feat: Add no-commented-out-code rule.

source/rules/no-commented-out-code.ts

@@ -0,0 +1,76 @@
+/**
+ * @license Use of this source code is governed by an MIT-style license that
+ * can be found in the LICENSE file at https://github.com/cartant/eslint-plugin-etc
+ */
+
+import { TSESTree as es } from "@typescript-eslint/experimental-utils";
+import { ruleCreator } from "../utils";
+
+const rule = ruleCreator({
+  defaultOptions: [],
+  meta: {
+    docs: {
+      category: "Best Practices",
+      description: "Forbids commented-out code.",
+      recommended: false,
+    },
+    fixable: undefined,
+    messages: {
+      forbidden: "Commented-out code is forbidden.",
+    },
+    schema: [],
+    type: "problem",
+  },
+  name: "no-commented-out-code",
+  create: (context) => {
+    const { parse } = require(context.parserPath);
+    const { project, ...parserOptions } = context.parserOptions;
+    return {
+      Program: () => {
+        const comments = context.getSourceCode().getAllComments();
+        const blocks = toBlocks(comments);
+        for (const block of blocks) {
+          try {
+            parse(block.content, parserOptions);
+            context.report({
+              loc: block.loc,
+              messageId: "forbidden",
+            });
+          } catch (error) {}
+        }
+      },
+    };
+  },
+});
+
+function toBlocks(comments: es.Comment[]) {
+  const blocks: {
+    content: string;
+    loc: es.SourceLocation;
+  }[] = [];
+  let prevLine: es.LineComment | undefined;
+  for (const comment of comments) {
+    if (comment.type === "Block") {
+      blocks.push({
+        content: comment.value.replace(/^\s+\*/, "").replace(/\n\s+\*/g, "\n"),
+        loc: { ...comment.loc },
+      });
+      prevLine = undefined;
+    } else if (comment.type === "Line") {
+      if (prevLine && prevLine.loc.start.line === comment.loc.start.line - 1) {
+        const prevBlock = blocks[blocks.length - 1];
+        prevBlock.content += `\n${comment.value}`;
+        prevBlock.loc.end = comment.loc.end;
+      } else {
+        blocks.push({
+          content: comment.value,
+          loc: { ...comment.loc },
+        });
+      }
+      prevLine = comment;
+    }
+  }
+  return blocks;
+}
+
+export = rule;

tests/rules/no-commented-out-code.ts

@@ -0,0 +1,160 @@
+/**
+ * @license Use of this source code is governed by an MIT-style license that
+ * can be found in the LICENSE file at https://github.com/cartant/eslint-plugin-etc
+ */
+
+import { stripIndent } from "common-tags";
+import { fromFixture } from "eslint-etc";
+import rule = require("../../source/rules/no-commented-out-code");
+import { ruleTester } from "../utils";
+
+ruleTester({ types: false }).run("no-commented-out-code", rule, {
+  valid: [
+    {
+      code: stripIndent`
+        // This comment isn't code.
+        const answer = 42;
+      `,
+    },
+    {
+      code: stripIndent`
+        // This comment includes some code:
+        // const answer = 54;
+        const answer = 42;
+      `,
+    },
+    {
+      code: stripIndent`
+        /* This comment isn't code. */
+        const answer = 42;
+      `,
+    },
+    {
+      code: stripIndent`
+        /*
+        This comment includes some code:
+        const answer = 54;
+        */
+        const answer = 42;
+      `,
+    },
+    {
+      code: stripIndent`
+        /*
+         * This comment isn't code.
+         */
+        const answer = 42;
+      `,
+    },
+    {
+      code: stripIndent`
+        /*
+         * This comment includes some code:
+         * const answer = 54;
+         */
+        const answer = 42;
+      `,
+    },
+  ],
+  invalid: [
+    fromFixture(
+      stripIndent`
+        // const answer = 54;
+        ~~~~~~~~~~~~~~~~~~~~~ [forbidden]
+        const answer = 42;
+      `
+    ),
+    fromFixture(
+      stripIndent`
+        /* const answer = 54; */
+        ~~~~~~~~~~~~~~~~~~~~~~~~ [forbidden]
+        const answer = 42;
+      `
+    ),
+    {
+      code: stripIndent`
+        /*
+         * const answer = 54;
+         */
+        const answer = 42;
+      `,
+      errors: [
+        {
+          column: 1,
+          endColumn: 4,
+          line: 1,
+          endLine: 3,
+          messageId: "forbidden",
+        },
+      ],
+    },
+    {
+      code: stripIndent`
+        // // Wrong answer
+        // const answer = 54;
+        const answer = 42;
+      `,
+      errors: [
+        {
+          column: 1,
+          endColumn: 22,
+          line: 1,
+          endLine: 2,
+          messageId: "forbidden",
+        },
+      ],
+    },
+    {
+      code: stripIndent`
+        // /* Wrong answer */
+        // const answer = 54;
+        const answer = 42;
+      `,
+      errors: [
+        {
+          column: 1,
+          endColumn: 22,
+          line: 1,
+          endLine: 2,
+          messageId: "forbidden",
+        },
+      ],
+    },
+    {
+      code: stripIndent`
+        /*
+        // Wrong answer
+        const answer = 54;
+        */
+        const answer = 42;
+      `,
+      errors: [
+        {
+          column: 1,
+          endColumn: 3,
+          line: 1,
+          endLine: 4,
+          messageId: "forbidden",
+        },
+      ],
+    },
+    {
+      code: stripIndent`
+        /*
+         * // Wrong answer
+         * const answer = 54;
+         */
+        const answer = 42;
+      `,
+      errors: [
+        {
+          column: 1,
+          endColumn: 4,
+          line: 1,
+          endLine: 4,
+          messageId: "forbidden",
+        },
+      ],
+    },
+  ],
+});