From 7a19ce3b5c42e78cd9217c6a4b2ecd51cee3bdcb Mon Sep 17 00:00:00 2001
From: Alexey Shlyk <shlyk@live.ru>
Date: Sat, 15 May 2021 15:05:52 +0300
Subject: [PATCH 1/9] feat: check postcss versions to avoid using PostCSS 7

---
 src/index.js                           | 17 +++++++++++++++++
 src/utils.js                           |  8 ++++++++
 test/__snapshots__/loader.test.js.snap |  8 ++++++++
 test/loader.test.js                    | 16 ++++++++++++++++
 4 files changed, 49 insertions(+)

diff --git a/src/index.js b/src/index.js
index a27bc0e0..61276d73 100644
--- a/src/index.js
+++ b/src/index.js
@@ -11,6 +11,7 @@ import {
   exec,
   normalizeSourceMap,
   normalizeSourceMapAfterPostcss,
+  readPackageJson,
 } from "./utils";
 
 /**
@@ -27,6 +28,8 @@ import {
  * @return {callback} callback Result
  */
 
+let isCheckedPostCSSVersion = false;
+
 export default async function loader(content, sourceMap, meta) {
   const options = this.getOptions(schema);
   const callback = this.async();
@@ -38,6 +41,20 @@ export default async function loader(content, sourceMap, meta) {
 
   const postcssFactory = options.implementation || postcss;
 
+  // Check postcss versions to avoid using PostCSS 7
+  if (!isCheckedPostCSSVersion && postcss().version.startsWith("7.")) {
+    isCheckedPostCSSVersion = true;
+    const pkg = readPackageJson();
+    if (!pkg.dependencies.postcss && !pkg.devDependencies.postcss) {
+      callback(
+        new Error(
+          "Add postcss as project dependency. postcss is not a peer dependency for postcss-loader. Use `npm install postcss` or `yarn add postcss`"
+        )
+      );
+      return;
+    }
+  }
+
   let loadedConfig;
 
   if (configOption) {
diff --git a/src/utils.js b/src/utils.js
index 4ca898ab..a1ef5288 100644
--- a/src/utils.js
+++ b/src/utils.js
@@ -1,4 +1,5 @@
 import path from "path";
+import fs from "fs";
 import Module from "module";
 
 import { klona } from "klona/full";
@@ -408,10 +409,17 @@ function normalizeSourceMapAfterPostcss(map, resourceContext) {
   return newMap;
 }
 
+function readPackageJson() {
+  return JSON.parse(
+    fs.readFileSync(path.resolve(process.cwd(), "package.json"), "utf8")
+  );
+}
+
 export {
   loadConfig,
   getPostcssOptions,
   exec,
   normalizeSourceMap,
   normalizeSourceMapAfterPostcss,
+  readPackageJson,
 };
diff --git a/test/__snapshots__/loader.test.js.snap b/test/__snapshots__/loader.test.js.snap
index e26bce3e..4ada1e7e 100644
--- a/test/__snapshots__/loader.test.js.snap
+++ b/test/__snapshots__/loader.test.js.snap
@@ -161,6 +161,14 @@ exports[`loader should reuse PostCSS AST: errors 1`] = `Array []`;
 
 exports[`loader should reuse PostCSS AST: warnings 1`] = `Array []`;
 
+exports[`loader should throw an error if postcss version is not explicitly specified: errors 1`] = `
+Array [
+  "ModuleBuildError: Module build failed (from \`replaced original path\`):
+Error: Add postcss as project dependency. postcss is not a peer dependency for postcss-loader. Use \`npm install postcss\` or \`yarn add postcss\`
+    at Object.loader (/src/index.js:49:16)",
+]
+`;
+
 exports[`loader should throw an error on invalid syntax: errors 1`] = `
 Array [
   "ModuleBuildError: Module build failed (from \`replaced original path\`):
diff --git a/test/loader.test.js b/test/loader.test.js
index 4cd9b196..77712a0f 100644
--- a/test/loader.test.js
+++ b/test/loader.test.js
@@ -197,4 +197,20 @@ describe("loader", () => {
     expect(getWarnings(stats)).toMatchSnapshot("warnings");
     expect(getErrors(stats)).toMatchSnapshot("errors");
   });
+
+  it("should throw an error if postcss version is not explicitly specified", async () => {
+    jest.mock("../src/utils", () => {
+      return {
+        readPackageJson: () => {
+          return { dependencies: {}, devDependencies: {} };
+        },
+      };
+    });
+    jest.mock("postcss", () => () => {
+      return { version: "7." };
+    });
+    const compiler = getCompiler("./css/index.js");
+    const stats = await compile(compiler);
+    expect(getErrors(stats)).toMatchSnapshot("errors");
+  });
 });

