Rust and C++ Interoperability in Chrome

#1

Post by ytausky » Wed, Aug 19, 2020, 3:49 PM UTC

Rust and C++ Interoperability in Chrome
chromium.org

Re: Rust and C++ Interoperability in Chrome

#2

Post by brian_herman__ » Wed, Aug 19, 2020, 5:34 PM UTC

I wonder how this compares to Mozilla's approach when they did something similar with Rust, Firefox and servo.

Re: Rust and C++ Interoperability in Chrome

#3

Post by adamnemecek » Wed, Aug 19, 2020, 5:35 PM UTC

They should probably look at how mozilla does it. From experience doing something similar, things get simpler when you write your code using handles rather than pointers but that's not how chrome is written.

https://floooh.github.io/2018/06/17/handles-vs-pointers.html

Re: Rust and C++ Interoperability in Chrome

#4

Post by bluejekyll » Wed, Aug 19, 2020, 5:40 PM UTC

> This seems to present some C++/Rust interoperability challenges which nobody else has faced.

Is this different from the Firefox integration with Rust in some meaningful way?

It looks like the cxx library is going to be critical for this. I’m curious how helpful others have found cxx for interop with C++?

> For a Rustacean, this is controversial - all C++ is unsafe! But “unsafe” should be a really bad code smell. If “unsafe” is needed for all C++ calls, there will be thousands of them, and the “unsafe” keyword will lose its meaning.

I don’t think the attitude about unsafe usage differs from the general Rust community. If there’s a lot of it, then it definitely is a code smell.

Re: Rust and C++ Interoperability in Chrome

#5

Post by rightbyte » Wed, Aug 19, 2020, 5:46 PM UTC

bluejekyll wrote: post #4

> This seems to present some C++/Rust interoperability challenges which nobody else has faced. Is this different from the Firefox integration with Rust in some meaningful way? It looks like the cxx library is going to be critical for this. I’m curious how helpful others have found cxx for interop with C++? > For a Rustacean, this is controversial - all C++ is unsafe! But “unsafe” should be a really bad code smell. If…

Can't you just do a:

      #define CPP_CALL unsafe

in the Rust equivalent to annotate "unsafe" cpp calls from Rust?

"No boilerplate or redeclarations. No C++ annotations. Ideally, no allowlist."

This seems like an unpractical approach. How do you even call C++ code from Rust without extern "C" linkage.

Re: Rust and C++ Interoperability in Chrome

#6

Post by Rochus » Wed, Aug 19, 2020, 5:51 PM UTC

So building Chromium becomes even more complex. Understanding the build system alone is a major achievement; I even had to build a tool for that: https://github.com/rochus-keller/gntools/. Unfortunately that's only half of the rent; it also needs hundereds of Python scripts; and now also crates will be added.

Re: Rust and C++ Interoperability in Chrome

#7

Post by [deleted] » Wed, Aug 19, 2020, 5:52 PM UTC

rightbyte wrote: post #5

bluejekyll wrote: post #4

> This seems to present some C++/Rust interoperability challenges which nobody else has faced. Is this different from the Firefox integration with Rust in some meaningful way? It looks like the cxx library is going to be critical for this. I’m curious how helpful others have found cxx for interop with C++? > For a Rustacean, this is controversial - all C++ is unsafe! But “unsafe” should be a really bad code smell. If…

Can't you just do a: #define CPP_CALL unsafe in the Rust equivalent to annotate "unsafe" cpp calls from Rust? "No boilerplate or redeclarations. No C++ annotations. Ideally, no allowlist." This seems like an unpractical approach. How do you even call C++ code from Rust without extern "C" linkage.

[deleted]

Re: Rust and C++ Interoperability in Chrome

#8

Post by steveklabnik » Wed, Aug 19, 2020, 5:57 PM UTC

rightbyte wrote: post #5

bluejekyll wrote: post #4

> This seems to present some C++/Rust interoperability challenges which nobody else has faced. Is this different from the Firefox integration with Rust in some meaningful way? It looks like the cxx library is going to be critical for this. I’m curious how helpful others have found cxx for interop with C++? > For a Rustacean, this is controversial - all C++ is unsafe! But “unsafe” should be a really bad code smell. If…

Can't you just do a: #define CPP_CALL unsafe in the Rust equivalent to annotate "unsafe" cpp calls from Rust? "No boilerplate or redeclarations. No C++ annotations. Ideally, no allowlist." This seems like an unpractical approach. How do you even call C++ code from Rust without extern "C" linkage.

Rust does not have a textual substitution pre-processor, so like, you can do this sorta kinda but it would be way more involved.

Re: Rust and C++ Interoperability in Chrome

#9

Post by hamaluik » Wed, Aug 19, 2020, 6:06 PM UTC

I integrated some basic CEF stuff (enough get to get a basic browser working) into a Rust codebase (https://github.com/hamaluik/cef-simple). It was a massive pain at first, but much easier once you give up on the safety and "idiomacy" of Rust and accept that you have to write in more of C/C++ style. For the parts that can't be written purely in Rust, it ends up being not really any more painful than writing it in C++ anyway.

Re: Rust and C++ Interoperability in Chrome

#10

Post by eggsnbacon1 » Wed, Aug 19, 2020, 6:16 PM UTC

Do they really need to access thousands of C++ API calls from Rust? Doesn't this defeat the purpose of writing safe code in Rust? This smells of "not invented here" which applies to Google projects pretty often.

They should focus on integrating Rust in portions of the API instead of exposing a gigantic unsafe API surface, essentially making all their code unsafe. Unless the Chrome codebase is really such a mess that they can't do anything without exposing this giant API surface. In that case they should rewrite it to... not do that.

"We can't use Rust unless it allows us to write all our code in C++ without showing unsafe warnings"