feat(plugins/local): add 'no-shadowing-underscore' rule to prevent shadowing of '_' identifier

Author: Rel1cx

eslint.config.ts

@@ -256,6 +256,7 @@ export default tseslint.config(
       "eslint-plugin/require-meta-docs-url": "off",
       // Part: local rules
       "local/avoid-multiline-template-expression": "warn",
+      "local/no-shadowing-underscore": "error",
       "local/prefer-eqeq-nullish-comparison": "warn",
     },
     settings: {

packages/plugins/eslint-plugin-react-web-api/src/rules/no-leaked-event-listener.ts

@@ -89,7 +89,7 @@ function getOptions(node: TSESTree.CallExpressionArgument, initialScope: Scope):
   }
   function getPropValue<A>(
     prop: TSESTree.Property | TSESTree.RestElement | TSESTree.SpreadElement | _,
-    filter: (value: unknown) => value is A = (_): _ is A => true,
+    filter: (value: unknown) => value is A = (a): a is A => true,
   ): A | _ {
     if (prop?.type !== T.Property) return _;
     const { value } = prop;

packages/types/src/rule-name.ts

@@ -137,4 +137,4 @@ type RuleName =
 type RuleNameWithAdditional = `${RuleName}-${Additional}`;
 
 // Example rule names
-const _: RuleName = "no-constructed-context-value";
+const ruleName: RuleName = "no-constructed-context-value";

packages/utilities/eff/docs/functions/returnVoid.md

@@ -6,10 +6,10 @@
 
 # Function: returnVoid()
 
-> **returnVoid**(): [`_`](../type-aliases.md)
+> **returnVoid**(): `undefined`
 
 Do nothing and return undefined
 
 ## Returns
 
-[`_`](../type-aliases.md)
+`undefined`

packages/utilities/eff/docs/type-aliases.md

@@ -8,4 +8,4 @@
 
 > **\_**: `undefined`
 
-1-byte version undefined, produces fewer bytes than `undefined` or `void 0` in the minified output d.ts.
+1-byte version undefined, produces fewer bytes than `undefined` or `void 0` in the minified output dts.

packages/utilities/eff/src/lang.ts

@@ -4,14 +4,14 @@
 import type { NarrowedTo } from "./type";
 
 /**
- * 1-byte version undefined, produces fewer bytes than `undefined` or `void 0` in the minified output d.ts.
+ * 1-byte version undefined, produces fewer bytes than `undefined` or `void 0` in the minified output dts.
  */
-export type _ = undefined;
+export type _ = undefined; // eslint-disable-line local/no-shadowing-underscore
 
 /**
  * 1-byte version undefined, produces fewer bytes than `undefined` or `void 0` in the minified output js.
  */
-export const _ = undefined;
+export const _ = undefined; // eslint-disable-line local/no-shadowing-underscore
 
 /**
  * Do nothing and return false
@@ -30,8 +30,8 @@ export function returnTrue(): true {
 /**
  * Do nothing and return undefined
  */
-export function returnVoid(): _ {
-  return _;
+export function returnVoid(): undefined {
+  return undefined;
 }
 
 /**

workspace/eslint-plugin-local/dist/index.d.ts

@@ -6,6 +6,7 @@ declare const _default: {
         readonly version: string;
     };
     readonly rules: {
+        readonly "no-shadowing-underscore": _typescript_eslint_utils_ts_eslint.RuleModule<"noShadowingUnderscore", [], unknown, _typescript_eslint_utils_ts_eslint.RuleListener>;
         readonly "avoid-multiline-template-expression": _typescript_eslint_utils_ts_eslint.RuleModule<"avoidMultilineTemplateExpression", [], unknown, _typescript_eslint_utils_ts_eslint.RuleListener>;
         readonly "prefer-eqeq-nullish-comparison": _typescript_eslint_utils_ts_eslint.RuleModule<"unexpectedComparison" | "useLooseComparisonSuggestion", [], unknown, _typescript_eslint_utils_ts_eslint.RuleListener>;
     };

workspace/eslint-plugin-local/dist/index.js

@@ -1,5 +1,6 @@
 import * as AST from '@eslint-react/ast';
 import { ESLintUtils, AST_NODE_TYPES } from '@typescript-eslint/utils';
+import * as VAR from '@eslint-react/var';
 import { nullThrows, NullThrowsReasons } from '@typescript-eslint/utils/eslint-utils';
 
