app-emacs/csharp-mode: warn on emacs >=29

Signed-off-by: Maciej Barć <xgqt@gentoo.org>

app-emacs/csharp-mode/csharp-mode-2.0.0.ebuild

@@ -7,7 +7,8 @@ inherit elisp
 
 DESCRIPTION="A derived Emacs mode implementing most of the C# rules"
 HOMEPAGE="https://github.com/emacs-csharp/csharp-mode"
-SRC_URI="https://github.com/emacs-csharp/${PN}/archive/refs/tags/${PV}.tar.gz -> ${P}.tar.gz"
+SRC_URI="https://github.com/emacs-csharp/${PN}/archive/refs/tags/${PV}.tar.gz
+	-> ${P}.tar.gz"
 
 LICENSE="GPL-2+"
 SLOT="0"
@@ -17,3 +18,12 @@ RESTRICT="test" # tries to install an old version of dash from the network
 DOCS=( README.org )
 ELISP_REMOVE="csharp-mode-tests.el"  # useless since we can not run tests
 SITEFILE="50${PN}-gentoo.el"
+
+pkg_setup() {
+	elisp_pkg_setup
+
+	if ver_test "$(elisp-emacs-version)" -ge 29 ; then
+		ewarn "csharp-mode is included in GNU Emacs >=29,"
+		ewarn "Emacs developers recommend that you use the provided mode instead."
+	fi
+}