[EH] Check if Exception.stack is writable

src/library_exceptions.js

@@ -335,11 +335,20 @@ var LibraryExceptions = {
     //     ...
     //
     // Remove this JS function name, which is in the second line, from the stack
-    // trace. Note that .stack does not yet exist in all browsers (see #18828).
+    // trace.
+    //
+    // Note that .stack does not yet exist in all browsers (see #18828).
+    // Also, WebAssembly.Exception.stack is currently readonly, but this can
+    // change, and it is implemented as writable in Chrome and Node. Will check
+    // the 'writable' condition for now and later resolve this by either
+    // deleting this altogether or removing this condition check.
     if (e.stack) {
-      var arr = e.stack.split('\n');
-      arr.splice(1,1);
-      e.stack = arr.join('\n');
+      var pd = Object.getOwnPropertyDescriptor(e, 'stack');
+      if (pd && pd.writable) {
+        var arr = e.stack.split('\n');
+        arr.splice(1,1);
+        e.stack = arr.join('\n');
+      }
     }
     throw e;
   },

test/common.py

@@ -301,6 +301,16 @@ def decorated(self, *args, **kwargs):
   return decorated
 
 
+def requires_spidermonkey(func):
+  assert callable(func)
+
+  def decorated(self, *args, **kwargs):
+    self.require_spidermonkey()
+    return func(self, *args, **kwargs)
+
+  return decorated
+
+
 def node_pthreads(f):
   @wraps(f)
   def decorated(self, *args, **kwargs):
@@ -698,6 +708,14 @@ def require_node_canary(self):
     else:
       self.fail('node canary required to run this test.  Use EMTEST_SKIP_NODE_CANARY to skip')
 
+  def require_spidermonkey(self):
+    if not config.SPIDERMONKEY_ENGINE or config.SPIDERMONKEY_ENGINE not in config.JS_ENGINES:
+      if 'EMTEST_SKIP_SPIDERMONKEY' in os.environ:
+        self.skipTest('test requires spidermonkey and EMTEST_SKIP_SPIDERMONKEY is set')
+      else:
+        self.fail('spidermonkey required to run this test.  Use EMTEST_SKIP_SPIDERMONKEY to skip')
+    self.require_engine(config.SPIDERMONKEY_ENGINE)
+
   def require_engine(self, engine):
     logger.debug(f'require_engine: {engine}')
     if self.required_engine and self.required_engine != engine:

test/test_core.py

@@ -27,7 +27,7 @@
 from common import RunnerCore, path_from_root, requires_native_clang, test_file, create_file
 from common import skip_if, needs_dylink, no_windows, no_mac, is_slow_test, parameterized
 from common import env_modify, with_env_modify, disabled, flaky, node_pthreads, also_with_wasm_bigint
-from common import read_file, read_binary, requires_v8, requires_node, requires_node_canary
+from common import read_file, read_binary, requires_v8, requires_node, requires_node_canary, requires_spidermonkey
 from common import compiler_for, crossplatform, no_4gb, no_2gb
 from common import with_both_sjlj, also_with_standalone_wasm, can_do_standalone, no_wasm64
 from common import NON_ZERO, WEBIDL_BINDER, EMBUILDER, PYTHON
@@ -9641,6 +9641,25 @@ def test_wasm_worker_wait_async(self):
     self.prep_wasm_worker_in_node()
     self.do_runf('atomic/test_wait_async.c', emcc_args=['-sWASM_WORKERS'])
 
+  @requires_spidermonkey
+  def test_exceptions_stack_trace_and_message_wasm_eh(self):
+    # Currently writing to WebAssembly.Exception.stack property is not allowed
+    # in Firefox, but we need to ensure generating stack traces runs on FireFox
+    # without erroring out, even though stack trace simplification will not be
+    # done. See https://github.com/emscripten-core/emscripten/pull/21050
+    src = r'''
+      #include <stdexcept>
+      int main() {
+        throw std::runtime_error("my message");
+        return 0;
+      }
+    '''
+    self.emcc_args = ['--profiling-funcs', '-gsource-map']
+    self.emcc_args = ['-g', '-fwasm-exceptions']
+    self.set_setting('EXCEPTION_STACK_TRACES', 1)
+    err = self.do_run(src, assert_returncode=NON_ZERO)
+    self.assertNotContained('setting getter-only property "stack"', err)
+
 
 # Generate tests for everything
 def make_run(name, emcc_args, settings=None, env=None,