Restore isString type methods (#6815)

PR ##6803 proposed removing Type::isString and HeapType::isString in
favor of more explicit, verbose callsites. There was no consensus to
make this change, but it was accidentally committed as part of #6804.

Revert the accidental change, except for the useful, noncontroversial
parts, such as fixing the `isString` implementation and a few other
locations to correctly handle shared types.

3 files changed, 4 insertions, 8 deletions

diff --git a/src/tools/execution-results.h b/src/tools/execution-results.h
index 31c572e65..920bb200a 100644
--- a/src/tools/execution-results.h
+++ b/src/tools/execution-results.h
@@ -148,8 +148,7 @@ struct ExecutionResults {
     // simple and stable internal structures that optimizations will not alter.
     auto type = value.type;
     if (type.isRef()) {
-      if (type.getHeapType().isMaybeShared(HeapType::string) ||
-          type.getHeapType().isMaybeShared(HeapType::i31)) {
+      if (type.isString() || type.getHeapType().isMaybeShared(HeapType::i31)) {
         std::cout << value << '\n';
       } else if (value.isNull()) {
         std::cout << "null\n";
@@ -190,8 +189,7 @@ struct ExecutionResults {
     // TODO: Once we support optimizing under some form of open-world
     // assumption, we should be able to check that the types and/or structure of
     // GC data passed out of the module does not change.
-    if (a.type.isRef() &&
-        !a.type.getHeapType().isMaybeShared(HeapType::string) &&
+    if (a.type.isRef() && !a.type.isString() &&
         !a.type.getHeapType().isMaybeShared(HeapType::i31)) {
       return true;
     }
diff --git a/src/tools/fuzzing/fuzzing.cpp b/src/tools/fuzzing/fuzzing.cpp
index 138831860..2aff7146e 100644
--- a/src/tools/fuzzing/fuzzing.cpp
+++ b/src/tools/fuzzing/fuzzing.cpp
@@ -2536,8 +2536,7 @@ Expression* TranslateToFuzzReader::makeConst(Type type) {
     if (type.isNullable() && oneIn(8)) {
       return builder.makeRefNull(type.getHeapType());
     }
-    if (type.getHeapType().isMaybeShared(HeapType::string)) {
-      assert(!type.getHeapType().isShared() && "TODO: shared strings");
+    if (type.getHeapType().isString()) {
       return makeStringConst();
     }
     if (type.getHeapType().isBasic()) {
diff --git a/src/tools/wasm-ctor-eval.cpp b/src/tools/wasm-ctor-eval.cpp
index 11fee72fb..22e666a52 100644
--- a/src/tools/wasm-ctor-eval.cpp
+++ b/src/tools/wasm-ctor-eval.cpp
@@ -841,8 +841,7 @@ public:
     // externalized i31s) can be handled by the general makeConstantExpression
     // logic (which knows how to handle externalization, for i31s; and it also
     // can handle string constants).
-    if (!value.isData() ||
-        value.type.getHeapType().isMaybeShared(HeapType::string)) {
+    if (!value.isData() || value.isString()) {
       return builder.makeConstantExpression(original);
     }