Add new Attribute#ivar API

lib/rbs/ast/members.rb

@@ -304,6 +304,21 @@ def update(name: self.name, type: self.type, ivar_name: self.ivar_name, kind: se
             visibility: visibility
           )
         end
+
+        def ivar
+          @ivar ||= begin
+            ivar_name = case self.ivar_name
+            when false
+              return nil # Skip the instance variable declaration entirely
+            when nil
+              :"@#{name}" # Infer the instance variable name from the attribute name
+            else
+              self.ivar_name # Use the custom instance variable name given by the user
+            end
+
+            InstanceVariable.new(name: ivar_name, type: type, location: location, comment: comment)
+          end
+        end
       end
 
       class AttrReader < Base

sig/members.rbs

@@ -185,6 +185,8 @@ module RBS
         include _HashEqual
 
         def update: (?name: Symbol, ?type: Types::t, ?ivar_name: Symbol | false | nil, ?kind: kind, ?annotations: Array[Annotation], ?location: loc?, ?comment: Comment?, ?visibility: visibility?) -> instance
+
+        def ivar: () -> InstanceVariable?
       end
 
       class AttrReader < Base

test/rbs/signature_parsing_test.rb

@@ -361,6 +361,13 @@ def self?.three: -> bool
         assert_equal :a, m.name
         assert_nil m.ivar_name
         assert_equal parse_type("Integer"), m.type
+
+        ivar = m.ivar
+        assert_instance_of Members::InstanceVariable, ivar
+        assert_equal :@a, ivar.name # Inferred from the attribute name
+        assert_equal m.type, ivar.type
+        assert_equal m.location, ivar.location
+        assert_equal m.comment, ivar.comment
       end
 
       module_decl.members[11].yield_self do |m|
@@ -369,6 +376,13 @@ def self?.three: -> bool
         assert_equal :a, m.name
         assert_equal :@A, m.ivar_name
         assert_equal parse_type("String"), m.type
+
+        ivar = m.ivar
+        assert_instance_of Members::InstanceVariable, ivar
+        assert_equal :@A, ivar.name # Explicitly given ivar name
+        assert_equal m.type, ivar.type
+        assert_equal m.location, ivar.location
+        assert_equal m.comment, ivar.comment
       end
 
       module_decl.members[12].yield_self do |m|
@@ -377,6 +391,8 @@ def self?.three: -> bool
         assert_equal :a, m.name
         assert_equal false, m.ivar_name
         assert_equal parse_type("bool"), m.type
+
+        assert_nil m.ivar # The instance variable was explicitly skipped
       end
 
       module_decl.members[13].yield_self do |m|
@@ -385,6 +401,13 @@ def self?.three: -> bool
         assert_equal :b, m.name
         assert_nil m.ivar_name
         assert_equal parse_type("Integer"), m.type
+
+        ivar = m.ivar
+        assert_instance_of Members::InstanceVariable, ivar
+        assert_equal :@b, ivar.name # Inferred from the attribute name
+        assert_equal m.type, ivar.type
+        assert_equal m.location, ivar.location
+        assert_equal m.comment, ivar.comment
       end
 
       module_decl.members[14].yield_self do |m|
@@ -393,6 +416,13 @@ def self?.three: -> bool
         assert_equal :b, m.name
         assert_equal :@B, m.ivar_name
         assert_equal parse_type("String"), m.type
+
+        ivar = m.ivar
+        assert_instance_of Members::InstanceVariable, ivar
+        assert_equal :@B, ivar.name # Explicitly given ivar name
+        assert_equal m.type, ivar.type
+        assert_equal m.location, ivar.location
+        assert_equal m.comment, ivar.comment
       end
 
       module_decl.members[15].yield_self do |m|
@@ -401,6 +431,8 @@ def self?.three: -> bool
         assert_equal :b, m.name
         assert_equal false, m.ivar_name
         assert_equal parse_type("bool"), m.type
+
+        assert_nil m.ivar # The instance variable was explicitly skipped
       end
 
       module_decl.members[16].yield_self do |m|
@@ -409,6 +441,13 @@ def self?.three: -> bool
         assert_equal :c, m.name
         assert_nil m.ivar_name
         assert_equal parse_type("Integer"), m.type
+
+        ivar = m.ivar
+        assert_instance_of Members::InstanceVariable, ivar
+        assert_equal :@c, ivar.name # Inferred from the attribute name
+        assert_equal m.type, ivar.type
+        assert_equal m.location, ivar.location
+        assert_equal m.comment, ivar.comment
       end
 
       module_decl.members[17].yield_self do |m|
@@ -417,6 +456,13 @@ def self?.three: -> bool
         assert_equal :c, m.name
         assert_equal :@C, m.ivar_name
         assert_equal parse_type("String"), m.type
+
+        ivar = m.ivar
+        assert_instance_of Members::InstanceVariable, ivar
+        assert_equal :@C, ivar.name # Explicitly given ivar name
+        assert_equal m.type, ivar.type
+        assert_equal m.location, ivar.location
+        assert_equal m.comment, ivar.comment
       end
 
       module_decl.members[18].yield_self do |m|
@@ -425,6 +471,8 @@ def self?.three: -> bool
         assert_equal :c, m.name
         assert_equal false, m.ivar_name
         assert_equal parse_type("bool"), m.type
+
+        assert_nil m.ivar # The instance variable was explicitly skipped
       end
     end
   end