From af64df4228b0d3b058c96e0092ea136e1314fdf9 Mon Sep 17 00:00:00 2001
From: Tomasz Kontusz <tomasz.kontusz@gmail.com>
Date: Mon, 10 Dec 2018 23:08:07 +0100
Subject: [PATCH] Add support for HMR with elm-hot

---
 packages/core/parcel-bundler/package.json          |  1 +
 .../core/parcel-bundler/src/assets/ElmAsset.js     |  5 ++++-
 packages/core/parcel-bundler/test/elm.js           | 14 ++++++++++++++
 yarn.lock                                          |  5 +++++
 4 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/packages/core/parcel-bundler/package.json b/packages/core/parcel-bundler/package.json
index 9c6463488dd..9642dc0dbfe 100644
--- a/packages/core/parcel-bundler/package.json
+++ b/packages/core/parcel-bundler/package.json
@@ -90,6 +90,7 @@
     "coffeescript": "^2.0.3",
     "cross-env": "^5.1.1",
     "elm": "^0.19.0",
+    "elm-hot": "^1.0.1",
     "eslint": "^4.13.0",
     "glslify-bundle": "^5.0.0",
     "glslify-deps": "^1.3.0",
diff --git a/packages/core/parcel-bundler/src/assets/ElmAsset.js b/packages/core/parcel-bundler/src/assets/ElmAsset.js
index 1bfa210140a..7a2309b3a5f 100644
--- a/packages/core/parcel-bundler/src/assets/ElmAsset.js
+++ b/packages/core/parcel-bundler/src/assets/ElmAsset.js
@@ -9,7 +9,6 @@ class ElmAsset extends Asset {
   constructor(name, options) {
     super(name, options);
     this.type = 'js';
-    this.hmrPageReload = true;
   }
 
   async parse() {
@@ -47,6 +46,10 @@ class ElmAsset extends Asset {
 
     let compiled = await this.elm.compileToString(this.name, options);
     this.contents = compiled.toString();
+    if (this.options.hmr) {
+      let {inject} = await localRequire('elm-hot', this.name);
+      this.contents = inject(this.contents);
+    }
   }
 
   async collectDependencies() {
diff --git a/packages/core/parcel-bundler/test/elm.js b/packages/core/parcel-bundler/test/elm.js
index 7a350ce9248..4ab71a716db 100644
--- a/packages/core/parcel-bundler/test/elm.js
+++ b/packages/core/parcel-bundler/test/elm.js
@@ -22,6 +22,20 @@ describe('elm', function() {
     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
+    });
+
+    await assertBundleTree(b, {
+      type: 'js',
+      assets: ['Main.elm', 'hmr-runtime.js', 'index.js']
+    });
+
+    let js = await fs.readFile(__dirname + '/dist/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
diff --git a/yarn.lock b/yarn.lock
index 085b24515c3..4323ea7028f 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -3413,6 +3413,11 @@ elliptic@^6.0.0:
     minimalistic-assert "^1.0.0"
     minimalistic-crypto-utils "^1.0.0"
 
+elm-hot@^1.0.1:
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/elm-hot/-/elm-hot-1.0.1.tgz#12751fc41ecf1ddc58b5492114d6f77395d3a440"
+  integrity sha512-C6VEX3TqVJv+OhUKMMb2mcaSuRArqvCFNItqxue81/mlfX4PWwvovE5vqocgO3AnrStyHElCRm0KNknfDttEBw==
+
 elm@^0.19.0:
   version "0.19.0"
   resolved "https://registry.yarnpkg.com/elm/-/elm-0.19.0.tgz#c6ad86afea9e971424ebe75e36c9d03412a787fa"