src: add --env-file-if-exists flag

Fixes: https://github.com/nodejs/node/issues/50993
Refs: https://github.com/nodejs/node/issues/51451

test: remove unnecessary comment

src: conform to style guidelines

src: change flag to `--env-file-optional`

test: revert automatic linter changes

doc: fix typos

src: change flag to `--env-file-if-exists`

src: refactor `env_file_data` and `GetEnvFileDataFromArgs`

test: clean up tests

src: print error when file not found

test: remove unnecessary extras
PR-URL: https://github.com/nodejs/node/pull/53060
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

doc/api/cli.md

@@ -828,6 +828,8 @@ in the file, the value from the environment takes precedence.
 You can pass multiple `--env-file` arguments. Subsequent files override
 pre-existing variables defined in previous files.
 
+An error is thrown if the file does not exist.
+
 ```bash
 node --env-file=.env --env-file=.development.env index.js
 ```
@@ -867,6 +869,9 @@ Export keyword before a key is ignored:
 export USERNAME="nodejs" # will result in `nodejs` as the value.
 ```
 
+If you want to load environment variables from a file that may not exist, you
+can use the [`--env-file-if-exists`][] flag instead.
+
 ### `-e`, `--eval "script"`
 
 <!-- YAML
@@ -1761,6 +1766,15 @@ is being linked to Node.js. Sharing the OpenSSL configuration may have unwanted
 implications and it is recommended to use a configuration section specific to
 Node.js which is `nodejs_conf` and is default when this option is not used.
 
+### `--env-file-if-exists=config`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+Behavior is the same as [`--env-file`][], but an error is not thrown if the file
+does not exist.
+
 ### `--pending-deprecation`
 
 <!-- YAML
@@ -3548,6 +3562,8 @@ node --stack-trace-limit=12 -p -e "Error.stackTraceLimit" # prints 12
 [`--build-snapshot`]: #--build-snapshot
 [`--cpu-prof-dir`]: #--cpu-prof-dir
 [`--diagnostic-dir`]: #--diagnostic-dirdirectory
+[`--env-file-if-exists`]: #--env-file-if-existsconfig
+[`--env-file`]: #--env-fileconfig
 [`--experimental-default-type=module`]: #--experimental-default-typetype
 [`--experimental-sea-config`]: single-executable-applications.md#generating-single-executable-preparation-blobs
 [`--experimental-strip-types`]: #--experimental-strip-types

src/node.cc

@@ -851,20 +851,26 @@ static ExitCode InitializeNodeWithArgsInternal(
   HandleEnvOptions(per_process::cli_options->per_isolate->per_env);
 
   std::string node_options;
-  auto file_paths = node::Dotenv::GetPathFromArgs(*argv);
+  auto env_files = node::Dotenv::GetDataFromArgs(*argv);
 
-  if (!file_paths.empty()) {
+  if (!env_files.empty()) {
     CHECK(!per_process::v8_initialized);
 
-    for (const auto& file_path : file_paths) {
-      switch (per_process::dotenv_file.ParsePath(file_path)) {
+    for (const auto& file_data : env_files) {
+      switch (per_process::dotenv_file.ParsePath(file_data.path)) {
         case Dotenv::ParseResult::Valid:
           break;
         case Dotenv::ParseResult::InvalidContent:
-          errors->push_back(file_path + ": invalid format");
+          errors->push_back(file_data.path + ": invalid format");
           break;
         case Dotenv::ParseResult::FileError:
-          errors->push_back(file_path + ": not found");
+          if (file_data.is_optional) {
+            fprintf(stderr,
+                    "%s not found. Continuing without it.\n",
+                    file_data.path.c_str());
+            continue;
+          }
+          errors->push_back(file_data.path + ": not found");
           break;
         default:
           UNREACHABLE();

src/node_dotenv.cc

@@ -11,36 +11,52 @@ using v8::NewStringType;
 using v8::Object;
 using v8::String;
 
