Add bundle install and yarn install to Dockerfile

Author: edwinv

.devcontainer/Dockerfile

@@ -18,7 +18,27 @@ RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
 
 
 # [Optional] Uncomment this line to install additional gems.
-# RUN gem install <your-gem-names-here>
+# Add the Rails main Gemfile and install the gems. This means the gem install can be done
+# during build instead of on start. When a fork or branch has different gems, we still have an
+# advantage due to caching of the other gems.
+RUN mkdir -p /tmp/rails
+COPY Gemfile Gemfile.lock RAILS_VERSION rails.gemspec package.json yarn.lock /tmp/rails/
+COPY actioncable/actioncable.gemspec /tmp/rails/actioncable/
+COPY actionmailbox/actionmailbox.gemspec /tmp/rails/actionmailbox/
+COPY actionmailer/actionmailer.gemspec /tmp/rails/actionmailer/
+COPY actionpack/actionpack.gemspec /tmp/rails/actionpack/
+COPY actiontext/actiontext.gemspec /tmp/rails/actiontext/
+COPY actionview/actionview.gemspec /tmp/rails/actionview/
+COPY activejob/activejob.gemspec /tmp/rails/activejob/
+COPY activemodel/activemodel.gemspec /tmp/rails/activemodel/
+COPY activerecord/activerecord.gemspec /tmp/rails/activerecord/
+COPY activestorage/activestorage.gemspec /tmp/rails/activestorage/
+COPY activesupport/activesupport.gemspec /tmp/rails/activesupport/
+COPY railties/railties.gemspec /tmp/rails/railties/
+RUN cd /tmp/rails \
+    && bundle install \
+    && yarn install \
+    && rm -rf /tmp/rails
 
 # [Optional] Uncomment this line to install global node packages.
 # RUN su vscode -c "source /usr/local/share/nvm/nvm.sh && npm install -g <your-package-here>" 2>&1

.devcontainer/devcontainer.json

@@ -4,6 +4,7 @@
 	"name": "Ruby",
 	"build": {
 		"dockerfile": "Dockerfile",
+		"context": "..",
 		"args": {
 			// Update 'VARIANT' to pick a Ruby version: 3, 3.0, 2, 2.7, 2.6
 			"VARIANT": "3",