vue/block-lang do not support enforcement of lang attritbutes for default langauges

[NVolcz]

Checklist

• I have tried restarting my IDE and the issue persists.
• I have read the FAQ and my problem is not listed.

Tell us about your environment

• ESLint version: 9.11.1
• eslint-plugin-vue version: 9.28.0
• Vue version: 3.5.10
• Node version: v20.14.0
• Operating System: Ubuntu
• vscode: 1.95.2

Please show your full configuration:

import { includeIgnoreFile } from "@eslint/compat";
import js from "@eslint/js";
import eslintConfigPrettier from "eslint-config-prettier";
import tailwind from "eslint-plugin-tailwindcss";
import pluginVue from "eslint-plugin-vue";
import globals from "globals";
import path from "node:path";
import { fileURLToPath } from "node:url";

const __filename = fileURLToPath(import.meta.url);
const __dirname = path.dirname(__filename);
const gitignorePath = path.resolve(__dirname, ".gitignore");

export default [
  {
    files: ["src/**/*.js", "src/**/*.vue"],
  },
  includeIgnoreFile(gitignorePath),
  js.configs.recommended,
  ...pluginVue.configs["flat/recommended"],
  ...tailwind.configs["flat/recommended"],
  eslintConfigPrettier,
  {
    languageOptions: {
      globals: {
        ...globals.node,
      },
    },
    rules: {
      "no-unused-vars": "warn",
      "tailwindcss/no-custom-classname": "off",
      "vue/no-v-html": "off",
      "vue/multi-word-component-names": "off",
      "vue/block-lang": [
        "error",
        {
          script: {
            lang: "js",
          },
        },
      ],
    },
  },
];

What did you do?
When using vscode with the "Vue - official" (vue.volar) extension in a Vite setup the Intellisense does not assume that the default language is JavaScript. In order to work around this limitation I was thinking of using the 'vue/block-lang` to enforce that a language is specified for every script block.

Formatting files like:

<script setup lang="js">
</script>

What did you expect to happen?
I expected rule to honor my settings to require script blocks to specify lang="js".

What actually happened?

The rule outputs errors regarding the default language is specified:

  11:15  error  Do not explicitly specify the default language for the 'lang' attribute of '<script>'  vue/block-lang

Based on my understanding of the rule's code, if an default language is specified, then omitting the language is preferred:

eslint-plugin-vue/lib/rules/block-lang.js

Lines 60 to 89 in 16c8778

	function normalizeOption(blockName, option) {
	/** @type {Set<string>} */
	let lang
	if (Array.isArray(option.lang)) {
	lang = new Set(option.lang)
	} else if (typeof option.lang === 'string') {
	lang = new Set([option.lang])
	} else {
	lang = new Set()
	}
	let hasDefault = false
	for (const def of DEFAULT_LANGUAGES[blockName] || []) {
	if (lang.has(def)) {
	lang.delete(def)
	hasDefault = true
	}
	}
	if (lang.size === 0) {
	return {
	lang,
	allowNoLang: true
	}
	}
	return {
	lang,
	allowNoLang: hasDefault || Boolean(option.allowNoLang)
	}
	}

It seems that this assumption was valid when Vetur was used for the official vscode extension:

eslint-plugin-vue/docs/rules/block-lang.md

Lines 57 to 62 in 16c8778

	::: warning Note
	If the default language is specified for `lang` option of `<template>`, `<style>` and `<script>`, it will be enforced to not specify `lang` attribute.
	This is to prevent unintended problems with [Vetur](https://vuejs.github.io/vetur/).
	See also [Vetur - Syntax Highlighting](https://vuejs.github.io/vetur/guide/highlighting.html).
	:::

It would be nice if the Vue vscode extension were better at handling the lang attribtue but I also feel that this rule shouldn't be as opinionated as it is now.

Repository to reproduce this issue