Steep doesn't check assignment to Instance Variables

[radiantshaw]

Assume the following RBS file:

class Foobar
  @baz: Integer

  def initialize: (Integer baz) -> void
end

and the following Ruby file:

class Foobar
  def initialize(baz)
    @baz = baz.to_s
  end
end

The above should give a warning about assigning type ::String to an instance variable of type ::Integer, but it doesn't.

[tk0miya]

Reproduced on my local.

This is not a bug of Steep. It's a bug of type of activesupport gem.

For example, I replaced baz.to_s with a string literal. Then Steep emits a warning.

class Foobar
  def initialize(baz)
    @baz = "string"
  end
end

$ bundle exec steep check
# Type checking files:

.F

app/app.rb:3:4: [error] Cannot assign a value of type `::String` to a variable of type `::Integer`
│   ::String <: ::Integer
│     ::Object <: ::Integer
│       ::BasicObject <: ::Integer
│
│ Diagnostic ID: Ruby::IncompatibleAssignment
│
└     @baz = "string"
      ~~~~~~~~~~~~~~~

Detected 1 problem from 1 file

I checked the type of Integer#to_s using rbs method command:

$ bundle exec rbs -Isig method Integer to_s
::Integer#to_s
  defined_in: ::ActiveSupport::NumericWithFormat
  implementation: ::ActiveSupport::NumericWithFormat
  accessibility: public
  types:
      (?untyped? format, ?untyped? options) -> untyped   at /Users/tkomiya/work/tmp/tmp/.gem_rbs_collection/activesupport/7.0/activesupport-generated.rbs:4169:14...4169:62

Could you check the gem is installed on your project? If installed, it's not a bug of Steep.

[tk0miya]

I posted the fix for the type of activesupport gem to the gem_rbs_collection repo. I suppose it will fix your problem. Please check it.