From e33c5d62b04eaa1e2332ae0768e034832aacd85f Mon Sep 17 00:00:00 2001
From: Alexey Shlyk <shlyk@live.ru>
Date: Sat, 15 May 2021 15:40:44 +0300
Subject: [PATCH 2/9] feat: added a flag which is responsible for having an
 explicit dependency on PostCSS

---
 src/index.js | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/index.js b/src/index.js
index 61276d73..53805229 100644
--- a/src/index.js
+++ b/src/index.js
@@ -28,7 +28,7 @@ import {
  * @return {callback} callback Result
  */
 
-let isCheckedPostCSSVersion = false;
+let hasExplicitDependencyOnPostCSS = false;
 
 export default async function loader(content, sourceMap, meta) {
   const options = this.getOptions(schema);
@@ -42,8 +42,7 @@ export default async function loader(content, sourceMap, meta) {
   const postcssFactory = options.implementation || postcss;
 
   // Check postcss versions to avoid using PostCSS 7
-  if (!isCheckedPostCSSVersion && postcss().version.startsWith("7.")) {
-    isCheckedPostCSSVersion = true;
+  if (!hasExplicitDependencyOnPostCSS && postcss().version.startsWith("7.")) {
     const pkg = readPackageJson();
     if (!pkg.dependencies.postcss && !pkg.devDependencies.postcss) {
       callback(
@@ -51,7 +50,8 @@ export default async function loader(content, sourceMap, meta) {
           "Add postcss as project dependency. postcss is not a peer dependency for postcss-loader. Use `npm install postcss` or `yarn add postcss`"
         )
       );
-      return;
+    } else {
+      hasExplicitDependencyOnPostCSS = true;
     }
   }
 

From aae55dfe0a2b9679e62c88fd91e3b5d9b29f7e4f Mon Sep 17 00:00:00 2001
From: Alexey Shlyk <shlyk@live.ru>
Date: Sat, 15 May 2021 16:28:22 +0300
Subject: [PATCH 3/9] feat: use readFileSync function from Webpack

---
 src/index.js                           |   7 +-
 src/utils.js                           |   7 +-
 test/__snapshots__/loader.test.js.snap | 227 +------------------------
 3 files changed, 10 insertions(+), 231 deletions(-)

diff --git a/src/index.js b/src/index.js
index 53805229..32f59976 100644
--- a/src/index.js
+++ b/src/index.js
@@ -43,16 +43,17 @@ export default async function loader(content, sourceMap, meta) {
 
   // Check postcss versions to avoid using PostCSS 7
   if (!hasExplicitDependencyOnPostCSS && postcss().version.startsWith("7.")) {
-    const pkg = readPackageJson();
+    // For caching reasons, we use the Webpack readFileSync function, not the function from `fs` module.
+    const pkg = readPackageJson(this.fs.readFileSync);
     if (!pkg.dependencies.postcss && !pkg.devDependencies.postcss) {
       callback(
         new Error(
           "Add postcss as project dependency. postcss is not a peer dependency for postcss-loader. Use `npm install postcss` or `yarn add postcss`"
         )
       );
-    } else {
-      hasExplicitDependencyOnPostCSS = true;
+      return;
     }
+    hasExplicitDependencyOnPostCSS = true;
   }
 
   let loadedConfig;
diff --git a/src/utils.js b/src/utils.js
index a1ef5288..62f1cce3 100644
--- a/src/utils.js
+++ b/src/utils.js
@@ -409,9 +409,12 @@ function normalizeSourceMapAfterPostcss(map, resourceContext) {
   return newMap;
 }
 
-function readPackageJson() {
+function readPackageJson(readFileSync) {
   return JSON.parse(
-    fs.readFileSync(path.resolve(process.cwd(), "package.json"), "utf8")
+    (readFileSync || fs.readFileSync)(
+      path.resolve(process.cwd(), "package.json"),
+      "utf8"
+    )
   );
 }
 
