Make final types the default (WebAssembly#5918)

Match the spec and parse the shorthand binary and text formats as final and emit
final types without supertypes using the shorthands as well. This is a
potentially-breaking change, since the text and binary shorthands can no longer
be used to define types that have subtypes.

Also make TypeBuilder entries final by default to better match the spec and
update the internal APIs to use the "open" terminology rather than "final"
terminology. Future changes will update the text format to use the standard "sub
open" rather than the current "sub final" keywords. The exception is the new wat
parser, which supporst "sub open" as of this change, since it didn't support
final types at all previously.

Author: tlively

CHANGELOG.md

@@ -22,6 +22,8 @@ Current Trunk
   and as a convenience.
 - The nonstandard, experimental gc-nn-locals feature has been removed now that
   standard non-nullable locals are supported.
+- Heap types are now final by default and openness must be opted into both in
+  the text and binary formats as well as in the TypeBuilder API.
 
 v114
 ----

src/binaryen-c.cpp

@@ -6413,6 +6413,9 @@ void TypeBuilderSetSubType(TypeBuilderRef builder,
                            BinaryenHeapType superType) {
   ((TypeBuilder*)builder)->setSubType(index, HeapType(superType));
 }
+void TypeBuilderSetOpen(TypeBuilderRef builder, BinaryenIndex index) {
+  ((TypeBuilder*)builder)->setOpen(index);
+}
 void TypeBuilderCreateRecGroup(TypeBuilderRef builder,
                                BinaryenIndex index,
                                BinaryenIndex length) {

src/binaryen-c.h

@@ -3572,6 +3572,9 @@ BINARYEN_API BinaryenType TypeBuilderGetTempRefType(TypeBuilderRef builder,
 BINARYEN_API void TypeBuilderSetSubType(TypeBuilderRef builder,
                                         BinaryenIndex index,
                                         BinaryenHeapType superType);
+// Sets the type at `index` to be open (i.e. non-final).
+BINARYEN_API void TypeBuilderSetOpen(TypeBuilderRef builder,
+                                     BinaryenIndex index);
 // Creates a new recursion group in the range `index` inclusive to `index +
 // length` exclusive. Recursion groups must not overlap.
 BINARYEN_API void TypeBuilderCreateRecGroup(TypeBuilderRef builder,

src/ir/type-updating.cpp

@@ -72,7 +72,7 @@ GlobalTypeRewriter::TypeMap GlobalTypeRewriter::rebuildTypes() {
   // Create the temporary heap types.
   i = 0;
   for (auto [type, _] : typeIndices) {
-    typeBuilder[i].setFinal(type.isFinal());
+    typeBuilder[i].setOpen(type.isOpen());
     if (type.isSignature()) {
       auto sig = type.getSignature();
       TypeList newParams, newResults;

src/passes/TypeMerging.cpp

@@ -538,7 +538,7 @@ bool shapeEq(HeapType a, HeapType b) {
   // Check whether `a` and `b` have the same top-level structure, including the
   // position and identity of any children that are not included as transitions
   // in the DFA, i.e. any children that are not nontrivial references.
-  if (a.isFinal() != b.isFinal()) {
+  if (a.isOpen() != b.isOpen()) {
     return false;
   }
   if (a.isStruct() && b.isStruct()) {
@@ -554,7 +554,7 @@ bool shapeEq(HeapType a, HeapType b) {
 }
 
 size_t shapeHash(HeapType a) {
-  size_t digest = hash(a.isFinal());
+  size_t digest = hash(a.isOpen());
   if (a.isStruct()) {
     rehash(digest, 0);
     hash_combine(digest, shapeHash(a.getStruct()));

src/passes/TypeSSA.cpp

@@ -110,7 +110,7 @@ std::vector<HeapType> ensureTypesAreInNewRecGroup(RecGroup recGroup,
         if (auto super = type.getSuperType()) {
           builder[i].subTypeOf(*super);
         }
-        builder[i].setFinal(type.isFinal());
+        builder[i].setOpen(type.isOpen());
       }
 
