODE_TYPES } from '@typescript-eslint/utils';
 
 import {
   createRule,
+  forEachChildESTree,
   isClosingParenToken,
   isCommaToken,
   isOpeningParenToken,
@@ -131,6 +132,7 @@ export default createRule<Options, MessageIds>({
             return;
           }
 
+          const skipFix = returnTypeReferencesThisType(methodNode.returnType);
           const parent = methodNode.parent;
           const members =
             parent.type === AST_NODE_TYPES.TSInterfaceBody
@@ -156,39 +158,41 @@ export default createRule<Options, MessageIds>({
               context.report({
                 node: methodNode,
                 messageId: 'errorMethod',
-                *fix(fixer) {
-                  const methodNodes = [
-                    methodNode,
-                    ...duplicatedKeyMethodNodes,
-                  ].sort((a, b) => (a.range[0] < b.range[0] ? -1 : 1));
-                  const typeString = methodNodes
-                    .map(node => {
-                      const params = getMethodParams(node);
-                      const returnType = getMethodReturnType(node);
-                      return `(${params} => ${returnType})`;
-                    })
-                    .join(' & ');
-                  const key = getMethodKey(methodNode);
-                  const delimiter = getDelimiter(methodNode);
-                  yield fixer.replaceText(
-                    methodNode,
-                    `${key}: ${typeString}${delimiter}`,
-                  );
-                  for (const node of duplicatedKeyMethodNodes) {
-                    const lastToken = context.sourceCode.getLastToken(node);
-                    if (lastToken) {
-                      const nextToken =
-                        context.sourceCode.getTokenAfter(lastToken);
-                      if (nextToken) {
-                        yield fixer.remove(node);
-                        yield fixer.replaceTextRange(
-                          [lastToken.range[1], nextToken.range[0]],
-                          '',
-                        );
+                fix: skipFix
+                  ? undefined
+                  : function* fix(fixer) {
+                      const methodNodes = [
+                        methodNode,
+                        ...duplicatedKeyMethodNodes,
+                      ].sort((a, b) => (a.range[0] < b.range[0] ? -1 : 1));
+                      const typeString = methodNodes
+                        .map(node => {
+                          const params = getMethodParams(node);
+                          const returnType = getMethodReturnType(node);
+                          return `(${params} => ${returnType})`;
+                        })
+                        .join(' & ');
+                      const key = getMethodKey(methodNode);
+                      const delimiter = getDelimiter(methodNode);
+                      yield fixer.replaceText(
+                        methodNode,
+                        `${key}: ${typeString}${delimiter}`,
+                      );
+                      for (const node of duplicatedKeyMethodNodes) {
+                        const lastToken = context.sourceCode.getLastToken(node);
+                        if (lastToken) {
+                          const nextToken =
+                            context.sourceCode.getTokenAfter(lastToken);
+                          if (nextToken) {
+                            yield fixer.remove(node);
+                            yield fixer.replaceTextRange(
+                              [lastToken.range[1], nextToken.range[0]],
+                              '',
+                            );
+                          }
+                        }
                       }
-                    }
-                  }
-                },
+                    },
               });
             }
             return;
@@ -203,16 +207,18 @@ export default createRule<Options, MessageIds>({
             context.report({
               node: methodNode,
               messageId: 'errorMethod',
-              fix: fixer => {
-                const key = getMethodKey(methodNode);
-                const params = getMethodParams(methodNode);
-                const returnType = getMethodReturnType(methodNode);
-                const delimiter = getDelimiter(methodNode);
-                return fixer.replaceText(
-                  methodNode,
-                  `${key}: ${params} => ${returnType}${delimiter}`,
-                );
-              },
+              fix: skipFix
+                ? undefined
+                : fixer => {
+                    const key = getMethodKey(methodNode);
+                    const params = getMethodParams(methodNode);
+                    const returnType = getMethodReturnType(methodNode);
+                    const delimiter = getDelimiter(methodNode);
+                    return fixer.replaceText(
+                      methodNode,
+                      `${key}: ${params} => ${returnType}${delimiter}`,
+                    );
+                  },
             });
           }
         },
@@ -243,3 +249,15 @@ export default createRule<Options, MessageIds>({
     };
   },
 });
+
+function returnTypeReferencesThisType(
+  node: TSESTree.TSTypeAnnotation | undefined,
+) {
+  return (
+    node &&
+    forEachChildESTree(
+      node.typeAnnotation,
+      child => child.type === AST_NODE_TYPES.TSThisType,
+    )
+  );
+}
diff --git a/packages/eslint-plugin/src/util/astUtils.ts b/packages/eslint-plugin/src/util/astUtils.ts
@@ -1,5 +1,6 @@
 import type { TSESLint, TSESTree } from '@typescript-eslint/utils';
 
