Fix Jest snapshot indentation for graphql-js AST

We need to re-indent the lines printed from `graphql-js` in `astSerializer`, because Jest has started to ignore indentation when diffing snapshots, and it does this by invoking snapshot serializers with these values set to 0.

Without re-indenting, every line printed from `graphql-js` would be shown as changed. See jestjs/jest#9203.

federation-integration-testsuite-js/src/snapshotSerializers/astSerializer.ts

@@ -1,26 +1,57 @@
-import { ASTNode, print, Kind, visit } from 'graphql';
-import { Plugin, Config, Refs } from 'pretty-format';
-import { QueryPlanSelectionNode, QueryPlanInlineFragmentNode } from '@apollo/gateway';
-import { SelectionNode as GraphQLJSSelectionNode } from 'graphql';
+import { QueryPlanInlineFragmentNode, QueryPlanSelectionNode } from '@apollo/gateway';
+import { ASTNode, Kind, print, SelectionNode as GraphQLJSSelectionNode, visit } from 'graphql';
+import { Config, NewPlugin, Refs } from 'pretty-format';
 
 export default {
   test(value: any) {
+    // Note that this isn't a reliable test because other objects may also have a `kind` property
+    // (like query plans!).
+    // `graphql-js` does have an unexported `isNode` function, but that currently performs the same check
+    // and doesn't check whether `kind` represents a valid AST node either:
+    // https://github.com/graphql/graphql-js/blob/998bea680d6e11e1c055a400a887a9539de08f75/src/language/ast.js#L135-L137
+    // Perhaps we should attempt to contribute an improved `isNode` function.
     return value && typeof value.kind === 'string';
   },
 
   serialize(
     value: ASTNode,
-    _config: Config,
+    config: Config,
     indentation: string,
     _depth: number,
     _refs: Refs,
     _printer: any,
   ): string {
-    return print(remapInlineFragmentNodes(value))
-      .trim()
-      .replace(/\n/g, '\n' + indentation);
+    const lines = print(remapInlineFragmentNodes(value)).trim().split('\n');
+
+    // Avoid adding newlines for single line results.
+    if (lines.length === 0) {
+      return '';
+    } else if (lines.length === 1) {
+      return lines[0];
+    }
+
+    return lines.map(line => {
+      // We re-indent the lines printed from `graphql-js` to respect the passed in `indentation`
+      // and`config.indent` values.
+      // This is important because Jest has started to ignore indentation when diffing snapshots,
+      // and it does this by invoking snapshot serializers with these values set to 0.
+      // Without re-indenting, every line printed from `graphql-js` would be shown as changed.
+      // See https://github.com/facebook/jest/pull/9203
+      const indentationLength = getIndentationLength(line);
+      const dedentedLine = line.slice(indentationLength);
+      // `graphql-js` always indents with 2 spaces
+      const indentationDepth = indentationLength / 2;
+
+      return indentation + config.indent.repeat(indentationDepth) + dedentedLine;
+    }).join(config.spacingOuter);
   },
-} as Plugin;
+} as NewPlugin;
+
+// From https://github.com/facebook/jest/blob/32aaff83f02c347ccd591727544002490fb4ee9a/packages/jest-snapshot/src/dedentLines.ts#L8
+function getIndentationLength(line: string): number {
+  const result = /^( {2})+/.exec(line);
+  return result === null ? 0 : result[0].length;
+};
 
 /**
  * This function converts potential InlineFragmentNodes that WE created
@@ -78,7 +109,7 @@ export function remapInlineFragmentNodes(node: ASTNode): ASTNode {
 
 function remapSelections(
   selections: QueryPlanSelectionNode[],
-): ReadonlyArray<GraphQLJSSelectionNode> {
+): readonly GraphQLJSSelectionNode[] {
   return selections.map((selection) => {
     switch (selection.kind) {
       case Kind.FIELD:

federation-integration-testsuite-js/src/snapshotSerializers/queryPlanSerializer.ts

@@ -48,7 +48,6 @@ function printNode(
         `Fetch(service: "${node.serviceName}")` +
         ' {' +
         config.spacingOuter +
-        indentationNext +
         (node.requires
           ? printer(
               // this is an array of selections, so we need to make it a proper
@@ -61,8 +60,7 @@ function printNode(
               printer,
             ) +
             ' =>' +
-            config.spacingOuter +
-            indentationNext
+            config.spacingOuter
           : '') +
         printer(
           flattenEntitiesField(parse(node.operation)),