Feature #15565


Circular dependency warnings - suggestions/ideas to improve the output from ruby

Added by shevegen (Robert A. Heiler) about 4 years ago. Updated about 4 years ago.

Target version:


Hello ruby folks (and everyone else) reading this suggestion.

I will start with a mini-summary first, a TL;DR - this proposal suggests
to "make it easier/better for us ruby users to solve/resolve/handle
circular dependency warnings" or situations similar to these cases.

For example, take three files, called - "a.rb", "b.rb", "c.rb", without
the "" quotes.

a.rb has a require line on b.rb, which in turn has a require line on
c.rb, which in turn has a require line on a.rb. So they are
inter-dependent on one another - a circular dependency situation.

Before I describe the suggestion in more detail, I will take shyouhei's
general advice and describe the primary use case, or problem domain that
I sometimes face in reguards to circular dependency warnings or circular
dependency situations in a ruby project.

The next section thus is an attempt to describe the problem domain, in
particular from my point of view (I can not talk for others, but I
can describe my use case or problem):

In my larger ruby projects, in particular for projects where you may have
quite a lot of files, say, ... upwards of +50 .rb files, I sometimes have
to re-arrange the project.

When I write to "re-arrange" the project, this means to rewrite some old
code, sometimes delete old code, sometimes add new code, and moving files
around, creating or removing or renaming directories. Things like that.

I guess everyone is doing this in general, even on windows (just when you
use a GUI to do most of this), but we also have to pay attention in general
as to where files are, so that we can find them. In ruby this is similar,
where we are often using require, require_relative or load - and we have to
know at the least the relative path to other .rb files. And the file also
must exist at that position, too (though you can rescue non-existing files
through a LoadError, of course).

Handling a ruby project is not so difficult when the project is in an overall
good shape - but I also have old code which is of a lower quality. And, even
more importantly, I make mistakes too. Sometimes I end up with circular
dependency warnings because I may require a .rb file that may pull in another
.rb file which may pull in another file ... I guess this may happen for other
people too sometimes. To me it is not always instantly obvious which .rb file
is the culprit. Sometimes I only notice this at a later time.

This does bring me sometimes into a situation where I have a circular dependency,
and it is not very easy to see which file depends on which other file - at the
least not for me.

Sometimes I also forget how I structured a project after some time, and it may
not always be easy to clean up a large project, due to inter-dependencies
and similar constraints. I have to think which .rb files should be loaded first,
for example. This is not so difficult, but it still takes time and concentration.

Such situations are not always a lot of fun to resolve. They also take
away time, since we may have to figure out which .rb file depends on which other
.rb file. (In the event where the project has been written by me, it is my own
code, so I blame myself for problems of course; but my general idea is that this
part of ruby could perhaps be improved, a bit similar how the did-you-mean gem
may have improved spotting typos in ruby code, or how rubocop can warn about
certain code layout issues. Things like that.)

There are of course some strategies to cope with a situation like a circular dependency.
A simple one that I have found works fairly well is to ... try to avoid any situation
that can lead to a circular dependency - which I found works best when you try to be
really minimal when starting with a (new) project.

You can start with the most important basic .rb files, and slowly extend from
this point onward, by adding more code.

For example, I often create base-files that I need to re-use, such as in a way to keep
track of the base directory of the given project (the one from where the other .rb
files may be called); then constants that are re-used within the given project.
Following this I may then add a base class from which I may be able to subclass,
followed by some other toplevel methods (such as "Foobar.create_directory()"), and
then often more specialized classes that do more project-specific activities.

When I approach projects in this way, I rarely end up with a circular dependency warning

  • but sometimes I still make mistakes, and in fact when I was adding functionality to
    one of my larger projects a few hours ago, I had a circular dependency warning. This was
    also the primary reason, or the main trigger, for writing this issue suggestion here. :)

If we look back at, I think, ruby 1.8.x, we did not have circular dependency warnings.
At the least I do not remember that we had ...

While this may not be a perfect situation either (since avoiding circular dependency will
also lead to cleaner, clearer and more consistently based projects), it was easier for
me to not have to think about circular dependency situations. When ruby 1.9.x or 2.0.x
emerged, I also had to resolve several of these circular dependency problems, which was
not as much fun. It's still not that much fun either, which is a major reason why I
wrote the suggestion here.

On a sidenote - I did want to suggest a better/different way before in how we can
handle/cope with larger ruby projects, many months ago already. One smaller component
was to make or ideally, avoid, circular dependency warnings/situations. But I still do
not have a good proposal for improving the way how ruby deals with lots of .rb files in
a new/better way, so this suggestion here is only about circular dependency warnings.
Perhaps the current status quo situation could be improved in regards to circular
dependency warnings.

I will next try to briefly describe what I would typically see when I invoke a
large ruby project that has circular dependencies, from the commandline.

I may see something like 2 up to 3 full-terminal sized output, where ruby
would tell me that there is a circular dependency in effect.

I always run my .rb files with the -w flag, so ruby sort of puts me into the "mood"
to get rid of any warnings here. I like to use -w, so I will always try to resolve
a situation rather than avoid it, even if it is "just" a warning.

From the output that ruby printed, I had a vague idea which file would complain,
but looking at that file I noticed that it would point to another file, which in
turn would point to several other files which may point to lots of other .rb
files ... and then I am confused.

