Re: [PATCH 6/7] xdiff: conditionally use Rust's implementation of xxhash

From: Phillip Wood <phillip.wood123@gmail.com>
Date: Jul 20, 2025, 10:14 UTC
Message-ID: <dd3a7ab0-947b-4592-a086-8c7028f02ffd@gmail.com>
In-Reply-To: <5596e569-6632-c2b1-37af-a978de5408cd@gmx.de>

Hi Johannes

On 19/07/2025 22:53, Johannes Schindelin wrote:

Show 23 quoted lines

> Hi Ezekiel,
> 
> On Thu, 17 Jul 2025, Ezekiel Newren via GitGitGadget wrote:
> 
>> diff --git a/rust/xdiff/src/lib.rs b/rust/xdiff/src/lib.rs
>> index e69de29bb2d1..96975975a1ba 100644
>> --- a/rust/xdiff/src/lib.rs
>> +++ b/rust/xdiff/src/lib.rs
>> @@ -0,0 +1,7 @@
>> +
>> +
>> +#[no_mangle]
>> +unsafe extern "C" fn xxh3_64(ptr: *const u8, size: usize) -> u64 {
>> +    let slice = std::slice::from_raw_parts(ptr, size);
>> +    xxhash_rust::xxh3::xxh3_64(slice)
>> +}
> 
> I know that this is a pretty small file, but I do notice that it does not
> have a license header.
> 
> This reminds me of the unfortunate oversight to be careful about making
> (and keeping) libgit.a's source files compatible with libgit2's license to
> nurture a fruitful exchange between those two projects.

I'm not sure I follow your reasoning here. libgit2 was started after git and chose to use an incompatible license. I wasn't around at the time but isn't there a list of git contributors who are happy to re-license their contributions with the linking exception used by libgit2?

Show 9 quoted lines

> With Rust, we still have a really good chance to learn from history and
> avoid that mistake: Gitoxide is a very exciting project with clear overlap
> in its mission to implement Git functionality in Rust. Gitoxide is
> dual-licensed under the Apache License v2 and the MIT license (see
> https://github.com/GitoxideLabs/gitoxide?tab=readme-ov-file#license).
> 
> Would you mind adding a license header to that file that explicitly allows
> the contents of the file to be used in Gitoxide, to get the Rust effort
> started on a good foot?

I wary of that for two reasons. Firstly over time it is de-facto re-licensing git as the amount of rust code grows and the amount of C code shrinks which deserves a wider discussion. Secondly it makes it harder to convert our C code which is licensed under GPL2 (or in the case of xdiff LGPL) to rust if the rust code uses a different license.

If someone wants to start a discussion about re-licensing git (and is prepared to do all of the associated admin in the event that it happens) then by all means do so but I don't think it we want to slip such a change into this series.

Thanks

Phillip