Index return types using RBS

[st0012]

No description provided.

[st0012]

Some notes:

• RBS' return values don't have variable names, just type names. The structure looks like:

  @return_type=
           #<RBS::Types::ClassInstance:0x0000000150b1cbb8
            @args=[#<RBS::Types::Variable:0x0000000150b1cc58 @location=#<RBS::Location:1190420 buffer=/Users/hung-wulo/.gem/ruby/3.3.4/gems/rbs-3.5.1/core/array.rbs, start=1139:54, pos=38639...38640, children= source="U">, @name=:U>],
            @location=#<RBS::Location:1190480 buffer=/Users/hung-wulo/.gem/ruby/3.3.4/gems/rbs-3.5.1/core/array.rbs, start=1139:46, pos=38631...38641, children=name,?args source="::Array[U]">,
            @name=#<RBS::TypeName:0x0000000150b1ccd0 @kind=:class, @name=:Array, @namespace=#<RBS::Namespace:0x0000000150b1ccf8 @absolute=true, @path=[]>>>,
          @trailing_positionals=[]>,
  

• Ruby LSP currently doesn't store any RBS type information. In overloads we only store the parameter names
• The return value information will more likely be used for type flow analysis, instead of being used to serve LSP requests

[st0012]

After working with @Morriar to collect some numbers, chained method invocations on literals only appears very rarely (~0.15% among all method calls). So we decided the code addition in #2496 is not worth the cost of maintenance and the extra memory usage caused by indexing return types.

And since chained method inference on literals is the only use case for indexing RBS' return type atm, I'm closing this as well.