Upgrade helper for 11ty/eleventy#3327

.eleventy.js

@@ -17,6 +17,7 @@ module.exports = function(eleventyConfig) {
   // Full list of issues: https://github.com/11ty/eleventy/issues?q=milestone%3A%22Eleventy+3.0.0%22+is%3Aclosed+label%3Abreaking-change
   eleventyConfig.addPlugin(require("./src/node-version.js"));
   eleventyConfig.addPlugin(require("./src/explicit-config-file.js"));
+  eleventyConfig.addPlugin(require("./src/html-output-suffix.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/html-output-suffix.js

@@ -0,0 +1,18 @@
+const chalk = require("kleur");
+const pkg = require("../package.json");
+
+// https://v2-0-1.11ty.dev/docs/languages/html/#using-the-same-input-and-output-directories
+module.exports = function(eleventyConfig) {
+	eleventyConfig.on("eleventy.config", ({ config }) => {
+		if(!("htmlOutputSuffix" in config)) {
+			console.log(chalk.blue(`[${pkg.name}]`), chalk.blue(`NOTICE`), `The \`htmlOutputSuffix\` feature was removed. It doesn’t look like you were using it!`);
+		} else {
+			console.log(chalk.red(`[${pkg.name}]`), chalk.red(`ERROR`), `The \`htmlOutputSuffix\` feature was removed. Learn more: https://github.com/11ty/eleventy/issues/3327`);
+		}
+	})
+
+	// Input and output are the same
+	if(eleventyConfig.directories.input === eleventyConfig.directories.output) {
+		console.log(chalk.yellow(`[${pkg.name}] WARNING`), `Your input and output folders are identical so please take note that Eleventy 3.0 will throw an error if any of your output files attempt to overwrite your input files. Learn more: https://github.com/11ty/eleventy/issues/3327`);
+	}
+};