[ruby-core:119044] [Ruby master Bug#20714] Handle optional dependencies in `bundled_gems.rb`

["Earlopain (A S) via ruby-core" <ruby-core@ml.ruby-lang.org>]

Issue #20714 has been updated by Earlopain (A S).


Thanks for you reply, I was about to write something similar about the older rubies.

At first I was writing about how I don't think a new api is really necessary since the compatibility code can simply be dropped once `required_ruby_version` is at or above the ruby version that would error but I don't think that is entirely true. For example, on ruby 3.4 the following script produces this output:

```rb
begin
  require "webrick"
rescue LoadError
end

if defined?(Webrick)
  puts "Do some things"
end

# test.rb:2: warning: webrick was loaded from the standard library, but is not part of the default gems starting from Ruby 3.0.0.
# You can add webrick to your Gemfile or gemspec to silence this warning.
```

So even though webrick is gone since Ruby 3.0, I'd still have to do some trickery to optionally enhance it without triggering the warning.

I see two solutions:
* `require "foo", optional: true` like you suggested
* Drop warnings when ruby would throw an error [here]. When the require will raise, it doesn't need to warn. This is how I already imagined it works. I guess it doesn't for visibility?

[here]: https://github.com/ruby/ruby/blob/294dad22d7ac5f307d567cff897507b9fd9d05e9/lib/bundled_gems.rb#L6-L36

----------------------------------------
Bug #20714: Handle optional dependencies in `bundled_gems.rb`
https://bugs.ruby-lang.org/issues/20714#change-109622

* Author: Earlopain (A S)
* Status: Open
* ruby -v: 3.3.5
* Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN
----------------------------------------
I've encountered a few places around bundled gems where the library doesn't care if the gem is available, but will still provide some functionallity if it is.

The way to accomplish that right now seems to be by setting `$VERBOSE = nil` and resetting it later again to not bother the user with the warning about the gem. However, this has the effect of silencing the warning about other gems as well, that may not be prepared about the bundling. 

>From `ruby/reline` for example: https://github.com/ruby/reline/blob/c90f08f7e308d2f1cdd7cfaf9939fe45ce546fd2/lib/reline/terminfo.rb#L1-L15
Or the `logging` gem: https://github.com/TwP/logging/blob/df41715364f7eb8c65098cd3c3316677ef1f3784/lib/logging.rb#L9-L15

I propose to simply delay the warning to the next require.

GitHub PR at https://github.com/ruby/ruby/pull/11545



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