Transformer for Elm (#4395)

packages/configs/default/index.json

@@ -27,6 +27,7 @@
     ],
     "*.pug": ["@parcel/transformer-pug"],
     "*.coffee": ["@parcel/transformer-coffeescript"],
+    "*.elm": ["@parcel/transformer-elm"],
     "*.mdx": ["@parcel/transformer-mdx"],
     "*.vue": ["@parcel/transformer-vue"],
     "template:*.vue": ["@parcel/transformer-vue"],

packages/configs/default/package.json

@@ -61,6 +61,7 @@
     "@parcel/transformer-sugarss": "2.0.0-beta.1",
     "@parcel/transformer-toml": "2.0.0-beta.1",
     "@parcel/transformer-typescript-types": "2.0.0-beta.1",
+    "@parcel/transformer-elm": "^2.0.0-alpha.3.1",
     "@parcel/transformer-yaml": "2.0.0-beta.1",
     "@parcel/transformer-image": "2.0.0-beta.1",
     "@parcel/transformer-vue": "2.0.0-beta.1"

packages/core/integration-tests/test/elm.js

@@ -1,59 +1,82 @@
 import assert from 'assert';
-import {bundle, assertBundleTree, run, outputFS} from '@parcel/test-utils';
+import path from 'path';
+import {
+  bundle,
+  distDir,
+  assertBundles,
+  run,
+  outputFS,
+} from '@parcel/test-utils';
 
-describe.skip('elm', function() {
+describe('elm', function() {
   it('should produce a basic Elm bundle', async function() {
-    let b = await bundle(__dirname + '/integration/elm/index.js');
+    let b = await bundle(path.join(__dirname, '/integration/elm/index.js'));
 
-    await assertBundleTree(b, {
-      type: 'js',
-      assets: ['Main.elm', 'index.js'],
-    });
+    await assertBundles(b, [
+      {
+        type: 'js',
+        assets: ['Main.elm', 'index.js'],
+      },
+    ]);
 
     let output = await run(b);
     assert.equal(typeof output().Elm.Main.init, 'function');
   });
   it('should produce a elm bundle with debugger', async function() {
-    let b = await bundle(__dirname + '/integration/elm/index.js');
+    let b = await bundle(path.join(__dirname, '/integration/elm/index.js'));
 
     await run(b);
-    let js = await outputFS.readFile(__dirname + '/dist/index.js', 'utf8');
+    let js = await outputFS.readFile(path.join(distDir, 'index.js'), 'utf8');
     assert(js.includes('elm$browser$Debugger'));
   });
 
   it('should apply elm-hot if HMR is enabled', async function() {
-    let b = await bundle(__dirname + '/integration/elm/index.js', {
-      hmr: true,
+    let b = await bundle(path.join(__dirname, '/integration/elm/index.js'), {
+      hot: true,
     });
 
-    await assertBundleTree(b, {
-      type: 'js',
-      assets: ['Main.elm', 'hmr-runtime.js', 'index.js'],
-    });
+    await assertBundles(b, [
+      {
+        type: 'js',
+        assets: ['HMRRuntime.js', 'Main.elm', 'index.js'],
+      },
+    ]);
 
-    let js = await outputFS.readFile(__dirname + '/dist/index.js', 'utf8');
+    let js = await outputFS.readFile(path.join(distDir, 'index.js'), 'utf8');
     assert(js.includes('[elm-hot]'));
   });
 
   it('should remove debugger in production', async function() {
-    let b = await bundle(__dirname + '/integration/elm/index.js', {
-      production: true,
+    let b = await bundle(path.join(__dirname, '/integration/elm/index.js'), {
+      mode: 'production',
     });
 
     await run(b);
-    let js = await outputFS.readFile(__dirname + '/dist/index.js', 'utf8');
+    let js = await outputFS.readFile(path.join(distDir, 'index.js'), 'utf8');
+    assert(!js.includes('elm$browser$Debugger'));
+  });
+
+  it('should remove debugger when environment variable `PARCEL_ELM_NO_DEBUG` is set to true', async function() {
+    let b = await bundle(path.join(__dirname, '/integration/elm/index.js'), {
+      env: {PARCEL_ELM_NO_DEBUG: true},
+    });
+
+    await run(b);
+    let js = await outputFS.readFile(path.join(distDir, 'index.js'), 'utf8');
     assert(!js.includes('elm$browser$Debugger'));
   });
 
   it('should minify Elm in production mode', async function() {
-    let b = await bundle(__dirname + '/integration/elm/index.js', {
-      production: true,
+    let b = await bundle(path.join(__dirname, '/integration/elm/index.js'), {
+      mode: 'production',
+      minify: true,
     });
 
