From 4b62e90c1049f2ecf2792a59ee21dc76b53de720 Mon Sep 17 00:00:00 2001
From: Quinton Miller <nicetas.c@gmail.com>
Date: Mon, 22 Mar 2021 17:16:37 +0800
Subject: [PATCH] Detect cyclic includes between generic modules

---
 spec/compiler/semantic/module_spec.cr | 61 +++++++++++++++++++++++++++
 src/compiler/crystal/types.cr         | 20 ++++++---
 2 files changed, 74 insertions(+), 7 deletions(-)

diff --git a/spec/compiler/semantic/module_spec.cr b/spec/compiler/semantic/module_spec.cr
index 457f00fe6a4a..2853f6936775 100644
--- a/spec/compiler/semantic/module_spec.cr
+++ b/spec/compiler/semantic/module_spec.cr
@@ -477,6 +477,67 @@ describe "Semantic: module" do
       ", "cyclic include detected"
   end
 
+  it "gives error when including self, generic module" do
+    assert_error "
+      module Foo(T)
+        include self
+      end
+      ", "cyclic include detected"
+  end
+
+  it "gives error when including instantiation of self, generic module" do
+    assert_error "
+      module Foo(T)
+        include Foo(Int32)
+      end
+      ", "cyclic include detected"
+  end
+
+  it "gives error with cyclic include, generic module" do
+    assert_error "
+      module Foo(T)
+      end
+
+      module Bar(T)
+        include Foo(T)
+      end
+
+      module Foo(T)
+        include Bar(T)
+      end
+      ", "cyclic include detected"
+  end
+
+  it "gives error with cyclic include between non-generic and generic module" do
+    assert_error "
+      module Foo
+      end
+
+      module Bar(T)
+        include Foo
+      end
+
+      module Foo
+        include Bar(Int32)
+      end
+      ", "cyclic include detected"
+  end
+
+  it "gives error with cyclic include between non-generic and generic module (2)" do
+    assert_error "
+      module Bar(T)
+      end
+
+      module Foo
+        include Bar(Int32)
+      end
+
+      module Bar(T)
+        include Foo
+      end
+      ", "cyclic include detected"
+  end
+
   it "finds types close to included module" do
     assert_type("
       module Foo
diff --git a/src/compiler/crystal/types.cr b/src/compiler/crystal/types.cr
index 11494bdaf7d4..c427e937217c 100644
--- a/src/compiler/crystal/types.cr
+++ b/src/compiler/crystal/types.cr
@@ -959,16 +959,22 @@ module Crystal
     end
 
     def include(mod)
-      if mod == self
-        raise TypeException.new "cyclic include detected"
-      elsif mod.ancestors.includes?(self)
+      generic_module = mod.is_a?(GenericModuleInstanceType) ? mod.generic_type : mod
+
+      if generic_module == self
         raise TypeException.new "cyclic include detected"
-      else
-        unless parents.includes?(mod)
-          parents.insert 0, mod
-          mod.add_including_type(self)
+      end
+
+      generic_module.ancestors.each do |ancestor|
+        if ancestor == self || ancestor.is_a?(GenericModuleInstanceType) && ancestor.generic_type == self
+          raise TypeException.new "cyclic include detected"
         end
       end
+
+      unless parents.includes?(mod)
+        parents.insert 0, mod
+        mod.add_including_type(self)
+      end
     end
 
     def covariant?(other_type)