 // package.json
@@ -42,7 +43,40 @@ var avoid_multiline_template_expression_default = createRule({
   },
   defaultOptions: []
 });
-var RULE_NAME2 = "prefer-eqeq-nullish-comparison";
+var RULE_NAME2 = "no-shadowing-underscore";
+var RULE_FEATURES2 = [
+  "CHK"
+];
+var no_shadowing_underscore_default = createRule({
+  meta: {
+    type: "problem",
+    docs: {
+      description: "disallow multiline template expressions",
+      [Symbol.for("rule_features")]: RULE_FEATURES2
+    },
+    messages: {
+      noShadowingUnderscore: "In this codebase, '_' is used to represent the undefined. Avoid shadowing it."
+    },
+    schema: []
+  },
+  name: RULE_NAME2,
+  create(context) {
+    return {
+      "Identifier[name='_']"(node) {
+        const initialScope = context.sourceCode.getScope(node);
+        const isFromImport = VAR.isInitializedFromSource("_", "@eslint-react/eff", initialScope);
+        if (!isFromImport) {
+          context.report({
+            messageId: "noShadowingUnderscore",
+            node
+          });
+        }
+      }
+    };
+  },
+  defaultOptions: []
+});
+var RULE_NAME3 = "prefer-eqeq-nullish-comparison";
 var prefer_eqeq_nullish_comparison_default = createRule({
   meta: {
     type: "suggestion",
@@ -57,7 +91,7 @@ var prefer_eqeq_nullish_comparison_default = createRule({
     },
     schema: []
   },
-  name: RULE_NAME2,
+  name: RULE_NAME3,
   create(context) {
     return {
       BinaryExpression(node) {
@@ -119,6 +153,7 @@ var index_default = {
     version
   },
   rules: {
+    "no-shadowing-underscore": no_shadowing_underscore_default,
     "avoid-multiline-template-expression": avoid_multiline_template_expression_default,
     "prefer-eqeq-nullish-comparison": prefer_eqeq_nullish_comparison_default
   }

workspace/eslint-plugin-local/src/index.ts

@@ -1,5 +1,6 @@
 import { name, version } from "../package.json";
 import avoidMultilineTemplateExpression from "./rules/avoid-multiline-template-expression";
+import noShadowingUnderscore from "./rules/no-shadowing-underscore";
 import preferEqeqNullishComparison from "./rules/prefer-eqeq-nullish-comparison";
 
 export default {
@@ -9,6 +10,7 @@ export default {
   },
   rules: {
     "avoid-multiline-template-expression": avoidMultilineTemplateExpression,
+    "no-shadowing-underscore": noShadowingUnderscore,
     "prefer-eqeq-nullish-comparison": preferEqeqNullishComparison,
   },
 } as const;

workspace/eslint-plugin-local/src/rules/no-shadowing-underscore.spec.ts

@@ -0,0 +1,51 @@
+import { ruleTester } from "../../../../test";
+import rule, { RULE_NAME } from "./no-shadowing-underscore";
+
+ruleTester.run(RULE_NAME, rule, {
+  invalid: [
+    {
+      code: /* ts */ `
+        const _ = 1;
+      `,
+      errors: [{ messageId: "noShadowingUnderscore" }],
+    },
+    {
+      code: /* ts */ `
+        const [_, foo] = [1, 2];
+      `,
+      errors: [{ messageId: "noShadowingUnderscore" }],
+    },
+    {
+      code: /* ts */ `
+        const { name: _, ...rest } = { name: "foo", age: 20 };
+      `,
+      errors: [{ messageId: "noShadowingUnderscore" }],
+    },
+  ],
+  valid: [
+    /* ts */ `
+      const __ = 1;
+    `,
+    /* ts */ `
+      const [__, foo] = [1, 2];
+    `,
+    /* ts */ `
+      const { name: __, ...rest } = { name: "foo", age: 20 };
+    `,
+    /* ts */ `
+      import { _ } from "@eslint-react/eff";
+    `,
+    /* ts */ `
+      import { _ } from "@eslint-react/eff";
+
+      const value = _;
+    `,
+    /* ts */ `
+      import { _ } from "@eslint-react/eff";
+
+      function foo() {
+        return _;
+      }
+    `,
+  ],
+});