FI-1704: Prevent initialization from modifying arguments

lib/fhir_models/bootstrap/hashable.rb

@@ -27,31 +27,35 @@ def prune(thing)
       blank = ->(obj) { obj.respond_to?(:empty?) ? obj.empty? : obj.nil? }
       if thing.is_a?(Array)
         return nil if thing.empty?
-        thing.map! { |i| prune(i) }
-        thing.reject!(&blank)
+
+        thing
+          .map { |i| prune(i) }
+          .reject(&blank)
       elsif thing.is_a?(Hash)
         return {} if thing.empty?
+
+        new_thing = {}
         thing.each do |key, value|
-          thing[key] = prune(value)
-        end
-        thing.delete_if do |_key, value|
-          blank.call(value)
+          new_thing[key] = prune(value) unless blank.call(value)
         end
+        new_thing
+      else
+        thing
       end
-      thing
     end
 
-    def from_hash(hash)
+    def from_hash(original_hash)
       # eliminate empty stuff
-      hash = prune(hash) unless hash.empty?
+      pruned_hash = prune(original_hash) unless original_hash.empty?
       # clear the existing variables
       self.class::METADATA.each do |key, value|
         local_name = key
         local_name = value['local_name'] if value['local_name']
         instance_variable_set("@#{local_name}", nil)
       end
       # set the variables to the hash values
-      hash.each do |key, value|
+      pruned_hash&.each_key do |key|
+        value = original_hash[key]
         key = key.to_s
         meta = self.class::METADATA[key]
         next if meta.nil?

test/unit/hashable_test.rb

@@ -1,10 +1,26 @@
 require_relative '../test_helper'
+
 class HashableTest < Test::Unit::TestCase
+  def test_to_hash
+    patient = FHIR::Patient.new
+    patient_hash = patient.to_hash
+    assert patient_hash.is_a?(Hash)
+  end
 
-def test_to_hash
-  patient = FHIR::Patient.new
-  patient_hash = patient.to_hash
-  assert patient_hash.is_a?(Hash)
-end
+  def test_prune_does_not_modify_hash
+    original_hash = {
+      a: nil,
+      b: [],
+      c: {},
+      d: [[]],
+      e: { a: nil, b: { c: [] }, d: [] }
+    }
+
+    original_hash_string = JSON.generate(original_hash)
+    resource = FHIR::Patient.new
 
-end
+    resource.send(:prune, original_hash)
+
+    assert JSON.generate(original_hash) == original_hash_string
+  end
+end