From ed8cf0c0c285abab24479b7af3bc73f2c7340822 Mon Sep 17 00:00:00 2001
From: Paul Buetow <paul@buetow.org>
Date: Mon, 17 Feb 2025 00:12:20 +0200
Subject: can detect dependency loop

---
 lib/dslkeywords/resource.rb             | 19 +++++++++++++++----
 test/lib/dslkeywords/dependency_test.rb | 17 +++++++++++++++++
 2 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/lib/dslkeywords/resource.rb b/lib/dslkeywords/resource.rb
index 1634061..2320077 100644
--- a/lib/dslkeywords/resource.rb
+++ b/lib/dslkeywords/resource.rb
@@ -40,14 +40,25 @@ module RCM
   module DependencyEvaluator
     attr_reader :evaluated
 
+    class DependencyLoop < StandardError; end
+    class UnresolvedDependency < StandardError; end
+
     def evaluate!
       return false if @evaluated
 
+      raise DependencyLoop, "Dependency loop detected for #{id}" if @loop_detection
+
+      @loop_detection = true
       @depends_on = {} if @depends_on.nil?
-      @depends_on.each_key do |id|
-        dependency = Resource.find(id)
-      end
 
+      # Try to evaluate all dependencies recursively.
+      @depends_on.each_key.map { Resource.find(_1) }.each(&:evaluate!)
+
+      # Raise an exception when there are still unresolved dependencies.
+      unresolved = @depends_on.each_key.map { Resource.find(_1) }.reject(&:evaluated)
+      raise UnresolvedDependency, "Unresolved dependencies: #{unresolved.map(&:id)}" if unresolved.count.positive?
+
+      @loop_detection = false
       @evaluated = true
     end
   end
@@ -61,7 +72,7 @@ module RCM
 
     def self.find(id)
       klass = Object.const_get("RCM::#{id.split('(').first.capitalize}")
-      resource = ObjectSpace.each_object(klass).find { |obj| obj.id == id }
+      resource = ObjectSpace.each_object(klass).find { _1.id == id }
       raise NoSuchResourceObject, "Unable to find resource #{id}" if resource.nil?
 
       resource
diff --git a/test/lib/dslkeywords/dependency_test.rb b/test/lib/dslkeywords/dependency_test.rb
index e9bc205..f1280eb 100644
--- a/test/lib/dslkeywords/dependency_test.rb
+++ b/test/lib/dslkeywords/dependency_test.rb
@@ -48,4 +48,21 @@ class RCMDependencyTest < Minitest::Test
       end
     end
   end
+
+  def test_dependency_loop
+    assert_raises(RCM::DependencyEvaluator::DependencyLoop) do
+      configure_from_scratch do
+        notify('loop') { depends_on notify('loop') }
+      end
+    end
+  end
+
+  def test_dependency_loop_indirect
+    assert_raises(RCM::DependencyEvaluator::DependencyLoop) do
+      configure_from_scratch do
+        notify('loop') { depends_on notify('pool') }
+        notify('pool') { depends_on notify('loop') }
+      end
+    end
+  end
 end
-- 
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