refactor: improve merge implementation quality and performance

CLAUDE.md

@@ -56,10 +56,16 @@ Tests use `esmock` for mocking ES modules. The test suite includes:
   - Keys in existing `.env` that aren't in `.env.example` are preserved
   - Order: keys from `.env.example` appear first, followed by preserved keys
   - If no `.env` exists, creates a new file (original behavior)
+  - Uses Set-based lookup for O(n) performance when checking for duplicate keys
 - The GCP project ID is parsed from the first `GCP_PROJECT` or `GCLOUD_PROJECT_ID` variable in the file
 - Empty lines in `.env.example` are preserved in the output
 - The tool uses Node's native fs/promises API for file operations
 - Splitting on `=` uses a regex `/=(.*)/s` to only split on the first `=`, preserving `=` in values
-- Whitespace is stripped from both keys and values during parsing
+- Whitespace is only trimmed from the beginning/end of keys and values, preserving internal spaces
 - The `GCP_PROJECT` variable must appear **before** any `envsync//` variables, otherwise an error is thrown
 - All secrets are fetched concurrently using `Promise.all()` for performance
+- Error handling distinguishes between expected errors (file not found) and unexpected errors (permissions, corruption)
+
+### Development Notes
+- This project uses ESLint 8.x with the legacy `.eslintrc` config format
+- Dependency updates (especially ESLint 9.x upgrade) are kept in separate PRs to maintain focus and avoid breaking changes requiring config migration

README.md

@@ -17,7 +17,13 @@ environment or update environment variables with on a single source of truth.
 `EnvSync` currently works with Google Cloud Platform (Secrets Manager). It reads
 the environment configuration from an `.env.example` file that is commonly used
 to help developers get started with a new project, fetches the values from the
-Google Cloud Platform (Secrets Manager) and writes them to a `.env` file.
+Google Cloud Platform (Secrets Manager) and intelligently merges them with your
+existing `.env` file.
+
+**Merge Behavior**: When you run `envsync`, it will:
+- Update keys from `.env.example` in your existing `.env` file
+- Preserve any custom keys in `.env` that aren't in `.env.example`
+- Create a new `.env` file if one doesn't exist
 
 For example, if you have the following `.env.example` file:
 

index.js

@@ -20,7 +20,11 @@ try {
   const existingFile = await fs.readFile(output, 'utf8')
   existingEnv = readEnv(existingFile)
 } catch (err) {
-  // File doesn't exist, that's okay
+  // File doesn't exist, that's okay - we'll create a new one
+  if (err.code !== 'ENOENT') {
+    // Unexpected error (permissions, corrupted file, etc.)
+    console.error(`Warning: Could not read existing ${output}: ${err.message}`)
+  }
 }
 
 // Merge: update existing keys with new values from .env.example
@@ -37,9 +41,10 @@ const mergedEnv = env.map(([key]) => {
 })
 
 // Add any remaining keys from existing .env that weren't in .env.example
+// Use Set for O(n) performance instead of O(n²)
+const exampleKeys = new Set(env.map(([key]) => key).filter((key) => key !== ''))
 for (const [key, value] of existingEnv.entries()) {
-  const existsInExample = env.some(([k]) => k === key)
-  if (!existsInExample) {
+  if (!exampleKeys.has(key)) {
     mergedEnv.push([key, value])
   }
 }

lib/readEnv.js

@@ -12,8 +12,8 @@ export function readEnv(envFile) {
     .split('\n')
     .map((line) => line.split(/=(.*)/s))
     .forEach(([key, value]) => {
-      key = key?.replace(/\s/g, '') || ''
-      value = value?.replace(/\s/g, '') || ''
+      key = key?.trim() || ''
+      value = value?.trim() || ''
 
       if (key !== '') {
         envMap.set(key, value)

lib/readExample.js

@@ -14,8 +14,8 @@ export async function readExample(exampleFile) {
     .split('\n')
     .map((line) => line.split(/=(.*)/s))
     .map(([key, value]) => {
-      key = key.replace(/\s/g, '')
-      value = value?.replace(/\s/g, '')
+      key = key.trim()
+      value = value?.trim()
 
       // set gcp project id for secret manager
       if (key === 'GCP_PROJECT') {

test/merge.test.js

@@ -128,3 +128,44 @@ NEW_KEY=new-value
     await fs.rm(tmpDir, { recursive: true, force: true })
   }
 })
+
+test('merge behavior: preserves values with spaces', async () => {
+  const tmpDir = await fs.mkdtemp(path.join(__dirname, 'tmp-'))
+  const examplePath = path.join(tmpDir, '.env.example')
+  const envPath = path.join(tmpDir, '.env')
+
+  try {
+    // Create .env.example
+    await fs.writeFile(
+      examplePath,
+      `GCP_PROJECT=test-project
+MESSAGE=Hello World
+`
+    )
+
+    // Create existing .env with value containing spaces
+    await fs.writeFile(
+      envPath,
+      `GCP_PROJECT=test-project
+DATABASE_URL=postgresql://user:my pass@localhost:5432/db
+`
+    )
+
+    // Run envsync
+    await execFileAsync('node', [path.join(rootDir, 'index.js'), examplePath], {
+      cwd: tmpDir
+    })
+
+    // Read result
+    const result = await fs.readFile(envPath, 'utf8')
+    const lines = result.split('\n')
+
+    // Should preserve spaces in both new and existing values
+    assert.ok(lines.some((line) => line === 'MESSAGE=Hello World'))
+    assert.ok(
+      lines.some((line) => line === 'DATABASE_URL=postgresql://user:my pass@localhost:5432/db')
+    )
+  } finally {
+    await fs.rm(tmpDir, { recursive: true, force: true })
+  }
+})

test/readEnv.test.js

@@ -45,3 +45,16 @@ JWT_SECRET=abc123==
   assert.equal(result.get('DATABASE_URL'), 'postgresql://user:pass=123@localhost:5432/db')
   assert.equal(result.get('JWT_SECRET'), 'abc123==')
 })
+
+test('readEnv() preserves spaces in values', () => {
+  const envFile = `MESSAGE=Hello World
+DATABASE_URL=postgresql://user:my pass@localhost:5432/db
+QUOTED="value with spaces"
+`
+
+  const result = readEnv(envFile)
+
+  assert.equal(result.get('MESSAGE'), 'Hello World')
+  assert.equal(result.get('DATABASE_URL'), 'postgresql://user:my pass@localhost:5432/db')
+  assert.equal(result.get('QUOTED'), '"value with spaces"')
+})