buildGoPackage: check/delete vendor

pkgs/development/go-packages/generic/default.nix

@@ -29,6 +29,9 @@
 # go2nix dependency file
 , goDeps ? null
 
+# Whether to delete the vendor folder supplied with the source.
+, deleteVendor ? false
+
 , dontRenameImports ? false
 
 # Do not enable this without good reason
@@ -96,6 +99,18 @@ let
       mkdir -p "go/src/$(dirname "$goPackagePath")"
       mv "$sourceRoot" "go/src/$goPackagePath"
 
+    '' + lib.optionalString (deleteVendor == true) ''
+      if [ ! -d "go/src/$goPackagePath/vendor" ]; then
+        echo "vendor folder does not exist, 'deleteVendor' is not needed"
+        exit 10
+      else
+        rm -rf "go/src/$goPackagePath/vendor"
+      fi
+    '' + lib.optionalString (goDeps != null) ''
+      if [ -d "go/src/$goPackagePath/vendor" ]; then
+        echo "vendor folder exists, 'goDeps' is not needed"
+        exit 10
+      fi
     '' + lib.flip lib.concatMapStrings goPath ({ src, goPackagePath }: ''
       mkdir goPath
       (cd goPath; unpackFile "${src}")