Exit HandleScope before snapshotting (denoland#4168)

The V8 documentation explicitly states that SnapshotCreator::CreateBlob()
should not be called from within a HandleScope.

Additionally, this patch removes some non-functional error handling code
from the deno_core::Isolate::snapshot() method.

core/isolate.rs

@@ -465,24 +465,26 @@ impl Isolate {
  /// ErrBox can be downcast to a type that exposes additional information about
  /// the V8 exception. By default this type is CoreJSError, however it may be a
  /// different type if Isolate::set_js_error_create() has been used.
- pub fn snapshot(&mut self) -> Result<v8::OwnedStartupData, ErrBox> {
+ pub fn snapshot(&mut self) -> v8::OwnedStartupData {
  assert!(self.snapshot_creator.is_some());
 
- let v8_isolate = self.v8_isolate.as_mut().unwrap();
- let js_error_create_fn = &*self.js_error_create_fn;
- let last_exception = &mut self.last_exception;
-
- let mut hs = v8::HandleScope::new(v8_isolate);
- let scope = hs.enter();
- self.global_context.reset(scope);
+ // Note: create_blob() method must not be called from within a HandleScope.
+ // The HandleScope created here is exited at the end of the block.
+ // TODO(piscisaureus): The rusty_v8 type system should enforce this.
+ {
+ let v8_isolate = self.v8_isolate.as_mut().unwrap();
+ let mut hs = v8::HandleScope::new(v8_isolate);
+ let scope = hs.enter();
+ self.global_context.reset(scope);
+ }
 
  let snapshot_creator = self.snapshot_creator.as_mut().unwrap();
  let snapshot = snapshot_creator
  .create_blob(v8::FunctionCodeHandling::Keep)
  .unwrap();
  self.has_snapshotted = true;
 
- check_last_exception(last_exception, js_error_create_fn).map(|_| snapshot)
+ snapshot
  }
 }
 
@@ -1160,9 +1162,7 @@ pub mod tests {
  let snapshot = {
  let mut isolate = Isolate::new(StartupData::None, true);
  js_check(isolate.execute("a.js", "a = 1 + 2"));
- let s = isolate.snapshot().unwrap();
- drop(isolate);
- s
+ isolate.snapshot()
  };
 
  let startup_data = StartupData::OwnedSnapshot(snapshot);

deno_typescript/lib.rs

@@ -232,7 +232,7 @@ fn write_snapshot(
  snapshot_filename: &Path,
 ) -> Result<(), ErrBox> {
  println!("Creating snapshot...");
- let snapshot = runtime_isolate.snapshot()?;
+ let snapshot = runtime_isolate.snapshot();
  let snapshot_slice: &[u8] = &*snapshot;
  println!("Snapshot size: {}", snapshot_slice.len());
  fs::write(&snapshot_filename, snapshot_slice)?;