feat: reuse AST from other loaders (#468)

package.json

@@ -45,7 +45,8 @@
   "dependencies": {
     "cosmiconfig": "^7.0.0",
     "loader-utils": "^2.0.0",
-    "schema-utils": "^2.7.1"
+    "schema-utils": "^2.7.1",
+    "semver": "^7.3.2"
   },
   "devDependencies": {
     "@babel/cli": "^7.11.6",

src/index.js

@@ -2,6 +2,8 @@ import { getOptions } from 'loader-utils';
 import validateOptions from 'schema-utils';
 
 import postcss from 'postcss';
+import { satisfies } from 'semver';
+import postcssPackage from 'postcss/package.json';
 
 import Warning from './Warning';
 import SyntaxError from './Error';
@@ -23,11 +25,12 @@ import {
  *
  * @param {String} content Source
  * @param {Object} sourceMap Source Map
+ * @param {Object} meta Meta
  *
  * @return {callback} callback Result
  */
 
-export default async function loader(content, sourceMap) {
+export default async function loader(content, sourceMap, meta) {
   const options = getOptions(this);
 
   validateOptions(schema, options, {
@@ -65,11 +68,6 @@ export default async function loader(content, sourceMap) {
     options.postcssOptions
   );
 
-  if (options.execute) {
-    // eslint-disable-next-line no-param-reassign
-    content = exec(content, this);
-  }
-
   if (useSourceMap) {
     processOptions.map = { inline: false, annotation: false };
 
@@ -84,10 +82,27 @@ export default async function loader(content, sourceMap) {
     processOptions.map.prev = sourceMap;
   }
 
+  let root;
+
+  // Reuse PostCSS AST from other loaders
+  if (
+    meta &&
+    meta.ast &&
+    meta.ast.type === 'postcss' &&
+    satisfies(meta.ast.version, `^${postcssPackage.version}`)
+  ) {
+    ({ root } = meta.ast);
+  }
+
+  if (!root && options.execute) {
+    // eslint-disable-next-line no-param-reassign
+    content = exec(content, this);
+  }
+
   let result;
 
   try {
-    result = await postcss(plugins).process(content, processOptions);
+    result = await postcss(plugins).process(root || content, processOptions);
   } catch (error) {
     if (error.file) {
       this.addDependency(error.file);

test/__snapshots__/execute.test.js.snap

@@ -1,5 +1,15 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`"execute" option should reuse PostCSS AST with JS styles: css 1`] = `
+"a {
+    color: green
+}"
+`;
+
+exports[`"execute" option should reuse PostCSS AST with JS styles: errors 1`] = `Array []`;
+
+exports[`"execute" option should reuse PostCSS AST with JS styles: warnings 1`] = `Array []`;
+
 exports[`"execute" option should work with "Boolean" value: css 1`] = `
 "a {
     color: green

test/__snapshots__/loader.test.js.snap

@@ -106,6 +106,57 @@ Warning
 ]
 `;
 
+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 on invalid syntax: errors 1`] = `
 Array [
   "ModuleBuildError: Module build failed (from \`replaced original path\`):

test/execute.test.js

@@ -36,7 +36,6 @@ describe('"execute" option', () => {
       }
     );
     const stats = await compile(compiler);
-
     const codeFromBundle = getCodeFromBundle('style.exec.js', stats);
 
     expect(codeFromBundle.css).toMatchSnapshot('css');
@@ -73,13 +72,51 @@ describe('"execute" option', () => {
         },
       }
     );
-
     const stats = await compile(compiler);
-
     const codeFromBundle = getCodeFromBundle('style.js', stats);
 
     expect(codeFromBundle.css).toMatchSnapshot('css');
     expect(getWarnings(stats)).toMatchSnapshot('warnings');
     expect(getErrors(stats)).toMatchSnapshot('errors');
   });
+
+  it('should reuse PostCSS AST with JS styles', async () => {
+    const spy = jest.fn();
+    const compiler = getCompiler(
+      './jss/exec/index.js',
+      {},
+      {
+        module: {
+          rules: [
+            {
+              test: /style\.(exec\.js|js)$/i,
+              use: [
+                {
+                  loader: require.resolve('./helpers/testLoader'),
+                  options: {},
+                },
+                {
+                  loader: path.resolve(__dirname, '../src'),
+                  options: {
+                    execute: true,
+                  },
+                },
+                {
+                  loader: require.resolve('./helpers/astLoader'),
+                  options: { spy, execute: true },
+                },
+              ],
+            },
+          ],
+        },
+      }
+    );
+    const stats = await compile(compiler);
+    const codeFromBundle = getCodeFromBundle('style.exec.js', stats);
+
+    expect(spy).toHaveBeenCalledTimes(1);
+    expect(codeFromBundle.css).toMatchSnapshot('css');
+    expect(getWarnings(stats)).toMatchSnapshot('warnings');
+    expect(getErrors(stats)).toMatchSnapshot('errors');
+  });
 });

test/helpers/astLoader.js

@@ -0,0 +1,46 @@
+import Module from 'module';
+
+const postcss = require('postcss');
+
+const parentModule = module;
+
+function exec(code, loaderContext) {
+  const { resource, context } = loaderContext;
+
+  const module = new Module(resource, parentModule);
+
+  // eslint-disable-next-line no-underscore-dangle
+  module.paths = Module._nodeModulePaths(context);
+  module.filename = resource;
+
+  // eslint-disable-next-line no-underscore-dangle
+  module._compile(code, resource);
+
+  return module.exports;
+}
+
+module.exports = function astLoader(content) {
+  const callback = this.async();
+  const { spy = jest.fn(), execute } = this.query;
+
+  if (execute) {
+    // eslint-disable-next-line no-param-reassign
+    content = exec(content, this);
+  }
+
+  postcss()
+    .process(content)
+    .then((result) => {
+      const ast = {
+        type: 'postcss',
+        version: result.processor.version,
+        root: result.root,
+      };
+
+      Object.defineProperty(ast, 'root', {
+        get: spy.mockReturnValue(result.root),
+      });
+
+      callback(null, result.css, result.map, { ast });
+    });
+};