右辺がundefinedやnullである厳密等価演算子を等価演算子に自動で修正できる設定を追加 (#1752)

* setup eslint plugin for this repository

* add rule no-strict-nullable

* separate createRule to a file

* add documentation for rule no-strict-nullable

* fix rule documentation url

* add trailing newline to eslint-plugin/package.json

---------

Co-authored-by: Hiroshiba <hihokaruta@gmail.com>

.eslintrc.js

@@ -11,6 +11,7 @@ module.exports = {
     "@vue/prettier",
     "@vue/eslint-config-typescript/recommended",
     "@vue/eslint-config-prettier",
+    "plugin:@voicevox/all",
   ],
   plugins: ["import"],
   parser: "vue-eslint-parser",
@@ -62,33 +63,6 @@ module.exports = {
       },
     ],
     "import/order": "error",
-    "no-restricted-syntax": [
-      "warn",
-      {
-        selector:
-          "BinaryExpression[operator='==='][right.type='Literal'][right.value=null]",
-        message:
-          "'=== null'ではなく'== null'を使用してください。詳細: https://github.com/VOICEVOX/voicevox/issues/1513",
-      },
-      {
-        selector:
-          "BinaryExpression[operator='!=='][right.type='Literal'][right.value=null]",
-        message:
-          "'!== null'ではなく'!= null'を使用してください。詳細: https://github.com/VOICEVOX/voicevox/issues/1513",
-      },
-      {
-        selector:
-          "BinaryExpression[operator='==='][right.type='Identifier'][right.name=undefined]",
-        message:
-          "'=== undefined'ではなく'== undefined'を使用してください。詳細: https://github.com/VOICEVOX/voicevox/issues/1513",
-      },
-      {
-        selector:
-          "BinaryExpression[operator='!=='][right.type='Identifier'][right.name=undefined]",
-        message:
-          "'!== undefined'ではなく'!= undefined'を使用してください。詳細: https://github.com/VOICEVOX/voicevox/issues/1513",
-      },
-    ],
   },
   overrides: [
     {

eslint-plugin/create-rule.js

@@ -0,0 +1,6 @@
+const { ESLintUtils } = require("@typescript-eslint/utils");
+
+exports.createRule = ESLintUtils.RuleCreator(
+  (name) =>
+    `https://github.com/VOICEVOX/voicevox/blob/main/eslint-plugin/${name}.md`
+);

eslint-plugin/index.js

@@ -0,0 +1,14 @@
+// @ts-check
+module.exports = {
+  configs: {
+    all: {
+      plugins: ["@voicevox"],
+      rules: {
+        "@voicevox/no-strict-nullable": "error",
+      },
+    },
+  },
+  rules: {
+    "no-strict-nullable": require("./no-strict-nullable"),
+  },
+};

eslint-plugin/no-strict-nullable.js

@@ -0,0 +1,58 @@
+// @ts-check
+const { AST_NODE_TYPES } = require("@typescript-eslint/utils");
+const { createRule } = require("./create-rule");
+
+/**
+ * @param {import("@typescript-eslint/types").TSESTree.BinaryExpression["left"]} node
+ */
+function isNull(node) {
+  return node.type === AST_NODE_TYPES.Literal && node.value == null;
+}
+
+/**
+ * @param {import("@typescript-eslint/types").TSESTree.BinaryExpression["right"]} node
+ */
+function isUndefined(node) {
+  return node.type === AST_NODE_TYPES.Identifier && node.name === "undefined";
+}
+
+module.exports = createRule({
+  create(context) {
+    return {
+      BinaryExpression(node) {
+        if (node.operator !== "===" && node.operator !== "!==") return;
+        if (!isNull(node.right) && !isUndefined(node.right)) return;
+
+        context.report({
+          node,
+          messageId: "report",
+          data: {
+            operator: node.operator.slice(0, 2),
+            expression: context.getSourceCode().getText(node.right),
+          },
+          fix(fixer) {
+            return fixer.replaceTextRange(
+              [node.left.range[1], node.right.range[0]],
+              node.operator.slice(0, 2) + " "
+            );
+          },
+        });
+      },
+    };
+  },
+  name: "no-strict-nullable",
+  meta: {
+    type: "problem",
+    docs: {
+      description: "undefinedとnullと比較する際に厳密等価演算子を使わない",
+      recommended: "error",
+    },
+    messages: {
+      report:
+        "'{{ operator }}= {{ expression }}'ではなく'{{ operator }} {{ expression }}'を使用してください。",
+    },
+    schema: [],
+    fixable: "code",
+  },
+  defaultOptions: [],
+});

eslint-plugin/no-strict-nullable.md

@@ -0,0 +1,18 @@
+# no-strict-nullable
+
+厳密等価演算子`===`は有用ですが，`undefined`や`null`を右辺に持ってくる時，左辺が`undefined`を取りうるのか，それとも`null`を取りうるのかを考える必要があります．
+一方，等価演算子`==`は`undefined`と`null`を区別しないため，このような場合に`==`を使うようにすることで，左辺が取る値を考える必要がなくなります．
+
+このルールでは，右辺が`null`または`undefined`の場合に，厳密等価演算子`===`を使うことを禁止し，代わりに等価演算子`==`を使うようにします．
+
+```ts
+const a = fuga === undefined;
+//        ^^^^^^^^^^^^^^^^^^ '=== null'ではなく'== null'を使用してください。
+const button = { text: null };
+const c = button.text !== null;
+//        ^^^^^^^^^^^^^^^^^^^^ '!== null'ではなく'!= null'を使用してください。
+```
+
+## リンク
+
+https://github.com/VOICEVOX/voicevox/issues/1513

eslint-plugin/package.json

@@ -0,0 +1,6 @@
+{
+  "name": "@voicevox/eslint-plugin",
+  "version": "0.0.0",
+  "description": "eslint plugin for voicevox",
+  "main": "index.js"
+}

package.json

@@ -87,7 +87,10 @@
     "@types/wicg-file-system-access": "2020.9.6",
     "@typescript-eslint/eslint-plugin": "5.38.1",
     "@typescript-eslint/parser": "5.38.1",
+    "@typescript-eslint/types": "5.38.1",
+    "@typescript-eslint/utils": "5.38.1",
     "@vitejs/plugin-vue": "4.0.0",
+    "@voicevox/eslint-plugin": "file:./eslint-plugin",
     "@vue/eslint-config-prettier": "7.0.0",
     "@vue/eslint-config-typescript": "11.0.2",
     "@vue/test-utils": "2.3.0",