Use Synvert to automatically upgrade rails 4.2 to 5.0 (Part 2)

• Use Synvert to automatically upgrade rails 4.2 to 5.0 (Part 1)

• Use Synvert to automatically upgrade rails 4.2 to 5.0 (Part 2) (you are here)

• Use Synvert to automatically upgrade rails 4.2 to 5.0 (Part 3)

In our previous tutorial, we learned how to use Synvert to upgrade rails 4.2 to 5.0 for some simple cases. In this tutorial, we’ll take things a step further and dive into more complex use cases.

The first one is ActiveModel::Errors#[]= is deprecated.

When you set the errors in model like errors[:base] = 'foobar' in rails 5.0, you will see the following warning:

ActiveModel::Errors#[]= is deprecated and will be removed in Rails 5.1.

Use model.errors.add(:#{attribute}, #{error.inspect}) instead.

So we need to replace them with errors.add(:base, 'foobar').

To get started with Synvert, open VSCode and activate the Synvert Extension. Select the language as ruby and click “Show Generate Snippet Form”.

Set the File Pattern as app/models/**/*.rb

Set the Gem Version as activerecord >= 5.0

Set the Input as errors[:name] = 'must be present' and Output as errors.add(:name, 'must be present')

Finally, click the “Generate Snippet” button. This will generate the following snippet:

Synvert::Rewriter.new 'group', 'name' do
  within_files 'app/models/**/*.rb' do
    with_node node_type: 'send', receiver: { node_type: 'send', receiver: nil, message: 'errors', arguments: { size: 0 } }, message: '[]=', arguments: { size: 2, '0': :name, '1': "'must be present'" } do
      replace_with '{{receiver}}.add({{arguments.0}}, {{arguments.1}})'
    end
  end
end

It searches for the send node whose receiver is also a send node, receiver’s message is errors, message is []=, and it has 2 arguments, the first one is :name, the second is 'must be present', then replaces it with {{receiver}}.add({{arguments.0}}), {{arguments.1}}).

As I shown in the previous tutorial, we can remove the rule argument.0 and arguments.1 to make it works with all cases. Here I’ll show you another way.

Let’s add a new input errors[:email] = 'must be unique' and output errors.add(:email, 'must be unique'). Then click the “Generate Snippet” button again. It will generate the following snippet:

Synvert::Rewriter.new 'group', 'name' do
  within_files 'app/models/**/*.rb' do
    with_node node_type: 'send', receiver: { node_type: 'send', receiver: nil, message: 'errors', arguments: { size: 0 } }, message: '[]=', arguments: { size: 2 } do
      replace_with '{{receiver}}.add({{arguments.0}}, {{arguments.1}})'
    end
  end
end

As we set the different values in arguments.0 and arguments.1, the new generated snippet will ignore them.

Now we can search in our project

And replace them all.

The next one is head response

If you use render nothing: true in rails 5.0, you will see the following warning:

:nothing option is deprecated and will be removed in Rails 5.1. Use head method to respond with empty response body.

There are two cases:

1. if you use render nothing: true without set status option, you can just replace it with head :ok.

2. if you set status option, render nothing: true, status: :created, you can replace it with head :created.

Open the VSCode Synvert Extension. Select the language as ruby and click “Show Generate Snippet Form”.

Set the File Pattern as app/controllers/**/*.rb

Set the Gem Version as actionpack >= 5.0

Set the Input as render nothing: true and Output as head :ok

Click the “Generate Snippet” button, then it will generate the following snippet:

Synvert::Rewriter.new 'group', 'name' do
  within_files 'app/controllers/**/*.rb' do
    with_node node_type: 'send', receiver: nil, message: 'render', arguments: { size: 1, '0': { node_type: 'hash', nothing_value: true } } do
      replace :arguments, with: ':ok'
      replace :message, with: 'head'
    end
  end
end

It searches for the send node whose message is render, and first argument is hash whose nothing_value is true, then replaces the message with head and replaces the arguments with :ok.

Let’s try another case. Set the Input as render nothing: true, status: :created and Output as head :created. Click the “Generate Snippet” button again. It will generate the following snippet:

Synvert::Rewriter.new 'group', 'name' do
  within_files 'app/controllers/**/*.rb' do
    with_node node_type: 'send', receiver: nil, message: 'render', arguments: { size: 1, '0': { node_type: 'hash', nothing_value: true, status_value: :created } } do
      replace :arguments, with: '{{arguments.0.status_source}}'
      replace :message, with: 'head'
    end
  end
end

The new snippet is similar to the previous one, but it has a new rule status_value, and it will replace the arguments with {{arguments.0.status_source}}. To make it work for all status, we can change the :created to { not: nil }.

We can handle the two cases in one snippet, it just needs to check if the status_value, if it is nil, we replace the arguments with :ok, otherwise we replace the arguments with {{arguments.0.status_source}}.

The updated snippet is as follows:

Synvert::Rewriter.new 'group', 'name' do
  within_files 'app/controllers/**/*.rb' do
    with_node node_type: 'send', receiver: nil, message: 'render', arguments: { size: 1, '0': { node_type: 'hash', nothing_value: true } } do
      replace :message, with: 'head'
      goto_node 'arguments.0' do
        with_node node_type: 'hash', status_value: nil do
          replace_with ':ok'
        end
        with_node node_type: 'hash', status_value: { not: nil } do
          replace_with '{{status_source}}'
        end
      end
    end
  end
end

Now we can search in our project.

And replace them all.

That concludes this tutorial. I’ll show you more cases in the next tutorial. See you then!