Template: `source: auto` but with non-matching name

[ineu]

At the moment one can use source: auto in the template resource to search for the matching file somewhere under the templates dir in the directory of the file. These two are different operations:

1. Search in subdirectories
2. Search for a file with the matching name

but in the current implementation they are tied together, so it's "all or nothing": one can search in the subdirectories, but only if the file name matches. Sometimes it's inconvenient:

def self.ssh_service(name, num:, remote_ip:)
  template "/etc/systemd/system/ssh-tunnel-#{name}.service" do
    mode "644"

    source "templates/etc/systemd/network/ssh-tunnel.service.erb"
    variables(name: name, num: num, remote_ip: remote_ip)

    notifies :run, "execute[systemctl daemon-reload]", :immediately
  end

  service("ssh-tunnel-#{name}") { action [:enable] }
end

In this case I use the same source file for a bunch of different destination files, so it cannot be automatically matched. So I have to specify the full path to the source file.

It would be great if there was an option to explicitly specify a name of the source file, but still let the code search the file for you in the subdirectories.

I see few possible approaches here:

1. Treat source "./templates/foo" as a specific path, but source "foo" as an autosearch path (so it must start with ./ to be specific). This could be the best option, but it will break existing code (just like in my snippet above), so I doubt it's viable.
2. Extend source to accept a new type. For example, a two-elements array like source: [:auto, "foo.erb"], where the second argument is the filename to search for.
3. Add a new attribute to the template, something like source_filename, defaulting to nil.

So it could look like this:

# current code, searches for "bar" inside the "templates" and its subdirectories
template "foo/bar"

# current code, doesn't search but uses the specific path
template "foo/bar" do
  source "templates/one/two/three/four.erb"
end

# proposed approach #2, searches for "four.erb" inside the "templates" and its subdirectories
template "foo/bar" do
  source [:auto, "four.erb"]
end

# proposed approach #3, searches for "four.erb" inside the "templates" and its subdirectories
template "foo/bar" do
  source_filename "four.erb"
end

If this proposal makes sense for you, I'll create a pull request.

[unasuke]

@ineu It makes sense. I like 3 the best, 2 is my second favorite.

However, I have a question about the name of the "source_filename" attribute in 3.

Is it really "source_filename"? I need some time to think about it. 🤔

If we cannot discover a good name, we may choose 2.

[ineu]

Yeah, naming is difficult. It's the best I thought of at the moment, but I don't like it too much either.