-    let output = await run(b);
-    assert.equal(typeof output().Elm.Main.init, 'function');
+    await run(b);
 
-    let js = await outputFS.readFile(__dirname + '/dist/index.js', 'utf8');
+    let js = await outputFS.readFile(path.join(distDir, 'index.js'), 'utf8');
     assert(!js.includes('elm$core'));
+    assert(js.includes('Elm'));
+    assert(js.includes('init'));
   });
 });

packages/core/integration-tests/test/integration/elm/elm.json

@@ -3,11 +3,11 @@
     "source-directories": [
         "src"
     ],
-    "elm-version": "0.19.0",
+    "elm-version": "0.19.1",
     "dependencies": {
         "direct": {
-            "elm/browser": "1.0.1",
-            "elm/core": "1.0.2",
+            "elm/browser": "1.0.2",
+            "elm/core": "1.0.5",
             "elm/html": "1.0.0"
         },
         "indirect": {

packages/core/integration-tests/test/integration/elm/package.json

@@ -0,0 +1 @@
+{}

packages/core/parcel/README.md

@@ -1118,6 +1118,7 @@ asset graph. They mostly call out to different compilers and preprocessors.
 - `@parcel/transformer-wasm`
 - `@parcel/transformer-webmanifest`
 - `@parcel/transformer-yaml`
+- `@parcel/transformer-elm`
 - ...
 
 ### Bundlers

packages/core/types/index.js

@@ -241,6 +241,7 @@ export type PackageJSON = {
   devDependencies?: PackageDependencies,
   peerDependencies?: PackageDependencies,
   sideEffects?: boolean | FilePath | Array<FilePath>,
+  bin?: string | {|[string]: FilePath|},
   ...
 };
 

packages/transformers/elm/package.json

@@ -0,0 +1,30 @@
+{
+  "name": "@parcel/transformer-elm",
+  "version": "2.0.0-beta.1",
+  "license": "MIT",
+  "publishConfig": {
+    "access": "public"
+  },
+  "funding": {
+    "type": "opencollective",
+    "url": "https://opencollective.com/parcel"
+  },
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/parcel-bundler/parcel.git"
+  },
+  "main": "lib/ElmTransformer.js",
+  "source": "src/ElmTransformer.js",
+  "engines": {
+    "node": ">= 10.0.0",
+    "parcel": "^2.0.0-alpha.3.1"
+  },
+  "dependencies": {
+    "@parcel/diagnostic": "^2.0.0-beta.1",
+    "@parcel/plugin": "^2.0.0-beta.1",
+    "command-exists": "^1.2.8",
+    "cross-spawn": "^7.0.3",
+    "nullthrows": "^1.1.1",
+    "terser": "^5.2.1"
+  }
+}