And to be honest, I am not clever enough to easily figure out which file is to be
blamed, from the generated output alone. This is another reason why I often "re-do"
a project from the get-go, and put things back into place one-by-one - a bit as if
you were to repair a mechanical clock that has many tiny pieces, where you re-build
it systematically step-by-step. It's still tedious, though, and not a lot of fun.

It is not ruby's fault that my projects are not always perfect; the mistake is a
user error in the end. But the situation is not a lot of fun, and I liked the
approach in 1.8.x because ... I did not have to deal with these situations.
Avoidance-behaviour from me, and I could stay lazy. :D

In fact, I am rewriting the project where I had this circular dependency warning
right now, starting with the "bottom-to-top" approach described above; and I know
that I will eventually resolve this problem, because I did so many times before,
and it always worked. It also made the new code cleaner, and clearer, because I
would often also improve it as I would "re-assemble" things - but it still takes
quite a lot of time, and is not a lot of fun. I would like to make it easier to
resolve such a problem.

What are the problems that I see?

I think I can only mention two points, a smaller one and then a larger one:

(1) Part of the problem may have to do with the changed way how errors are shown
on the commandline; the older output may have been a bit less confusing for me, but
I do not feel that strongly about it, only may have a slight preference for the
older variant. But this is probably not the large issue, as the warning may still
not be very helpful, so let's go to the larger problem perceived (2).

(2) I think the larger issue is that the output related from circular dependency warnings
isn't too terribly useful as it is. If you compare the situation to the did-you-mean
gem, or rubocop warnings in general, then the latter two are a lot more useful to me.

I do not have a good suggestion as to how to make the output from circular dependency
warnings much better, but I would think that something like the did-you-mean gem would
possibly be useful here. There could be suggestion, at the least into which files
may have a problem; and perhaps even so which files are involved in the circular
warning. That does not have to be a full stack trace, mind you; just something that
may help get ruby folks started.

For example, a table or tabular output of which file may pull in which other file, sorted
in some way could be used. The most problematic file could be shown on top of that table
output or something like that (e. g. the file that may impact many other .rb files).
To not make the output too long, perhaps only a maximum of 6-8 lines should be shown
here. Ideally this would be enabled to be the default in a future ruby version (if
the changes are approved), or it could be a gem, similar like the did-you-mean gem.
That way people could decide on their own what they would prefer (since I like the
did-you-mean gem, I always have it on).

When I write "the most problematic file could be shown on top", this may be a bit
similar in how gcc or llvm/clang may indicate where an error is, in a given C or C++
file. Like the output with the " ^-----" indicator line; I read that LLVM
shows somewhat better messages here.

Coming back to ruby here, I would like to see which files are the one that are directly
involved with a given circular dependency situation. For example, if it is these
three files a.rb, b.rb and c.rb given out, the output could be something like:

     a.rb -> depends on b.rb
     b.rb -> depends on c.rb
     c.rb -> depends on a.rb

The three ^^^ could be colourized in red (but this may be optional). Perhaps we
could also get some more detailed output, like a verbose-flag, or the like. A
small treeview showing which file may depend on which other file; to not show
too much perhaps only three levels of directory structure, at max, should be
checked. And, as said, perhaps only some .rb files checked that way on a given

Perhaps only show for the very last c.rb that it has a circular dependency - this
could simplify the suggestion a little.

Of course it is up to the ruby user to resolve any situation related to circular
dependencies in the end, but any extra information ruby could give could be
helpful, in my opinion.

The above just shows some suggestions, of course; other layouts may be helpful
as well - for example, it could be counted how often a file is required, or
how many circular dependencies that file has, and this finding be reported, so
that the ruby user can first look at such a file (biggest troublemaker).

I understand that the above may not be very trivial to write code for as of yet,
but part of my suggestion is to get the ruby core team aware that there might be
situations where parts of ruby could possibly be improved (perhaps in ruby 3.0).

I remember the time when we did not have the did-you-mean gem, and in fact, many
years ago I mentioned that I sometimes accidentally write "def intialize", and
the did-you-mean gem also handles such a situation. So sometimes it takes a
while for change to happen. :)

(I also understand that not everyone may wish to see more verbose output in
regards to circular-dependency warnings perhaps, which is why a gem may be
ideal; but part of my suggestion is also to try to see that MRI ruby could
be improved in this regard. Perhaps some of you have suggestions how to make
MRI ruby behaviour more useful or better here.)

My hope is that we can, in the long run, lessen any frustration with circular
dependencies in ruby; and, even more importantly so, be able to more
easily/quickly resolve these situations. It is of course a user error in the
end, but some projects are more complex than others, so it may be more likely
that you may add a circular dependency without this being intentional.

I finally found the time to go ahead and write this suggestion. Sorry for it being long -
the TL;DR comes again at the end to help anyone who only wants to jump through it
and perhaps quickly make a short comment:

  • Please consider making it easier/better to resolve/handle circular dependency
    warnings in ruby, especially in larger ruby projects. Possibly with visual
    output/identifiers/cues similar to the did-you-mean gem.

Updated by shevegen (Robert A. Heiler) about 4 years ago

(The output here on redmine is a bit different to how I wrote it in a local editor - sorry for some of the
overflowing lines; I tried to align it to ~80 characters. I am not sure how to edit the first thread, only
replies to an issue.)


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