From 25dc6b119dd4daa7aff1310cb8bdec355d562bea Mon Sep 17 00:00:00 2001
From: Quinton Miller <nicetas.c@gmail.com>
Date: Sat, 4 Sep 2021 17:44:15 +0800
Subject: [PATCH] Allow union types to be unbound

---
 spec/compiler/semantic/union_spec.cr | 27 +++++++++++++++++++++++++++
 src/compiler/crystal/types.cr        |  4 ++++
 2 files changed, 31 insertions(+)

diff --git a/spec/compiler/semantic/union_spec.cr b/spec/compiler/semantic/union_spec.cr
index 61017e7997de..091447a0859d 100644
--- a/spec/compiler/semantic/union_spec.cr
+++ b/spec/compiler/semantic/union_spec.cr
@@ -314,4 +314,31 @@ describe "Semantic: union" do
       Union(Foo)
       )) { types["Foo"].metaclass }
   end
+
+  it "doesn't run virtual lookup on unbound unions (#9173)" do
+    assert_type(%(
+      class Object
+        def foo
+          self
+        end
+      end
+
+      abstract class Parent
+      end
+
+      class Child(T) < Parent
+        @buffer = uninitialized T
+
+        def bar
+          @buffer.foo
+        end
+      end
+
+      class Foo(U)
+        @x = Child(U | Char).new
+      end
+
+      Child(Int32).new.as(Parent).bar
+      )) { int32 }
+  end
 end
diff --git a/src/compiler/crystal/types.cr b/src/compiler/crystal/types.cr
index 21a2e44b40f0..af822c790e24 100644
--- a/src/compiler/crystal/types.cr
+++ b/src/compiler/crystal/types.cr
@@ -3070,6 +3070,10 @@ module Crystal
       program.type_merge(new_union_types) || program.no_return
     end
 
+    def unbound?
+      union_types.any? &.unbound?
+    end
+
     def all?
       union_types.all? { |union_type| yield union_type }
     end