diff --git a/test/__snapshots__/loader.test.js.snap b/test/__snapshots__/loader.test.js.snap
index 4ada1e7e..0e9f41f5 100644
--- a/test/__snapshots__/loader.test.js.snap
+++ b/test/__snapshots__/loader.test.js.snap
@@ -1,171 +1,10 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`loader should emit asset using the "messages" API: errors 1`] = `Array []`;
-
-exports[`loader should emit asset using the "messages" API: warnings 1`] = `Array []`;
-
-exports[`loader should emit warning using the "messages" API: css 1`] = `
-"a {
-  color: black;
-}
-
-a {
-  color: red;
-}
-
-a {
-  color: green;
-}
-
-a {
-  color: blue;
-}
-
-.class {
-  -x-border-color: blue blue *;
-  -x-color: * #fafafa;
-}
-
-.class-foo {
-  -z-border-color: blue blue *;
-  -z-color: * #fafafa;
-}
-
-.phone {
-  &_title {
-    width: 500px;
-
-    @media (max-width: 500px) {
-      width: auto;
-    }
-
-    body.is_dark & {
-      color: white;
-    }
-  }
-
-  img {
-    display: block;
-  }
-}
-"
-`;
-
-exports[`loader should emit warning using the "messages" API: errors 1`] = `Array []`;
-
-exports[`loader should emit warning using the "messages" API: warnings 1`] = `
-Array [
-  "ModuleWarning: Module Warning (from \`replaced original path\`):
-Warning
-
-(10:3) postcss-plugin: <Message>",
-  "ModuleWarning: Module Warning (from \`replaced original path\`):
-Warning
-
-(14:3) postcss-plugin: <Message>",
-  "ModuleWarning: Module Warning (from \`replaced original path\`):
-Warning
-
-(18:3) postcss-plugin: <Message>",
-  "ModuleWarning: Module Warning (from \`replaced original path\`):
-Warning
-
-(19:3) postcss-plugin: <Message>",
-  "ModuleWarning: Module Warning (from \`replaced original path\`):
-Warning
-
-(23:3) postcss-plugin: <Message>",
-  "ModuleWarning: Module Warning (from \`replaced original path\`):
-Warning
-
-(24:3) postcss-plugin: <Message>",
-  "ModuleWarning: Module Warning (from \`replaced original path\`):
-Warning
-
-(29:5) postcss-plugin: <Message>",
-  "ModuleWarning: Module Warning (from \`replaced original path\`):
-Warning
-
-(2:3) postcss-plugin: <Message>",
-  "ModuleWarning: Module Warning (from \`replaced original path\`):
-Warning
-
-(32:7) postcss-plugin: <Message>",
-  "ModuleWarning: Module Warning (from \`replaced original path\`):
-Warning
-
-(36:7) postcss-plugin: <Message>",
-  "ModuleWarning: Module Warning (from \`replaced original path\`):
-Warning
-
-(41:5) postcss-plugin: <Message>",
-  "ModuleWarning: Module Warning (from \`replaced original path\`):
-Warning
-
-(6:3) postcss-plugin: <Message>",
-]
-`;
-
-exports[`loader should register dependencies using the "messages" API: errors 1`] = `Array []`;
-
-exports[`loader should register dependencies using the "messages" API: warnings 1`] = `Array []`;
-
-exports[`loader should reuse PostCSS AST: css 1`] = `
-"a {
-  color: black;
-}
-
-a {
-  color: red;
-}
-
-a {
-  color: green;
-}
-
-a {
-  color: blue;
-}
-
-.class {
-  -x-border-color: blue blue *;
-  -x-color: * #fafafa;
-}
-
-.class-foo {
-  -z-border-color: blue blue *;
-  -z-color: * #fafafa;
-}
-
-.phone {
-  &_title {
-    width: 500px;
-
-    @media (max-width: 500px) {
-      width: auto;
-    }
-
-    body.is_dark & {
-      color: white;
-    }
-  }
-
-  img {
-    display: block;
-  }
-}
-"
-`;
-
-exports[`loader should reuse PostCSS AST: errors 1`] = `Array []`;
-
-exports[`loader should reuse PostCSS AST: warnings 1`] = `Array []`;
-
 exports[`loader should throw an error if postcss version is not explicitly specified: errors 1`] = `
 Array [
   "ModuleBuildError: Module build failed (from \`replaced original path\`):
 Error: Add postcss as project dependency. postcss is not a peer dependency for postcss-loader. Use \`npm install postcss\` or \`yarn add postcss\`
-    at Object.loader (/src/index.js:49:16)",
+    at Object.loader (/src/index.js:50:9)",
 ]
 `;
 
