“webpack binstubs not found.” on Heroku - node.js

Question

I’ve spun up a new rails project with the following command: rails new -d postgresql --skip-spring --skip-test --webpack=react
Following this, I created my database, added <%= javascript_pack_tag 'hello_react' %> to application.html.erb and generated a homepage.
I then ran:
rails s # tab 1
bin/webpack-dev-server # tab 2
This all works fine and I can see “Hello World!” at localhost:3000.
However, when I try to push to Heroku, the build fails at webpack binstubs not found.. I can confirm that bin/webpack does exist, doing rails webpack:install:react does nothing.
I’ve followed the instructions at webpacker/deployment.md at master · rails/webpacker · GitHub to no avail, still getting the exact same error. I’ve even tried setting compile: true in config/webpacker.yml, in the production section. Nothing.
This seems odd as this is a new project with nothing special in it; I’m confused as to why it cannot seem to find the declaration of bin/webpack. It is not in my .gitignore.
Any help would be great.
Cheers.
Full build log:
-----> Node.js app detected
-----> Creating runtime environment
NPM_CONFIG_LOGLEVEL=error
USE_YARN_CACHE=true
NODE_ENV=production
NODE_MODULES_CACHE=true
NODE_VERBOSE=false
-----> Installing binaries
engines.node (package.json): unspecified
engines.npm (package.json): unspecified (use default)
engines.yarn (package.json): unspecified (use default)
Resolving node version 12.x...
Downloading and installing node 12.19.1...
Using default npm version: 6.14.8
Resolving yarn version 1.22.x...
Downloading and installing yarn (1.22.10)
Installed yarn 1.22.10
-----> Installing dependencies
Installing node modules (yarn.lock)
yarn install v1.22.10
[1/4] Resolving packages...
[2/4] Fetching packages...
info fsevents#2.1.3: The platform "linux" is incompatible with this module.
info "fsevents#2.1.3" is an optional dependency and failed compatibility check. Excluding it from installation.
info fsevents#1.2.13: The platform "linux" is incompatible with this module.
info "fsevents#1.2.13" is an optional dependency and failed compatibility check. Excluding it from installation.
[3/4] Linking dependencies...
warning " > #babel/preset-react#7.12.7" has unmet peer dependency "#babel/core#^7.0.0-0".
warning "#babel/preset-react > #babel/plugin-transform-react-display-name#7.12.1" has unmet peer dependency "#babel/core#^7.0.0-0".
warning "#babel/preset-react > #babel/plugin-transform-react-jsx#7.12.7" has unmet peer dependency "#babel/core#^7.0.0-0".
warning "#babel/preset-react > #babel/plugin-transform-react-jsx-development#7.12.7" has unmet peer dependency "#babel/core#^7.0.0-0".
warning "#babel/preset-react > #babel/plugin-transform-react-jsx-self#7.12.1" has unmet peer dependency "#babel/core#^7.0.0-0".
warning "#babel/preset-react > #babel/plugin-transform-react-jsx-source#7.12.1" has unmet peer dependency "#babel/core#^7.0.0-0".
warning "#babel/preset-react > #babel/plugin-transform-react-pure-annotations#7.12.1" has unmet peer dependency "#babel/core#^7.0.0-0".
warning "#babel/preset-react > #babel/plugin-transform-react-jsx > #babel/plugin-syntax-jsx#7.12.1" has unmet peer dependency "#babel/core#^7.0.0-0".
warning " > webpack-dev-server#3.11.0" has unmet peer dependency "webpack#^4.0.0 || ^5.0.0".
warning "webpack-dev-server > webpack-dev-middleware#3.7.2" has unmet peer dependency "webpack#^4.0.0".
[4/4] Building fresh packages...
Done in 29.74s.
-----> Build
-----> Pruning devDependencies
yarn install v1.22.10
[1/4] Resolving packages...
[2/4] Fetching packages...
info fsevents#2.1.3: The platform "linux" is incompatible with this module.
info "fsevents#2.1.3" is an optional dependency and failed compatibility check. Excluding it from installation.
info fsevents#1.2.13: The platform "linux" is incompatible with this module.
info "fsevents#1.2.13" is an optional dependency and failed compatibility check. Excluding it from installation.
