Merge pull request #3440 from rmosolgo/fix-union-interface-field-merging

Fix fields-will-merge for fields that return unions and have spreads on mutually exclusive interfaces

Author: Robert Mosolgo

lib/graphql/static_validation/rules/fields_will_merge.rb

@@ -373,17 +373,26 @@ def compared_fragments_key(frag1, frag2, exclusive)
       # In this context, `parents` represends the "self scope" of the field,
       # what types may be found at this point in the query.
       def mutually_exclusive?(parents1, parents2)
-        parents1.each do |type1|
-          parents2.each do |type2|
-            # If the types we're comparing are both different object types,
-            # they have to be mutually exclusive.
-            if type1 != type2 && type1.kind.object? && type2.kind.object?
-              return true
+        if parents1.empty? || parents2.empty?
+          false
+        elsif parents1.length == parents2.length
+          parents1.length.times.any? do |i|
+            type1 = parents1[i - 1]
+            type2 = parents2[i - 1]
+            if type1 == type2
+              # If the types we're comparing are the same type,
+              # then they aren't mutually exclusive
+              false
+            else
+              # Check if these two scopes have _any_ types in common.
+              possible_right_types = context.query.possible_types(type1)
+              possible_left_types = context.query.possible_types(type2)
+              (possible_right_types & possible_left_types).empty?
             end
           end
+        else
+          true
         end
-
-        false
       end
     end
   end

spec/graphql/static_validation/rules/fields_will_merge_spec.rb

@@ -11,8 +11,11 @@
         cat: Cat
         pet: Pet
         toy: Toy
+        animal: Animal
       }
 
+      union Animal = Dog \| Cat
+
       type Mutation {
         registerPet(params: PetParams): Pet
       }
@@ -50,15 +53,23 @@
         toys: [Toy!]!
       }
 
-      type Dog implements Pet & Mammal {
+      interface Canine {
+        barkVolume: Int!
+      }
+
+      interface Feline {
+        meowVolume: Int!
+      }
+
+      type Dog implements Pet & Mammal & Canine {
         name(surname: Boolean = false): String!
         nickname: String
         doesKnowCommand(dogCommand: PetCommand): Boolean!
         barkVolume: Int!
         toys: [Toy!]!
       }
 
-      type Cat implements Pet & Mammal {
+      type Cat implements Pet & Mammal & Feline {
         name(surname: Boolean = false): String!
         nickname: String
         doesKnowCommand(catCommand: PetCommand): Boolean!
@@ -477,6 +488,25 @@
     end
   end
 
+  describe "same aliases on divergent abstract types" do
+    let(:query_string) {%|
+      {
+        animal {
+          ... on Feline {
+            volume: meowVolume
+          }
+          ... on Canine {
+            volume: barkVolume
+          }
+        }
+      }
+    |}
+
+    it "passes rule" do
+      assert_equal [], errors
+    end
+  end
+
   describe "same aliases allowed on different parent interfaces and different concrete types" do
     let(:query_string) {%|
       {