       // Implement the hash as a struct with "random" fields, and add it.
@@ -255,6 +255,7 @@ struct TypeSSA : public Pass {
         builder[i] = oldType.getArray();
       }
       builder[i].subTypeOf(oldType);
+      builder[i].setOpen();
     }
     builder.createRecGroup(0, num);
     auto result = builder.build();
@@ -311,7 +312,7 @@ struct TypeSSA : public Pass {
       return false;
     }
 
-    if (curr->type.getHeapType().isFinal()) {
+    if (!curr->type.getHeapType().isOpen()) {
       // We can't create new subtypes of a final type anyway.
       return false;
     }

src/tools/fuzzing/heap-types.cpp

@@ -87,9 +87,7 @@ struct HeapTypeGeneratorImpl {
 
     // Types without nontrivial subtypes may be marked final.
     for (Index i = 0; i < builder.size(); ++i) {
-      if (subtypeIndices[i].size() == 1 && rand.oneIn(2)) {
-        builder[i].setFinal();
-      }
+      builder[i].setOpen(subtypeIndices[i].size() > 1 || rand.oneIn(2));
     }
 
     // Initialize the recursion groups.
@@ -894,7 +892,7 @@ std::vector<HeapType> Inhabitator::build() {
         builder[i].subTypeOf(*super);
       }
     }
-    builder[i].setFinal(types[i].isFinal());
+    builder[i].setOpen(types[i].isOpen());
   }
 
   auto built = builder.build();

src/tools/wasm-fuzz-types.cpp

@@ -264,7 +264,7 @@ void Fuzzer::checkCanonicalization() {
 
       // Set finality
       for (size_t i = 0; i < types.size(); ++i) {
-        builder[i].setFinal(types[i].isFinal());
+        builder[i].setOpen(types[i].isOpen());
       }
 
       // Set up recursion groups and record group ends to ensure we only select

src/wasm-type.h

@@ -361,7 +361,7 @@ class HeapType {
   bool isArray() const;
   bool isString() const;
   bool isBottom() const;
-  bool isFinal() const;
+  bool isOpen() const;
 
   Signature getSignature() const;
   const Struct& getStruct() const;
@@ -587,7 +587,7 @@ struct TypeBuilder {
   // not overlap or go out of bounds.
   void createRecGroup(size_t i, size_t length);
 
-  void setFinal(size_t i, bool final = true);
+  void setOpen(size_t i, bool open = true);
 
   enum class ErrorReason {
     // There is a cycle in the supertype relation.
@@ -650,8 +650,8 @@ struct TypeBuilder {
       builder.setSubType(index, other);
       return *this;
     }
-    Entry& setFinal(bool final = true) {
-      builder.setFinal(index, final);
+    Entry& setOpen(bool open = true) {
+      builder.setOpen(index, open);
       return *this;
     }
   };

src/wasm/wasm-binary.cpp

@@ -265,13 +265,11 @@ void WasmBinaryWriter::writeTypes() {
     // Emit the type definition.
     BYN_TRACE("write " << type << std::endl);
     auto super = type.getSuperType();
-    // TODO: Use the binary shorthand for final types once we parse MVP
-    // signatures as final.
-    if (type.isFinal() || super || hasSubtypes[i]) {
-      if (type.isFinal()) {
-        o << S32LEB(BinaryConsts::EncodedType::SubFinal);
-      } else {
+    if (super || type.isOpen()) {
+      if (type.isOpen()) {
         o << S32LEB(BinaryConsts::EncodedType::Sub);
+      } else {
+        o << S32LEB(BinaryConsts::EncodedType::SubFinal);
       }
       if (super) {
         o << U32LEB(1);
@@ -2268,9 +2266,8 @@ void WasmBinaryReader::readTypes() {
     std::optional<uint32_t> superIndex;
     if (form == BinaryConsts::EncodedType::Sub ||
         form == BinaryConsts::EncodedType::SubFinal) {
-      if (form == BinaryConsts::EncodedType::SubFinal) {
-        // TODO: Interpret type definitions without any `sub` as final as well.
-        builder[i].setFinal();
+      if (form == BinaryConsts::EncodedType::Sub) {
+        builder[i].setOpen();
       }
       uint32_t supers = getU32LEB();
       if (supers > 0) {