Add NODE_HOST_ENV to mirror host env vars under node (emscripten-core#18820)

This setting is enabled by default when `NODERAWFS` is enabled, but can
also be disabled explicitly.

Fixes: emscripten-core#18816, emscripten-core#25791

Author: sbc100

ChangeLog.md

@@ -26,6 +26,10 @@ See docs/process.md for more on how version tagging works.
   use case. (#25645, #25440)
 - The fetch library now supports streaming data requests when
   `-sFETCH_STREAMING` is enabled.
+- A new `NODE_HOST_ENV` setting was added which exposes the host environment
+  variables to the generated program, when running under Node. This setting is
+  enabled by default when `-sNODERAWFS` is used but can also be controlled
+  separately. (#18820)
 
 4.0.20 - 11/18/25
 -----------------

site/source/docs/tools_reference/settings_reference.rst

@@ -1494,7 +1494,7 @@ Default value: false
 NODERAWFS
 =========
 
-Enables support for the NODERAWFS filesystem backend. This is a special
+Enables support for the ``NODERAWFS`` filesystem backend. This is a special
 backend as it replaces all normal filesystem access with direct Node.js
 operations, without the need to do ``FS.mount()``, and this backend only
 works with Node.js. The initial working directory will be same as
@@ -1504,6 +1504,20 @@ necessarily be portable between OSes - it will be as portable as a Node.js
 program would be, which means that differences in how the underlying OS
 handles permissions and errors and so forth may be noticeable.
 
+Enabling this setting will also enable :ref:`NODE_HOST_ENV` by default.
+
+Default value: false
+
+.. _node_host_env:
+
+NODE_HOST_ENV
+=============
+
+When running under Node, expose the underlying OS environment variables.
+This is similar to how ``NODERAWFS`` exposes the underlying FS.
+This setting gets enabled by default when ``NODERAWFS`` is enabled, but can
+also be controlled separately.
+
 Default value: false
 
 .. _node_code_caching:

src/lib/libwasi.js

@@ -67,6 +67,12 @@ var WasiLibrary = {
         '_': getExecutableName()
 #endif
       };
+#if ENVIRONMENT_MAY_BE_NODE && NODE_HOST_ENV
+      if (ENVIRONMENT_IS_NODE) {
+        // When NODE_HOST_ENV is enabled we mirror then entire host environment.
+        env = process.env;
+      }
+#endif
       // Apply the user-provided values, if any.
       for (var x in ENV) {
         // x is a key in ENV; if ENV[x] is undefined, that means it was

src/settings.js

@@ -1023,7 +1023,7 @@ var FILESYSTEM = true;
 // [link]
 var FORCE_FILESYSTEM = false;
 
-// Enables support for the NODERAWFS filesystem backend. This is a special
+// Enables support for the ``NODERAWFS`` filesystem backend. This is a special
 // backend as it replaces all normal filesystem access with direct Node.js
 // operations, without the need to do ``FS.mount()``, and this backend only
 // works with Node.js. The initial working directory will be same as
@@ -1032,9 +1032,17 @@ var FORCE_FILESYSTEM = false;
 // necessarily be portable between OSes - it will be as portable as a Node.js
 // program would be, which means that differences in how the underlying OS
 // handles permissions and errors and so forth may be noticeable.
+//
+// Enabling this setting will also enable :ref:`NODE_HOST_ENV` by default.
 // [link]
 var NODERAWFS = false;
 
+// When running under Node, expose the underlying OS environment variables.
+// This is similar to how ``NODERAWFS`` exposes the underlying FS.
+// This setting gets enabled by default when ``NODERAWFS`` is enabled, but can
+// also be controlled separately.
+var NODE_HOST_ENV = false;
+
 // This saves the compiled wasm module in a file with name
 // ``$WASM_BINARY_NAME.$V8_VERSION.cached``
 // and loads it on subsequent runs. This caches the compiled wasm code from

test/other/test_std_filesystem_tempdir.cpp

@@ -0,0 +1,27 @@
+#include <cassert>
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+
+namespace fs = std::filesystem;
+
+int main() {
+  // libc++'s temp_directory_path depends on one of these env vars
+  // being set, and falls back to /tmp as a default.
+  // Log these values in case this test ever fails:
+  const char* env_paths[] = {"TMPDIR", "TMP", "TEMP", "TEMPDIR"};
+  for (int i = 0; i < sizeof(env_paths)/sizeof(char*); i++) {
+    const char* p = getenv(env_paths[i]);
+    std::cout << env_paths[i] << " -> " << (p ? p : "(NULL)") << "\n";
+    if (p) {
+      std::cout <<  env_paths[i] << " exists: " << fs::exists(env_paths[i]) << "\n";
+    }
+  }
+  std::cout << "default /tmp exists: " << fs::exists("/tmp") << "\n";
+
+  fs::path tmp{fs::temp_directory_path()};
+  std::cout << "temp_directory_path: " << tmp << "\n";
+  assert(fs::exists(tmp));
+  std::cout << "exists ok!" << "\n";
+  return 0;
+}

test/other/test_std_filesystem_tempdir.out

@@ -0,0 +1 @@
+exists ok!

