GraphQL 11 should work too

src/stitching/typeFromAST.ts

@@ -23,15 +23,11 @@ import {
   UnionTypeDefinitionNode,
   valueFromAST,
 } from 'graphql';
-
+//
 // TODO put back import once PR is merged
 // https://github.com/graphql/graphql-js/pull/1165
 // import { getDescription } from 'graphql/utilities/buildASTSchema';
 
-// TODO remove import once PR is merged
-// https://github.com/graphql/graphql-js/pull/1165
-import blockStringValue from 'graphql/language/blockStringValue';
-
 const backcompatOptions = { commentDescriptions: true };
 
 import resolveFromParentType from './resolveFromParentTypename';
@@ -190,7 +186,6 @@ function resolveType(typeRegistry: TypeRegistry, node: TypeNode): GraphQLType {
   }
 }
 
-
 // Code below temporarily copied from graphql/graphql-js pending PR
 // https://github.com/graphql/graphql-js/pull/1165
 
@@ -248,3 +243,59 @@ function getLeadingCommentBlock(node: any): void | string {
   }
   return comments.reverse().join('\n');
 }
+
+/**
+ * Produces the value of a block string from its parsed raw value, similar to
+ * Coffeescript's block string, Python's docstring trim or Ruby's strip_heredoc.
+ *
+ * This implements the GraphQL spec's BlockStringValue() static algorithm.
+ */
+function blockStringValue(rawString: string): string {
+  // Expand a block string's raw value into independent lines.
+  const lines = rawString.split(/\r\n|[\n\r]/g);
+
+  // Remove common indentation from all lines but first.
+  let commonIndent = null;
+  for (let i = 1; i < lines.length; i++) {
+    const line = lines[i];
+    const indent = leadingWhitespace(line);
+    if (
+      indent < line.length &&
+      (commonIndent === null || indent < commonIndent)
+    ) {
+      commonIndent = indent;
+      if (commonIndent === 0) {
+        break;
+      }
+    }
+  }
+
+  if (commonIndent) {
+    for (let i = 1; i < lines.length; i++) {
+      lines[i] = lines[i].slice(commonIndent);
+    }
+  }
+
+  // Remove leading and trailing blank lines.
+  while (lines.length > 0 && isBlank(lines[0])) {
+    lines.shift();
+  }
+  while (lines.length > 0 && isBlank(lines[lines.length - 1])) {
+    lines.pop();
+  }
+
+  // Return a string of the lines joined with U+000A.
+  return lines.join('\n');
+}
+
+function leadingWhitespace(str: string): number {
+  let i = 0;
+  while (i < str.length && (str[i] === ' ' || str[i] === '\t')) {
+    i++;
+  }
+  return i;
+}
+
+function isBlank(str: string): boolean {
+  return leadingWhitespace(str) === str.length;
+}

src/test/testMergeSchemas.ts

@@ -69,6 +69,11 @@ type Query {
 }
 `;
 
+let graphql11compat = '';
+if (process.env.GRAPHQL_VERSION === '^0.11') {
+  graphql11compat = '{}';
+}
+
 const linkSchema = `
   # A new type linking the Property type.
   type LinkType {
@@ -104,7 +109,7 @@ const linkSchema = `
     nodes: [Node]
   }
 
-  extend type Customer implements Node
+  extend type Customer implements Node ${graphql11compat}
 `;
 
 testCombinations.forEach(async combination => {