Subject: Re: [PATCH v2 1/1] xdiff: provide indirection to git functions

From: Edward Thomson <[email-masked]>
Date: Fri, 25 Feb 2022 18:38:54 +0000

On Fri, Feb 25, 2022 at 10:24:14AM -0800, Junio C Hamano wrote:
> 
> Not so fast.  I still do not see a strong reason to support
> xdl_malloc() and other wrappers.

git has an `xmalloc` but no matching `xfree`.  libgit2 does not
necessarily use the system allocator (and on Windows, you run into the
question of _which_ system allocator you're using) and therefore has its
own allocation _and_ deallocation functions.

When libgit2 includes xdiff, I don't want to monkey around and try to
redefine `free` to our deallocator.

There are several options that could suffice for this.  A different
tactic is to have xdiff call `xfree` which is just defined as `free` in
git.  This would feel non-obvious to me as a git developer that in this
one part of the project, I need to use `xfree` instead of `free` on
memory that I have `xmalloc`ed.  Using a net new name for allocation
functions may help serve as a reminder that it is a different API.

> Is the expectation for other projects when using the unified code,
> they do not use xdiff/git-xdiff.h and instead add
> xdiff/frotz-xdiff.h that defines xdl_malloc() and friends with the
> infrastructure they provide as part of the Frotz project (and the
> Xyzzy project would do the same with xdiff/xyzzy-xdiff.h header for
> them), making "git" the first among equal other consumers?

No, the thinking is that they would provide their own `git-xdiff.h` that
defines the mappings to their project-specific APIs.

Cheers-
-ed