network-manager/pptp: replace patch by substitutions to simplify upgrades

pkgs/tools/networking/network-manager/pptp-purity.patch

@@ -1,26 +0,0 @@
-diff --git a/src/nm-pptp-service.c b/src/nm-pptp-service.c
-index 68a5759..568bbfe 100644
---- a/src/nm-pptp-service.c
-+++ b/src/nm-pptp-service.c
-@@ -730,9 +730,7 @@ nm_find_pppd (void)
- {
- 	static const char *pppd_binary_paths[] =
- 		{
--			"/sbin/pppd",
--			"/usr/sbin/pppd",
--			"/usr/local/sbin/pppd",
-+			"@ppp@/sbin/pppd",
- 			NULL
- 		};
-
-@@ -752,9 +750,7 @@ nm_find_pptp (void)
- {
- 	static const char *pptp_binary_paths[] =
- 		{
--			"/sbin/pptp",
--			"/usr/sbin/pptp",
--			"/usr/local/sbin/pptp",
-+			"@pptp@/sbin/pptp",
- 			NULL
- 		};
- 

pkgs/tools/networking/network-manager/pptp.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchurl, networkmanager, pptp, ppp, intltool, pkgconfig, substituteAll
+{ stdenv, fetchurl, networkmanager, pptp, ppp, intltool, pkgconfig
 , libsecret, withGnome ? true, gnome3 }:
 
 stdenv.mkDerivation rec {
@@ -17,18 +17,19 @@ stdenv.mkDerivation rec {
 
   nativeBuildInputs = [ intltool pkgconfig ];
 
+  postPatch = ''
+    sed -i -e 's%"\(/usr/sbin\|/usr/pkg/sbin\|/usr/local/sbin\)/[^"]*",%%g' ./src/nm-pptp-service.c
+
+    substituteInPlace ./src/nm-pptp-service.c \
+      --replace /sbin/pptp ${pptp}/bin/pptp \
+      --replace /sbin/pppd ${ppp}/bin/pppd
+  '';
+
   configureFlags =
     if withGnome then "--with-gnome --with-gtkver=3" else "--without-gnome";
 
   postConfigure = "sed 's/-Werror//g' -i Makefile */Makefile";
 
-  patches =
-    [ ( substituteAll {
-        src = ./pptp-purity.patch;
-        inherit ppp pptp;
-      })
-    ];
-
   meta = {
     description = "PPtP plugin for NetworkManager";
     inherit (networkmanager.meta) maintainers platforms;