@@ -183,67 +22,3 @@ SyntaxError
 ",
 ]
 `;
-
-exports[`loader should throw an error on invalid syntax: warnings 1`] = `Array []`;
-
-exports[`loader should work with SugarSS: css 1`] = `
-"a {
-  color: black
-}
-"
-`;
-
-exports[`loader should work with SugarSS: errors 1`] = `Array []`;
-
-exports[`loader should work with SugarSS: warnings 1`] = `Array []`;
-
-exports[`loader should work: css 1`] = `
-"a {
-  color: black;
-}
-
-a {
-  color: red;
-}
-
-a {
-  color: green;
-}
-
-a {
-  color: blue;
-}
-
-.class {
-  -x-border-color: blue blue *;
-  -x-color: * #fafafa;
-}
-
-.class-foo {
-  -z-border-color: blue blue *;
-  -z-color: * #fafafa;
-}
-
-.phone {
-  &_title {
-    width: 500px;
-
-    @media (max-width: 500px) {
-      width: auto;
-    }
-
-    body.is_dark & {
-      color: white;
-    }
-  }
-
-  img {
-    display: block;
-  }
-}
-"
-`;
-
-exports[`loader should work: errors 1`] = `Array []`;
-
-exports[`loader should work: warnings 1`] = `Array []`;

From ba3446be2de1fadf5b3beae7bfd4cca32483b0b2 Mon Sep 17 00:00:00 2001
From: Alexey Shlyk <shlyk@live.ru>
Date: Sat, 15 May 2021 16:30:27 +0300
Subject: [PATCH 4/9] feat: reverted snapshots

---
 test/__snapshots__/loader.test.js.snap | 227 ++++++++++++++++++++++++-
 1 file changed, 223 insertions(+), 4 deletions(-)

diff --git a/test/__snapshots__/loader.test.js.snap b/test/__snapshots__/loader.test.js.snap
index 0e9f41f5..8eb0481f 100644
--- a/test/__snapshots__/loader.test.js.snap
+++ b/test/__snapshots__/loader.test.js.snap
@@ -1,13 +1,168 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`loader should throw an error if postcss version is not explicitly specified: errors 1`] = `
+exports[`loader should emit asset using the "messages" API: errors 1`] = `Array []`;
+
+exports[`loader should emit asset using the "messages" API: warnings 1`] = `Array []`;
+
+exports[`loader should emit warning using the "messages" API: css 1`] = `
+"a {
+  color: black;
+}
+
+a {
+  color: red;
+}
+
+a {
+  color: green;
+}
+
+a {
+  color: blue;
+}
+
+.class {
+  -x-border-color: blue blue *;
+  -x-color: * #fafafa;
+}
+
+.class-foo {
+  -z-border-color: blue blue *;
+  -z-color: * #fafafa;
+}
+
+.phone {
+  &_title {
+    width: 500px;
+
+    @media (max-width: 500px) {
+      width: auto;
+    }
+
+    body.is_dark & {
+      color: white;
+    }
+  }
+
+  img {
+    display: block;
+  }
+}
+"
+`;
+
+exports[`loader should emit warning using the "messages" API: errors 1`] = `Array []`;
+
+exports[`loader should emit warning using the "messages" API: warnings 1`] = `
 Array [
-  "ModuleBuildError: Module build failed (from \`replaced original path\`):
-Error: Add postcss as project dependency. postcss is not a peer dependency for postcss-loader. Use \`npm install postcss\` or \`yarn add postcss\`
-    at Object.loader (/src/index.js:50:9)",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(10:3) postcss-plugin: <Message>",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(14:3) postcss-plugin: <Message>",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(18:3) postcss-plugin: <Message>",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(19:3) postcss-plugin: <Message>",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(23:3) postcss-plugin: <Message>",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(24:3) postcss-plugin: <Message>",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(29:5) postcss-plugin: <Message>",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(2:3) postcss-plugin: <Message>",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(32:7) postcss-plugin: <Message>",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(36:7) postcss-plugin: <Message>",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(41:5) postcss-plugin: <Message>",
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+Warning
+
+(6:3) postcss-plugin: <Message>",
 ]
 `;
 
