2 files changed, 68 insertions, 0 deletions
diff --git a/src/wasm/wasm-type.cpp b/src/wasm/wasm-type.cpp
index c77099a1d..d24e42acb 100644
--- a/src/wasm/wasm-type.cpp
+++ b/src/wasm/wasm-type.cpp
@@ -1392,6 +1392,36 @@ size_t HeapType::getDepth() const {
   for (auto curr = *this; (super = curr.getSuperType()); curr = *super) {
     ++depth;
   }
+  // In addition to the explicit supertypes we just traversed over, there is
+  // implicit supertyping wrt basic types. A signature type always has one more
+  // super, HeapType::func, etc.
+  if (!isBasic()) {
+    if (isFunction()) {
+      depth++;
+    } else if (isData()) {
+      // specific struct types <: data <: eq <: any
+      depth += 3;
+    }
+  } else {
+    // Some basic types have supers.
+    switch (getBasic()) {
+      case HeapType::ext:
+      case HeapType::func:
+      case HeapType::any:
+        break;
+      case HeapType::eq:
+        depth++;
+        break;
+      case HeapType::i31:
+      case HeapType::data:
+      case HeapType::string:
+      case HeapType::stringview_wtf8:
+      case HeapType::stringview_wtf16:
+      case HeapType::stringview_iter:
+        depth += 2;
+        break;
+    }
+  }
   return depth;
 }
 
diff --git a/test/gtest/type-builder.cpp b/test/gtest/type-builder.cpp
index 525a45c31..bc7b72e5d 100644
--- a/test/gtest/type-builder.cpp
+++ b/test/gtest/type-builder.cpp
@@ -619,3 +619,41 @@ TEST_F(IsorecursiveTest, TestExistingSuperType) {
   EXPECT_EQ(A1.getHeapType(), A2.getHeapType());
   EXPECT_EQ(B1.getHeapType(), B2.getHeapType());
 }
+
+// Test .depth() helper.
+TEST_F(NominalTest, TestDepth) {
+  HeapType A, B, C;
+  {
+    TypeBuilder builder(3);
+    builder[0] = Struct();
+    builder[1] = Struct();
+    builder[2] = Array(Field(Type::i32, Immutable));
+    builder.setSubType(1, builder.getTempHeapType(0));
+    auto result = builder.build();
+    ASSERT_TRUE(result);
+    auto built = *result;
+    A = built[0];
+    B = built[1];
+    C = built[2];
+  }
+
+  // any < eq < data < specific struct and array types
+  EXPECT_EQ(HeapType(HeapType::any).getDepth(), 0U);
+  EXPECT_EQ(HeapType(HeapType::eq).getDepth(), 1U);
+  EXPECT_EQ(HeapType(HeapType::data).getDepth(), 2U);
+  EXPECT_EQ(A.getDepth(), 3U);
+  EXPECT_EQ(B.getDepth(), 4U);
+  EXPECT_EQ(C.getDepth(), 3U);
+
+  // Signature types are subtypes of func.
+  EXPECT_EQ(HeapType(HeapType::func).getDepth(), 0U);
+  EXPECT_EQ(HeapType(Signature(Type::none, Type::none)).getDepth(), 1U);
+
+  EXPECT_EQ(HeapType(HeapType::ext).getDepth(), 0U);
+
+  EXPECT_EQ(HeapType(HeapType::i31).getDepth(), 2U);
+  EXPECT_EQ(HeapType(HeapType::string).getDepth(), 2U);
+  EXPECT_EQ(HeapType(HeapType::stringview_wtf8).getDepth(), 2U);
+  EXPECT_EQ(HeapType(HeapType::stringview_wtf16).getDepth(), 2U);
+  EXPECT_EQ(HeapType(HeapType::stringview_iter).getDepth(), 2U);
+}