Fuzzer: Use types from imported module (#7990)

Also improve the rate-handling in other places. Pick a rate of 0-10,
then random numbers 0-9 compared with `num < rate`, which
allows a rate of 0 to mean "never" and 10 to mean "always".

Author: kripken

src/tools/fuzzing/fuzzing.cpp

@@ -450,6 +450,17 @@ void TranslateToFuzzReader::setupHeapTypes() {
   // initial content we began with.
   auto possibleHeapTypes = ModuleUtils::collectHeapTypes(wasm);
 
+  // Use heap types from an imported module, if present.
+  if (importedModule) {
+    auto importedHeapTypes = ModuleUtils::collectHeapTypes(*importedModule);
+    auto rate = upTo(11);
+    for (auto type : importedHeapTypes) {
+      if (upTo(10) < rate) {
+        possibleHeapTypes.push_back(type);
+      }
+    }
+  }
+
   // Filter away uninhabitable heap types, that is, heap types that we cannot
   // construct, like a type with a non-nullable reference to itself.
   interestingHeapTypes = HeapTypeGenerator::getInhabitable(possibleHeapTypes);
@@ -1213,9 +1224,9 @@ void TranslateToFuzzReader::useImportedFunctions() {
   }
 
   // Add some of the module's exported functions as imports, at a random rate.
-  auto rate = upTo(100);
+  auto rate = upTo(11);
   for (auto& exp : importedModule->exports) {
-    if (exp->kind != ExternalKind::Function || upTo(100) > rate) {
+    if (exp->kind != ExternalKind::Function || upTo(10) >= rate) {
       continue;
     }
 
@@ -1243,9 +1254,9 @@ void TranslateToFuzzReader::useImportedGlobals() {
   }
 
   // Add some of the module's exported globals as imports, at a random rate.
-  auto rate = upTo(100);
+  auto rate = upTo(11);
   for (auto& exp : importedModule->exports) {
-    if (exp->kind != ExternalKind::Global || upTo(100) > rate) {
+    if (exp->kind != ExternalKind::Global || upTo(10) >= rate) {
       continue;
     }