Refactoring and bug fixes in the V8 API #13754

190n · 2024-09-05T21:59:49Z

What does this PR do?

Refactors and bugfixes in our V8 API implementation. So far:

Fix some places that did not handle oddballs (booleans or nullish JS values) properly (EscapableHandleScope, Global)
Support NewStringType::kInternalized
- Previously the type was ignored. Now internalized strings are created with WTF::AtomString.
Remove or merge many functions that convert between V8 and JSC values
Make v8::Context be a Zig::GlobalObject instead of the same thing as v8::Isolate, which lets us access the global object with less indirection in functions that take a Context
- side effect: there are now only 2 kinds of V8 handle, for cells and doubles, instead of 3. Context was the only place a void * handle was used.
Make v8::Isolate an actual class containing everything v8::Roots used to, and delete v8::Roots, instead of reinterpreting between Isolate and Roots
- v8::Roots's only purpose was to hold values at the offsets from an Isolate pointer that V8 expects. Now we actually store those values in the Isolate like V8 does.
Test case and bug fix for EscapableHandleScope
Use m_ on C++ class field names for clarity
Move Bun-specific classes (i.e. classes that we use to implement the V8 API, but that don't actually exist in the real V8 API) into the namespace v8::shim.
- All V8 classes that are kept in a Local (String, ObjectTemplate, etc.) now have zero fields, matching how V8's API works and making it less likely to crash by accessing a member while this is the invalid pointer that we get from V8. The cell pointer stored in the handle is either a built-in type (JSString, JSObject) or a type in v8::shim (v8::shim::InternalFieldObject, v8::shim::Function)
Move isosubspace declarations for V8 types next to the ones for other Bun-specific types
Support Function::GetName and Value::IsFunction
Make the this value received by native functions correct (it should be coerced to an object, or overridden by globalThis if null or undefined, like in JavaScript sloppy mode)

How did you verify your code works?

Most of the V8 API is covered by existing tests. A couple new tests were added.

…the necessary refactoring

The v8 namespace was confusingly polluted with both classes that exist in the actual V8 API, as well as new classes to support Bun's specific implementation of that API. This commit moves the latter into the namespace v8::shim. It also makes a duplicate of classes with fields in the v8::shim namespace. For those classes, the v8:: version has no fields, no JSC superclass, and only implements the actual V8 API functions, while the v8::shim:: version has the inheritance and functions necessary to be allocated as a JSC object and implements helper functions to support the V8 APIs.