From bdbc209538e9058f1690ee4c841f43d1a2cd8c5a Mon Sep 17 00:00:00 2001
From: Ivan Savytskyi <ivan.savitsky@gmail.com>
Date: Mon, 2 Sep 2019 20:44:26 -0400
Subject: [PATCH] Fix issue with checking if one type is assignable from
 another (#1570)

This query should not fail
```
query TestQuery {
  search(text: "test") {
    ... on Character {
...
```

where `Character` is interface with `Human, Droid` possible types and `SearchResult` is a UNION type with `Human, Droid, Starship` possible types.
---
 .../compiler/parser/GraphQLDocumentParser.kt  | 38 +++++++++++++++++--
 1 file changed, 35 insertions(+), 3 deletions(-)

diff --git a/apollo-compiler/src/main/kotlin/com/apollographql/apollo/compiler/parser/GraphQLDocumentParser.kt b/apollo-compiler/src/main/kotlin/com/apollographql/apollo/compiler/parser/GraphQLDocumentParser.kt
index df532bf9868..847bead54b3 100644
--- a/apollo-compiler/src/main/kotlin/com/apollographql/apollo/compiler/parser/GraphQLDocumentParser.kt
+++ b/apollo-compiler/src/main/kotlin/com/apollographql/apollo/compiler/parser/GraphQLDocumentParser.kt
@@ -754,14 +754,46 @@ class GraphQLDocumentParser(val schema: Schema) {
   }
 
   private fun Schema.Type.isAssignableFrom(other: Schema.Type): Boolean {
+    if (name == other.name) {
+      return true
+    }
     return when (this) {
-      is Schema.Type.Union -> name == other.name || (possibleTypes ?: emptyList()).mapNotNull { it.rawType.name }.contains(other.name)
-      is Schema.Type.Interface -> name == other.name || (possibleTypes ?: emptyList()).mapNotNull { it.rawType.name }.contains(other.name)
-      is Schema.Type.Object -> name == other.name
+      is Schema.Type.Union -> possibleTypes().intersect(other.possibleTypes()).isNotEmpty()
+      is Schema.Type.Interface -> {
+        val possibleTypes = (possibleTypes ?: emptyList()).mapNotNull { it.rawType.name }
+        possibleTypes.contains(other.name) || possibleTypes.any { typeName ->
+          val schemaType = schema[typeName] ?: throw throw GraphQLParseException(
+              message = "Unknown possible type `$typeName` for INTERFACE `$name`"
+          )
+          schemaType.isAssignableFrom(other)
+        }
+      }
       else -> false
     }
   }
 
+  private fun Schema.Type.possibleTypes(): Set<String> {
+    return when (this) {
+      is Schema.Type.Union -> (possibleTypes ?: emptyList()).flatMap { typeRef ->
+        val typeName = typeRef.rawType.name!!
+        val schemaType = schema[typeName] ?: throw throw GraphQLParseException(
+            message = "Unknown possible type `$typeName` for UNION `$name`"
+        )
+        schemaType.possibleTypes()
+      }.toSet()
+
+      is Schema.Type.Interface -> (possibleTypes ?: emptyList()).flatMap { typeRef ->
+        val typeName = typeRef.rawType.name!!
+        val schemaType = schema[typeName] ?: throw throw GraphQLParseException(
+            message = "Unknown possible type `$typeName` for INTERFACE `$name`"
+        )
+        schemaType.possibleTypes()
+      }.toSet()
+
+      else -> setOf(name)
+    }
+  }
+
   private fun String.isGraphQLTypeAssignableFrom(otherType: String): Boolean {
     var i = 0
     var j = 0