Webpacker Error While Creating Ruby On Rails App - ruby-on-rails

Question

$ rails 6.0.2 new sample_app2
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Using web-console 4.0.1
Using webdrivers 4.1.3
Using webpacker 4.2.2
Bundle complete! 17 Gemfile dependencies, 75 gems now installed.
Use `bundle info [gemname]` to see where a bundled gem is installed.
run bundle binstubs bundler
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`.
Skipped bundle since it already exists.
If you want to overwrite skipped stubs, use --force.
run bundle exec spring binstub --all
* bin/rake: Spring inserted
* bin/rails: Spring inserted
rails webpacker:install
Traceback (most recent call last):
4: from /home/emsawy/.rvm/gems/ruby-2.6.3/bin/ruby_executable_hooks:24:in `'
3: from /home/emsawy/.rvm/gems/ruby-2.6.3/bin/ruby_executable_hooks:24:in `eval'
2: from /home/emsawy/.rvm/gems/ruby-2.6.3/bin/yarn:23:in `'
1: from /home/emsawy/.rvm/rubies/ruby-2.6.3/lib/ruby/site_ruby/2.6.0/bundler/rubygems_integration.rb:400:in `block in replace_bin_path'
/home/emsawy/.rvm/rubies/ruby-2.6.3/lib/ruby/site_ruby/2.6.0/bundler/rubygems_integration.rb:372:in `block in replace_bin_path': can't find executable yarn for gem yarn. yarn is not currently included in the bundle, perhaps you meant to add it to your Gemfile? (Gem::Exception)
Yarn not installed. Please download and install Yarn from https://yarnpkg.com/lang/en/docs/install/
Also after performing Yarn not installed. Please download and install Yarn from https://yarnpkg.com/lang/en/docs/install/
I got the same result
$ yarn -v
[DEPRECATION] The trollop gem has been renamed to optimist
and will no longer be supported. Please switch to optimist
as soon as possible. Yarn v0.1.1 2011 Jesper Kjeldgaard
$ ruby -v
ruby 2.6.3p62 (2019-04-16 revision 67580) [x86_64-linux]
$ rails -v
Rails 6.0.2.1

Answer 1

You installed yarn as a gem https://rubygems.org/gems/yarn and this is wrong.
Now you should do:
Uninstall this gem, gem uninstall yarn
On mac os brew install yarn if other platform then look here: https://yarnpkg.com/lang/en/docs/install/#debian-stable
Check version, should be something like:
yarn -v
1.21.1

Answer 2

Got the same error.
First uninstall yarn by commanding gem uninstall yarn.
It will ask yn, Enter yn
Next run: command gem update
Finally check yarn --version