[torque] Don't crash when failing to find a non-constexpr type

Marja pointed out that the following code causes a Torque crash:

Convert<Smi>(MessageTemplate::kFoo)

This change is a small fix to not crash in that case.

Bug: v8:7793, v8:10475
Change-Id: I7856366856a4cd7facdb19686a2d4c92b0d04516
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2182175Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#67580}

src/torque/types.h

@@ -300,8 +300,13 @@ class AbstractType final : public Type {
   }
 
   std::string SimpleNameImpl() const override {
-    if (IsConstexpr())
-      return "constexpr_" + NonConstexprVersion()->SimpleName();
+    if (IsConstexpr()) {
+      const Type* non_constexpr_version = NonConstexprVersion();
+      if (non_constexpr_version == nullptr) {
+        ReportError("Cannot find non-constexpr type corresponding to ", *this);
+      }
+      return "constexpr_" + non_constexpr_version->SimpleName();
+    }
     return name();
   }
 

test/unittests/torque/torque-unittest.cc

@@ -336,6 +336,22 @@ TEST(Torque, ConstexprLetBindingDoesNotCrash) {
       HasSubstr("Use 'const' instead of 'let' for variable 'foo'"));
 }
 
+TEST(Torque, FailedImplicitCastFromConstexprDoesNotCrash) {
+  ExpectFailingCompilation(
+      R"(
+    extern enum SomeEnum {
+      kValue,
+      ...
+    }
+    macro Foo() {
+      Bar(SomeEnum::kValue);
+    }
+    macro Bar<T: type>(value: T) {}
+  )",
+      HasSubstr(
+          "Cannot find non-constexpr type corresponding to constexpr kValue"));
+}
+
 TEST(Torque, DoubleUnderScorePrefixIllegalForIdentifiers) {
   ExpectFailingCompilation(R"(
     @export macro Foo() {