Unable to compile after failure in webpack

[rossta]

Ruby: 2.3.0
node: 6.11.5
Webpacker: 3.2.0
@rails/webpacker: 3.2.0

We recently encountered an issue where a failure in webpack during a deploy left Webpacker in a bad state.

In our case, during the webpacker:compile phase of the first deployment, the webpack executable threw the following error: Error: ENOSPC: no space left on device.

After clearing up space on the device, we attempted to redeploy and got a new error during webpacker:compile, this time from Webpacker almost immediately:

01 JSON::ParserError: A JSON text must at least contain two octets!
01 /path/to/bundle/ruby/2.3.0/gems/json-1.8.6/lib/json/common.rb:155:in `initialize'
01 /path/to/bundle/ruby/2.3.0/gems/json-1.8.6/lib/json/common.rb:155:in `new'
01 /path/to/bundle/ruby/2.3.0/gems/json-1.8.6/lib/json/common.rb:155:in `parse'
01 /path/to/bundle/ruby/2.3.0/gems/webpacker-3.2.0/lib/webpacker/manifest.rb:70:in `load'
01 /path/to/bundle/ruby/2.3.0/gems/webpacker-3.2.0/lib/webpacker/manifest.rb:18:in `refresh'
01 /path/to/bundle/ruby/2.3.0/gems/webpacker-3.2.0/lib/webpacker/commands.rb:20:in `block in compile'
01 /path/to/bundle/ruby/2.3.0/gems/webpacker-3.2.0/lib/webpacker/commands.rb:19:in `tap'
01 /path/to/bundle/ruby/2.3.0/gems/webpacker-3.2.0/lib/webpacker/commands.rb:19:in `compile'
01 /path/to/bundle/ruby/2.3.0/gems/webpacker-3.2.0/lib/webpacker.rb:18:in `compile'
01 /path/to/bundle/ruby/2.3.0/gems/webpacker-3.2.0/lib/tasks/webpacker/compile.rake:25:in `block (3 levels) in <top (required)>'
01 /path/to/bundle/ruby/2.3.0/gems/webpacker-3.2.0/lib/tasks/webpacker/compile.rake:6:in `ensure_log_goes_to_stdout'
01 /path/to/bundle/ruby/2.3.0/gems/webpacker-3.2.0/lib/tasks/webpacker/compile.rake:24:in `block (2 levels) in <top (required)>'
01 /path/to/bundle/ruby/2.3.0/gems/webpacker-3.2.0/lib/tasks/webpacker/compile.rake:17:in `block in enhance_assets_precompile'
01 /path/to/bundle/ruby/2.3.0/gems/rake-12.3.0/exe/rake:27:in `<top (required)>'
01 Tasks: TOP => webpacker:compile

As it turns out, following the first deploy, the last_compilation_digest was recorded despite the webpack failure, and the contents of our packs/manifest.json was blank. The failure above occurred because Webpacker determined the compilation was fresh? and it attempted to skip compilation and jump straight to refreshing the (invalid) manifest file.

We were only able to compile successfully through Webpacker after removing one of the two files.