Tapioca does not generate a signature for ActiveSupport's `Time#rfc3339`

I've discussed this with @andyw8 on Slack.
I'm working on a Rails application that uses Sorbet and Tapioca.
Using Time.now.rfc3339 in the app introduced a Sorbet error:

app/jobs/dead_translations/snapshot_job.rb:190: Method rfc3339 does not exist on Time https://srb.help/7003
     190 |          time: end_time.rfc3339,
                                   ^^^^^^^
  Got Time originating from:
    app/jobs/dead_translations/snapshot_job.rb:186:
     186 |    def get_live_translations(prefix, end_time)
                                                ^^^^^^^^
  There is a singleton class method with the same name:
    sorbet/rbi/gems/activesupport@8.0.0.rbi:21563: Defined here
       21563 |    def rfc3339(str); end
                  ^^^^^^^^^^^^^^^^
    Either:
    - use .class to call it, or
    - remove self. from its definition to make it an instance method
  Autocorrect: Use -a to autocorrect
    app/jobs/dead_translations/snapshot_job.rb:190: Insert .class
     190 |          time: end_time.rfc3339,

Time#rfc3339 is defined in an ActiveSupport core extension: activesupport/core_ext/time/conversions, as an alias to Time#xmlschema, which itself is defined in Ruby's Time class (here).

$ ruby -e "puts Time.now.xmlschema"
-e:1:in `<main>': undefined method `xmlschema' for an instance of Time (NoMethodError)

puts Time.now.xmlschema
             ^^^^^^^^^^

$ ruby -rtime -e "puts Time.now.xmlschema"
2024-11-22T01:16:39+09:00

$ ruby -rtime -e "puts Time.now.rfc3339"
-e:1:in `<main>': undefined method `rfc3339' for an instance of Time (NoMethodError)

puts Time.now.rfc3339
             ^^^^^^^^

$ ruby -ractive_support/core_ext/time/conversions -e "puts Time.now.rfc3339"
2024-11-22T01:17:10+09:00

What's weird is that Tapioca appears to be able to pick up another method defined with alias_method in the same active_support/core_ext/time/conversions file. (This one: to_formatted_s.)

In another experiment, I tried adding def xmlschema; end in that file, active_support/core_ext/time/conversions, before the line alias_method :rfc3339, :xmlschema. When I run bin/tapioca gem activesupport, it adds the signatures for both Time#xmlschema and Time#rfc3339 to sorbet/rbi/gems/activesupport@8.0.0.rbi.

I tried adding either or both of the two lines below in the sorbet/tapioca/require.rb file, but it does not seem to change anything, unfortunately.

require "time"
require "active_support/core_ext/time/conversions"

Also note that Sorbet defines a signature for Time#xmlschema, here.

Finally, I tried replacing Time.now.rfc3339 with Time.now.xmlschema in my code, and now the Sorbet error is gone, so I'll simply go with that for now.

Start by reproducing the issue with bin/tapioca gem activesupport and inspect active_support/core_ext/time/conversions, where Time#rfc3339 is aliased. Review sorbet/tapioca/require.rb and the generated activesupport RBI, comparing rfc3339 with to_formatted_s; done means the generated RBI includes the correct instance signature for Time#rfc3339.