Allow @interfaceObject to stand in for all runtime types (#3087)

Rather than relying on the fact that one filteredPaths is reached, allow
@interfaceObject types to intersect with all runtime types

Author: clenfest

.changeset/curvy-papayas-sit.md

@@ -0,0 +1,5 @@
+---
+"@apollo/composition": patch
+---
+
+When doing interface type intersection detection, allow @interfaceObject to stand in for any type

composition-js/src/__tests__/compose.test.ts

@@ -5220,4 +5220,73 @@ describe('@source* directives', () => {
       );
     });
   });
+  
+  it('fed-354 repro @interfaceObject failure', () => {
+    const subgraph1 = {
+      name: 'Subgraph1',
+      url: 'https://Subgraph1',
+      typeDefs: gql`
+        type Query {
+          error_query: TicketField!
+        }
+
+        type User @interfaceObject @key(fields: "id") {
+          id: ID!
+        }
+
+        interface TicketField {
+          id: ID!
+          createdBy: User
+        }
+
+        type TextTicketField implements TicketField @key(fields: "id") @shareable {
+          id: ID!
+          createdBy: User
+        }
+      `
+    };
+    
+    const subgraph2 = {
+      name: 'Subgraph2',
+      url: 'https://Subgraph2',
+      typeDefs: gql`
+        interface Ticket @key(fields : "id", resolvable : true) {
+          id: ID!
+        }
+
+        interface User @key(fields : "id", resolvable : true) {
+          id: ID!
+          requestedTickets: [Ticket!]!
+        }
+
+        interface TicketField {
+          createdBy: User
+          id: ID!
+        }
+
+        type TextTicketField implements TicketField @shareable {
+          createdBy: User
+          id: ID!
+        }
+
+        type Customer implements User @key(fields : "id", resolvable : true) @shareable {
+          id: ID!
+          requestedTickets: [Ticket!]!
+        }
+
+        type Agent implements User @key(fields : "id", resolvable : true) @shareable {
+          id: ID!
+          requestedTickets: [Ticket!]!
+        }
+
+        type Question implements Ticket @key(fields : "id", resolvable : true) {
+          fields: [TicketField!]!
+          id: ID!
+        }
+      `
+    };
+    
+    const result = composeAsFed2Subgraphs([subgraph1, subgraph2]);
+    assertCompositionSuccess(result);
+  });
 });

composition-js/src/validate.ts

@@ -580,6 +580,14 @@ export class ValidationState {
         for (const { path } of newSubgraphPathInfos) {
           const subgraph = path.path.tail.source;
           const typeNames = possibleRuntimeTypeNamesSorted(path.path);
+          
+          // if we see a type here that is not included in the list of all
+          // runtime types, it is safe to assume that it is an interface
+          // behaving like a runtime type (i.e. an @interfaceObject) and 
+          // we should allow it to stand in for any runtime type          
+          if (typeNames.length === 1 && !allRuntimeTypes.includes(typeNames[0])) {
+            continue;
+          }
           runtimeTypesPerSubgraphs.set(subgraph, typeNames);
           // Note: we're formatting the elements in `runtimeTYpesToSubgraphs` because we're going to use it if we display an error. This doesn't
           // impact our set equality though since the formatting is consistent betweeen elements and type names syntax is sufficiently restricted