+exports[`loader should register dependencies using the "messages" API: errors 1`] = `Array []`;
+
+exports[`loader should register dependencies using the "messages" API: warnings 1`] = `Array []`;
+
+exports[`loader should reuse PostCSS AST: css 1`] = `
+"a {
+  color: black;
+}
+
+a {
+  color: red;
+}
+
+a {
+  color: green;
+}
+
+a {
+  color: blue;
+}
+
+.class {
+  -x-border-color: blue blue *;
+  -x-color: * #fafafa;
+}
+
+.class-foo {
+  -z-border-color: blue blue *;
+  -z-color: * #fafafa;
+}
+
+.phone {
+  &_title {
+    width: 500px;
+
+    @media (max-width: 500px) {
+      width: auto;
+    }
+
+    body.is_dark & {
+      color: white;
+    }
+  }
+
+  img {
+    display: block;
+  }
+}
+"
+`;
+
+exports[`loader should reuse PostCSS AST: errors 1`] = `Array []`;
+
+exports[`loader should reuse PostCSS AST: warnings 1`] = `Array []`;
+
+exports[`loader should throw an error if postcss version is not explicitly specified: errors 1`] = `Array []`;
+
 exports[`loader should throw an error on invalid syntax: errors 1`] = `
 Array [
   "ModuleBuildError: Module build failed (from \`replaced original path\`):
@@ -22,3 +177,67 @@ SyntaxError
 ",
 ]
 `;
+
+exports[`loader should throw an error on invalid syntax: warnings 1`] = `Array []`;
+
+exports[`loader should work with SugarSS: css 1`] = `
+"a {
+  color: black
+}
+"
+`;
+
+exports[`loader should work with SugarSS: errors 1`] = `Array []`;
+
+exports[`loader should work with SugarSS: warnings 1`] = `Array []`;
+
+exports[`loader should work: css 1`] = `
+"a {
+  color: black;
+}
+
+a {
+  color: red;
+}
+
+a {
+  color: green;
+}
+
+a {
+  color: blue;
+}
+
+.class {
+  -x-border-color: blue blue *;
+  -x-color: * #fafafa;
+}
+
+.class-foo {
+  -z-border-color: blue blue *;
+  -z-color: * #fafafa;
+}
+
+.phone {
+  &_title {
+    width: 500px;
+
+    @media (max-width: 500px) {
+      width: auto;
+    }
+
+    body.is_dark & {
+      color: white;
+    }
+  }
+
+  img {
+    display: block;
+  }
+}
+"
+`;
+
+exports[`loader should work: errors 1`] = `Array []`;
+
+exports[`loader should work: warnings 1`] = `Array []`;

From a4a762577b7ea13dceb17b45b60f56a00fcca02d Mon Sep 17 00:00:00 2001
From: Alexey Shlyk <ashlyk@iponweb.net>
Date: Sat, 15 May 2021 20:52:55 +0300
Subject: [PATCH 5/9] feat: print warning when the loader is failed

---
 src/index.js                           | 36 +++++++++++++-------------
 test/__snapshots__/loader.test.js.snap |  9 +++++--
 test/loader.test.js                    | 29 ++++++++++++---------
 3 files changed, 42 insertions(+), 32 deletions(-)

diff --git a/src/index.js b/src/index.js
index 32f59976..ba6f6702 100644
--- a/src/index.js
+++ b/src/index.js
@@ -14,6 +14,8 @@ import {
   readPackageJson,
 } from "./utils";
 
+let hasExplicitDependencyOnPostCSS = false;
+
 /**
  * **PostCSS Loader**
  *
@@ -27,9 +29,6 @@ import {
  *
  * @return {callback} callback Result
  */
-
-let hasExplicitDependencyOnPostCSS = false;
-
 export default async function loader(content, sourceMap, meta) {
   const options = this.getOptions(schema);
   const callback = this.async();
@@ -41,21 +40,6 @@ export default async function loader(content, sourceMap, meta) {
 
   const postcssFactory = options.implementation || postcss;
 
-  // Check postcss versions to avoid using PostCSS 7
-  if (!hasExplicitDependencyOnPostCSS && postcss().version.startsWith("7.")) {
-    // For caching reasons, we use the Webpack readFileSync function, not the function from `fs` module.
-    const pkg = readPackageJson(this.fs.readFileSync);
-    if (!pkg.dependencies.postcss && !pkg.devDependencies.postcss) {
-      callback(
-        new Error(
-          "Add postcss as project dependency. postcss is not a peer dependency for postcss-loader. Use `npm install postcss` or `yarn add postcss`"
-        )
-      );
-      return;
-    }
-    hasExplicitDependencyOnPostCSS = true;
-  }
-
   let loadedConfig;
 
   if (configOption) {
@@ -120,6 +104,22 @@ export default async function loader(content, sourceMap, meta) {
       processOptions
     );
   } catch (error) {
+    // Check postcss versions to avoid using PostCSS 7.
+    if (
+      !hasExplicitDependencyOnPostCSS &&
+      postcssFactory().version.startsWith("7.")
+    ) {
+      // For caching reasons, we use the readFileSync function from the context, not the function from the `fs` module.
+      const pkg = readPackageJson(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. Use `npm install postcss` or `yarn add postcss`"
+        );
+      } else {
+        hasExplicitDependencyOnPostCSS = true;
+      }
+    }
+
     if (error.file) {
       this.addDependency(error.file);
     }
diff --git a/test/__snapshots__/loader.test.js.snap b/test/__snapshots__/loader.test.js.snap
index 8eb0481f..a6bfb504 100644
--- a/test/__snapshots__/loader.test.js.snap
+++ b/test/__snapshots__/loader.test.js.snap
@@ -1,5 +1,12 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`loader should emit a warning if postcss version is not explicitly specified when the loader is failed: warnings 1`] = `
+Array [
+  "ModuleWarning: Module Warning (from \`replaced original path\`):
+(Emitted value instead of an instance of Error) Add postcss as project dependency. postcss is not a peer dependency for postcss-loader. Use \`npm install postcss\` or \`yarn add postcss\`",
+]
+`;
+
 exports[`loader should emit asset using the "messages" API: errors 1`] = `Array []`;
 
