Fix type inference for multiple assignment of generic Array[T]

Handle Type::Instance (e.g. from RBS Array[T]) in MAsgnBox#run0 by
distributing the element type to variables.

Previously, only Type::Array (literal arrays) was handled correctly.
For other types, it assigned the entire array object to the first variable
on the left-hand side, leaving subsequent variables as untyped.

Author: sekito1107

lib/typeprof/core/graph/box.rb

@@ -1156,25 +1156,27 @@ def destroy(genv)
     def ret = @rhs
 
     def run0(genv, changes)
-      edges = []
       @value.each_type do |ty|
         # TODO: call to_ary?
         case ty
         when Type::Array
-          edges.concat(ty.splat_assign(genv, @lefts, @rest_elem, @rights))
-        else
-          if @lefts.size >= 1
-            edges << [Source.new(ty), @lefts[0]]
-          elsif @rights && @rights.size >= 1
-            edges << [Source.new(ty), @rights[0]]
+          ty.splat_assign(genv, @lefts, @rest_elem, @rights).each do |src, dst|
+            changes.add_edge(genv, src, dst)
+          end
+        when Type::Instance
+          if ty.mod == genv.mod_ary && (elem_vtx = ty.args[0])
+            @lefts.each {|lhs| changes.add_edge(genv, elem_vtx, lhs) }
+            changes.add_edge(genv, elem_vtx, @rest_elem) if @rest_elem
+            @rights&.each {|rhs| changes.add_edge(genv, elem_vtx, rhs) }
           else
-            edges << [Source.new(ty), @rest_elem]
+            lhs = @lefts[0] || (@rights && @rights[0]) || @rest_elem
+            changes.add_edge(genv, Source.new(ty), lhs) if lhs
           end
+        else
+          lhs = @lefts[0] || (@rights && @rights[0]) || @rest_elem
+          changes.add_edge(genv, Source.new(ty), lhs) if lhs
         end
       end
-      edges.each do |src, dst|
-        changes.add_edge(genv, src, dst)
-      end
     end
   end
 

scenario/variable/masgn-generic-array.rb

@@ -0,0 +1,23 @@
+## update: test.rbs
+class Foo
+  def get_ints: () -> Array[Integer]
+end
+
+## update: test.rb
+class Foo
+  def test_masgn
+    a, b, c = get_ints
+    [a, b, c]
+  end
+
+  def test_star
+    a, *rest = get_ints
+    rest
+  end
+end
+
+## assert: test.rb
+class Foo
+  def test_masgn: -> [Integer, Integer, Integer]
+  def test_star: -> Array[Integer]
+end