Guard against duplicate fragment names in near-operations-file

packages/presets/near-operation-file/src/index.ts

@@ -102,6 +102,7 @@ export const preset: Types.OutputPreset<NearOperationFileConfig> = {
       add: addPlugin,
     };
 
+    const duplicateFragmentNames: string[] = [];
     const fragmentNameToFile: FragmentNameToFile = options.documents.reduce((prev, documentRecord) => {
       const fragments: FragmentDefinitionNode[] = documentRecord.content.definitions.filter(d => d.kind === Kind.FRAGMENT_DEFINITION) as FragmentDefinitionNode[];
 
@@ -110,13 +111,21 @@ export const preset: Types.OutputPreset<NearOperationFileConfig> = {
           const filePath = appendExtensionToFilePath(documentRecord.filePath, extension);
           const importName = baseVisitor.convertName(fragment, { suffix: 'Fragment' });
 
+          if (prev[fragment.name.value]) {
+            duplicateFragmentNames.push(fragment.name.value);
+          }
+
           prev[fragment.name.value] = { filePath, importName, onType: fragment.typeCondition.name.value, node: fragment };
         }
       }
 
       return prev;
     }, {});
 
+    if (duplicateFragmentNames.length) {
+      throw new Error(`Multiple fragments with the name(s) "${duplicateFragmentNames.join(', ')}" were found.`);
+    }
+
     const absTypesPath = resolve(baseDir, join(options.baseOutputDir, options.presetConfig.baseTypesPath));
 
     return options.documents

packages/presets/near-operation-file/tests/near-operation-file.spec.ts

@@ -155,6 +155,23 @@ describe('near-operation-file preset', () => {
     expect(result.map(o => o.plugins)[0]).toEqual(expect.arrayContaining([{ add: `import * as Types from '../types';\n` }]));
   });
 
+  it('should fail when multiple fragments with the same name are found', () => {
+    expect(() =>
+      preset.buildGeneratesSection({
+        baseOutputDir: './src/',
+        config: {},
+        presetConfig: {
+          cwd: '/some/deep/path',
+          baseTypesPath: 'types.ts',
+        },
+        schema: schemaDocumentNode,
+        documents: [testDocuments[1], testDocuments[1]],
+        plugins: [{ typescript: {} }],
+        pluginMap: { typescript: {} as any },
+      })
+    ).toThrow('Multiple fragments with the name(s) "UserFields" were found.');
+  });
+
   it('Should NOT prepend the "add" plugin with Types import when selection set does not include direct fields', async () => {
     const result = await preset.buildGeneratesSection({
       baseOutputDir: './src/',