From 29e1b711dc76efec1265f7e3ad2983c68b8c837d Mon Sep 17 00:00:00 2001
From: Quinton Miller <nicetas.c@gmail.com>
Date: Mon, 24 Feb 2025 03:49:28 +0800
Subject: [PATCH] Add file name to file-private metaclass types during codegen
 (#15505)

File-private types with the same name get collapsed into a single type during codegen, which messes up any dispatch over them: only one of their type IDs is considered, and the other is assumed to be unreachable.
Adding the file name as namespace keeps them apart.
---
 spec/compiler/codegen/class_spec.cr | 32 +++++++++++++++++++++++++++++
 src/compiler/crystal/types.cr       |  6 ++++++
 2 files changed, 38 insertions(+)

diff --git a/spec/compiler/codegen/class_spec.cr b/spec/compiler/codegen/class_spec.cr
index c6c697f29e29..e16788d453b4 100644
--- a/spec/compiler/codegen/class_spec.cr
+++ b/spec/compiler/codegen/class_spec.cr
@@ -659,6 +659,38 @@ describe "Code gen: class" do
       )).to_string.should eq("Baz")
   end
 
+  it "does not combine types with same name but different file scopes (#15503)" do
+    run(<<-CRYSTAL, Int32, filename: "foo.cr").should eq(11)
+      module Foo
+        def self.foo
+          1
+        end
+      end
+
+      alias Bar = Foo
+
+      {% Bar %} # forces immediate resolution of `Bar`
+
+      private module Foo
+        def self.foo
+          10
+        end
+      end
+
+      module Baz
+        def self.foo
+          100
+        end
+      end
+
+      def foo(x)
+        x.foo
+      end
+
+      foo(Foo || Baz) &+ foo(Bar || Baz)
+      CRYSTAL
+  end
+
   it "builds generic class bug" do
     codegen(%(
       abstract class Base
diff --git a/src/compiler/crystal/types.cr b/src/compiler/crystal/types.cr
index 7df02924793f..dc2be80b0ae2 100644
--- a/src/compiler/crystal/types.cr
+++ b/src/compiler/crystal/types.cr
@@ -2935,6 +2935,12 @@ module Crystal
     end
 
     def to_s_with_options(io : IO, skip_union_parens : Bool = false, generic_args : Bool = true, codegen : Bool = false) : Nil
+      if codegen
+        if (namespace = instance_type.namespace).is_a?(FileModule)
+          namespace.to_s_with_options(io, generic_args: false, codegen: codegen)
+          io << "::"
+        end
+      end
       io << @name
     end