Allow rescuing exceptions that include a module

spec/compiler/codegen/exception_spec.cr

@@ -1319,4 +1319,97 @@ describe "Code gen: exception" do
       end
     ))
   end
+
+  it "handles rescuing module type" do
+    run(%(
+      require "prelude"
+
+      module Foo; end
+
+      class Ex1 < Exception
+        include Foo
+      end
+
+      x = 0
+      begin
+        raise Ex1.new
+      rescue Foo
+        x = 1
+      end
+      x
+      )).to_i.should eq(1)
+  end
+
+  it "handles rescuing union between module type and class type" do
+    run(%(
+      require "prelude"
+
+      module Foo; end
+
+      abstract class BaseError < Exception; end
+      class Ex2 < BaseError; end
+
+      class Ex1 < BaseError
+        include Foo
+      end
+
+      x = 0
+      begin
+        raise Ex1.new
+      rescue Foo | BaseError
+        x = 1
+      end
+      x
+      )).to_i.should eq(1)
+  end
+
+  it "handles rescuing union between module types" do
+    run(%(
+      require "prelude"
+
+      module Foo; end
+      module Bar; end
+
+      class Ex1 < Exception
+        include Foo
+      end
+
+      class Ex2 < Exception
+        include Bar
+      end
+
+      x = 0
+      begin
+        raise Ex1.new
+      rescue Foo | Bar
+        x = 1
+      end
+      x
+      )).to_i.should eq(1)
+  end
+
+  it "does not rescue just any module" do
+    run(%(
+      require "prelude"
+
+      module Foo; end
+      module Bar; end
+
+      class Ex < Exception
+        include Foo
+      end
+
+      x = 0
+      begin
+        begin
+          raise Ex.new("oh no")
+        rescue Bar
+          x = 1
+        end
+      rescue ex
+        x = 2
+      end
+      x
+      )).to_i.should eq(2)
+  end
 end

src/compiler/crystal/semantic/main_visitor.cr

@@ -2775,7 +2775,7 @@ module Crystal
         types = node_types.map do |type|
           type.accept self
           instance_type = type.type.instance_type
-          unless instance_type.implements?(@program.exception)
+          unless instance_type.implements?(@program.exception) || instance_type.module?
             type.raise "#{instance_type} is not a subclass of Exception"
           end
           instance_type