Add upgrade helper for 11ty/eleventy#3255

.eleventy.js

@@ -19,6 +19,7 @@ module.exports = function(eleventyConfig) {
   eleventyConfig.addPlugin(require("./src/explicit-config-file.js"));
   eleventyConfig.addPlugin(require("./src/html-output-suffix.js"));
   eleventyConfig.addPlugin(require("./src/alias-template-formats.js"));
+  eleventyConfig.addPlugin(require("./src/empty-formats.js"));
 
   eleventyConfig.on("eleventy.after", () => {
     console.log(chalk.blue(`[${pkg.name}] This plugin is intended for temporary use: once you’re satisfied please remove this plugin from your project!`));

src/empty-formats.js

@@ -0,0 +1,17 @@
+const fs = require("node:fs");
+const chalk = require("kleur");
+const pkg = require("../package.json");
+
+const minimist = require("minimist");
+
+const argv = minimist(process.argv.slice(2), {
+	string: ["formats"]
+});
+
+module.exports = function(eleventyConfig) {
+	if(argv.formats || argv.formats === undefined) {
+		console.log(chalk.green(`[${pkg.name}] PASSED`), `You aren’t using \`--formats=\` or  \`--formats=''\` but if you were you should know that these are now empty template format sets. In previous versions, they were aliased to "*". Read more: https://github.com/11ty/eleventy/issues/3255`);
+	} else if(argv.formats === "" || argv.formats === null) {
+		console.log(chalk.red(`[${pkg.name}] ERROR`), `In Eleventy 3.0 \`--formats=""\` and \`formats=\` are empty template format sets. Previous versions aliased these to "*". Use \`--formats=*\` if you want that behavior in 3.0. Read more: https://github.com/11ty/eleventy/issues/3255`);
+	}
+};