Extend the functionality of hover in rbs files.

lib/steep/server/interaction_worker.rb

@@ -107,7 +107,27 @@ def format_hover(content)
 #{comment}
 
 ```rbs
-#{content.decl.type}
+#{retrieve_decl_information(content.decl)}
+```
+          MD
+        when Services::HoverContent::InterfaceContent
+          comment = content.decl.comment&.string || ''
+
+          <<-MD
+#{comment}
+
+```rbs
+#{retrieve_decl_information(content.decl)}
+```
+          MD
+        when Services::HoverContent::ClassContent
+          comment = content.decl.comment&.string || ''
+
+          <<-MD
+#{comment}
+
+```rbs
+#{retrieve_decl_information(content.decl)}
 ```
           MD
         when Services::HoverContent::VariableContent
@@ -188,6 +208,59 @@ def process_completion(job)
         end
       end
 
+      def name_and_params(name, params)
+        if params.empty?
+          "#{name}"
+        else
+          ps = params.each.map do |param|
+            s = ""
+            if param.skip_validation
+              s << "unchecked "
+            end
+            case param.variance
+            when :invariant
+              # nop
+            when :covariant
+              s << "out "
+            when :contravariant
+              s << "in "
+            end
+            s + param.name.to_s
+          end
+
+          "#{name}[#{ps.join(", ")}]"
+        end
+      end
+
+      def name_and_args(name, args)
+        if name && args
+          if args.empty?
+            "#{name}"
+          else
+            "#{name}[#{args.join(", ")}]"
+          end
+        end
+      end
+
+      def retrieve_decl_information(decl)
+        case decl
+        when RBS::AST::Declarations::Class
+          super_class = if super_class = decl.super_class
+                          " < #{name_and_args(super_class.name, super_class.args)}"
+                        end
+          "class #{name_and_params(decl.name, decl.type_params)}#{super_class}"
+        when RBS::AST::Declarations::Module
+          self_type = unless decl.self_types.empty?
+                        " : #{decl.self_types.join(", ")}"
+                      end
+          "module #{name_and_params(decl.name, decl.type_params)}#{self_type}"
+        when RBS::AST::Declarations::Alias
+          "type #{decl.name} = #{decl.type}"
+        when RBS::AST::Declarations::Interface
+          "interface #{name_and_params(decl.name, decl.type_params)}"
+        end
+    end
+
       def format_completion_item(item)
         range = LanguageServer::Protocol::Interface::Range.new(
           start: LanguageServer::Protocol::Interface::Position.new(

lib/steep/services/hover_content.rb

@@ -6,6 +6,9 @@ class HoverContent
       MethodCallContent = Struct.new(:node, :method_name, :type, :definition, :location, keyword_init: true)
       DefinitionContent = Struct.new(:node, :method_name, :method_type, :definition, :location, keyword_init: true) do
       TypeAliasContent = Struct.new(:location, :decl, keyword_init: true)
+      ClassContent = Struct.new(:location, :decl, keyword_init: true)
+      InterfaceContent = Struct.new(:location, :decl, keyword_init: true)
+
         def comment_string
           if comments = definition&.comments
             comments.map {|c| c.string.chomp }.uniq.join("\n----\n")
@@ -76,6 +79,25 @@ def content_for(path:, line:, column:)
               location: location,
               decl: alias_decl
             )
+          when RBS::Types::ClassInstance, RBS::Types::ClassSingleton
+            if hd == :name
+              env = service.latest_env
+              class_decl = env.class_decls[type.name]&.decls[0]&.decl or raise
+              location = tail[0].location[:name]
+              ClassContent.new(
+                location: location,
+                decl: class_decl
+              )
+            end
+          when RBS::Types::Interface
+            env = service.latest_env
+            interface_decl = env.interface_decls[type.name]&.decl or raise
+            location = type.location[:name]
+
+            InterfaceContent.new(
+              location: location,
+              decl: interface_decl
+            )
           end
         end
       end

test/hover_test.rb

@@ -218,9 +218,9 @@ def foo: (Integer x) -> String
     end
   end
 
-  def test_hover_on_rbs
+  def test_hover_alias_on_rbs
     in_tmpdir do
-      service = typecheck_service()
+      service = typecheck_service
 
       service.update(
         changes: {
@@ -246,6 +246,86 @@ def f: (foo) -> void
     end
   end
 
