fix(cli): send debug diagnostics to stderr

cli.js

@@ -156,19 +156,19 @@ function loadEnvFiles (options) {
     const resolvedPath = path.resolve(process.cwd(), resolveHome(filepath))
     try {
       const parsed = dotenv.parse(fs.readFileSync(resolvedPath, { encoding: options.encoding }), { fast: options.fast })
-      dotenv.populate(parsedAll, parsed, populateOptions)
+      dotenv.populate(parsedAll, parsed, populateOptions, console.error)
       loadedPaths.push(filepath)
     } catch (e) {
       if (options.debug) {
-        console.log(`┆ failed to load ${filepath} ${e.message}`)
+        console.error(`┆ failed to load ${filepath} ${e.message}`)
       }
       if (!(options.defaultPath && e.code === 'ENOENT')) {
         throw e
       }
     }
   }
 
-  const injected = dotenv.populate(process.env, parsedAll, populateOptions)
+  const injected = dotenv.populate(process.env, parsedAll, populateOptions, console.error)
   return { injected, loadedPaths }
 }
 

lib/main.js

@@ -249,8 +249,8 @@ function parse (src, options) {
   return parseRegex(src)
 }
 
-function _debug (message) {
-  console.log(`┆ ${message}`)
+function _debug (message, output = console.log) {
+  output(`┆ ${message}`)
 }
 
 function _log (message) {
@@ -359,7 +359,7 @@ function config (options) {
 }
 
 // Populate process.env with parsed values
-function populate (processEnv, parsed, options = {}) {
+function populate (processEnv, parsed, options = {}, debugOutput) {
   const debug = parseBoolean(options && options.debug)
   const override = parseBoolean(options && options.override)
   const populated = {}
@@ -380,9 +380,9 @@ function populate (processEnv, parsed, options = {}) {
 
       if (debug) {
         if (override === true) {
-          _debug(`"${key}" is already defined and WAS overwritten`)
+          _debug(`"${key}" is already defined and WAS overwritten`, debugOutput)
         } else {
-          _debug(`"${key}" is already defined and was NOT overwritten`)
+          _debug(`"${key}" is already defined and was NOT overwritten`, debugOutput)
         }
       }
     } else {

tests/test-cli.js

@@ -52,6 +52,25 @@ t.test('help before the command still shows dotenv help', ct => {
   ct.end()
 })
 
+for (const testCase of [
+  { name: 'an existing environment variable', files: { '.env': 'BASIC=file\n' }, diagnostic: /"BASIC" is already defined and was NOT overwritten/ },
+  { name: 'a missing default file', files: {}, diagnostic: /failed to load \.env/ }
+]) {
+  t.test(`CLI debug logging for ${testCase.name} goes to stderr`, ct => {
+    const cwd = ct.testdir(testCase.files)
+    const env = Object.fromEntries(Object.entries(process.env).filter(([key]) => !key.toUpperCase().startsWith('DOTENV_')))
+    const result = cp.spawnSync(process.execPath, [
+      path.resolve(__dirname, '../dist/index.cjs'), 'run', '--debug', '--quiet',
+      process.execPath, '-e', 'console.log(JSON.stringify({ basic: process.env.BASIC }))'
+    ], { cwd, encoding: 'utf8', env: { ...env, BASIC: 'original' } })
+
+    ct.equal(result.status, 0, result.stderr)
+    ct.equal(result.stdout, '{"basic":"original"}\n')
+    ct.match(result.stderr, testCase.diagnostic)
+    ct.end()
+  })
+}
+
 const fileSelections = [
   ['-f', 'tests/.env.local,tests/.env'],
   ['--file', 'tests/.env.local,tests/.env'],