V8 is used by many different embedders: Chrome, NodeJS, gjstest, etc. When changing V8 public API we need to ensure that the embedders can smoothly update to the new V8 version. In particular, we cannot assume that an embedder updates to the new V8 version and adjusts their code to the new API in one atomic change.
The embedder should be able to adjust their code to the new API while still using the previous version of V8. All instructions below follow from this rule.
Adding new types, constants, and functions is safe with one caveat: do not add a new pure virtual function to an existing class. New virtual functions should have default implementation.
Adding a new parameter to a function is safe if the parameter has the default value.
Removing or renaming types, constants, functions is unsafe. Use
V8_DEPRECATE_SOON macros. For example, let's say we want to rename function
foo to function
bar. Then we need to do the following:
barnear the existing function
V8_DEPRECATED("Use bar instead", void foo());
V8_DEPRECATE_SOON is a softer version of
V8_DEPRECATED. Chrome will not break with it, so step b is not need.
V8_DEPRECATE_SOON is not sufficient for removing the function. You still need to annotate with
V8_DEPRECATED and wait for the next branch before removing the function.
V8_DEPRECATED can be tested using
v8_deprecation_warnings gn flag.
V8_DEPRECATE_SOON can be tested using
Changing function signature is unsafe. Use
V8_DEPRECATE_SOON macros as described above.