steamtinkerlaunch: add steamcompattool output

This makes it possible to integrate this into our steam derivation's
extraCompatPackages

pkgs/tools/games/steamtinkerlaunch/default.nix

@@ -25,8 +25,20 @@ stdenvNoCC.mkDerivation {
     hash = "sha256-CGtSGAm+52t2zFsPJEsm76w+FEHhbOd9NYuerGa31tc=";
   };
 
+  outputs = [ "out" "steamcompattool" ];
+
   installFlags = [ "PREFIX=\${out}" ];
 
+  nativeBuildInputs = let
+    # We need a `steam` command in order to install the compat tool
+    fakeSteam = writeShellApplication {
+      name = "steam";
+      text = "exit 0";
+    };
+  in [
+    fakeSteam
+  ];
+
   postInstall =
     let
       # We (ab)use writeShellApplication to produce a header for a shell script
@@ -52,11 +64,31 @@ stdenvNoCC.mkDerivation {
         text = "";
         bashOptions = [ ];
       };
+      fakeYad = writeShellApplication {
+        name = "yad";
+        text = "echo ${yad.version} FAKE";
+      };
     in
     ''
       cp $out/bin/steamtinkerlaunch $TMPDIR/steamtinkerlaunch
       install ${lib.getExe header} -T $out/bin/steamtinkerlaunch
       tail -n +2 $TMPDIR/steamtinkerlaunch >> $out/bin/steamtinkerlaunch
+
+      # Create a fake steam dir, it checks this and reads a few values
+      steamdir=$TMPDIR/.local/share/Steam/
+      mkdir -p $steamdir/config/
+      echo \"path\" \"$steamdir\" > $steamdir/config/config.vdf
+      mkdir $TMPDIR/.steam/
+      ln -s $steamdir $TMPDIR/.steam/steam
+
+      cp -a $out/bin/steamtinkerlaunch $TMPDIR/steamtinkerlaunch
+      # yad cannot print its version without a graphical session https://github.com/v1cont/yad/issues/277
+      substituteInPlace $TMPDIR/steamtinkerlaunch --replace ${yad} ${fakeYad}
+      HOME=$TMPDIR $TMPDIR/steamtinkerlaunch compat add
+
+      cp -a $steamdir/compatibilitytools.d/SteamTinkerLaunch $steamcompattool
+      # It creates this symlink but it points to $TMPDIR
+      ln -sfn $out/bin/steamtinkerlaunch $steamcompattool/
     '';
 
   meta = with lib; {