feat: add support for prettier 3.x

This fixes diffplug#1751

Author: simschla

lib/src/main/resources/com/diffplug/spotless/npm/prettier-serve.js

@@ -1,15 +1,15 @@
 const prettier = require("prettier");
 
 app.post("/prettier/config-options", (req, res) => {
-	var config_data = req.body;
-	var prettier_config_path = config_data.prettier_config_path;
-	var prettier_config_options = config_data.prettier_config_options || {};
+	const config_data = req.body;
+	const prettier_config_path = config_data.prettier_config_path;
+	const prettier_config_options = config_data.prettier_config_options || {};
 
 	if (prettier_config_path) {
 		prettier
 			.resolveConfig(undefined, { config: prettier_config_path })
 			.then(options => {
-				var mergedConfigOptions = mergeConfigOptions(options, prettier_config_options);
+				const mergedConfigOptions = mergeConfigOptions(options, prettier_config_options);
 				res.set("Content-Type", "application/json")
 				res.json(mergedConfigOptions);
 			})
@@ -20,12 +20,12 @@ app.post("/prettier/config-options", (req, res) => {
 	res.json(prettier_config_options);
 });
 
-app.post("/prettier/format", (req, res) => {
-	var format_data = req.body;
+app.post("/prettier/format", async (req, res) => {
+	const format_data = req.body;
 
-	var formatted_file_content = "";
+	let formatted_file_content = "";
 	try {
-		formatted_file_content = prettier.format(format_data.file_content, format_data.config_options);
+		formatted_file_content = await prettierFormat(format_data.file_content, format_data.config_options);
 	} catch(err) {
 		res.status(500).send("Error while formatting: " + err);
 		return;
@@ -34,7 +34,20 @@ app.post("/prettier/format", (req, res) => {
 	res.send(formatted_file_content);
 });
 
-var mergeConfigOptions = function(resolved_config_options, config_options) {
+const prettierFormat = async function(file_content, config_options) {
+	const result = prettier.format(file_content, config_options);
+
+	// Check if result is a Promise (version 3.0.0 and above)
+	if (typeof result.then === 'function') {
+		return result;
+	}
+
+	// If it's not a Promise (meaning it's a string), wrap it in a Promise (< 3.0.0)
+	return Promise.resolve(result);
+}
+
+
+const mergeConfigOptions = function(resolved_config_options, config_options) {
 	if (resolved_config_options !== undefined && config_options !== undefined) {
 		return extend(resolved_config_options, config_options);
 	}
@@ -46,15 +59,15 @@ var mergeConfigOptions = function(resolved_config_options, config_options) {
 	}
 };
 
-var extend = function() {
+const extend = function() {
 	// Variables
-	var extended = {};
-	var i = 0;
-	var length = arguments.length;
+	const extended = {};
+	let i = 0;
+	const length = arguments.length;
 
 	// Merge the object into the extended object
-	var merge = function(obj) {
-		for (var prop in obj) {
+	const merge = function (obj) {
+		for (const prop in obj) {
 			if (Object.prototype.hasOwnProperty.call(obj, prop)) {
 				extended[prop] = obj[prop];
 			}
@@ -63,9 +76,8 @@ var extend = function() {
 
 	// Loop through each object and conduct a merge
 	for (; i < length; i++) {
-		var obj = arguments[i];
+		const obj = arguments[i];
 		merge(obj);
 	}
-
 	return extended;
 };

testlib/src/test/java/com/diffplug/spotless/npm/PrettierFormatterStepTest.java

@@ -17,6 +17,7 @@
 
 import java.io.File;
 import java.util.Collections;
+import java.util.Map;
 
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
@@ -38,17 +39,27 @@ class PrettierFormatterStepTest extends ResourceHarness {
 	@Nested
 	class PrettierFormattingOfFileTypesIsWorking extends NpmFormatterStepCommonTests {
 
-		@ParameterizedTest(name = "{index}: prettier can be applied to {0}")
+		@ParameterizedTest(name = "{index}: prettier 2.x can be applied to {0}")
 		@ValueSource(strings = {"html", "typescript", "json", "javascript-es5", "javascript-es6", "css", "scss", "markdown", "yaml"})
-		void formattingUsingConfigFile(String fileType) throws Exception {
+		void formattingUsingPrettier2WithConfigFile(String fileType) throws Exception {
+			runTestUsingPrettier(fileType, PrettierFormatterStep.defaultDevDependencies());
+		}
+
+		@ParameterizedTest(name = "{index}: prettier 3.x can be applied to {0}")
+		@ValueSource(strings = {"html", "typescript", "json", "javascript-es5", "javascript-es6", "css", "scss", "markdown", "yaml"})
+		void formattingUsingPrettier3WithConfigFile(String fileType) throws Exception {
+			runTestUsingPrettier(fileType, ImmutableMap.of("prettier", "3.0.0"));
+		}
+
+		private void runTestUsingPrettier(String fileType, Map<String, String> dependencies) throws Exception {
 			String filedir = "npm/prettier/filetypes/" + fileType + "/";
 
 			final File prettierRc = createTestFile(filedir + ".prettierrc.yml");
 			final String dirtyFile = filedir + fileType + ".dirty";
 			final String cleanFile = filedir + fileType + ".clean";
 
 			final FormatterStep formatterStep = PrettierFormatterStep.create(
-					PrettierFormatterStep.defaultDevDependencies(),
+					dependencies,
 					TestProvisioner.mavenCentral(),
 					projectDir(),
 					buildDir(),