feat: search the package.json file in the current and parent directories

Author: shlykai

src/index.js

@@ -14,12 +14,11 @@ import {
   normalizeSourceMap,
   normalizeSourceMapAfterPostcss,
   parsePackageJson,
-  isFileExists,
+  findPackageJsonDir,
 } from "./utils";
 
 let hasExplicitDependencyOnPostCSS = false;
-
-const PACKAGE_JSON_PATH = path.resolve(process.cwd(), "package.json");
+let packageJsonDir;
 
 /**
  * **PostCSS Loader**
@@ -109,15 +108,22 @@ export default async function loader(content, sourceMap, meta) {
       processOptions
     );
   } catch (error) {
+    // The `findPackageJsonDir` function returns `string` or `null`.
+    // This is used to do for caching, that is, an explicit comparison with `undefined`
+    // is used to make the condition body run once.
+    if (packageJsonDir === undefined) {
+      packageJsonDir = findPackageJsonDir(process.cwd(), this.fs.statSync);
+    }
     // Check postcss versions to avoid using PostCSS 7.
     // For caching reasons, we use the readFileSync and existsSync functions from the context,
     // not the functions from the `fs` module.
     if (
       !hasExplicitDependencyOnPostCSS &&
       postcssFactory().version.startsWith("7.") &&
-      isFileExists(PACKAGE_JSON_PATH, this.fs.statSync)
+      packageJsonDir
     ) {
-      const pkg = parsePackageJson(PACKAGE_JSON_PATH, this.fs.readFileSync);
+      const filePath = path.resolve(packageJsonDir, "package.json");
+      const pkg = parsePackageJson(filePath, this.fs.readFileSync);
       if (!pkg.dependencies.postcss && !pkg.devDependencies.postcss) {
         this.emitWarning(
           "Add postcss as project dependency. postcss is not a peer dependency for postcss-loader. " +

src/utils.js

@@ -408,24 +408,33 @@ function normalizeSourceMapAfterPostcss(map, resourceContext) {
   return newMap;
 }
 
-function isFileExists(filePath, statSync) {
-  try {
-    return statSync(filePath).isFile();
-  } catch (error) {
-    return false;
-  }
-}
-
 function parsePackageJson(filePath, readFileSync) {
   return JSON.parse(readFileSync(filePath, "utf8"));
 }
 
+function findPackageJsonDir(cwd, statSync) {
+  let dir = cwd;
+  for (;;) {
+    try {
+      if (statSync(path.join(dir, "package.json")).isFile()) break;
+      // eslint-disable-next-line no-empty
+    } catch (error) {}
+    const parent = path.dirname(dir);
+    if (dir === parent) {
+      dir = null;
+      break;
+    }
+    dir = parent;
+  }
+  return dir;
+}
+
 export {
   loadConfig,
   getPostcssOptions,
   exec,
   normalizeSourceMap,
   normalizeSourceMapAfterPostcss,
   parsePackageJson,
-  isFileExists,
+  findPackageJsonDir,
 };

test/loader.test.js

@@ -224,7 +224,7 @@ describe("check postcss versions to avoid using PostCSS 7", async () => {
     expect(getWarnings(stats)).toMatchSnapshot("warnings");
   });
 
-  it("disable checking when postcss version is explicitly defined", async () => {
+  it("should not show a warning if postcss version is explicitly defined", async () => {
     jest.spyOn(utils, "parsePackageJson").mockReturnValue({
       dependencies: {},
       devDependencies: { postcss: "8.0.0" },
@@ -233,8 +233,8 @@ describe("check postcss versions to avoid using PostCSS 7", async () => {
     expect(stats.compilation.warnings.length).toBe(0);
   });
 
-  it("disable checking when package.json doesn't exist", async () => {
-    jest.spyOn(utils, "isFileExists").mockReturnValue(false);
+  it("should not show a warning if the package.json file was not found", async () => {
+    jest.spyOn(utils, "findPackageJsonDir").mockReturnValue(null);
     jest.spyOn(utils, "parsePackageJson").mockReturnValue({
       dependencies: {},
       devDependencies: { postcss: "8.0.0" },