+  def test_hover_class_singleton_on_rbs
+    in_tmpdir do
+      service = typecheck_service
+
+      service.update(
+        changes: {
+          Pathname("hello.rbs") => [ContentChange.string(<<RBS)]
+class C
+  def foo: () -> singleton(String)
+end
+RBS
+        }
+      ) {}
+
+      hover = HoverContent.new(service: service)
+      hover.content_for(path: Pathname("hello.rbs"), line: 2, column: 28).tap do |content|
+        assert_instance_of HoverContent::ClassContent, content
+        assert_instance_of RBS::Location, content.location
+        assert_equal content.location.start_line, 2
+        assert_equal content.location.start_column, 27
+        assert_instance_of RBS::AST::Declarations::Class, content.decl
+      end
+    end
+  end
+
+  def test_hover_class_instance_on_rbs
+    in_tmpdir do
+      service = typecheck_service
+
+      service.update(
+        changes: {
+          Pathname("hello.rbs") => [ContentChange.string(<<RBS)]
+class Hoge end
+class Qux
+  @foo: Hoge
+end
+RBS
+        }
+      ) {}
+
+      hover = HoverContent.new(service: service)
+      hover.content_for(path: Pathname("hello.rbs"), line: 3, column: 9).tap do |content|
+        assert_instance_of HoverContent::ClassContent, content
+        assert_instance_of RBS::Location, content.location
+        assert_equal content.location.start_line, 3
+        assert_equal content.location.start_column, 8
+        assert_instance_of RBS::AST::Declarations::Class, content.decl
+      end
+    end
+  end
+
+  def test_hover_interface_on_rbs
+    in_tmpdir do
+      service = typecheck_service()
+
+      service.update(
+        changes: {
+          Pathname("hello.rbs") => [ContentChange.string(<<RBS)]
+interface _Fooable
+  def foo: () -> nil
+end
+
+class Foo
+  def foo: (_Fooable) -> singleton(String)
+end
+RBS
+        }
+      ) {}
+
+      hover = HoverContent.new(service: service)
+      hover.content_for(path: Pathname("hello.rbs"), line: 6, column: 13).tap do |content|
+        assert_instance_of HoverContent::InterfaceContent, content
+        assert_instance_of RBS::Location, content.location
+        assert_equal content.location.start_line, 6
+        assert_equal content.location.start_column, 12
+        assert_instance_of RBS::AST::Declarations::Interface, content.decl
+      end
+    end
+  end
+
   def test_hover_on_syntax_error
     in_tmpdir do
       service = typecheck_service()

test/interaction_worker_test.rb

@@ -173,7 +173,7 @@ def test_handle_hover_job_success
     end
   end
 
-  def test_handle_hover_job_success_on_rbs
+  def test_handle_alias_hover_job_success_on_rbs
     in_tmpdir do
       project = Project.new(steepfile_path: current_dir + "Steepfile")
       Project::DSL.parse(project, <<EOF)
@@ -205,14 +205,96 @@ def f: (foo) -> void
 
 
 ```rbs
-::Integer | ::String
+type ::foo = ::Integer | ::String
 ```
 "
       assert_equal({ kind: "markdown", value: expected_value }, response[:contents])
       assert_equal({ start: { line: 4, character: 10 }, end: { line: 4, character: 13 }}, response[:range])
     end
   end
 
+  def test_handle_interface_hover_job_success_on_rbs
+    in_tmpdir do
+      project = Project.new(steepfile_path: current_dir + "Steepfile")
+      Project::DSL.parse(project, <<EOF)
+target :lib do
+  check "lib"
+  signature "sig"
+end
+EOF
+
+      worker = InteractionWorker.new(project: project, reader: worker_reader, writer: worker_writer)
+
+      worker.service.update(
+        changes: {
+          Pathname("sig/hello.rbs") => [ContentChange.string(<<RBS)]
+# here is your comments
+interface _Fooable
+  def foo: () -> nil
+end
+
+class Test
+  def foo: (_Fooable) -> nil
+end
+RBS
+        }
+      ) {}
+
+      response = worker.process_hover(InteractionWorker::HoverJob.new(path: Pathname("sig/hello.rbs"), line: 7, column: 13))
+
+      response = response.attributes
+      expected_value = "here is your comments
+
+
+```rbs
+interface ::_Fooable
+```
+"
+      assert_equal({ kind: "markdown", value: expected_value }, response[:contents])
+      assert_equal({ start: { line: 6, character: 12 }, end: { line: 6, character: 20 }}, response[:range])
+    end
+  end
+
+  def test_handle_class_hover_job_success_on_rbs
+    in_tmpdir do
+      project = Project.new(steepfile_path: current_dir + "Steepfile")
+      Project::DSL.parse(project, <<EOF)
+target :lib do
+  check "lib"
+  signature "sig"
+end
+EOF
+
+      worker = InteractionWorker.new(project: project, reader: worker_reader, writer: worker_writer)
+
+      worker.service.update(
+        changes: {
+          Pathname("sig/hello.rbs") => [ContentChange.string(<<RBS)]
+# here is your comments
+class Foo [T] < Parent[T] end
+class Parent [in T] end
+module Hoge end
+class Qux
+  @foo: Foo[Hoge]
+end
+RBS
+        }
+      ) {}
+
+      response = worker.process_hover(InteractionWorker::HoverJob.new(path: Pathname("sig/hello.rbs"), line: 6, column: 10))
+
+      response = response.attributes
+      expected_value = "here is your comments
+
+
+```rbs
+class ::Foo[T] < ::Parent[T]
+```
+"
+      assert_equal({ kind: "markdown", value: expected_value }, response[:contents])
+      assert_equal({ start: { line: 5, character: 8 }, end: { line: 5, character: 11 }}, response[:range])
+    end
+  end
 
   def test_handle_hover_invalid
     in_tmpdir do