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Validate descriptor declarations (WebAssembly#7392)
To ensure soundness, there are very particular rules about how described and descriptor type declarations must relate to one another and their supertypes. Implement and test these rules.
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‎src/wasm-type.h‎

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Original file line numberDiff line numberDiff line change
@@ -816,6 +816,20 @@ struct TypeBuilder {
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InvalidFuncType,
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// A non-shared field of a shared heap type.
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InvalidUnsharedField,
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// A describes clause on a non-struct type.
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NonStructDescribes,
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// The described type is an invalid forward reference.
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ForwardDescribesReference,
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// The described type does not have this type as a descriptor.
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MismatchedDescribes,
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// A descriptor clause on a non-struct type.
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NonStructDescriptor,
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// The descriptor type does not describe this type.
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MismatchedDescriptor,
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// A non-shared descriptor on a shared type.
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InvalidUnsharedDescriptor,
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// A non-shared type described by a shared type.
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InvalidUnsharedDescribes,
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};
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struct Error {

‎src/wasm/wasm-type.cpp‎

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Original file line numberDiff line numberDiff line change
@@ -1464,6 +1464,20 @@ std::ostream& operator<<(std::ostream& os, TypeBuilder::ErrorReason reason) {
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return os << "Continuation has invalid function type";
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case TypeBuilder::ErrorReason::InvalidUnsharedField:
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return os << "Heap type has an invalid unshared field";
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case TypeBuilder::ErrorReason::NonStructDescribes:
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return os << "Describes clause on a non-struct type";
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case TypeBuilder::ErrorReason::ForwardDescribesReference:
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return os << "Describes clause is a forward reference";
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case TypeBuilder::ErrorReason::MismatchedDescribes:
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return os << "Described type is not a matching descriptor";
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case TypeBuilder::ErrorReason::NonStructDescriptor:
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return os << "Descriptor clause on a non-struct type";
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case TypeBuilder::ErrorReason::MismatchedDescriptor:
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return os << "Descriptor type does not describe heap type";
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case TypeBuilder::ErrorReason::InvalidUnsharedDescriptor:
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return os << "Heap type has an invalid unshared descriptor";
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case TypeBuilder::ErrorReason::InvalidUnsharedDescribes:
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return os << "Heap type describes an invalid unshared type";
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}
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WASM_UNREACHABLE("Unexpected error reason");
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}
@@ -2370,6 +2384,25 @@ bool isValidSupertype(const HeapTypeInfo& sub, const HeapTypeInfo& super) {
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if (sub.kind != super.kind) {
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return false;
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}
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if (sub.descriptor) {
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// A supertype of a type with a (descriptor $x) must either not have a
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// descriptor or have a (descriptor $y) where $y is the declared supertype
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// of $x.
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if (super.descriptor && sub.descriptor->supertype != super.descriptor) {
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return false;
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}
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} else {
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// A supertype of a type without a descriptor must also not have a
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// descriptor.
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if (super.descriptor) {
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return false;
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}
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}
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// A supertype of a type must have a describes clause iff the type has a
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// describes clause.
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if (bool(sub.described) != bool(super.described)) {
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return false;
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}
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SubTyper typer;
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switch (sub.kind) {
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case HeapTypeKind::Func:
@@ -2399,12 +2432,38 @@ validateType(HeapTypeInfo& info, std::unordered_set<HeapType>& seenTypes) {
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return TypeBuilder::ErrorReason::InvalidSupertype;
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}
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}
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if (auto* desc = info.described) {
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if (info.kind != HeapTypeKind::Struct) {
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return TypeBuilder::ErrorReason::NonStructDescribes;
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}
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assert(desc->isTemp && "unexpected canonical described type");
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if (!seenTypes.count(HeapType(uintptr_t(desc)))) {
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return TypeBuilder::ErrorReason::ForwardDescribesReference;
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}
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if (desc->descriptor != &info) {
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return TypeBuilder::ErrorReason::MismatchedDescribes;
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}
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}
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if (auto* desc = info.descriptor) {
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if (info.kind != HeapTypeKind::Struct) {
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return TypeBuilder::ErrorReason::NonStructDescriptor;
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}
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if (desc->described != &info) {
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return TypeBuilder::ErrorReason::MismatchedDescriptor;
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}
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}
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if (info.isContinuation()) {
24032456
if (!info.continuation.type.isSignature()) {
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return TypeBuilder::ErrorReason::InvalidFuncType;
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}
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}
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if (info.share == Shared) {
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if (info.described && info.described->share != Shared) {
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return TypeBuilder::ErrorReason::InvalidUnsharedDescribes;
2463+
}
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if (info.descriptor && info.descriptor->share != Shared) {
2465+
return TypeBuilder::ErrorReason::InvalidUnsharedDescriptor;
2466+
}
24082467
switch (info.kind) {
24092468
case HeapTypeKind::Func:
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// TODO: Figure out and enforce shared function rules.