packages/transformers/elm/src/ElmTransformer.js

@@ -0,0 +1,162 @@
+// @flow strict-local
+
+import {Transformer} from '@parcel/plugin';
+import commandExists from 'command-exists';
+import spawn from 'cross-spawn';
+import path from 'path';
+import {minify} from 'terser';
+import nullthrows from 'nullthrows';
+import ThrowableDiagnostic from '@parcel/diagnostic';
+
+let isWorker;
+try {
+  let worker_threads = require('worker_threads');
+  isWorker = worker_threads.threadId > 0;
+} catch (_) {
+  isWorker = false;
+}
+
+export default (new Transformer({
+  async loadConfig({config, options}) {
+    const elmConfig = await config.getConfig(['elm.json']);
+    if (!elmConfig) {
+      await elmBinaryPath(config.searchPath, options); // Check if elm is even installed
+      throw new ThrowableDiagnostic({
+        diagnostic: {
+          message: "The 'elm.json' file is missing.",
+          hints: [
+            "Initialize your elm project by running 'elm init'",
+            "If you installed elm as project dependency then run 'yarn elm init' or 'npx elm init'",
+          ],
+        },
+      });
+    }
+    config.setResult(elmConfig.contents);
+  },
+
+  async transform({asset, options}) {
+    const elmBinary = await elmBinaryPath(asset.filePath, options);
+    const elm = await options.packageManager.require(
+      'node-elm-compiler',
+      asset.filePath,
+      {
+        autoinstall: options.autoinstall,
+        saveDev: true,
+      },
+    );
+
+    const compilerConfig = {
+      spawn,
+      cwd: path.dirname(asset.filePath),
+      // $FlowFixMe[sketchy-null-string]
+      debug: !options.env.PARCEL_ELM_NO_DEBUG && options.mode !== 'production',
+      optimize: asset.env.minify,
+    };
+    asset.invalidateOnEnvChange('PARCEL_ELM_NO_DEBUG');
+    for (const filePath of await elm.findAllDependencies(asset.filePath)) {
+      asset.addIncludedFile(filePath);
+    }
+
+    // Workaround for `chdir` not working in workers
+    // this can be removed after https://github.com/isaacs/node-graceful-fs/pull/200 was mergend and used in parcel
+    process.chdir.disabled = isWorker;
+
+    let code = await compileToString(elm, elmBinary, asset, compilerConfig);
+    if (options.hot) {
+      code = await injectHotModuleReloadRuntime(code, asset.filePath, options);
+    }
+    if (compilerConfig.optimize) code = await minifyElmOutput(code);
+
+    asset.type = 'js';
+    asset.setCode(code);
+    return [asset];
+  },
+}): Transformer);
+
+async function elmBinaryPath(searchPath, options) {
+  let elmBinary = await resolveLocalElmBinary(searchPath, options);
+
+  if (elmBinary == null && !commandExists.sync('elm')) {
+    throw new ThrowableDiagnostic({
+      diagnostic: {
+        message: "Can't find 'elm' binary.",
+        hints: [
+          "You can add it as an dependency for your project by running 'yarn add -D elm' or 'npm add -D elm'",
+          'If you want to install it globally then follow instructions on https://elm-lang.org/',
+        ],
+        origin: '@parcel/elm-transformer',
+      },
+    });
+  }
+
+  return elmBinary;
+}
+
+async function resolveLocalElmBinary(searchPath, options) {
+  try {
+    let result = await options.packageManager.resolve(
+      'elm/package.json',
+      searchPath,
+      {autoinstall: false},
+    );
+
+    let bin = nullthrows(result.pkg?.bin);
+    return path.join(
+      path.dirname(result.resolved),
+      typeof bin === 'string' ? bin : bin.elm,
+    );
+  } catch (_) {
+    return null;
+  }
+}
+
+function compileToString(elm, elmBinary, asset, config) {
+  return elm.compileToString(asset.filePath, {
+    pathToElm: elmBinary,
+    ...config,
+  });
+}
+
+async function injectHotModuleReloadRuntime(code, filePath, options) {
+  const elmHMR = await options.packageManager.require('elm-hot', filePath, {
+    autoinstall: options.autoinstall,
+    saveDev: true,
+  });
+  return elmHMR.inject(code);
+}
+
+async function minifyElmOutput(source) {
+  // Recommended minification
+  // Based on: http://elm-lang.org/0.19.0/optimize
+  let result = await minify(source, {
+    compress: {
+      keep_fargs: false,
+      passes: 2,
+      pure_funcs: [
+        'F2',
+        'F3',
+        'F4',
+        'F5',
+        'F6',
+        'F7',
+        'F8',
+        'F9',
+        'A2',
+        'A3',
+        'A4',
+        'A5',
+        'A6',
+        'A7',
+        'A8',
+        'A9',
+      ],
+      pure_getters: true,
+      unsafe: true,
+      unsafe_comps: true,
+    },
+    mangle: true,
+  });
+
+  if (result.code != null) return result.code;
+  throw result.error;
+}