[threads] Parse, build, and print shared composite types (#6654)

Parse the text format for shared composite types as described in the
shared-everything thread proposal. Update the parser to use 'comptype' instead
of 'strtype' to match the final GC spec and add the new syntactic class
'sharecomptype'.

Update the type canonicalization logic to take sharedness into account to avoid
merging shared and unshared types. Make the same change in the TypeMerging pass.
Ensure that shared and unshared types cannot be in a subtype relationship with
each other.

Follow-up PRs will add shared abstract heap types, binary parsing and emitting
for shared types, and fuzzer support for shared types.

1 files changed, 8 insertions, 3 deletions

diff --git a/src/wasm-type.h b/src/wasm-type.h
index b02484ae3..3e9fa4db3 100644
--- a/src/wasm-type.h
+++ b/src/wasm-type.h
@@ -377,6 +377,7 @@ public:
   bool isString() const;
   bool isBottom() const;
   bool isOpen() const;
+  bool isShared() const;
 
   Signature getSignature() const;
   Continuation getContinuation() const;
@@ -614,9 +615,8 @@ struct TypeBuilder {
   Type getTempTupleType(const Tuple&);
   Type getTempRefType(HeapType heapType, Nullability nullable);
 
-  // In nominal mode, or for nominal types, declare the HeapType being built at
-  // index `i` to be an immediate subtype of the given HeapType. Does nothing
-  // for equirecursive types.
+  // Declare the HeapType being built at index `i` to be an immediate subtype of
+  // the given HeapType.
   void setSubType(size_t i, HeapType super);
 
   // Create a new recursion group covering slots [i, i + length). Groups must
@@ -624,6 +624,7 @@ struct TypeBuilder {
   void createRecGroup(size_t i, size_t length);
 
   void setOpen(size_t i, bool open = true);
+  void setShared(size_t i, bool shared = true);
 
   enum class ErrorReason {
     // There is a cycle in the supertype relation.
@@ -696,6 +697,10 @@ struct TypeBuilder {
       builder.setOpen(index, open);
       return *this;
     }
+    Entry& setShared(bool shared = true) {
+      builder.setShared(index, shared);
+      return *this;
+    }
   };
 
   Entry operator[](size_t i) { return Entry{*this, i}; }