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

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,
+      );
+    });
+  }
+});