Explain why comparison of versions failed (#701)

packages/services/api/src/modules/schema/resolvers.ts

@@ -8,6 +8,7 @@ import {
   isInputObjectType,
   isScalarType,
   GraphQLNamedType,
+  GraphQLError,
 } from 'graphql';
 import type { SchemaModule } from './__generated__/types';
 import { SchemaManager } from './providers/schema-manager';
@@ -575,7 +576,26 @@ export const resolvers: SchemaModule.Resolvers = {
         return [];
       }
 
-      return injector.get(Inspector).diff(buildSchema(before), buildSchema(after));
+      const previousSchema = buildSchema(
+        before,
+        error =>
+          new GraphQLError(
+            `Failed to build the previous version: ${
+              error instanceof GraphQLError ? error.message : error
+            }`,
+          ),
+      );
+      const currentSchema = buildSchema(
+        after,
+        error =>
+          new GraphQLError(
+            `Failed to build the selected version: ${
+              error instanceof GraphQLError ? error.message : error
+            }`,
+          ),
+      );
+
+      return injector.get(Inspector).diff(previousSchema, currentSchema);
     },
     diff([before, after]) {
       return {

packages/services/api/src/shared/schema.ts

@@ -24,13 +24,20 @@ export function hashSchema(schema: Schema): string {
 /**
  * Builds GraphQLSchema without validation of SDL
  */
-export function buildSchema(schema: SchemaObject): GraphQLSchema {
-  return lexicographicSortSchema(
-    buildASTSchema(schema.document, {
-      assumeValid: true,
-      assumeValidSDL: true,
-    }),
-  );
+export function buildSchema(
+  schema: SchemaObject,
+  transformError = (error: unknown) => error,
+): GraphQLSchema {
+  try {
+    return lexicographicSortSchema(
+      buildASTSchema(schema.document, {
+        assumeValid: true,
+        assumeValidSDL: true,
+      }),
+    );
+  } catch (error) {
+    throw transformError(error);
+  }
 }
 
 export function findSchema(schemas: readonly Schema[], expected: Schema): Schema | undefined {

packages/web/app/pages/[orgId]/[projectId]/[targetId]/history.tsx

@@ -95,6 +95,24 @@ const DiffView = ({
     },
   });
   const comparison = compareQuery.data?.schemaCompareToPrevious;
+  const error = compareQuery.error;
+
+  if (error) {
+    return (
+      <div className="m-3 rounded-lg bg-red-500/20 p-8">
+        <div className="mb-3 flex items-center gap-3">
+          <VscBug className="h-8 w-8 text-red-500" />
+          <h2 className="text-lg font-medium text-white">Failed to compare schemas</h2>
+        </div>
+        <p className="text-base text-gray-500">
+          Previous or current schema is most likely incomplete and was force published
+        </p>
+        <pre className="mt-5 rounded-lg bg-red-900 p-3 text-xs text-white">
+          {error.graphQLErrors[0].message}
+        </pre>
+      </div>
+    );
+  }
 
   if (!comparison) {
     return null;
@@ -108,8 +126,11 @@ const DiffView = ({
           <h2 className="text-lg font-medium text-white">Failed to build GraphQL Schema</h2>
         </div>
         <p className="text-base text-gray-500">
-          Schema is most likely incomplete and was force published
+          Previous or current schema is most likely incomplete and was force published
         </p>
+        <pre className="mt-5 rounded-lg bg-red-900 p-3 text-xs text-white">
+          {comparison.message}
+        </pre>
       </div>
     );
   }