add mergeAST from GraphiQL, refactor using visit()

src/utilities/__tests__/mergeAST-fixture.js

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+/**
+ *  Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ *  This source code is licensed under the MIT license found in the
+ *  LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict
+ *
+ */
+
+export const fixtures = [
+  {
+    desc: 'does not modify query with no fragments',
+    query: `
+      query Test {
+        id
+      }`,
+    mergedQuery: `
+      query Test {
+        id
+      }`,
+  },
+  {
+    desc: 'inlines simple nested fragment',
+    query: `
+      query Test {
+        ...Fragment1
+      }
+
+      fragment Fragment1 on Test {
+        id
+      }`,
+    mergedQuery: `
+      query Test {
+        ...on Test {
+          id
+        }
+      }`,
+  },
+  {
+    desc: 'inlines triple nested fragment',
+    query: `
+      query Test {
+        ...Fragment1
+      }
+      
+      fragment Fragment1 on Test {
+        ...Fragment2
+      }
+      
+      fragment Fragment2 on Test {
+        ...Fragment3
+      }
+      
+      fragment Fragment3 on Test {
+        id
+      }`,
+    mergedQuery: `
+      query Test {
+        ...on Test {
+          ...on Test {
+            ...on Test {
+              id
+            }
+          }
+        }
+      }`,
+  },
+  {
+    desc: 'inlines multiple fragments',
+    query: `
+      query Test {
+        ...Fragment1
+        ...Fragment2
+        ...Fragment3
+      }
+
+      fragment Fragment1 on Test {
+        id
+      }
+
+      fragment Fragment2 on Test {
+        id
+      }
+
+      fragment Fragment3 on Test {
+        id
+      }`,
+    mergedQuery: `
+      query Test {
+        ...on Test {
+          id
+        }
+        ...on Test {
+          id
+        }
+        ...on Test {
+          id
+        }
+      }`,
+  },
+  {
+    desc: 'removes duplicate fragment spreads',
+    query: `
+      query Test {
+        ...Fragment1
+        ...Fragment1
+      }
+
+      fragment Fragment1 on Test {
+        id
+      }`,
+    mergedQuery: `
+      query Test {
+        ...on Test {
+          id
+        }
+      }`,
+  },
+];

src/utilities/__tests__/mergeAST-test.js

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+/**
+ *  Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ *  This source code is licensed under the MIT license found in the
+ *  LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict
+ *
+ */
+
+import { expect } from 'chai';
+import { describe, it } from 'mocha';
+
+import { parse, print } from '../../index';
+
+import { mergeAST } from '../mergeAST';
+
+import { fixtures } from './mergeAST-fixture';
+
+describe.only('MergeAST', () => {
+  fixtures.forEach(fixture => {
+    it(fixture.desc, () => {
+      const result = print(mergeAST(parse(fixture.query))).replace(/\s/g, '');
+      expect(result).to.equal(fixture.mergedQuery.replace(/\s/g, ''));
+    });
+  });
+});

src/utilities/mergeAST.js

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+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict
+ */
+
+import { visit } from '../language/visitor';
+import { print } from '../';
+import {
+  type DocumentNode,
+  type FragmentDefinitionNode,
+  type FragmentSpreadNode,
+} from '../language/ast';
+
+/**
+ * Given a document AST, merge all fragments definitions into the
+ * operations using inline fragments.
+ */
+
+export function mergeAST(ast: DocumentNode): DocumentNode {
+  const fragmentDefinitions: { [name: string]: FragmentDefinitionNode } = {};
+  const inlinedFragments: { [name: string]: FragmentSpreadNode } = {};
+
+  visit(ast, {
+    FragmentDefinition(node) {
+      // collect the existing FragmentDefinition nodes
+      fragmentDefinitions[node.name.value] = node;
+    },
+  });
+
+  return visit(ast, {
+    FragmentSpread(node) {
+
+      // no repeats
+      if (inlinedFragments[node.name.value]) {
+        return null;
+      }
+
+      // otherwise, we are inlining a new fragment definition
+      inlinedFragments[node.name.value] = node;
+
+      // retrieve the original definition, and convert 
+      // all FragmentSpread nodes to InlineFragment nodes
+      return {
+        ...fragmentDefinitions[node.name.value],
+        kind: 'InlineFragment',
+      };
+    },
+    FragmentDefinition(node) {
+      // remove the original FragmentDefinition nodes
+      return null;
+    },
+  });
+}