From 7f3fba348d432d7637e1c737df943ee1f9105062 Mon Sep 17 00:00:00 2001
From: Sosuke Suzuki <aosukeke@gmail.com>
Date: Mon, 4 May 2020 13:50:27 +0900
Subject: [PATCH] fix(eslint-plugin): [method-signature-style] fix overloaded
 methods to an intersection type (#1966)

---
 .../docs/rules/method-signature-style.md      |  11 ++
 .../src/rules/method-signature-style.ts       |  50 +++++++
 .../rules/method-signature-style.test.ts      | 123 ++++++++++++++++++
 3 files changed, 184 insertions(+)

diff --git a/packages/eslint-plugin/docs/rules/method-signature-style.md b/packages/eslint-plugin/docs/rules/method-signature-style.md
index d760c8d0193..4358ee36ca0 100644
--- a/packages/eslint-plugin/docs/rules/method-signature-style.md
+++ b/packages/eslint-plugin/docs/rules/method-signature-style.md
@@ -43,6 +43,11 @@ interface T1 {
 type T2 = {
   func(arg: boolean): void;
 };
+interface T3 {
+  func(arg: number): void;
+  func(arg: string): void;
+  func(arg: boolean): void;
+}
 ```
 
 Examples of **correct** code with `property` option.
@@ -54,6 +59,12 @@ interface T1 {
 type T2 = {
   func: (arg: boolean) => void;
 };
+// this is equivalent to the overload
+interface T3 {
+  func: ((arg: number) => void) &
+    ((arg: string) => void) &
+    ((arg: boolean) => void);
+}
 ```
 
 Examples of **incorrect** code with `method` option.
diff --git a/packages/eslint-plugin/src/rules/method-signature-style.ts b/packages/eslint-plugin/src/rules/method-signature-style.ts
index 2d6366bbda1..45f7fdbd711 100644
--- a/packages/eslint-plugin/src/rules/method-signature-style.ts
+++ b/packages/eslint-plugin/src/rules/method-signature-style.ts
@@ -103,6 +103,56 @@ export default util.createRule<Options, MessageIds>({
           return;
         }
 
+        const duplicatedKeyMethodNodes: TSESTree.TSMethodSignature[] =
+          methodNode.parent?.type === AST_NODE_TYPES.TSInterfaceBody
+            ? methodNode.parent.body.filter(
+                (element): element is TSESTree.TSMethodSignature =>
+                  element.type === AST_NODE_TYPES.TSMethodSignature &&
+                  element !== methodNode &&
+                  getMethodKey(element) === getMethodKey(methodNode),
+              )
+            : [];
+
+        if (duplicatedKeyMethodNodes.length > 0) {
+          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.reduce((str, node, idx, nodes) => {
+                const params = getMethodParams(node);
+                const returnType = getMethodReturnType(node);
+                return `${str}(${params} => ${returnType})${
+                  idx !== nodes.length - 1 ? ' & ' : ''
+                }`;
+              }, '');
+              const key = getMethodKey(methodNode);
+              const delimiter = getDelimiter(methodNode);
+              yield fixer.replaceText(
+                methodNode,
+                `${key}: ${typeString}${delimiter}`,
+              );
+              for (const node of duplicatedKeyMethodNodes) {
+                const lastToken = sourceCode.getLastToken(node);
+                if (lastToken) {
+                  const nextToken = sourceCode.getTokenAfter(lastToken);
+                  if (nextToken) {
+                    yield fixer.remove(node);
+                    yield fixer.replaceTextRange(
+                      [lastToken.range[1], nextToken.range[0]],
+                      '',
+                    );
+                  }
+                }
+              }
+            },
+          });
+          return;
+        }
+
         context.report({
           node: methodNode,
           messageId: 'errorMethod',
diff --git a/packages/eslint-plugin/tests/rules/method-signature-style.test.ts b/packages/eslint-plugin/tests/rules/method-signature-style.test.ts
index dc938ff8cb9..62383014082 100644
--- a/packages/eslint-plugin/tests/rules/method-signature-style.test.ts
+++ b/packages/eslint-plugin/tests/rules/method-signature-style.test.ts
@@ -226,5 +226,128 @@ interface Foo {
         },
       ],
     },
+    {
+      code: noFormat`
+interface Foo {
+  foo(): one;
+  foo(): two;
+  foo(): three;
+}
+      `,
+      output: noFormat`
+interface Foo {
+  foo: (() => one) & (() => two) & (() => three);
+}
+      `,
+      errors: [
+        {
+          messageId: 'errorMethod',
+          line: 3,
+        },
+        {
+          messageId: 'errorMethod',
+          line: 4,
+        },
+        {
+          messageId: 'errorMethod',
+          line: 5,
+        },
+      ],
+    },
+    {
+      code: noFormat`
+interface Foo {
+  foo(bar: string): one;
+  foo(bar: number, baz: string): two;
+  foo(): three;
+}
+      `,
+      output: noFormat`
+interface Foo {
+  foo: ((bar: string) => one) & ((bar: number, baz: string) => two) & (() => three);
+}
+      `,
+      errors: [
+        {
+          messageId: 'errorMethod',
+          line: 3,
+        },
+        {
+          messageId: 'errorMethod',
+          line: 4,
+        },
+        {
+          messageId: 'errorMethod',
+          line: 5,
+        },
+      ],
+    },
+    {
+      code: noFormat`
+interface Foo {
+  [foo](bar: string): one;
+  [foo](bar: number, baz: string): two;
+  [foo](): three;
+}
+      `,
+      output: noFormat`
+interface Foo {
+  [foo]: ((bar: string) => one) & ((bar: number, baz: string) => two) & (() => three);
+}
+      `,
+      errors: [
+        {
+          messageId: 'errorMethod',
+          line: 3,
+        },
+        {
+          messageId: 'errorMethod',
+          line: 4,
+        },
+        {
+          messageId: 'errorMethod',
+          line: 5,
+        },
+      ],
+    },
+    {
+      code: noFormat`
+interface Foo {
+  [foo](bar: string): one;
+  [foo](bar: number, baz: string): two;
+  [foo](): three;
+  bar(arg: string): void;
+  bar(baz: number): Foo;
+}
+      `,
+      output: noFormat`
+interface Foo {
+  [foo]: ((bar: string) => one) & ((bar: number, baz: string) => two) & (() => three);
+  bar: ((arg: string) => void) & ((baz: number) => Foo);
+}
+      `,
+      errors: [
+        {
+          messageId: 'errorMethod',
+          line: 3,
+        },
+        {
+          messageId: 'errorMethod',
+          line: 4,
+        },
+        {
+          messageId: 'errorMethod',
+          line: 5,
+        },
+        {
+          messageId: 'errorMethod',
+          line: 6,
+        },
+        {
+          messageId: 'errorMethod',
+          line: 7,
+        },
+      ],
+    },
   ],
 });