Add CARGO_HOME

Signed-off-by: Nikolaos Karaolidis <nick@karaolidis.com>

hosts/common/shells/rust/default.nix

@@ -8,4 +8,15 @@ pkgs.mkShell {
     cargo-udeps
     cargo-outdated
   ];
+
+  shellHook = ''
+    if git rev-parse --is-inside-work-tree &> /dev/null; then
+      TOP="$(git rev-parse --show-toplevel)"
+      if ! grep -q "^\.cargo$" "$TOP/.gitignore" "$TOP/.git/info/exclude"; then echo ".cargo" >> "$TOP/.git/info/exclude"; fi
+    else
+      TOP="$(pwd)"
+    fi
+
+    export CARGO_HOME="$TOP/.cargo"
+  '';
 }