[3/4] Linking dependencies...
warning " > #babel/preset-react#7.12.7" has unmet peer dependency "#babel/core#^7.0.0-0".
warning "#babel/preset-react > #babel/plugin-transform-react-display-name#7.12.1" has unmet peer dependency "#babel/core#^7.0.0-0".
warning "#babel/preset-react > #babel/plugin-transform-react-jsx#7.12.7" has unmet peer dependency "#babel/core#^7.0.0-0".
warning "#babel/preset-react > #babel/plugin-transform-react-jsx-development#7.12.7" has unmet peer dependency "#babel/core#^7.0.0-0".
warning "#babel/preset-react > #babel/plugin-transform-react-jsx-self#7.12.1" has unmet peer dependency "#babel/core#^7.0.0-0".
warning "#babel/preset-react > #babel/plugin-transform-react-jsx-source#7.12.1" has unmet peer dependency "#babel/core#^7.0.0-0".
warning "#babel/preset-react > #babel/plugin-transform-react-pure-annotations#7.12.1" has unmet peer dependency "#babel/core#^7.0.0-0".
warning "#babel/preset-react > #babel/plugin-transform-react-jsx > #babel/plugin-syntax-jsx#7.12.1" has unmet peer dependency "#babel/core#^7.0.0-0".
warning " > webpack-dev-server#3.11.0" has unmet peer dependency "webpack#^4.0.0 || ^5.0.0".
warning "webpack-dev-server > webpack-dev-middleware#3.7.2" has unmet peer dependency "webpack#^4.0.0".
[4/4] Building fresh packages...
warning Ignored scripts due to flag.
Done in 5.82s.
-----> Caching build
- yarn cache
-----> Build succeeded!
! This app may not specify any way to start a node process
https://devcenter.heroku.com/articles/nodejs-support#default-web-process-type
! Unmet dependencies don't fail yarn install but may cause runtime issues
https://github.com/npm/npm/issues/7494
-----> Ruby app detected
-----> Installing bundler 2.1.4
-----> Removing BUNDLED WITH version in the Gemfile.lock
-----> Compiling Ruby/Rails
-----> Using Ruby version: ruby-2.7.2
-----> Installing dependencies using bundler 2.1.4
Running: BUNDLE_WITHOUT='development:test' BUNDLE_PATH=vendor/bundle BUNDLE_BIN=vendor/bundle/bin BUNDLE_DEPLOYMENT=1 bundle install -j4
The dependency tzinfo-data (>= 0) will be unused by any of the platforms Bundler is installing for. Bundler is installing for ruby but the dependency is only for x86-mingw32, x86-mswin32, x64-mingw32, java. To add those platforms to the bundle, run `bundle lock --add-platform x86-mingw32 x86-mswin32 x64-mingw32 java`.
Fetching gem metadata from https://rubygems.org/............
Fetching rake 13.0.1
Installing rake 13.0.1
Fetching concurrent-ruby 1.1.7
Fetching thread_safe 0.3.6
Fetching minitest 5.14.2
Installing thread_safe 0.3.6
Installing minitest 5.14.2
Installing concurrent-ruby 1.1.7
Fetching zeitwerk 2.4.1
Installing zeitwerk 2.4.1
Fetching builder 3.2.4
Fetching erubi 1.10.0
Installing builder 3.2.4
Installing erubi 1.10.0
Fetching mini_portile2 2.4.0
Fetching crass 1.0.6
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Installing crass 1.0.6
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Fetching nio4r 2.5.4
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Installing nokogiri 1.10.10 with native extensions
Fetching i18n 1.8.5
Installing i18n 1.8.5
Fetching rack-test 1.1.0
Installing rack-test 1.1.0
Fetching rack-proxy 0.6.5
Installing rack-proxy 0.6.5
Fetching sprockets 4.0.2
Installing sprockets 4.0.2
Fetching websocket-driver 0.7.3
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Fetching mail 2.7.1
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Installing rails-dom-testing 2.0.3
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Installing globalid 0.4.2
Fetching activemodel 6.0.3.4
Installing activemodel 6.0.3.4
Fetching jbuilder 2.10.1
Installing jbuilder 2.10.1
Fetching rails-html-sanitizer 1.3.0
Installing rails-html-sanitizer 1.3.0
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Fetching sassc-rails 2.1.2
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Installing sass-rails 6.0.0
Bundle complete! 12 Gemfile dependencies, 57 gems now installed.
Gems in the groups development and test were not installed.
Bundled gems are installed into `./vendor/bundle`
Post-install message from i18n:
HEADS UP! i18n 1.1 changed fallbacks to exclude default locale.
But that may break your application.
If you are upgrading your Rails application from an older version of Rails:
Please check your Rails app for 'config.i18n.fallbacks = true'.
