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

From: Edward Thomson <ethomson@edwardthomson.com>
Date: Feb 25, 2022, 18:38 UTC
Message-ID: <20220225183854.GA9@811aa366e12e>
In-Reply-To: <xmqqo82udctt.fsf@gitster.g>

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.

Show 6 quoted lines

> 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