From a61eecc1d988cec312ddda3bfacf6c077978dd65 Mon Sep 17 00:00:00 2001
From: yeonjuan <yeonjuan93@naver.com>
Date: Mon, 11 Mar 2024 19:13:05 +0900
Subject: [PATCH] feat(eslint-plugin): [prefer-reduce-type-parameter] supports
 tuple, union, intersection

---
 .../src/rules/prefer-reduce-type-parameter.ts | 14 +++-
 .../prefer-reduce-type-parameter.test.ts      | 69 +++++++++++++++++++
 2 files changed, 82 insertions(+), 1 deletion(-)

diff --git a/packages/eslint-plugin/src/rules/prefer-reduce-type-parameter.ts b/packages/eslint-plugin/src/rules/prefer-reduce-type-parameter.ts
index 9a196e7be0d..7eb781ed0d1 100644
--- a/packages/eslint-plugin/src/rules/prefer-reduce-type-parameter.ts
+++ b/packages/eslint-plugin/src/rules/prefer-reduce-type-parameter.ts
@@ -1,5 +1,7 @@
 import type { TSESTree } from '@typescript-eslint/utils';
 import { AST_NODE_TYPES } from '@typescript-eslint/utils';
+import * as tsutils from 'ts-api-utils';
+import type * as ts from 'typescript';
 
 import {
   createRule,
@@ -51,6 +53,16 @@ export default createRule({
     const services = getParserServices(context);
     const checker = services.program.getTypeChecker();
 
+    function isArrayType(type: ts.Type): boolean {
+      return tsutils
+        .unionTypeParts(type)
+        .every(unionPart =>
+          tsutils
+            .intersectionTypeParts(unionPart)
+            .every(t => checker.isArrayType(t) || checker.isTupleType(t)),
+        );
+    }
+
     return {
       'CallExpression > MemberExpression.callee'(
         callee: MemberExpressionWithCallExpressionParent,
@@ -72,7 +84,7 @@ export default createRule({
         );
 
         // Check the owner type of the `reduce` method.
-        if (checker.isArrayType(calleeObjType)) {
+        if (isArrayType(calleeObjType)) {
           context.report({
             messageId: 'preferTypeParameter',
             node: secondArg,
diff --git a/packages/eslint-plugin/tests/rules/prefer-reduce-type-parameter.test.ts b/packages/eslint-plugin/tests/rules/prefer-reduce-type-parameter.test.ts
index 43aadcec074..d93212ae43f 100644
--- a/packages/eslint-plugin/tests/rules/prefer-reduce-type-parameter.test.ts
+++ b/packages/eslint-plugin/tests/rules/prefer-reduce-type-parameter.test.ts
@@ -39,6 +39,24 @@ ruleTester.run('prefer-reduce-type-parameter', rule, {
     '[1, 2, 3].reduce((sum, num) => sum + num, 0);',
     '[1, 2, 3].reduce<number[]>((a, s) => a.concat(s * 2), []);',
     '[1, 2, 3]?.reduce<number[]>((a, s) => a.concat(s * 2), []);',
+    `
+      declare const tuple: [number, number, number];
+      tuple.reduce<number[]>((a, s) => a.concat(s * 2), []);
+    `,
+    `
+      type Reducer = { reduce: (callback: (arg: any) => any, arg: any) => any };
+      declare const tuple: [number, number, number] | Reducer;
+      tuple.reduce(a => {
+        return a.concat(1);
+      }, [] as number[]);
+    `,
+    `
+      type Reducer = { reduce: (callback: (arg: any) => any, arg: any) => any };
+      declare const arrayOrReducer: number[] & Reducer;
+      arrayOrReducer.reduce(a => {
+        return a.concat(1);
+      }, [] as number[]);
+    `,
   ],
   invalid: [
     {
@@ -206,5 +224,56 @@ function f<T, U extends T[]>(a: U) {
         },
       ],
     },
+    {
+      code: `
+declare const tuple: [number, number, number];
+tuple.reduce((a, s) => a.concat(s * 2), [] as number[]);
+      `,
+      output: `
+declare const tuple: [number, number, number];
+tuple.reduce<number[]>((a, s) => a.concat(s * 2), []);
+      `,
+      errors: [
+        {
+          messageId: 'preferTypeParameter',
+          column: 41,
+          line: 3,
+        },
+      ],
+    },
+    {
+      code: `
+declare const tupleOrArray: [number, number, number] | number[];
+tupleOrArray.reduce((a, s) => a.concat(s * 2), [] as number[]);
+      `,
+      output: `
+declare const tupleOrArray: [number, number, number] | number[];
+tupleOrArray.reduce<number[]>((a, s) => a.concat(s * 2), []);
+      `,
+      errors: [
+        {
+          messageId: 'preferTypeParameter',
+          column: 48,
+          line: 3,
+        },
+      ],
+    },
+    {
+      code: `
+declare const tuple: [number, number, number] & number[];
+tuple.reduce((a, s) => a.concat(s * 2), [] as number[]);
+      `,
+      output: `
+declare const tuple: [number, number, number] & number[];
+tuple.reduce<number[]>((a, s) => a.concat(s * 2), []);
+      `,
+      errors: [
+        {
+          messageId: 'preferTypeParameter',
+          column: 41,
+          line: 3,
+        },
+      ],
+    },
   ],
 });