-std::vector<std::string> Dotenv::GetPathFromArgs(
+std::vector<Dotenv::env_file_data> Dotenv::GetDataFromArgs(
     const std::vector<std::string>& args) {
+  const std::string_view optional_env_file_flag = "--env-file-if-exists";
+
   const auto find_match = [](const std::string& arg) {
-    return arg == "--" || arg == "--env-file" || arg.starts_with("--env-file=");
+    return arg == "--" || arg == "--env-file" ||
+           arg.starts_with("--env-file=") || arg == "--env-file-if-exists" ||
+           arg.starts_with("--env-file-if-exists=");
   };
-  std::vector<std::string> paths;
-  auto path = std::find_if(args.begin(), args.end(), find_match);
 
-  while (path != args.end()) {
-    if (*path == "--") {
-      return paths;
+  std::vector<Dotenv::env_file_data> env_files;
+  // This will be an iterator, pointing to args.end() if no matches are found
+  auto matched_arg = std::find_if(args.begin(), args.end(), find_match);
+
+  while (matched_arg != args.end()) {
+    if (*matched_arg == "--") {
+      return env_files;
     }
-    auto equal_char = path->find('=');
 
-    if (equal_char != std::string::npos) {
-      paths.push_back(path->substr(equal_char + 1));
+    auto equal_char_index = matched_arg->find('=');
+
+    if (equal_char_index != std::string::npos) {
+      // `--env-file=path`
+      auto flag = matched_arg->substr(0, equal_char_index);
+      auto file_path = matched_arg->substr(equal_char_index + 1);
+
+      struct env_file_data env_file_data = {
+          file_path, flag.starts_with(optional_env_file_flag)};
+      env_files.push_back(env_file_data);
     } else {
-      auto next_path = std::next(path);
+      // `--env-file path`
+      auto file_path = std::next(matched_arg);
 
-      if (next_path == args.end()) {
-        return paths;
+      if (file_path == args.end()) {
+        return env_files;
       }
 
-      paths.push_back(*next_path);
+      struct env_file_data env_file_data = {
+          *file_path, matched_arg->starts_with(optional_env_file_flag)};
+      env_files.push_back(env_file_data);
     }
 
-    path = std::find_if(++path, args.end(), find_match);
+    matched_arg = std::find_if(++matched_arg, args.end(), find_match);
   }
 
-  return paths;
+  return env_files;
 }
 
 void Dotenv::SetEnvironment(node::Environment* env) {

src/node_dotenv.h

@@ -13,6 +13,10 @@ namespace node {
 class Dotenv {
  public:
   enum ParseResult { Valid, FileError, InvalidContent };
+  struct env_file_data {
+    std::string path;
+    bool is_optional;
+  };
 
   Dotenv() = default;
   Dotenv(const Dotenv& d) = delete;
@@ -27,7 +31,7 @@ class Dotenv {
   void SetEnvironment(Environment* env);
   v8::Local<v8::Object> ToObject(Environment* env) const;
 
-  static std::vector<std::string> GetPathFromArgs(
+  static std::vector<env_file_data> GetDataFromArgs(
       const std::vector<std::string>& args);
 
  private:

src/node_options.cc

@@ -640,6 +640,10 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
             "set environment variables from supplied file",
             &EnvironmentOptions::env_file);
   Implies("--env-file", "[has_env_file_string]");
+  AddOption("--env-file-if-exists",
+            "set environment variables from supplied file",
+            &EnvironmentOptions::optional_env_file);
+  Implies("--env-file-if-exists", "[has_env_file_string]");
   AddOption("--test",
             "launch test runner on startup",
             &EnvironmentOptions::test_runner);

src/node_options.h

@@ -177,6 +177,7 @@ class EnvironmentOptions : public Options {
   std::string redirect_warnings;
   std::string diagnostic_dir;
   std::string env_file;
+  std::string optional_env_file;
   bool has_env_file_string = false;
   bool test_runner = false;
   uint64_t test_runner_concurrency = 0;

