Add MIN_NODE_VERSION setting

This, along with #18465 (which run tests on the oldest supported
version of node) should pave the way for us to update the emsdk version
node to something a little more modern.

See emscripten-core/emsdk#829

This first thing I do with this setting is use it do disable
`NODEJS_CATCH_REJECTION` by default when we are targeting node 15 and
above.

.circleci/config.yml

@@ -553,17 +553,24 @@ jobs:
       - install-node-version:
           node_version: "10.19.0"
       - run-tests:
-          title: "core2.test_hello_world"
-          test_targets: "core2.test_hello_world"
+          title: "selected subset"
+          test_targets: "
+            other.test_node_unhandled_rejection
+            core2.test_hello_world"
       # Run a few test with the most recent version of node
       # In particular we have some tests that require node flags on older
       # versions of node but not with the most recent version.
       - install-latest-node
       - run-tests:
           # Run tests that on older versions of node would require flags, but
           # those flags should not be injected on newer versions.
-          title: "core2 subset"
-          test_targets: "-v core2.test_pthread_create core2.test_i64_invoke_bigint core2.test_source_map core2.test_exceptions_wasm"
+          title: "selected subset"
+          test_targets: "-v
+            other.test_node_unhandled_rejection
+            core2.test_pthread_create
+            core2.test_i64_invoke_bigint
+            core2.test_source_map
+            core2.test_exceptions_wasm"
       - upload-test-results
   test-other:
     executor: bionic

emcc.py

@@ -2152,10 +2152,20 @@ def phase_linker_setup(options, state, newargs):
     settings.MIN_IE_VERSION = 0
     settings.MIN_EDGE_VERSION = 0
     settings.MIN_CHROME_VERSION = 0
+    settings.MIN_NODE_VERSION = 0
 
   if settings.MIN_CHROME_VERSION <= 37:
     settings.WORKAROUND_OLD_WEBGL_UNIFORM_UPLOAD_IGNORED_OFFSET_BUG = 1
 
+  # 10.19.0 is the oldest version of node that we do any testing with.
+  # Keep this in sync with the test-node-compat in .circleci/config.yml
+  # and MINIMUM_NODE_VERSION in tools/shared.py
+  if settings.MIN_NODE_VERSION:
+    if settings.MIN_NODE_VERSION < 101900:
+      exit_with_error('targetting node older than 10.19.00 is not supported')
+    if settings.MIN_NODE_VERSION >= 15000:
+      default_setting('NODEJS_CATCH_REJECTION', 0)
+
   setup_environment_settings()
 
   if options.use_closure_compiler != 0:

src/runtime_debug.js

@@ -39,13 +39,15 @@ function isExportedByForceFilesystem(name) {
 }
 
 function missingGlobal(sym, msg) {
-  Object.defineProperty(globalThis, sym, {
-    configurable: true,
-    get: function() {
-      warnOnce('`' + sym + '` is not longer defined by emscripten. ' + msg);
-      return undefined;
-    }
-  });
+  if (typeof globalThis !== 'undefined') {
+    Object.defineProperty(globalThis, sym, {
+      configurable: true,
+      get: function() {
+        warnOnce('`' + sym + '` is not longer defined by emscripten. ' + msg);
+        return undefined;
+      }
+    });
+  }
 }
 
 missingGlobal('buffer', 'Please use HEAP8.buffer or wasmMemory.buffer');

src/settings.js

@@ -725,21 +725,22 @@ var DISABLE_EXCEPTION_THROWING = false;
 
 // By default we handle exit() in node, by catching the Exit exception. However,
 // this means we catch all process exceptions. If you disable this, then we no
-// longer do that, and exceptions work normally, which can be useful for libraries
-// or programs that don't need exit() to work.
-
+// longer do that, and exceptions work normally, which can be useful for
+// libraries or programs that don't need exit() to work.
+//
 // Emscripten uses an ExitStatus exception to halt when exit() is called.
 // With this option, we prevent that from showing up as an unhandled
 // exception.
 // [link]
 var NODEJS_CATCH_EXIT = true;
 
-// Catch unhandled rejections in node. Without this, node may print the error,
-// and that this behavior will change in future node, wait a few seconds, and
-// then exit with 0 (which hides the error if you don't read the log). With
-// this, we catch any unhandled rejection and throw an actual error, which will
-// make the process exit immediately with a non-0 return code.
-// This should be fixed in Node 15+.
+// Catch unhandled rejections in node. This only effect versions of node older
+// than 15.  Without this, old version node will print a warning, but exit
+// with a zero return code.  With this setting enabled, we handle any unhandled
+// rejection and throw an exception, which will cause  the process exit
+// immediately with a non-0 return code.
+// This should is no needed in Node 15+ so this setting will default to false
+// if MIN_NODE_VERSION is greater than 150000.
 // [link]
 var NODEJS_CATCH_REJECTION = true;
 
@@ -1785,6 +1786,12 @@ var MIN_EDGE_VERSION = 0x7FFFFFFF;
 // [link]
 var MIN_CHROME_VERSION = 75;
 
+// Specifies minimum node version to target for the generated code.  This is
+// distinct from the minimum version required run the emscripten compiler.
+// This version aligns with the current Ubuuntu TLS 20.04 (Focal).
+// Version is encoded in MMmmVV, e.g. 1814101 denotes Node 18.14.01.
+var MIN_NODE_VERSION = 101900;
+
 // Tracks whether we are building with errno support enabled. Set to 0
 // to disable compiling errno support in altogether. This saves a little
 // bit of generated code size in applications that do not care about

src/shell.js

@@ -245,7 +245,10 @@ if (ENVIRONMENT_IS_NODE) {
   // not be needed with node v15 and about because it is now the default
   // behaviour:
   // See https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode
-  process['on']('unhandledRejection', function(reason) { throw reason; });
+  var nodeMajor = process.version.match(/^v(\d+)\./)[1];
+  if (nodeMajor < 15) {
+    process['on']('unhandledRejection', function(reason) { throw reason; });
+  }
 #endif
 
   quit_ = (status, toThrow) => {

test/test_other.py

@@ -12041,18 +12041,19 @@ def test_node_unhandled_rejection(self):
     # exit code and log the stack trace correctly.
     self.run_process([EMCC, '--pre-js=pre.js', '-sNODEJS_CATCH_REJECTION', 'main.c'])
     output = self.run_js('a.out.js', assert_returncode=NON_ZERO)
+    self.assertContained('unhandledRejection', read_file('a.out.js'))
     self.assertContained('ReferenceError: missing is not defined', output)
     self.assertContained('at foo (', output)
 
-    version = self.run_process(config.NODE_JS + ['--version'], stdout=PIPE).stdout.strip()
-    version = [int(v) for v in version.replace('v', '').replace('-pre', '').split('.')]
-    if version[0] >= 15:
-      self.skipTest('old behaviour of node JS cannot be tested on node v15 or above')
-
     # Without NODEJS_CATCH_REJECTION we expect node to log the unhandled rejection
     # but return 0.
     self.node_args = [a for a in self.node_args if '--unhandled-rejections' not in a]
     self.run_process([EMCC, '--pre-js=pre.js', '-sNODEJS_CATCH_REJECTION=0', 'main.c'])
+    self.assertNotContained('unhandledRejection', read_file('a.out.js'))
+
+    if shared.check_node_version()[0] >= 15:
+      self.skipTest('old behaviour of node JS cannot be tested on node v15 or above')
+
     output = self.run_js('a.out.js')
     self.assertContained('ReferenceError: missing is not defined', output)
     self.assertContained('at foo (', output)