+import { visitorKeys } from '@typescript-eslint/visitor-keys';
 import * as ts from 'typescript';
 
 import { escapeRegExp } from './escapeRegExp';
@@ -79,3 +80,58 @@ export function forEachReturnStatement<T>(
     return undefined;
   }
 }
+
+function isESTreeNodeLike(node: unknown): node is TSESTree.Node {
+  return (
+    typeof node === 'object' &&
+    node != null &&
+    'type' in node &&
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any, @typescript-eslint/no-unsafe-member-access
+    typeof (node as any).type === 'string'
+  );
+}
+
+/**
+ * Rough equivalent to ts.forEachChild for ESTree nodes.
+ * It returns the first truthy value returned by the callback, if any.
+ */
+export function forEachChildESTree<Result>(
+  node: TSESTree.Node,
+  callback: (child: TSESTree.Node) => false | Result | null | undefined,
+): Result | undefined {
+  function visit(currentNode: TSESTree.Node): Result | undefined {
+    const result = callback(currentNode);
+    if (result) {
+      return result;
+    }
+
+    const currentKeys = visitorKeys[currentNode.type];
+    if (!currentKeys) {
+      return undefined;
+    }
+
+    for (const key of currentKeys) {
+      const currentProperty = currentNode[key as keyof typeof currentNode];
+
+      if (Array.isArray(currentProperty)) {
+        for (const child of currentProperty) {
+          if (isESTreeNodeLike(child)) {
+            const result = visit(child);
+            if (result) {
+              return result;
+            }
+          }
+        }
+      } else if (isESTreeNodeLike(currentProperty)) {
+        const result = visit(currentProperty);
+        if (result) {
+          return result;
+        }
+      }
+    }
+
+    return undefined;
+  }
+
+  return visit(node);
+}
diff --git a/packages/eslint-plugin/tests/rules/method-signature-style.test.ts b/packages/eslint-plugin/tests/rules/method-signature-style.test.ts
@@ -670,5 +670,80 @@ interface MyInterface {
 }
       `,
     },
+    {
+      code: `
+interface Test {
+  f(value: number): this;
+}
+      `,
+      errors: [
+        {
+          line: 3,
+          messageId: 'errorMethod',
+        },
+      ],
+      output: null,
+    },
+    {
+      code: `
+interface Test {
+  foo(): this;
+  foo(): Promise<this>;
+}
+      `,
+      errors: [
+        {
+          line: 3,
+          messageId: 'errorMethod',
+        },
+        {
+          line: 4,
+          messageId: 'errorMethod',
+        },
+      ],
+      output: null,
+    },
+    {
+      code: `
+interface Test {
+  f(value: number): this | undefined;
+}
+      `,
+      errors: [
+        {
+          line: 3,
+          messageId: 'errorMethod',
+        },
+      ],
+      output: null,
+    },
+    {
+      code: `
+interface Test {
+  f(value: number): Promise<this>;
+}
+      `,
+      errors: [
+        {
+          line: 3,
+          messageId: 'errorMethod',
+        },
+      ],
+      output: null,
+    },
+    {
+      code: `
+interface Test {
+  f(value: number): Promise<this | undefined>;
+}
+      `,
+      errors: [
+        {
+          line: 3,
+          messageId: 'errorMethod',
+        },
+      ],
+      output: null,
+    },
   ],
 });