truncator: fix circular references

Fixes #285 (Error in stackframe json)

lib/airbrake-ruby/truncator.rb

@@ -12,10 +12,15 @@ class Truncator
     #   strings with +ENCODING_OPTIONS+
     TEMP_ENCODING = 'utf-16'.freeze
 
+    # @return [String] what to append when something is a circular reference
     CIRCULAR = '[Circular]'.freeze
 
+    # @return [String] what to append when something is truncated
     TRUNCATED = '[Truncated]'.freeze
 
+    # @return [Array<Class>] The types that can contain references to itself
+    CIRCULAR_TYPES = [Array, Hash, Set].freeze
+
     # @param [Integer] max_size maximum size of hashes, arrays and strings
     def initialize(max_size)
       @max_size = max_size
@@ -28,7 +33,10 @@ def initialize(max_size)
     # @param [Set] seen The cache that helps to detect recursion
     # @return [Object] truncated object
     def truncate(object, seen = Set.new)
-      return CIRCULAR if seen.include?(object)
+      if seen.include?(object)
+        return CIRCULAR if CIRCULAR_TYPES.any? { |t| object.is_a?(t) }
+        return object
+      end
       truncate_object(object, seen << object)
     end
 

spec/truncator_spec.rb

@@ -211,5 +211,28 @@ def obj.to_json
         expect(subject).to be_frozen
       end
     end
+
+    context "given an array with hashes and hash-like objects with identical keys" do
+      let(:hashie) { Class.new(Hash) }
+
+      let(:object) do
+        {
+          errors: [
+            { file: 'a' },
+            hashie.new.merge(file: 'bcde')
+          ]
+        }
+      end
+
+      it "truncates values" do
+        expect(subject).to eq(
+          errors: [
+            { file: 'a' },
+            hashie.new.merge(file: 'bcd[Truncated]')
+          ]
+        )
+        expect(subject).to be_frozen
+      end
+    end
   end
 end