Add hover support for :through associations

Author: joshuay03

lib/ruby_lsp/ruby_lsp_rails/hover.rb

@@ -118,26 +118,44 @@ def format_default(default_value, type)
 
       #: (Prism::SymbolNode node) -> void
       def handle_possible_dsl(node)
-        node = @node_context.call_node
-        return unless node
-        return unless self_receiver?(node)
+        call_node = @node_context.call_node
+        return unless call_node
+        return unless self_receiver?(call_node)
 
-        message = node.message
+        message = call_node.message
 
         return unless message
 
         if Support::Associations::ALL.include?(message)
-          handle_association(node)
+          handle_association(node, call_node)
         end
       end
 
-      #: (Prism::CallNode node) -> void
-      def handle_association(node)
-        first_argument = node.arguments&.arguments&.first
+      #: ((Prism::SymbolNode | Prism::StringNode) node, Prism::CallNode call_node) -> void
+      def handle_association(node, call_node)
+        arguments = call_node.arguments&.arguments
+        return unless arguments
+
+        first_argument = arguments.first
         return unless first_argument.is_a?(Prism::SymbolNode)
 
         association_name = first_argument.unescaped
 
+        through_element = arguments
+          .filter_map { |arg| arg.elements if arg.is_a?(Prism::KeywordHashNode) }
+          .flatten
+          .find { |elem| elem.key.value == "through" }
+
+        if node == first_argument
+          handle_association_name(association_name)
+        elsif through_element && node == through_element.value
+          through_association_name = through_element.value.unescaped
+          handle_association_name(through_association_name)
+        end
+      end
+
+      #: (String association_name) -> void
+      def handle_association_name(association_name)
         result = @client.association_target(
           model_name: @nesting.join("::"),
           association_name: association_name,

test/ruby_lsp_rails/hover_test.rb

@@ -321,6 +321,106 @@ class Bar < ApplicationRecord
         CONTENT
       end
 
+      test "returns main association on has_many :through association" do
+        expected_response = {
+          location: "#{dummy_root}/app/models/user.rb:2",
+          name: "User",
+        }
+        RunnerClient.any_instance.stubs(association_target: expected_response)
+
+        response = hover_on_source(<<~RUBY, { line: 4, character: 12 })
+          # typed: false
+
+          class Organization < ActiveRecord::Base
+            has_many :memberships
+            has_many :users, through: :memberships
+          end
+        RUBY
+
+        assert_equal(<<~CONTENT.chomp, response.contents.value)
+          ```ruby
+          User
+          ```
+
+          **Definitions**: [fake.rb](file:///fake.rb#L2,1-2,4)
+        CONTENT
+      end
+
+      test "returns main association on has_one :through association" do
+        expected_response = {
+          location: "#{dummy_root}/app/models/flag.rb:2",
+          name: "Flag",
+        }
+        RunnerClient.any_instance.stubs(association_target: expected_response)
+
+        response = hover_on_source(<<~RUBY, { line: 4, character: 19 })
+          # typed: false
+
+          class User < ActiveRecord::Base
+            belongs_to :location, class_name: "Country"
+            has_one :country_flag, through: :location, source: :flag
+          end
+        RUBY
+
+        assert_equal(<<~CONTENT.chomp, response.contents.value)
+          ```ruby
+          Flag
+          ```
+
+          **Definitions**: [fake.rb](file:///fake.rb#L2,1-2,4)
+        CONTENT
+      end
+
+      test "returns through association on has_many :through association" do
+        expected_response = {
+          location: "#{dummy_root}/app/models/membership.rb:3",
+          name: "Membership",
+        }
+        RunnerClient.any_instance.stubs(association_target: expected_response)
+
+        response = hover_on_source(<<~RUBY, { line: 4, character: 29 })
+          # typed: false
+
+          class Organization < ActiveRecord::Base
+            has_many :memberships
+            has_many :users, through: :memberships
+          end
+        RUBY
+
+        assert_equal(<<~CONTENT.chomp, response.contents.value)
+          ```ruby
+          Membership
+          ```
+
+          **Definitions**: [fake.rb](file:///fake.rb#L3,1-3,4)
+        CONTENT
+      end
+
+      test "returns through association on has_one :through association" do
+        expected_response = {
+          location: "#{dummy_root}/app/models/country.rb:2",
+          name: "Country",
+        }
+        RunnerClient.any_instance.stubs(association_target: expected_response)
+
+        response = hover_on_source(<<~RUBY, { line: 4, character: 35 })
+          # typed: false
+
+          class User < ActiveRecord::Base
+            belongs_to :location, class_name: "Country"
+            has_one :country_flag, through: :location, source: :flag
+          end
+        RUBY
+
+        assert_equal(<<~CONTENT.chomp, response.contents.value)
+          ```ruby
+          Country
+          ```
+
+          **Definitions**: [fake.rb](file:///fake.rb#L2,1-2,4)
+        CONTENT
+      end
+
       private
 
       def hover_on_source(source, position)