[web snapshots] Fix error reporting

We have 4 different cases:
1) Explicit web snapshots (--web-snapshot) & errors in the snapshot
2) Explicit web snapshots & errors in the embedded script
3) Auto-detected web snapshots (--experimental-web-snapshots) & errors
in the snapshot
4) Auto-detected web snapshots & errors in the embedded script

Before this CL: cases 2 & 4 resulted in a DCHECK failing and the error
in case 3 wasn't reported correctly.

This CL implements consistent error reporting for all of them.

Bug: v8:11525
Change-Id: If2e5039d9769b9cad2175dfd5c4f91edf61111ae
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3277877Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77963}

src/common/message-template.h

@@ -633,7 +633,9 @@ namespace internal {
   T(OptionalChainingNoSuper, "Invalid optional chain from super property")     \
   T(OptionalChainingNoTemplate, "Invalid tagged template on optional chain")   \
   /* AggregateError */                                                         \
-  T(AllPromisesRejected, "All promises were rejected")
+  T(AllPromisesRejected, "All promises were rejected")                         \
+  /* Web snapshots */                                                          \
+  T(WebSnapshotError, "Web snapshot failed: %")
 
 enum class MessageTemplate {
 #define TEMPLATE(NAME, STRING) k##NAME,

src/d8/d8.cc

@@ -1434,26 +1434,16 @@ bool Shell::ExecuteWebSnapshot(Isolate* isolate, const char* file_name) {
 
   std::string absolute_path = NormalizePath(file_name, GetWorkingDirectory());
 
-  TryCatch try_catch(isolate);
-  try_catch.SetVerbose(true);
   int length = 0;
   std::unique_ptr<uint8_t[]> snapshot_data(
       reinterpret_cast<uint8_t*>(ReadChars(absolute_path.c_str(), &length)));
   if (length == 0) {
     isolate->ThrowError("Error reading the web snapshot");
-    DCHECK(try_catch.HasCaught());
-    ReportException(isolate, &try_catch);
     return false;
   }
   i::WebSnapshotDeserializer deserializer(isolate);
-  if (!deserializer.UseWebSnapshot(snapshot_data.get(),
-                                   static_cast<size_t>(length))) {
-    DCHECK(try_catch.HasCaught());
-    ReportException(isolate, &try_catch);
-    return false;
-  }
-  DCHECK(!try_catch.HasCaught());
-  return true;
+  return deserializer.UseWebSnapshot(snapshot_data.get(),
+                                     static_cast<size_t>(length));
 }
 
 PerIsolateData::PerIsolateData(Isolate* isolate)

src/web-snapshot/web-snapshot.h

@@ -234,6 +234,8 @@ class V8_EXPORT WebSnapshotDeserializer
 
  private:
   bool Deserialize();
+  bool DeserializeSnapshot();
+  bool DeserializeScript();
 
   WebSnapshotDeserializer(const WebSnapshotDeserializer&) = delete;
   WebSnapshotDeserializer& operator=(const WebSnapshotDeserializer&) = delete;

test/cctest/test-web-snapshots.cc

@@ -748,5 +748,47 @@ TEST(Concatenation) {
   }
 }
 
+// Test that errors from invalid concatenated code are handled correctly.
+TEST(ConcatenationErrors) {
+  CcTest::InitializeVM();
+  v8::Isolate* isolate = CcTest::isolate();
+
+  const char* snapshot_source = "var foo = {a: 1};\n";
+  const char* source_to_append = "wontparse+[)";
+  uint32_t kObjectCount = 1;
+
+  WebSnapshotData snapshot_data;
+  {
+    v8::HandleScope scope(isolate);
+    v8::Local<v8::Context> new_context = CcTest::NewContext();
+    v8::Context::Scope context_scope(new_context);
+
+    CompileRun(snapshot_source);
+    v8::Local<v8::PrimitiveArray> exports = v8::PrimitiveArray::New(isolate, 1);
+    v8::Local<v8::String> str =
+        v8::String::NewFromUtf8(isolate, "foo").ToLocalChecked();
+    exports->Set(isolate, 0, str);
+    WebSnapshotSerializer serializer(isolate);
+    CHECK(serializer.TakeSnapshot(new_context, exports, snapshot_data));
+    CHECK(!serializer.has_error());
+    CHECK_NOT_NULL(snapshot_data.buffer);
+    CHECK_EQ(kObjectCount, serializer.object_count());
+  }
+
+  auto buffer_size = snapshot_data.buffer_size + strlen(source_to_append);
+  std::unique_ptr<uint8_t[]> buffer(new uint8_t[buffer_size]);
+  memcpy(buffer.get(), snapshot_data.buffer, snapshot_data.buffer_size);
+  memcpy(buffer.get() + snapshot_data.buffer_size, source_to_append,
+         strlen(source_to_append));
+
+  {
+    v8::HandleScope scope(isolate);
+    v8::Local<v8::Context> new_context = CcTest::NewContext();
+    v8::Context::Scope context_scope(new_context);
+    WebSnapshotDeserializer deserializer(isolate);
+    CHECK(!deserializer.UseWebSnapshot(buffer.get(), buffer_size));
+  }
+}
+
 }  // namespace internal
 }  // namespace v8