 exports[`loader should emit asset using the "messages" API: warnings 1`] = `Array []`;
@@ -161,8 +168,6 @@ exports[`loader should reuse PostCSS AST: errors 1`] = `Array []`;
 
 exports[`loader should reuse PostCSS AST: warnings 1`] = `Array []`;
 
-exports[`loader should throw an error if postcss version is not explicitly specified: errors 1`] = `Array []`;
-
 exports[`loader should throw an error on invalid syntax: errors 1`] = `
 Array [
   "ModuleBuildError: Module build failed (from \`replaced original path\`):
diff --git a/test/loader.test.js b/test/loader.test.js
index 77712a0f..f63e1fc0 100644
--- a/test/loader.test.js
+++ b/test/loader.test.js
@@ -2,6 +2,9 @@ import path from "path";
 
 import postcss from "postcss";
 
+// eslint-disable-next-line import/no-namespace
+import * as utils from "../src/utils";
+
 import {
   compile,
   getCompiler,
@@ -198,19 +201,21 @@ describe("loader", () => {
     expect(getErrors(stats)).toMatchSnapshot("errors");
   });
 
-  it("should throw an error if postcss version is not explicitly specified", async () => {
-    jest.mock("../src/utils", () => {
-      return {
-        readPackageJson: () => {
-          return { dependencies: {}, devDependencies: {} };
-        },
-      };
-    });
-    jest.mock("postcss", () => () => {
-      return { version: "7." };
+  it("should emit a warning if postcss version is not explicitly specified when the loader is failed", async () => {
+    jest
+      .spyOn(utils, "readPackageJson")
+      .mockReturnValue({ dependencies: {}, devDependencies: {} });
+    const spy = jest.fn(postcss);
+    const compiler = getCompiler("./css/index.js", {
+      implementation: (...args) => {
+        const result = spy(...args);
+        result.version = "7.0.0";
+        result.process = () =>
+          Promise.reject(new Error("Something went wrong."));
+        return result;
+      },
     });
-    const compiler = getCompiler("./css/index.js");
     const stats = await compile(compiler);
-    expect(getErrors(stats)).toMatchSnapshot("errors");
+    expect(getWarnings(stats)).toMatchSnapshot("warnings");
   });
 });

From 4fd7cde62a87460078998d7e66e64f1f94558788 Mon Sep 17 00:00:00 2001
From: Alexey Shlyk <shlyk@live.ru>
Date: Sat, 15 May 2021 21:37:39 +0300
Subject: [PATCH 6/9] feat: there should be no warnings if the version is
 defined in package.json

---
 test/__snapshots__/loader.test.js.snap |  2 +-
 test/loader.test.js                    | 30 ++++++++++++++++++++------
 2 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/test/__snapshots__/loader.test.js.snap b/test/__snapshots__/loader.test.js.snap
index a6bfb504..75379459 100644
--- a/test/__snapshots__/loader.test.js.snap
+++ b/test/__snapshots__/loader.test.js.snap
@@ -1,6 +1,6 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`loader should emit a warning if postcss version is not explicitly specified when the loader is failed: warnings 1`] = `
+exports[`check postcss versions to avoid using PostCSS 7 should emit a warning if postcss version is not explicitly specified when the loader is failed: warnings 1`] = `
 Array [
   "ModuleWarning: Module Warning (from \`replaced original path\`):
 (Emitted value instead of an instance of Error) Add postcss as project dependency. postcss is not a peer dependency for postcss-loader. Use \`npm install postcss\` or \`yarn add postcss\`",
diff --git a/test/loader.test.js b/test/loader.test.js
index f63e1fc0..de7930d1 100644
--- a/test/loader.test.js
+++ b/test/loader.test.js
@@ -200,22 +200,38 @@ describe("loader", () => {
     expect(getWarnings(stats)).toMatchSnapshot("warnings");
     expect(getErrors(stats)).toMatchSnapshot("errors");
   });
+});
 
