rails import / require mechanism fails

Question

This question is (very) similar to this post, but not a duplicate IMHO, because:

• my setting is completely reproducible ( docker )
• I use gem to install everything explictly
• I have a "non-rails-related" script to "prove" gem is "operational"
• the mentioned question is "ancient" in internet time (nearly 8 years old)

Here is the completely reproducible docker image of a REST API rails server:

FROM ruby
RUN apt-get update
RUN apt-get install vim -y
RUN gem install rails
RUN rails new translator --api --skip-action-mailer --skip-active-record
WORKDIR translator
RUN gem install syntax_tree
COPY routes.rb config
COPY translator_controller.rb app/controllers
COPY test.rb test.rb
COPY primes.rb primes.rb
EXPOSE 3000

I build and run my docker image normally:

$ docker build --tag host.front.rb --file Dockerfile .
$ docker run -p 8012:3000 -d -t --name front.rb host.front.rb
$ docker exec -it front.rb bash

First I make sure the syntax_tree gem is installed properly:

$ cat test.rb # <----- independent test file
require "json"
require "syntax_tree"

file = File.open('primes.rb')
content = file.read
file.close

program = SyntaxTree.parse(content)
puts JSON.dump(program)

$ ruby test.rb | head -c 41
{"type":"program","location":[1,0,19,265] # <---- good !

Then I verify I can reach my dockerized server:

# on docker
$ rails server -b 0.0.0.0
=> Booting Puma
=> Rails 7.1.3.2 application starting in development
< ... omitted for brevity ... >
* Listening on http://0.0.0.0:3000

# my local machine
$ curl -X POST -F "[email protected]" http://127.0.0.1:8012/translator1
>> 247
$ stat --format=%n:%s primes.rb
primes.rb:247 # <----- good ! 

When I try my second endpoint (which requires the syntax_tree) it fails:

$ curl -X POST -F "[email protected]" http://127.0.0.1:8012/translator2
{"status":500,...,"exception":"LoadError: cannot load such file -- syntax_tree

Here is my translator_controller.rb:

require "json"

class TranslatorController < ApplicationController

  def post_handler_simple

    # get the sent file entity
    source = params["source"]

    # read ruby source code
    file = File.open(source.tempfile)
    content = file.read
    file.close

    # return content length -> works fine !
    render plain: ">> #{content.length()}\n"

 end

  def post_handler

    # get the sent file entity
    source = params["source"]

    # read ruby source code
    file = File.open(source.tempfile)
    content = file.read
    file.close

    # this import doesn't work ...
    require "syntax_tree"

    # parse it
    program = SyntaxTree.parse(content)

    # return AST (json format)
    render plain: JSON.dump(program)

  end

end

And here is my routes.rb for completeness

Rails.application.routes.draw do

  post "/translator1", to: "translator#post_handler_simple"
  post "/translator2", to: "translator#post_handler"

end

Answer 1

I use gem to install everything explictly ... RUN gem install syntax_tree

By default Rails knows nothing about gems you have installed locally (via gem install ...).

First I make sure the syntax_tree gem is installed properly: ...

You have no problem in test.rb because it's a pure non-Rails Ruby file - and locally installed gem was found by ruby_gems.

LoadError: cannot load such file -- syntax_tree

If you want syntax_tree to be available in controller (or require it from there) - define this dependency in project Gemfile.