Update to postcss-loader 4.0.2.

postcss-loader 4.0 improves compatibility with webpack 5.
4.0.2 release notes also mention improved PostCSS 8 compatibility (see issue #17242)
The ident loader option is not needed anymore.
postcss-loader now detects external postcss configs and merges them with loader options.

packages/next/build/webpack/config/blocks/css/loaders/global.ts

@@ -36,7 +36,6 @@ export function getGlobalCssLoader(
   loaders.push({
     loader: require.resolve('next/dist/compiled/postcss-loader'),
     options: {
-      ident: '__nextjs_postcss',
       plugins: postCssPlugins,
       sourceMap: true,
     },

packages/next/build/webpack/config/blocks/css/loaders/modules.ts

@@ -52,7 +52,6 @@ export function getCssModuleLoader(
   loaders.push({
     loader: require.resolve('next/dist/compiled/postcss-loader'),
     options: {
-      ident: '__nextjs_postcss',
       plugins: postCssPlugins,
       sourceMap: true,
     },

packages/next/package.json

@@ -194,7 +194,7 @@
     "ora": "4.0.4",
     "path-to-regexp": "6.1.0",
     "postcss-flexbugs-fixes": "4.2.1",
-    "postcss-loader": "3.0.0",
+    "postcss-loader": "4.0.2",
     "postcss-preset-env": "6.7.0",
     "raw-body": "2.4.1",
     "recast": "0.18.5",

yarn.lock

@@ -5723,6 +5723,17 @@ cosmiconfig@^6.0.0:
     path-type "^4.0.0"
     yaml "^1.7.2"
 
+cosmiconfig@^7.0.0:
+  version "7.0.0"
+  resolved "https://registry.yarnpkg.com/cosmiconfig/-/cosmiconfig-7.0.0.tgz#ef9b44d773959cae63ddecd122de23853b60f8d3"
+  integrity sha512-pondGvTuVYDk++upghXJabWzL6Kxu6f26ljFw64Swq9v6sQPUL3EUlVDV56diOjpCayKihL6hVe8exIACU4XcA==
+  dependencies:
+    "@types/parse-json" "^4.0.0"
+    import-fresh "^3.2.1"
+    parse-json "^5.0.0"
+    path-type "^4.0.0"
+    yaml "^1.10.0"
+
 coveralls@3.0.3:
   version "3.0.3"
   resolved "https://registry.yarnpkg.com/coveralls/-/coveralls-3.0.3.tgz#83b1c64aea1c6afa69beaf50b55ac1bc4d13e2b8"
@@ -8609,7 +8620,7 @@ import-fresh@^2.0.0:
     caller-path "^2.0.0"
     resolve-from "^3.0.0"
 
-import-fresh@^3.0.0, import-fresh@^3.1.0:
+import-fresh@^3.0.0, import-fresh@^3.1.0, import-fresh@^3.2.1:
   version "3.2.1"
   resolved "https://registry.yarnpkg.com/import-fresh/-/import-fresh-3.2.1.tgz#633ff618506e793af5ac91bf48b72677e15cbe66"
   dependencies:
@@ -12873,6 +12884,17 @@ postcss-loader@3.0.0:
     postcss-load-config "^2.0.0"
     schema-utils "^1.0.0"
 
+postcss-loader@4.0.2:
+  version "4.0.2"
+  resolved "https://registry.yarnpkg.com/postcss-loader/-/postcss-loader-4.0.2.tgz#b9e55a6126ee67bb7b94bbfcbf1aa24c69f11229"
+  integrity sha512-u7Qoa6GSPIeg9/hHbNnXspzuD5jjCIWKgk1fJ/gGJPS0uaj6Whk2zjXhDAiHZyYSrDmIzUQk7GgwRF22eRIQGQ==
+  dependencies:
+    cosmiconfig "^7.0.0"
+    klona "^2.0.3"
+    loader-utils "^2.0.0"
+    schema-utils "^2.7.1"
+    semver "^7.3.2"
+
 postcss-logical@^3.0.0:
   version "3.0.0"
   resolved "https://registry.yarnpkg.com/postcss-logical/-/postcss-logical-3.0.0.tgz#2495d0f8b82e9f262725f75f9401b34e7b45d5b5"
@@ -17140,6 +17162,11 @@ yallist@^4.0.0:
   version "4.0.0"
   resolved "https://registry.yarnpkg.com/yallist/-/yallist-4.0.0.tgz#9bb92790d9c0effec63be73519e11a35019a3a72"
 
+yaml@^1.10.0:
+  version "1.10.0"
+  resolved "https://registry.yarnpkg.com/yaml/-/yaml-1.10.0.tgz#3b593add944876077d4d683fee01081bd9fff31e"
+  integrity sha512-yr2icI4glYaNG+KWONODapy2/jDdMSDnrONSjblABjD9B4Z5LgiircSt8m8sRZFNi08kG9Sm0uSHtEmP3zaEGg==
+
 yaml@^1.7.2:
   version "1.9.2"
   resolved "https://registry.yarnpkg.com/yaml/-/yaml-1.9.2.tgz#f0cfa865f003ab707663e4f04b3956957ea564ed"