-  it("should emit a warning if postcss version is not explicitly specified when the loader is failed", async () => {
-    jest
-      .spyOn(utils, "readPackageJson")
-      .mockReturnValue({ dependencies: {}, devDependencies: {} });
-    const spy = jest.fn(postcss);
+describe("check postcss versions to avoid using PostCSS 7", async () => {
+  async function getStats() {
     const compiler = getCompiler("./css/index.js", {
       implementation: (...args) => {
-        const result = spy(...args);
+        const result = postcss(...args);
         result.version = "7.0.0";
         result.process = () =>
           Promise.reject(new Error("Something went wrong."));
         return result;
       },
     });
-    const stats = await compile(compiler);
+    return compile(compiler);
+  }
+
+  it("should emit a warning if postcss version is not explicitly specified when the loader is failed", async () => {
+    jest
+      .spyOn(utils, "readPackageJson")
+      .mockReturnValue({ dependencies: {}, devDependencies: {} });
+    const stats = await getStats();
     expect(getWarnings(stats)).toMatchSnapshot("warnings");
   });
+
+  it("disable checking when postcss version is explicitly defined", async () => {
+    jest
+      .spyOn(utils, "readPackageJson")
+      .mockReturnValue({
+        dependencies: {},
+        devDependencies: { postcss: "8.0.0" },
+      });
+    const stats = await getStats();
+    expect(stats.compilation.warnings.length).toBe(0);
+  });
 });

From 216f462ea114e226387b151646eb8be9bb7e943e Mon Sep 17 00:00:00 2001
From: Alexey Shlyk <shlyk@live.ru>
Date: Sun, 16 May 2021 11:18:13 +0300
Subject: [PATCH 7/9] feat: check the package.json file before the main check

---
 src/index.js        | 16 ++++++++++++----
 src/utils.js        | 20 ++++++++++++--------
 test/loader.test.js | 22 +++++++++++++++-------
 3 files changed, 39 insertions(+), 19 deletions(-)

diff --git a/src/index.js b/src/index.js
index ba6f6702..52cc295a 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,3 +1,5 @@
+import path from "path";
+
 import postcss from "postcss";
 import { satisfies } from "semver";
 import postcssPackage from "postcss/package.json";
@@ -11,11 +13,14 @@ import {
   exec,
   normalizeSourceMap,
   normalizeSourceMapAfterPostcss,
-  readPackageJson,
+  parsePackageJson,
+  isFileExists,
 } from "./utils";
 
 let hasExplicitDependencyOnPostCSS = false;
 
+const PACKAGE_JSON_PATH = path.resolve(process.cwd(), "package.json");
+
 /**
  * **PostCSS Loader**
  *
@@ -105,15 +110,18 @@ export default async function loader(content, sourceMap, meta) {
     );
   } catch (error) {
     // 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 &&
+      isFileExists(PACKAGE_JSON_PATH, this.fs.existsSync) &&
       postcssFactory().version.startsWith("7.")
     ) {
-      // For caching reasons, we use the readFileSync function from the context, not the function from the `fs` module.
-      const pkg = readPackageJson(this.fs.readFileSync);
+      const pkg = parsePackageJson(PACKAGE_JSON_PATH, 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. Use `npm install postcss` or `yarn add postcss`"
+          "Add postcss as project dependency. postcss is not a peer dependency for postcss-loader. " +
+            "Use `npm install postcss` or `yarn add postcss`"
         );
       } else {
         hasExplicitDependencyOnPostCSS = true;
diff --git a/src/utils.js b/src/utils.js
index 62f1cce3..ac294734 100644
--- a/src/utils.js
+++ b/src/utils.js
@@ -409,13 +409,16 @@ function normalizeSourceMapAfterPostcss(map, resourceContext) {
   return newMap;
 }
 
-function readPackageJson(readFileSync) {
-  return JSON.parse(
-    (readFileSync || fs.readFileSync)(
-      path.resolve(process.cwd(), "package.json"),
-      "utf8"
-    )
-  );
+function isFileExists(filePath, existsSync = fs.existsSync) {
+  try {
+    return existsSync(filePath);
+  } catch (error) {
+    return false;
+  }
+}
+
+function parsePackageJson(filePath, readFileSync = fs.readFileSync) {
+  return JSON.parse(readFileSync(filePath, "utf8"));
 }
 
 export {
@@ -424,5 +427,6 @@ export {
   exec,
   normalizeSourceMap,
   normalizeSourceMapAfterPostcss,
-  readPackageJson,
+  parsePackageJson,
+  isFileExists,
 };
diff --git a/test/loader.test.js b/test/loader.test.js
index de7930d1..54e3e4f7 100644
--- a/test/loader.test.js
+++ b/test/loader.test.js
@@ -218,19 +218,27 @@ describe("check postcss versions to avoid using PostCSS 7", async () => {
 
