fix: ensure newline separator when appending to files

.changeset/append-separators.md

@@ -0,0 +1,5 @@
+---
+"@tanstack/create": patch
+---
+
+Keep appended add-on files on separate lines when existing content has no final newline, in both Node and edge generation.

packages/create/src/edge-template-file.ts

@@ -199,7 +199,14 @@ export function createTemplateFile(environment: Environment, options: Options) {
     }
 
     if (append) {
-      await environment.appendFile(joinPaths(options.targetDir, target), content)
+      const targetPath = joinPaths(options.targetDir, target)
+      if (content && !/^[\r\n]/.test(content) && environment.exists(targetPath)) {
+        const existing = await environment.readFile(targetPath)
+        if (existing && !/[\r\n]$/.test(existing)) {
+          content = `\n${content}`
+        }
+      }
+      await environment.appendFile(targetPath, content)
     } else {
       await environment.writeFile(joinPaths(options.targetDir, target), content)
     }

packages/create/src/frameworks/react/add-ons/mcp/assets/_dot_gitignore.append

@@ -1 +1 @@
-mcp-todos.json
+mcp-todos.json

packages/create/src/frameworks/react/add-ons/sentry/assets/_dot_env.local.append

@@ -8,4 +8,4 @@ VITE_SENTRY_ORG=
 VITE_SENTRY_PROJECT=
 
 # Your Sentry authentication token (from your Sentry account)
-SENTRY_AUTH_TOKEN=
+SENTRY_AUTH_TOKEN=

packages/create/src/frameworks/react/add-ons/strapi/assets/_dot_env.local.append

@@ -1,2 +1,2 @@
 # Strapi configuration
-VITE_STRAPI_URL="http://localhost:1337"
+VITE_STRAPI_URL="http://localhost:1337"

packages/create/src/frameworks/solid/add-ons/strapi/assets/_dot_env.local.append

@@ -1,2 +1,2 @@
 # Strapi configuration
-VITE_STRAPI_URL="http://localhost:1337/api"
+VITE_STRAPI_URL="http://localhost:1337/api"

packages/create/src/template-file.ts

@@ -212,7 +212,14 @@ export function createTemplateFile(environment: Environment, options: Options) {
     }
 
     if (append) {
-      await environment.appendFile(resolve(options.targetDir, target), content)
+      const targetPath = resolve(options.targetDir, target)
+      if (content && !/^[\r\n]/.test(content) && environment.exists(targetPath)) {
+        const existing = await environment.readFile(targetPath)
+        if (existing && !/[\r\n]$/.test(existing)) {
+          content = `\n${content}`
+        }
+      }
+      await environment.appendFile(targetPath, content)
     } else {
       await environment.writeFile(resolve(options.targetDir, target), content)
     }

packages/create/tests/append-separators.test.ts

@@ -0,0 +1,59 @@
+import { mkdtemp, rm } from 'node:fs/promises'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { describe, expect, it } from 'vitest'
+
+import { createDefaultEnvironment, createMemoryEnvironment } from '../src/environment.js'
+import { createMemoryEnvironment as createEdgeMemoryEnvironment } from '../src/edge-environment.js'
+import { createTemplateFile } from '../src/template-file.js'
+import { createTemplateFile as createEdgeTemplateFile } from '../src/edge-template-file.js'
+import type { Options } from '../src/types.js'
+
+const cases = [
+  { name: 'missing target', before: undefined, incoming: 'next\n', expected: 'next\n' },
+  { name: 'empty target', before: '', incoming: 'next\n', expected: 'next\n' },
+  { name: 'missing separator', before: '*.local', incoming: 'mcp-todos.json\n', expected: '*.local\nmcp-todos.json\n' },
+  { name: 'existing trailing newline', before: 'first\n', incoming: 'next', expected: 'first\nnext' },
+  { name: 'incoming leading newline', before: 'first', incoming: '\nnext', expected: 'first\nnext' },
+  { name: 'intentional blank line', before: 'first\n', incoming: '\nnext', expected: 'first\n\nnext' },
+  { name: 'empty append', before: 'first', incoming: '', expected: 'first' },
+  { name: 'existing CRLF', before: 'first\r\n', incoming: 'next', expected: 'first\r\nnext' },
+  { name: 'incoming CRLF', before: 'first', incoming: '\r\nnext', expected: 'first\r\nnext' },
+]
+
+for (const kind of ['disk', 'node-memory', 'edge-memory'] as const) {
+  describe(`${kind} append templates`, () => {
+    it.each(cases)('$name', async ({ before, incoming, expected }) => {
+      const targetDir = await mkdtemp(join(tmpdir(), 'tanstack-append-'))
+      const environment = kind === 'disk'
+        ? createDefaultEnvironment()
+        : kind === 'node-memory'
+          ? createMemoryEnvironment().environment
+          : createEdgeMemoryEnvironment().environment
+      const options: Options = {
+        projectName: 'test', targetDir,
+        framework: {
+          id: 'test', name: 'Test', description: '', version: '1',
+          basePackageJSON: {}, optionalPackages: {}, supportedModes: {},
+          getFiles: async () => [], getFileContents: async () => '',
+          getDeletedFiles: async () => [], getAddOns: () => [],
+        },
+        chosenAddOns: [], addOnOptions: {}, packageManager: 'npm',
+        typescript: true, tailwind: false, mode: 'file-router',
+        git: false, intent: false,
+      }
+      const templateFile = kind === 'edge-memory'
+        ? createEdgeTemplateFile(environment, options)
+        : createTemplateFile(environment, options)
+      try {
+        environment.startRun()
+        if (before !== undefined) await templateFile('_dot_gitignore', before)
+        await templateFile('_dot_gitignore.append', incoming)
+        expect(await environment.readFile(join(targetDir, '.gitignore'))).toBe(expected)
+      } finally {
+        environment.finishRun()
+        await rm(targetDir, { recursive: true, force: true })
+      }
+    })
+  })
+}