Support configuration files with UTF-8 BOM (#20127)

changelog_unreleased/api/20127.md

@@ -0,0 +1,19 @@
+#### Support configuration files with UTF-8 BOM (#20127 by @fisker)
+
+<!-- prettier-ignore -->
+```console
+# Input
+$ cat .prettierrc.json
+{"semi":false}
+$ prettier example.js --check
+
+# Prettier stable
+Invalid configuration for file "example.js":
+JSON Error in .prettierrc.json:
+Unexpected token "" (\u{feff})
+
+# Prettier main
+Checking formatting...
+[warn] example.js
+[warn] Code style issues found in the above file. Run Prettier with --write to fix.
+```

src/config/prettier-config/loaders.js

@@ -2,10 +2,12 @@ import { pathToFileURL } from "node:url";
 import { parse as parseJson5 } from "@bybrave/json5";
 import parseJson from "parse-json";
 import { parse as parseToml } from "smol-toml";
+import { stripBom } from "../../utilities/bom.js";
 import readFile from "../../utilities/read-file.js";
 
 async function readJson(file) {
-  const content = await readFile(file);
+  let content = await readFile(file);
+  content = stripBom(content);
   try {
     return parseJson(content);
   } catch (/** @type {any} */ error) {
@@ -70,7 +72,8 @@ async function loadYaml(file) {
 }
 
 async function loadToml(file) {
-  const content = await readFile(file);
+  let content = await readFile(file);
+  content = stripBom(content);
   try {
     return parseToml(content);
   } catch (/** @type {any} */ error) {

src/main/core.js

@@ -12,6 +12,7 @@ import {
   printDocToDebug,
   printDocToString as printDocToStringWithoutNormalizeOptions,
 } from "../document/index.js";
+import { addBom, hasBom as stringHasBom } from "../utilities/bom.js";
 import getAlignmentSize from "../utilities/get-alignment-size.js";
 import { prepareToPrint, printAstToDoc } from "./ast-to-doc.js";
 import getCursorLocation from "./get-cursor-node.js";
@@ -21,8 +22,6 @@ import parseText from "./parse.js";
 import { resolveParser } from "./parser-and-printer.js";
 import { calculateRange } from "./range.js";
 
-const BOM = "\uFEFF";
-
 const CURSOR = Symbol("cursor");
 
 async function coreFormat(originalText, opts, addAlignmentSize = 0) {
@@ -271,9 +270,9 @@ function normalizeInputAndOptions(text, options) {
     options,
   );
 
-  const hasBOM = text.charAt(0) === BOM;
+  const hasBom = stringHasBom(text);
 
-  if (hasBOM) {
+  if (hasBom) {
     text = text.slice(1);
     cursorOffset--;
     rangeStart--;
@@ -297,7 +296,7 @@ function normalizeInputAndOptions(text, options) {
   }
 
   return {
-    hasBOM,
+    hasBom,
     text,
     options: normalizeIndexes(text, {
       ...options,
@@ -320,7 +319,7 @@ async function hasIgnorePragma(text, options) {
 }
 
 async function formatWithCursor(originalText, originalOptions) {
-  let { hasBOM, text, options } = normalizeInputAndOptions(
+  let { hasBom, text, options } = normalizeInputAndOptions(
     originalText,
     await normalizeFormatOptions(originalOptions),
   );
@@ -353,8 +352,8 @@ async function formatWithCursor(originalText, originalOptions) {
     result = await coreFormat(text, options);
   }
 
-  if (hasBOM) {
-    result.formatted = BOM + result.formatted;
+  if (hasBom) {
+    result.formatted = addBom(result.formatted);
 
     if (result.cursorOffset >= 0) {
       result.cursorOffset++;

src/utilities/bom.js

@@ -0,0 +1,12 @@
+const BOM = "\uFEFF";
+
+/** @type {(string: string) => boolean} */
+const hasBom = (string) => string.charAt(0) === BOM;
+
+/** @type {(string: string) => string} */
+const stripBom = (string) => (hasBom(string) ? string.slice(1) : string);
+
+/** @type {(string: string) => string} */
+const addBom = (string) => BOM + string;
+
+export { addBom, hasBom, stripBom };

tests/unit/config-loader.js

@@ -0,0 +1,36 @@
+import fs from "node:fs/promises";
+import path from "node:path";
+import { temporaryDirectory as getTemporaryDirectory } from "tempy";
+import loadConfig from "../../src/config/prettier-config/load-config.js";
+
+describe("Support BOM", () => {
+  const files = [
+    { filename: "package.json", content: '{"prettier": {"tabWidth": 5}}' },
+    { filename: ".prettierrc", content: "tabWidth: 5" },
+    { filename: ".prettierrc.json", content: '{"tabWidth": 5}' },
+    { filename: ".prettierrc.yml", content: "tabWidth: 5" },
+    { filename: ".prettierrc.json5", content: "{tabWidth: 5}" },
+    { filename: ".prettierrc.toml", content: "tabWidth = 5" },
+  ];
+
+  const directory = getTemporaryDirectory();
+  const expected = { tabWidth: 5 };
+  beforeAll(async () => {
+    await Promise.all(
+      files.map(({ filename, content }) =>
+        fs.writeFile(path.join(directory, filename), `\ufeff${content}`),
+      ),
+    );
+  });
+  afterAll(async () => {
+    await fs.rm(directory, { recursive: true, force: true });
+  });
+
+  for (const { filename } of files) {
+    test(filename, async () => {
+      expect(await loadConfig(path.join(directory, filename))).toStrictEqual(
+        expected,
+      );
+    });
+  }
+});