   it("should emit a warning if postcss version is not explicitly specified when the loader is failed", async () => {
     jest
-      .spyOn(utils, "readPackageJson")
+      .spyOn(utils, "parsePackageJson")
       .mockReturnValue({ dependencies: {}, devDependencies: {} });
     const stats = await getStats();
     expect(getWarnings(stats)).toMatchSnapshot("warnings");
   });
 
   it("disable checking when postcss version is explicitly defined", async () => {
-    jest
-      .spyOn(utils, "readPackageJson")
-      .mockReturnValue({
-        dependencies: {},
-        devDependencies: { postcss: "8.0.0" },
-      });
+    jest.spyOn(utils, "parsePackageJson").mockReturnValue({
+      dependencies: {},
+      devDependencies: { postcss: "8.0.0" },
+    });
+    const stats = await getStats();
+    expect(stats.compilation.warnings.length).toBe(0);
+  });
+
+  it("disable checking when package.json doesn't exist", async () => {
+    jest.spyOn(utils, "isFileExists").mockReturnValue(false);
+    jest.spyOn(utils, "parsePackageJson").mockReturnValue({
+      dependencies: {},
+      devDependencies: { postcss: "8.0.0" },
+    });
     const stats = await getStats();
     expect(stats.compilation.warnings.length).toBe(0);
   });

From eac5f85dd7b578b7d6dbe67b38af8c5f6fc8ea32 Mon Sep 17 00:00:00 2001
From: Alexey Shlyk <shlyk@live.ru>
Date: Mon, 17 May 2021 08:57:45 +0300
Subject: [PATCH 8/9] feat: removed unnecessary default values in utils
 functions

---
 src/index.js | 4 ++--
 src/utils.js | 7 +++----
 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/src/index.js b/src/index.js
index 52cc295a..bcad4f12 100644
--- a/src/index.js
+++ b/src/index.js
@@ -114,8 +114,8 @@ export default async function loader(content, sourceMap, meta) {
     // not the functions from the `fs` module.
     if (
       !hasExplicitDependencyOnPostCSS &&
-      isFileExists(PACKAGE_JSON_PATH, this.fs.existsSync) &&
-      postcssFactory().version.startsWith("7.")
+      postcssFactory().version.startsWith("7.") &&
+      isFileExists(PACKAGE_JSON_PATH, this.fs.statSync)
     ) {
       const pkg = parsePackageJson(PACKAGE_JSON_PATH, this.fs.readFileSync);
       if (!pkg.dependencies.postcss && !pkg.devDependencies.postcss) {
diff --git a/src/utils.js b/src/utils.js
index ac294734..ab710877 100644
--- a/src/utils.js
+++ b/src/utils.js
@@ -1,5 +1,4 @@
 import path from "path";
-import fs from "fs";
 import Module from "module";
 
 import { klona } from "klona/full";
@@ -409,15 +408,15 @@ function normalizeSourceMapAfterPostcss(map, resourceContext) {
   return newMap;
 }
 
-function isFileExists(filePath, existsSync = fs.existsSync) {
+function isFileExists(filePath, statSync) {
   try {
-    return existsSync(filePath);
+    return statSync(filePath).isFile();
   } catch (error) {
     return false;
   }
 }
 
-function parsePackageJson(filePath, readFileSync = fs.readFileSync) {
+function parsePackageJson(filePath, readFileSync) {
   return JSON.parse(readFileSync(filePath, "utf8"));
 }
 

From 833f56b1d90da0f7528de3681d3852b9f3f40a47 Mon Sep 17 00:00:00 2001
From: Alexey Shlyk <ashlyk@iponweb.net>
Date: Mon, 17 May 2021 18:25:16 +0300
Subject: [PATCH 9/9] feat: search the package.json file in the current and
 parent directories

---
 src/index.js        | 16 +++++++++++-----
 src/utils.js        | 27 ++++++++++++++++++---------
 test/loader.test.js |  6 +++---
 3 files changed, 32 insertions(+), 17 deletions(-)

diff --git a/src/index.js b/src/index.js
index bcad4f12..7c72c08a 100644
--- a/src/index.js
+++ b/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. " +
diff --git a/src/utils.js b/src/utils.js
index ab710877..1c847f5b 100644
--- a/src/utils.js
+++ b/src/utils.js
@@ -408,18 +408,27 @@ 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,
@@ -427,5 +436,5 @@ export {
   normalizeSourceMap,
   normalizeSourceMapAfterPostcss,
   parsePackageJson,
-  isFileExists,
+  findPackageJsonDir,
 };
diff --git a/test/loader.test.js b/test/loader.test.js
index 54e3e4f7..2d218943 100644
--- a/test/loader.test.js
+++ b/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" },