‎test/spec/descriptors.wast‎

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,158 @@
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(module
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(rec
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(type (descriptor 1 (struct)))
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(type (describes 0 (struct)))
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)
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)
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(assert_invalid
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(module
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(rec
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(type (descriptor 1 (struct)))
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(type (struct))
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)
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)
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"descriptor with no matching describes"
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)
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18+
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(assert_invalid
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(module
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(rec
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(type (struct))
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(type (describes 0 (struct)))
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)
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)
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"describes with no matching descriptor"
27+
)
28+
29+
(assert_invalid
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(module
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(rec
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(type (describes 1 (struct)))
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(type (descriptor 0 (struct)))
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)
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)
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"forward describes reference"
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)
38+
39+
(assert_invalid
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(module
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(rec
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(type (descriptor 1 (array i8)))
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(type (describes 0 (struct)))
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)
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)
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"descriptor clause on non-struct type"
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)
48+
49+
(assert_invalid
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(module
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(rec
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(type (descriptor 1 (struct)))
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(type (describes 0 (array i8)))
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)
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)
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"describes clause on non-struct type"
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)
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(module
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(rec
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(type (shared (descriptor 1 (struct))))
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(type (shared (describes 0 (struct))))
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)
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)
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(assert_invalid
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(module
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(rec
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(type (shared (descriptor 1 (struct))))
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(type (describes 0 (struct)))
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)
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)
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"unshared descriptor type"
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)
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;; TODO: allow this?
77+
(assert_invalid
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(module
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(rec
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(type (descriptor 1 (struct)))
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(type (shared (describes 0 (struct))))
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)
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)
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"unshared described types"
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)
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(module
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(rec
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(type $super (sub (descriptor $super-desc (struct))))
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(type $super-desc (sub (describes $super (struct))))
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)
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(rec
93+
(type $sub (sub $super (descriptor $sub-desc (struct))))
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(type $sub-desc (sub $super-desc (describes $sub (struct))))
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)
96+
)
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(module
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(type $super (sub (struct)))
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(rec
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(type $other (sub (descriptor $super-desc (struct))))
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(type $super-desc (sub (describes $other (struct))))
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)
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(rec
105+
(type $sub (sub $super (descriptor $sub-desc (struct))))
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(type $sub-desc (sub $super-desc (describes $sub (struct))))
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)
108+
)
109+
110+
(assert_invalid
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(module
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(type $super (sub (struct)))
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(type $super-desc (sub (struct)))
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(rec
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(type $sub (sub $super (descriptor $sub-desc (struct))))
116+
(type $sub-desc (sub $super-desc (describes $sub (struct))))
117+
)
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)
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"supertype of descriptor must be a descriptor"
120+
)
121+
122+
(assert_invalid
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(module
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(rec
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(type $other (sub (descriptor $super-desc (struct))))
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(type $super-desc (sub (describes $other (struct))))
127+
(type $super (sub (descriptor $other-desc (struct))))
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(type $other-desc (sub (describes $super (struct))))
129+
)
130+
(rec
131+
(type $sub (sub $super (descriptor $sub-desc (struct))))
132+
(type $sub-desc (sub $super-desc (describes $sub (struct))))
133+
)
134+
)
135+
"supertype of described type must be described by supertype of descriptor"
136+
)
137+
138+
(assert_invalid
139+
(module
140+
(rec
141+
(type $super (sub (descriptor $super-desc (struct))))
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(type $super-desc (sub (describes $super (struct))))
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)
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(type $sub (sub $super (struct)))
145+
)
146+
"supertype of type without descriptor cannot have descriptor"
147+
)
148+
149+
(assert_invalid
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(module
151+
(rec
152+
(type $super (sub (descriptor $super-desc (struct))))
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(type $super-desc (sub (describes $super (struct))))
154+
)
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(type $sub (sub $super-desc (struct)))
156+
)
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"supertype of non-descriptor type cannot be a descriptor"
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)

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