test/test_other.py

@@ -7840,6 +7840,24 @@ def test_override_js_execution_environment(self):
         seen = self.run_js('test.js', engine=engine, assert_returncode=NON_ZERO)
         self.assertContained('Module.ENVIRONMENT has been deprecated. To force the environment, use the ENVIRONMENT compile-time option (for example, -sENVIRONMENT=web or -sENVIRONMENT=node', seen)
 
+  @requires_node
+  @with_env_modify({'FOO': 'bar'})
+  @parameterized({
+    '': ([], '|(null)|\n'),
+    'rawfs': (['-sNODERAWFS'], '|bar|\n'),
+    'rawfs_no_env': (['-sNODERAWFS', '-sNODE_HOST_ENV=0'], '|(null)|\n'),
+    'enabled': (['-sNODE_HOST_ENV'], '|bar|\n'),
+  })
+  def test_node_host_env(self, args, expected):
+     create_file('src.c', r'''
+      #include <stdlib.h>
+      #include <stdio.h>
+      int main() {
+        printf("|%s|\n", getenv("FOO"));
+      }
+    ''')
+     self.do_runf('src.c', expected, cflags=args)
+
   def test_override_c_environ(self):
     create_file('pre.js', r'''
       Module.preRun = () => { ENV.hello = '💩 world'; ENV.LANG = undefined; }
@@ -13644,12 +13662,20 @@ def test_fs_icase(self):
     # c++20 for ends_with().
     self.do_other_test('test_fs_icase.cpp', cflags=['-sCASE_INSENSITIVE_FS', '-std=c++20'])
 
+  @crossplatform
   @with_all_fs
   def test_std_filesystem(self):
     if (WINDOWS or MACOS) and self.get_setting('NODERAWFS'):
       self.skipTest('Rawfs directory removal works only on Linux')
     self.do_other_test('test_std_filesystem.cpp')
 
+  @crossplatform
+  @with_all_fs
+  def test_std_filesystem_tempdir(self):
+    if (WINDOWS or MACOS) and self.get_setting('NODERAWFS') and self.get_setting('WASMFS'):
+      self.skipTest('NODERAWFS + WASMFS is does not allow access to arbitrary paths')
+    self.do_other_test('test_std_filesystem_tempdir.cpp', cflags=['-g'])
+
   def test_strict_js_closure(self):
     self.do_runf('hello_world.c', cflags=['-sSTRICT_JS', '-Werror=closure', '--closure=1', '-O3'])
 

tools/link.py

@@ -1405,7 +1405,6 @@ def limit_incoming_module_api():
   # see https://github.com/emscripten-core/emscripten/issues/18723#issuecomment-1429236996
   if settings.MODULARIZE:
     default_setting('NODEJS_CATCH_REJECTION', 0)
-    default_setting('NODEJS_CATCH_EXIT', 0)
 
   if settings.POLYFILL:
     # Emscripten requires certain ES6+ constructs by default in library code
@@ -1884,6 +1883,20 @@ def get_full_import_name(name):
   if settings.PTHREADS:
     settings.REQUIRED_EXPORTS.append('_emscripten_tls_init')
 
+  if settings.NODERAWFS:
+    default_setting('NODE_HOST_ENV', 1)
+
+  if not settings.ENVIRONMENT_MAY_BE_NODE:
+    # Node-specific settings only make sense if ENVIRONMENT_MAY_BE_NODE
+    if settings.NODERAWFS:
+      diagnostics.warning('unused-command-line-argument', 'NODERAWFS ignored since `node` not in `ENVIRONMENT`')
+    if settings.NODE_CODE_CACHING:
+      diagnostics.warning('unused-command-line-argument', 'NODE_CODE_CACHING ignored since `node` not in `ENVIRONMENT`')
+    if settings.NODEJS_CATCH_EXIT:
+      diagnostics.warning('unused-command-line-argument', 'NODEJS_CATCH_EXIT ignored since `node` not in `ENVIRONMENT`')
+    if settings.NODEJS_CATCH_REJECTION and 'NODEJS_CATCH_REJECTION' in user_settings:
+      diagnostics.warning('unused-command-line-argument', 'NODEJS_CATCH_REJECTION ignored since `node` not in `ENVIRONMENT`')
+
   settings.PRE_JS_FILES = options.pre_js
   settings.POST_JS_FILES = options.post_js