fix: Make single-package mkTf2Config derivations neatly overridable

tf2/mkTf2Config.nix

@@ -1,7 +1,7 @@
-{ runCommand, lib }:
+{ stdenv, lib }:
 
 { pname
-, version ? null
+, version ? "nover"
 , custom ? []
 , cfg ? []
 , maps ? []
@@ -18,13 +18,50 @@ let
       mkdir -p "$out/${output}"
       ${lib.toShellVar "outputList_${output}" var}
       for i in "''${outputList_${output}[@]}"; do
-        ln -s "$i" "$out/${output}/$(basename "$i")"
+        name="$(stripHash "$i")"
+        vpkDir="#vpk-''${name}#" 
+        if [ -d "$vpkDir" ]; then
+          mv "$vpkDir/$name" "$out/${output}/$name"
+        else
+          mv "$name" "$out/${output}/$name"
+        fi
       done
     '';
-in runCommand name env ''
+
+  allSrcs = cfg ++ maps ++ custom;
+
+  srcArg =
+    if builtins.length allSrcs == 1
+    then { src = builtins.head allSrcs; }
+    else { srcs = allSrcs; sourceRoot = "."; };
+in stdenv.mkDerivation ({
+  inherit pname version;
+  # Adapted from stdenv's _defaultUnpack().
+  unpackCmd = ''
+    if [ "''${curSrc##*.}" = "vpk" ]; then
+      destination="#vpk-$(stripHash "$curSrc")#/$(stripHash "$curSrc")"
+      mkdir "$(dirname "$destination")"
+      if [ -e "$destination" ]; then
+          echo "Cannot copy $curSrc to $destination: destination already exists!"
+          echo "Did you specify two \"srcs\" with the same \"name\"?"
+          return 1
+      fi
+      # We can't preserve hardlinks because they may have been
+      # introduced by store optimization, which might break things
+      # in the build.
+      cp -r --preserve=mode,timestamps --reflink=auto -- "$curSrc" "$destination"
+    else
+      return 1
+    fi
+  '';
+  installPhase = ''
     set -xe
     mkdir -p $out
+    ${lib.optionalString (builtins.length allSrcs == 1)
+      "cd .."}
+    ls -la
     ${make-output "cfg" cfg}
     ${make-output "custom" custom}
     ${make-output "maps" maps}
-''
+  '';
+} // srcArg // env)