Cargo.nix override instead of requiring manual intervention

nix/Cargo.nix_patches.md

@@ -1,6 +0,0 @@
-Apply these instructions after generating the `Cargo.nix` file.
-
-- Find `veloren-common` crate in `Cargo.nix`:
-	- Comment the `optional = true;` line for "structopt" and "csv" dependencies.
-	- See [this issue](https://github.com/kolloch/crate2nix/issues/129) on `crate2nix` repository for more info.
-	- Note that the suggested workaround in the issue **does not** work for us.

nix/README.md

@@ -192,7 +192,6 @@ To update `Cargo.nix` (and `crate-hashes.json`) using latest `Cargo.lock`, run:
 ```shell
 crate2nix generate -f ../Cargo.toml
 ```
-Then follow the instructions in the `Cargo.nix_patches.md` file.
 
 ### Rust toolchain
 

nix/veloren.nix

@@ -73,7 +73,16 @@ let
     callPackage ./Cargo.nix {
       defaultCrateOverrides = with common; with crateDeps;
         defaultCrateOverrides // {
-          veloren-common = _: {
+          veloren-common = oldAttrs: {
+            # see: https://github.com/kolloch/crate2nix/issues/129
+            dependencies =
+              map
+                (dep:
+                  if dep.name == "csv" || dep.name == "structopt"
+                  then builtins.removeAttrs dep [ "optional" ]
+                  else dep)
+                oldAttrs.dependencies;
+
             # Disable `git-lfs` check here since we check it ourselves
             # We have to include the command output here, otherwise Nix won't run it
             DISABLE_GIT_LFS_CHECK = utils.isGitLfsSetup common.gitLfsCheckFile;