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denoland-rusty-v8/README.md
Ry Dahl 0430c43ec2
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2019-12-05 21:03:28 -05:00

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Rusty V8 Binding

Status: Early development, not usable.

V8 Version: 8.0.427

ci crates docs

Goals

  1. Provide high quality Rust bindings to V8's C++ API. The API should match the original API as closely as possible

  2. Do not introduce additional call overhead. (For example, previous attempts at Rust V8 bindings forced the use of Persistent handles.)

  3. Do not rely on a binary libv8.a built outside of cargo. V8 is a very large project (over 600,000 lines of C++) which often takes 30 minutes to compile. Furthermore, V8 relies on Chromium's bespoke build system (gn + ninja) which is not easy to use outside of Chromium. For this reason many attempts to bind to V8 rely on pre-built binaries that are built separately from the binding itself. While this is simple, it makes upgrading V8 difficult, it makes CI difficult, it makes producing builds with different configurations difficult, and it is a security concern since binary blobs can hide malicious code. For this reason we believe it is imperative to build V8 from source code during "cargo build".

  4. Publish the crate on crates.io and allow docs.rs to generate documentation. Due to the complexity and size of V8's build, this is nontrivial. For example the crate size must be kept under 10 MiB in order to publish.

Build

Use cargo build -vv to build the crate.

Depends on Python 2.7, not Python 3. Do not open issues with us regarding Python 3; it's something that must be fixed in Chromium..

There are several binary tools that are automatically downloaded during the build: clang, gn, and ninja. V8 relies on bleeding edge features of clang that are not generally available, so we download the clang binary that chromium uses. gn and ninja are also not generally available so we download them. It should be possible to opt out of the gn and ninja download by specifying the $GN and $NINJA environmental variables. The clang download cannot currently be skipped, but we welcome any patches to make that possible.

Env vars used in build.rs: SCCACHE, GN, NINJA

FAQ

Building V8 takes over 30 minutes, this is too slow for me to use this crate. What should I do?

Install sccache. Our build scripts will detect and use sccache. Set the $SCCACHE environmental variable if it's not in your path.

What are all these random directories for like build and buildtools are these really necessary?

In order to build V8 from source code, we must provide a certain directory structure with some git submodules from Chromium. We welcome any simplifications to the code base, but this is a structure we have found after many failed attempts that carefully balances the requirements of cargo crates and GN/Ninja.

V8 has a very large API with hundreds of methods. Why don't you automate the generation of this binding code?

In the limit we would like to auto-generate bindings. We have actually started down this route several times, however due to many excentric features of the V8 API, this has not proven successful. Therefore we are proceeding in a brute-force fashion for now, focusing on solving our stated goals first. We hope to auto-generate bindings in the future.

Why are you building this?

This is to support the Deno project. We previously have gotten away with a simpler high-level Rust binding to V8 called libdeno. But as Deno has matured we've found ourselves continually needing access to an increasing amount of V8's API in Rust.