feat: write file auto detect newline & indent

package.json

@@ -24,6 +24,7 @@
     "test:types": "tsc --noEmit --module esnext --skipLibCheck --moduleResolution node ./test/*.test.ts"
   },
   "dependencies": {
+    "detect-indent": "^7.0.1",
     "jsonc-parser": "^3.2.0",
     "mlly": "^1.1.1",
     "pathe": "^1.1.0"

src/index.ts

@@ -1,7 +1,13 @@
 import { promises as fsp } from "node:fs";
 import { dirname, resolve, isAbsolute } from "pathe";
 import { ResolveOptions as _ResolveOptions, resolvePath } from "mlly";
-import { findFile, FindFileOptions, findNearestFile } from "./utils";
+import {
+  findFile,
+  FindFileOptions,
+  findNearestFile,
+  writeJsonFile,
+  WriteOptions,
+} from "./utils";
 import type { PackageJson, TSConfig } from "./types";
 
 export * from "./types";
@@ -42,9 +48,10 @@ export async function readPackageJSON(
 
 export async function writePackageJSON(
   path: string,
-  package_: PackageJson
+  package_: PackageJson,
+  options: WriteOptions = {}
 ): Promise<void> {
-  await fsp.writeFile(path, JSON.stringify(package_, undefined, 2));
+  await writeJsonFile(path, package_, options);
 }
 
 export async function readTSConfig(
@@ -68,9 +75,10 @@ export async function readTSConfig(
 
 export async function writeTSConfig(
   path: string,
-  tsconfig: TSConfig
+  tsconfig: TSConfig,
+  options: WriteOptions = {}
 ): Promise<void> {
-  await fsp.writeFile(path, JSON.stringify(tsconfig, undefined, 2));
+  await writeJsonFile(path, tsconfig, options);
 }
 
 export async function resolvePackageJSON(

src/utils.ts

@@ -1,5 +1,7 @@
-import { statSync } from "node:fs";
+import { statSync, existsSync } from "node:fs";
+import { readFile, writeFile } from "node:fs/promises";
 import { join, resolve } from "pathe";
+import detectIndent from "detect-indent";
 
 export interface FindFileOptions {
   /**
@@ -30,6 +32,16 @@ export interface FindFileOptions {
 /** @deprecated */
 export type FindNearestFileOptions = FindFileOptions;
 
+export type WriteOptions = {
+  indent?: number | string;
+  newline?: boolean | string;
+};
+
+export type ResolvedWriteOptions = {
+  indent: number | string;
+  newline: string;
+};
+
 const defaultFindOptions: Required<FindFileOptions> = {
   startingFrom: ".",
   rootPattern: /^node_modules$/,
@@ -97,3 +109,35 @@ export function findFarthestFile(
 ): Promise<string> {
   return findFile(filename, { ..._options, reverse: true });
 }
+
+export async function resolveWriteOptions(
+  path: string,
+  options: WriteOptions
+): Promise<ResolvedWriteOptions> {
+  const file = existsSync(path) ? await readFile(path, "utf8") : undefined;
+  const indent = options.indent ?? (file ? detectIndent(file).indent : 2);
+  const newline =
+    options.newline === true
+      ? "\n"
+      : options.newline === false
+      ? ""
+      : options.newline ?? (file ? (file.endsWith("\n") ? "\n" : "") : "\n");
+
+  return {
+    indent,
+    newline,
+  };
+}
+
+export async function writeJsonFile(
+  path: string,
+  value: any,
+  options: WriteOptions = {}
+): Promise<void> {
+  const resolvedOpts = await resolveWriteOptions(path, options);
+
+  let content = JSON.stringify(value, undefined, resolvedOpts.indent);
+  content += resolvedOpts.newline;
+
+  await writeFile(path, content);
+}

test/index.test.ts

@@ -1,7 +1,9 @@
 import { fileURLToPath } from "node:url";
+import { readFile } from "node:fs/promises";
 import { dirname, resolve } from "pathe";
 import { describe, expect, it } from "vitest";
 import { expectTypeOf } from "expect-type";
+import detectIndent from "detect-indent";
 import {
   readPackageJSON,
   readTSConfig,
@@ -90,6 +92,36 @@ describe("package.json", () => {
       "string"
     );
   });
+
+  it("write package.json with tab indent", async () => {
+    const path = rFixture("package.json.tab.tmp");
+    const indent = "\t";
+    await writePackageJSON(path, { version: "1.0.0" }, { indent });
+    const file = await readFile(path, "utf8");
+    expect(detectIndent(file).indent).toBe(indent);
+  });
+
+  it("write package.json with 4 space indent", async () => {
+    const path = rFixture("package.json.3space.tmp");
+    const indent = 4;
+    await writePackageJSON(path, { version: "1.0.0" }, { indent });
+    const file = await readFile(path, "utf8");
+    expect(detectIndent(file).indent).toBe("    ");
+  });
+
+  it("write package.json with newline", async () => {
+    const path = rFixture("package.json.newline.tmp");
+    await writePackageJSON(path, { version: "1.0.0" }, { newline: true });
+    const file = await readFile(path, "utf8");
+    expect(file.endsWith("\n")).toBe(true);
+  });
+
+  it("write package.json with no newline", async () => {
+    const path = rFixture("package.json.no-newline.tmp");
+    await writePackageJSON(path, { version: "1.0.0" }, { newline: false });
+    const file = await readFile(path, "utf8");
+    expect(file.endsWith("\n")).toBe(false);
+  });
 });
 
 describe("tsconfig.json", () => {