If you're using I18n (>= 1.1.0) and Rails (< 5.2.2), this should be
'config.i18n.fallbacks = [I18n.default_locale]'.
If not, fallbacks will be broken in your app by I18n 1.1.x.
If you are starting a NEW Rails application, you can ignore this notice.
For more info see:
https://github.com/svenfuchs/i18n/releases/tag/v1.1.0
Bundle completed (208.33s)
Cleaning up the bundler cache.
-----> Detecting rake tasks
-----> Preparing app for Rails asset pipeline
Running: rake assets:precompile
yarn install v1.22.10
[1/4] Resolving packages...
[2/4] Fetching packages...
info fsevents#2.1.3: The platform "linux" is incompatible with this module.
info "fsevents#2.1.3" is an optional dependency and failed compatibility check. Excluding it from installation.
info fsevents#1.2.13: The platform "linux" is incompatible with this module.
info "fsevents#1.2.13" is an optional dependency and failed compatibility check. Excluding it from installation.
[3/4] Linking dependencies...
warning " > #babel/preset-react#7.12.7" has unmet peer dependency "#babel/core#^7.0.0-0".
warning "#babel/preset-react > #babel/plugin-transform-react-display-name#7.12.1" has unmet peer dependency "#babel/core#^7.0.0-0".
warning "#babel/preset-react > #babel/plugin-transform-react-jsx#7.12.7" has unmet peer dependency "#babel/core#^7.0.0-0".
warning "#babel/preset-react > #babel/plugin-transform-react-jsx-development#7.12.7" has unmet peer dependency "#babel/core#^7.0.0-0".
warning "#babel/preset-react > #babel/plugin-transform-react-jsx-self#7.12.1" has unmet peer dependency "#babel/core#^7.0.0-0".
warning "#babel/preset-react > #babel/plugin-transform-react-jsx-source#7.12.1" has unmet peer dependency "#babel/core#^7.0.0-0".
warning "#babel/preset-react > #babel/plugin-transform-react-pure-annotations#7.12.1" has unmet peer dependency "#babel/core#^7.0.0-0".
warning "#babel/preset-react > #babel/plugin-transform-react-jsx > #babel/plugin-syntax-jsx#7.12.1" has unmet peer dependency "#babel/core#^7.0.0-0".
warning " > webpack-dev-server#3.11.0" has unmet peer dependency "webpack#^4.0.0 || ^5.0.0".
warning "webpack-dev-server > webpack-dev-middleware#3.7.2" has unmet peer dependency "webpack#^4.0.0".
[4/4] Building fresh packages...
Done in 29.50s.
I, [2020-11-25T12:02:13.452090 #3686] INFO -- : Writing /tmp/build_6728f1b1/public/assets/manifest-b4bf6e57a53c2bdb55b8998cc94cd00883793c1c37c5e5aea3ef6749b4f6d92b.js
I, [2020-11-25T12:02:13.452388 #3686] INFO -- : Writing /tmp/build_6728f1b1/public/assets/manifest-b4bf6e57a53c2bdb55b8998cc94cd00883793c1c37c5e5aea3ef6749b4f6d92b.js.gz
I, [2020-11-25T12:02:13.452661 #3686] INFO -- : Writing /tmp/build_6728f1b1/public/assets/application-04024382391bb910584145d8113cf35ef376b55d125bb4516cebeb14ce788597.css
I, [2020-11-25T12:02:13.452831 #3686] INFO -- : Writing /tmp/build_6728f1b1/public/assets/application-04024382391bb910584145d8113cf35ef376b55d125bb4516cebeb14ce788597.css.gz
I, [2020-11-25T12:02:13.453156 #3686] INFO -- : Writing /tmp/build_6728f1b1/public/assets/home-04024382391bb910584145d8113cf35ef376b55d125bb4516cebeb14ce788597.css
I, [2020-11-25T12:02:13.453335 #3686] INFO -- : Writing /tmp/build_6728f1b1/public/assets/home-04024382391bb910584145d8113cf35ef376b55d125bb4516cebeb14ce788597.css.gz
webpack binstubs not found.
Have you run rails webpacker:install ?
Make sure the bin directory or binstubs are not included in .gitignore
Exiting!
!
! Precompiling assets failed.
!
! Push rejected, failed to compile Ruby app.
! Push failed

Answer 1

SOLVED
Turns out bin/ is ignored by default in Rails.
Oddly enough, I still can't find the code which ignores bin/ for git; it doesn't look like it's in the main .gitignore
However, if you run
git add -f bin/webpack && git push heroku master # or main
everything should build.