Remove the 'ENVIRONMENT=worker implies ENVIRONMENT=web' assumption (#25514)

Remove the 'ENVIRONMENT=worker implies ENVIRONMENT=web' assumption.
Fixes
#25414 (review).
Add test to verify the expectation mentioned in that comment.

Author: juj

ChangeLog.md

@@ -25,6 +25,11 @@ See docs/process.md for more on how version tagging works.
   - Firefox: v65 -> v68
 - For windows users, colored console output for error messages and logging now
   requires Windows 10 or above. (#25502)
+- Fixed an issue from previous release 4.0.16 where "-sENVIRONMENT=worker" was
+  erroneously made to imply "-sENVIRONMENT=web,worker" (#25514)
+- Passing '-sENVIRONMENT=worker' is now disallowed due to being ambiguous in
+  its meaning. Instead, use '-sENVIRONMENT=web,worker' or
+  '-sENVIRONMENT=node,worker' to refer to either Web or Node.js multithreading.
 
 4.0.16 - 10/07/25
 -----------------

test/test_other.py

@@ -14395,6 +14395,15 @@ def test_double_disable_environment(self):
     self.run_process([EMCC, test_file('hello_world.c'), '-Werror', '-sENVIRONMENT=node', '-sMIN_CHROME_VERSION=-1'])
     self.run_process([EMCC, test_file('hello_world.c'), '-Werror', '-sENVIRONMENT=node', '-sMIN_SAFARI_VERSION=-1'])
 
+  # Test that passing "-sENVIRONMENT=node -pthread" will generate code that only targets Node.js multithreading, and
+  # does not pull in code that supports browser multithreading.
+  def test_only_target_node_pthreads(self):
+    self.run_process([EMCC, test_file('hello_world.c'), '-Werror', '-sENVIRONMENT=node', '-pthread'])
+    content = read_file('a.out.js')
+    self.assertContained('This page was compiled without support for Safari browser', content)
+    self.assertContained('This page was compiled without support for Firefox browser', content)
+    self.assertContained('This page was compiled without support for Chrome browser', content)
+
   def test_signext_lowering(self):
     # Use `-v` to show the sub-commands being run by emcc.
     cmd = [EMCC, test_file('other/test_signext_lowering.c'), '-v']

tools/link.py

@@ -165,14 +165,16 @@ def setup_environment_settings():
   # The worker environment is automatically added if any of the pthread or Worker features are used.
   # Note: we need to actually modify ENVIRONMENTS variable here before the parsing,
   # because some JS code reads it back so modifying parsed info alone is not sufficient.
+  maybe_web_worker = not settings.ENVIRONMENT or 'worker' in settings.ENVIRONMENT
+
   if settings.SHARED_MEMORY and settings.ENVIRONMENT:
     settings.ENVIRONMENT.append('worker')
 
   # Environment setting based on user input
   if any(x for x in settings.ENVIRONMENT if x not in VALID_ENVIRONMENTS):
     exit_with_error(f'Invalid environment specified in "ENVIRONMENT": {settings.ENVIRONMENT}. Should be one of: {",".join(VALID_ENVIRONMENTS)}')
 
-  settings.ENVIRONMENT_MAY_BE_WEB = not settings.ENVIRONMENT or 'web' in settings.ENVIRONMENT or 'worker' in settings.ENVIRONMENT
+  settings.ENVIRONMENT_MAY_BE_WEB = not settings.ENVIRONMENT or 'web' in settings.ENVIRONMENT
   settings.ENVIRONMENT_MAY_BE_WEBVIEW = not settings.ENVIRONMENT or 'webview' in settings.ENVIRONMENT
   settings.ENVIRONMENT_MAY_BE_NODE = not settings.ENVIRONMENT or 'node' in settings.ENVIRONMENT
   settings.ENVIRONMENT_MAY_BE_SHELL = not settings.ENVIRONMENT or 'shell' in settings.ENVIRONMENT
@@ -183,11 +185,11 @@ def setup_environment_settings():
       diagnostics.warning('unused-command-line-argument', 'ignoring MIN_NODE_VERSION because `node` environment is not enabled')
     settings.MIN_NODE_VERSION = feature_matrix.UNSUPPORTED
 
-  if not (settings.ENVIRONMENT_MAY_BE_WEB or settings.ENVIRONMENT_MAY_BE_WEBVIEW):
+  if not (settings.ENVIRONMENT_MAY_BE_WEB or maybe_web_worker or settings.ENVIRONMENT_MAY_BE_WEBVIEW):
     for browser in ('FIREFOX', 'SAFARI', 'CHROME'):
       key = f'MIN_{browser}_VERSION'
       if key in user_settings and settings[key] != feature_matrix.UNSUPPORTED:
-        diagnostics.warning('unused-command-line-argument', 'ignoring %s because `web` and `webview` environments are not enabled', key)
+        diagnostics.warning('unused-command-line-argument', 'ignoring %s because `web`, `worker` and `webview` environments are not enabled', key)
       settings[key] = feature_matrix.UNSUPPORTED