test/parallel/test-dotenv-edge-cases.js

@@ -10,21 +10,31 @@ const validEnvFilePath = '../fixtures/dotenv/valid.env';
 const nodeOptionsEnvFilePath = '../fixtures/dotenv/node-options.env';
 
 describe('.env supports edge cases', () => {
-
-  it('supports multiple declarations', async () => {
-    // process.env.BASIC is equal to `basic` because the second .env file overrides it.
+  it('supports multiple declarations, including optional ones', async () => {
     const code = `
       const assert = require('assert');
       assert.strictEqual(process.env.BASIC, 'basic');
       assert.strictEqual(process.env.NODE_NO_WARNINGS, '1');
     `.trim();
-    const child = await common.spawnPromisified(
-      process.execPath,
-      [ `--env-file=${nodeOptionsEnvFilePath}`, `--env-file=${validEnvFilePath}`, '--eval', code ],
-      { cwd: __dirname },
-    );
-    assert.strictEqual(child.stderr, '');
-    assert.strictEqual(child.code, 0);
+    const children = await Promise.all(Array.from({ length: 4 }, (_, i) =>
+      common.spawnPromisified(
+        process.execPath,
+        [
+          // Bitwise AND to create all 4 possible combinations:
+          // i & 0b01 is truthy when i has value 0bx1 (i.e. 0b01 (1) and 0b11 (3)), falsy otherwise.
+          // i & 0b10 is truthy when i has value 0b1x (i.e. 0b10 (2) and 0b11 (3)), falsy otherwise.
+          `${i & 0b01 ? '--env-file' : '--env-file-if-exists'}=${nodeOptionsEnvFilePath}`,
+          `${i & 0b10 ? '--env-file' : '--env-file-if-exists'}=${validEnvFilePath}`,
+          '--eval', code,
+        ],
+        { cwd: __dirname },
+      )));
+    assert.deepStrictEqual(children, Array.from({ length: 4 }, () => ({
+      code: 0,
+      signal: null,
+      stdout: '',
+      stderr: '',
+    })));
   });
 
   it('supports absolute paths', async () => {
@@ -39,6 +49,19 @@ describe('.env supports edge cases', () => {
     assert.strictEqual(child.code, 0);
   });
 
+  it('supports a space instead of \'=\' for the flag ', async () => {
+    const code = `
+      require('assert').strictEqual(process.env.BASIC, 'basic');
+    `.trim();
+    const child = await common.spawnPromisified(
+      process.execPath,
+      [ '--env-file', validEnvFilePath, '--eval', code ],
+      { cwd: __dirname },
+    );
+    assert.strictEqual(child.stderr, '');
+    assert.strictEqual(child.code, 0);
+  });
+
   it('should handle non-existent .env file', async () => {
     const code = `
       require('assert').strictEqual(1, 1)
@@ -48,10 +71,23 @@ describe('.env supports edge cases', () => {
       [ '--env-file=.env', '--eval', code ],
       { cwd: __dirname },
     );
-    assert.notStrictEqual(child.stderr.toString(), '');
+    assert.notStrictEqual(child.stderr, '');
     assert.strictEqual(child.code, 9);
   });
 
+  it('should handle non-existent optional .env file', async () => {
+    const code = `
+      require('assert').strictEqual(1,1);
+    `.trim();
+    const child = await common.spawnPromisified(
+      process.execPath,
+      ['--env-file-if-exists=.env', '--eval', code],
+      { cwd: __dirname },
+    );
+    assert.notStrictEqual(child.stderr, '');
+    assert.strictEqual(child.code, 0);
+  });
+
   it('should not override existing environment variables but introduce new vars', async () => {
     const code = `
       require('assert').strictEqual(process.env.BASIC, 'existing');
@@ -106,7 +142,7 @@ describe('.env supports edge cases', () => {
         '--eval', `require('assert').strictEqual(process.env.BASIC, undefined);`,
         '--', '--env-file', validEnvFilePath,
       ],
-      { cwd: fixtures.path('dotenv') },
+      { cwd: __dirname },
     );
     assert.strictEqual(child.stdout, '');
     assert.strictEqual(child.stderr, '');