Typed Continuations: Add cont type (#5998)

This PR is part of a series that adds basic support for the [typed continuations proposal](https://github.com/wasmfx/specfx).

This PR adds continuation types, of the form `(cont $foo)` for some function type `$foo`.

The only notable changes affecting existing code are the following:
- This is the first `HeapType` which has another `HeapType` (rather than, say, a `Type`) as its immediate child. This required fixes to certain traversals that have a flag for being at the toplevel of a type.
- Some shared logic for parsing `HeapType`s has been factored out.

1 files changed, 12 insertions, 0 deletions

diff --git a/test/unit/test_features.py b/test/unit/test_features.py
index d2d72a8e4..cd8aebbb1 100644
--- a/test/unit/test_features.py
+++ b/test/unit/test_features.py
@@ -294,6 +294,18 @@ class FeatureValidationTest(utils.BinaryenTestCase):
                                        'Tags with result types require typed '
                                        'continuations feature [--enable-typed-continuations]')
 
+    def test_cont_type(self):
+        module = '''
+        (module
+         (type $ft (func (param i32) (result i32)))
+         (type $ct (cont $ft))
+         (func $foo
+          (local $0 (ref $ct))
+         )
+        )
+        '''
+        self.check_typed_continuations(module, 'all used types should be allowed')
+
 
 class TargetFeaturesSectionTest(utils.BinaryenTestCase):
     def test_atomics(self):