Prioritize RBS ivar declarations over inferred types on read

lib/typeprof/core/ast/sig_decl.rb

@@ -505,20 +505,20 @@ def attrs = { cpath:, class_scope: }
 
       def define0(genv)
         @type.define(genv)
-        mod = genv.resolve_ivar(cpath, @class_scope, @var)
-        mod.add_decl(self)
-        mod
+        mod = genv.resolve_cpath(cpath)
+        mod.add_ivar_decl(genv, @class_scope, @var, self)
       end
 
       def define_copy(genv)
-        mod = genv.resolve_ivar(cpath, @class_scope, @var)
-        mod.add_decl(self)
-        mod.remove_decl(@prev_node)
+        mod = genv.resolve_cpath(cpath)
+        mod.add_ivar_decl(genv, @class_scope, @var, self)
+        mod.remove_ivar_decl(genv, @class_scope, @var, @prev_node)
         super(genv)
       end
 
       def undefine0(genv)
-        genv.resolve_ivar(cpath, @class_scope, @var).remove_decl(self)
+        mod = genv.resolve_cpath(cpath)
+        mod.remove_ivar_decl(genv, @class_scope, @var, self)
         @type.undefine(genv)
       end
 

lib/typeprof/core/env/module_entity.rb

@@ -436,6 +436,19 @@ def get_ivar(singleton, name)
       @ivars[singleton][name] ||= ValueEntity.new
     end
 
+    def add_ivar_decl(genv, singleton, name, decl)
+      ive = get_ivar(singleton, name)
+      ive.add_decl(decl)
+      ive.on_decl_changed(genv)
+      ive
+    end
+
+    def remove_ivar_decl(genv, singleton, name, decl)
+      ive = get_ivar(singleton, name)
+      ive.remove_decl(decl)
+      ive.on_decl_changed(genv)
+    end
+
     def get_cvar(name)
       @cvars[name] ||= ValueEntity.new
     end

lib/typeprof/core/env/value_entity.rb

@@ -17,6 +17,14 @@ def remove_decl(decl)
       @decls.delete(decl) || raise
     end
 
+    # Re-run all read boxes that depend on this entity. Used when a
+    # declaration is added or removed so that dependents (e.g. an
+    # IVarReadBox that previously fell back to the inferred type) can
+    # observe the new state.
+    def on_decl_changed(genv)
+      @read_boxes.each {|box| genv.add_run(box) }
+    end
+
     def add_def(def_)
       @defs << def_
     end

lib/typeprof/core/graph/box.rb

@@ -1280,23 +1280,44 @@ def run0(genv, changes)
       singleton = @singleton
       cur_ive = mod.get_ivar(singleton, @name)
       target_vtx = nil
+      target_decls = nil
       genv.each_direct_superclass(mod, singleton) do |mod, singleton|
         ive = mod.get_ivar(singleton, @name)
+        # Subscribe to every visited ive so that, if one later acquires an
+        # RBS declaration, this box is re-run and switches to the declared
+        # type instead of the inferred one.
+        changes.add_depended_value_entity(ive)
         if ive.exist?
           target_vtx = ive.vtx
+          target_decls = ive.decls unless ive.decls.empty?
+          break if target_decls
         end
       end
-      edges = []
-      if target_vtx
+
+      if target_decls
+        # When declarations exist, return declared types instead of assigned types
+        target_decls.each do |decl|
+          subst = {}
+          if decl.cpath
+            decl_mod = genv.resolve_cpath(decl.cpath)
+            if decl_mod.type_params && !decl_mod.type_params.empty?
+              subst = decl_mod.type_params.to_h do |param, _default_ty|
+                [param, Vertex.new(@node)]
+              end
+            end
+          end
+          vtx = decl.type.covariant_vertex(genv, changes, subst)
+          changes.add_edge(genv, vtx, @ret)
+        end
+      elsif target_vtx
+        edges = []
         if target_vtx != cur_ive.vtx
           edges << [cur_ive.vtx, @proxy] << [@proxy, target_vtx]
         end
         edges << [target_vtx, @ret]
-      else
-        # TODO: error?
-      end
-      edges.each do |src, dst|
-        changes.add_edge(genv, src, dst)
+        edges.each do |src, dst|
+          changes.add_edge(genv, src, dst)
+        end
       end
     end
   end

scenario/rbs/ivar_decl_late_load.rb

@@ -0,0 +1,21 @@
+## update: test.rb
+class Foo
+  def initialize
+    @x = nil
+  end
+
+  def get_x
+    @x
+  end
+end
+
+## update: test.rbs
+class Foo
+  @x: Integer
+end
+
+## assert: test.rb
+class Foo
+  def initialize: -> void
+  def get_x: -> Integer
+end

scenario/rbs/ivar_decl_priority.rb

@@ -0,0 +1,34 @@
+## update: test.rbs
+class Base
+end
+
+class Child < Base
+  @x: Integer
+end
+
+## update: test.rb
+class Base
+  def initialize
+    @x = nil
+  end
+end
+
+class Child < Base
+  def initialize
+    super
+    @x = 1
+  end
+
+  def get_x
+    @x
+  end
+end
+
+## assert
+class Base
+  def initialize: -> void
+end
+class Child < Base
+  def initialize: -> void
+  def get_x: -> Integer
+end