feat: Set darwin cflags fd_setsize and darwin_unlimited_select

[djgoku]

I’m not sure if you’re open to this change. If not, we can close this PR.

I’ve been having issues with macOS when I have too many files open. I’ve been testing this for a few weeks, and I haven’t encountered any more errors from Emacs about too many files open.

Prior work

d12frosted/homebrew-emacs-plus@4b34ed7

Context

https://en.liujiacai.net/2022/09/03/emacs-maxopenfiles/

[jian-lin]

I will not comment on the specific added cflags because I do not know darwin.

To avoid duplication, you should add cflags here.

To support __structuredAttrs, those flags should be added like this:

env = old.env or { } // {
  CFLAGS = env.CFLAGS or "" + self.lib.optionalString self.stdenv.hostPlatform.isDarwin " -DFD_SETSIZE=10000 -DDARWIN_UNLIMITED_SELECT ";
}

Probably, CFLAGS should be changed to NIX_CFLAGS_COMPILE.

[djgoku]

@jian-lin, thank you for your review and guidance.

I couldn’t get NIX_CFLAGS_COMPILE to work either with the same code or other examples I found. So, I stuck with CFLAGS.

Please let me know if there are any other changes that are needed.

[jian-lin]

I couldn’t get NIX_CFLAGS_COMPILE to work either

What is the error when you try NIX_CFLAGS_COMPILE?

Ah, I had a typo in my previous code: env.CFLAGS should be old.env.CFLAGS.

I just tested the following code and it compiled fine.

              env = old.env or { } // {
                NIX_CFLAGS_COMPILE = (old.env.NIX_CFLAGS_COMPILE or "") +  self.lib.optionalString self.stdenv.hostPlatform.isDarwin " -DFD_SETSIZE=10000 -DDARWIN_UNLIMITED_SELECT ";
              };

Please use this code if it works.

---

This PR should be created in Nixpkgs instead of emacs-overlay and modify this code.

---

I searched github for nix code containing DARWIN_UNLIMITED_SELECT and only found 4 results. This makes me question the necessity of these flags.

[djgoku]

@jian-lin there were no errors I just didn't see CFLAGS apart of M-x emacs-build-description`.

I know this isn't nix but but it is specific to macOS only:

railwaycat/homebrew-emacsmacport#338

Let me see if there is a better way to test and show emacs behaving when these options are passed in or not passed in.

[jian-lin]

I believe both NIX_CFLAGS_COMPILE and CFLAGS have the same effect. If you add NIX_DEBUG=4; inside overrideAttrs, you can see these two flags are passed to the compiler in build log.

NIX_CFLAGS_COMPILE is just a bit more idiomatic.

[djgoku]

EDIT I switched to your nix code and it is working.

Only way I know to confirm is by running in emacs gu: (shell-command-to-string "ulimit -n") which returns 7168.

Only a build without NIX_CFLAGS_COMPILE (shell-command-to-string "ulimit -n") will return 1024.

One reason I would say use CFLAGS over NIX_CFLAGS_COMPILE is you can see the CFLAGS compiled in with M-x emacs-build-description:

CFLAGS:

In GNU Emacs 31.0.50 (build 1, aarch64-apple-darwin24.3.0, NS
appkit-2575.40 Version 15.3.2 (Build 24D81))
Repository revision: d708ebe401a2001e764821b7e43d9e9aaa23ea95
Repository branch: master
Windowing system distributor 'Apple', version 10.3.2575
System Description:  macOS 15.3.2

Configured using:
 'configure
 --prefix=/nix/store/9jqfifh63x5cwm5ahy8pfz09jjsl8a6j-emacs-git-pgtk-20250317.0
 --disable-build-details --with-modules --disable-ns-self-contained
 --with-ns --with-compress-install --with-toolkit-scroll-bars
 --with-native-compilation --without-imagemagick --with-mailutils
 --without-small-ja-dic --with-tree-sitter --without-xinput2
 --without-xwidgets --without-dbus --without-selinux 'CFLAGS=
 -DFD_SETSIZE=10000 -DDARWIN_UNLIMITED_SELECT ''

NIX_CFLAGS_COMPILE (no indication CFLAGS were changed):

In GNU Emacs 31.0.50 (build 1, aarch64-apple-darwin24.3.0, NS
appkit-2575.40 Version 15.3.2 (Build 24D81))
Repository revision: d708ebe401a2001e764821b7e43d9e9aaa23ea95
Repository branch: master
Windowing system distributor 'Apple', version 10.3.2575
System Description:  macOS 15.3.2

Configured using:
 'configure
 --prefix=/nix/store/iamdx0i38garf2rrc4dcbbzcz7lfr0ig-emacs-git-pgtk-20250317.0
 --disable-build-details --with-modules --disable-ns-self-contained
 --with-ns --with-compress-install --with-toolkit-scroll-bars
 --with-native-compilation --without-imagemagick --with-mailutils
 --without-small-ja-dic --with-tree-sitter --without-xinput2
 --without-xwidgets --without-dbus --without-selinux'

[jian-lin]

LGTM

As I said above, this change should go into Nixpkgs instead of emacs-overlay. Could you create a PR there? I am happy to merger it.

[djgoku]

LGTM

As I said above, this change should go into Nixpkgs instead of emacs-overlay. Could you create a PR there? I am happy to merger it.

Thanks for the review. Hoping to have a pr to nixpkgs master today.

[djgoku]

@jian-lin closing this since I have opened NixOS/nixpkgs#391407

[opsroller]

Great, so the sane people should go back to a completely custom overlay to remove this hack?

This screams of a severe local misconfiguration.