Initial implementation

.babelrc

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+{}

.eslintrc

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+{
+  "extends": "node-important-stuff",
+  "parser": "@babel/eslint-parser",
+  "rules": {
+    "node/no-unsupported-features/es-syntax": "off"
+  }
+}

.github/workflows/build_and_test.yml

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+on:
+  - push
+  - pull_request
+
+jobs:
+  build-test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: pnpm/action-setup@v2.0.1
+        with:
+          version: 6.11.5
+          run_install: |
+            - recursive: true
+              args: [--frozen-lockfile, --strict-peer-dependencies]
+      - run: pnpm run lint
+      - run: pnpm run test

.husky/pre-commit

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+#!/bin/sh
+. "$(dirname "$0")/_/husky.sh"
+
+pnpm run lint && pnpm exec pretty-quick --staged

README.md

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-# node-loader-postcss
+# @node-loader/postcss
+
+A [nodejs loader](https://nodejs.org/dist/latest-v13.x/docs/api/esm.html#esm_experimental_loaders) for [postcss](https://postcss.org/). This allows you to load CSS files into NodeJS programs by converting them into Javascript modules. The returned ES module has a `default` property whose value is the compiled CSS string.
+
+## Installation
+
+```sh
+npm install --save @node-loader/postcss
+```
+
+## Usage
+
+Now run node with the `--loader` (or `--experimental-loader` for older NodeJS version) flag:
+
+```sh
+node --loader @node-loader/postcss file.js
+```
+
+## Configuration
+
+By default, node-loader postcss looks for a configuration file called `postcss.config.js` in the current working directory. To specify the file path to the configuration file, provide the `POSTCSS_CONFIG` environment variable:
+
+```sh
+POSTCSS_CONFIG=/Users/name/some/dir/.postcssrc node --loader @node-loader/postcss file.js
+```
+
+## Composition
+
+If you wish to combine postcss loading with other NodeJS loaders, you may do so by using [node-loader-core](https://github.com/node-loader/node-loader-core).

lib/node-loader-postcss.js

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+import postcss from "postcss";
+import path from "path";
+
+export async function transformSource(
+  originalSource,
+  context,
+  defaultTransformSource
+) {
+  if (useLoader(context.url)) {
+    const postCssConfigFilePath = path.resolve(
+      process.cwd(),
+      process.env.POSTCSS_CONFIG || "postcss.config.js"
+    );
+
+    const { default: postCssConfig } = await import(postCssConfigFilePath);
+    let css;
+    try {
+      const result = await postcss(postCssConfig.plugins).process(
+        originalSource.toString(),
+        {
+          from: context.url,
+          to: context.url,
+        }
+      );
+
+      css = result.css;
+    } catch (err) {
+      console.error("@node-loader/postcss: PostCSS compilation error");
+      console.error(err);
+      throw err;
+    }
+
+    const source =
+      "export default `" +
+      css.replace(/\\/g, "\\\\").replace(/`/g, "\\`") +
+      "`";
+
+    return {
+      source,
+    };
+  }
+
+  return defaultTransformSource(
+    originalSource,
+    context,
+    defaultTransformSource
+  );
+}
+
+export function getFormat(url, context, defaultGetFormat) {
+  if (useLoader(url)) {
+    return {
+      format: "module",
+    };
+  } else {
+    return defaultGetFormat(url, context, defaultGetFormat);
+  }
+}
+
+function useLoader(url) {
+  return url.endsWith(".css");
+}

package.json

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+{
+  "name": "@node-loader/postcss",
+  "version": "1.0.0",
+  "description": "A NodeJS loader for processing PostCSS ",
+  "type": "module",
+  "main": "lib/node-loader-postcss.js",
+  "scripts": {
+    "test": "node --loader ./lib/node-loader-postcss.js ./test/run-tests.js",
+    "lint": "eslint lib",
+    "prepare": "husky install"
+  },
+  "files": [
+    "lib"
+  ],
+  "engines": {
+    "node": ">=14"
+  },
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/node-loader/node-loader-postcss.git"
+  },
+  "keywords": [
+    "node",
+    "loader",
+    "postcss"
+  ],
+  "author": "Joel Denning",
+  "license": "MIT",
+  "bugs": {
+    "url": "https://github.com/node-loader/node-loader-postcss/issues"
+  },
+  "homepage": "https://github.com/node-loader/node-loader-postcss#readme",
+  "dependencies": {
+    "postcss": "^8.3.6"
+  },
+  "devDependencies": {
+    "@babel/core": "^7.14.8",
+    "@babel/eslint-parser": "^7.14.9",
+    "autoprefixer": "^10.3.1",
+    "eslint": "^7.32.0",
+    "eslint-config-node-important-stuff": "^1.1.0",
+    "husky": "^7.0.0",
+    "mocha": "^9.0.3",
+    "prettier": "^2.3.2",
+    "pretty-quick": "^3.1.1"
+  }
+}