populate file: add exclude option

README.md

@@ -114,6 +114,13 @@ Supported attributes:
   boolean that controls whether file contents should be checked to decide
   whether a file has changed.  This is useful when `path` points at files
   with mangled timestamps, e.g. the Nix store.
+  
+* `exclude` (optional)
+  List of patterns that should excluded from being synced. The list will be
+  passed to the `--exclude` option of [`rsync`](https://rsync.samba.org/).
+  Checkout the filter rules section in the [rsync
+  manual](https://download.samba.org/pub/rsync/rsync.html) for further
+  information.
 
 
 ### `git`

lib/types/populate.nix

@@ -71,6 +71,11 @@
           default = false;
           type = lib.types.bool;
         };
+        exclude = lib.mkOption {
+          type = lib.types.listOf lib.types.str;
+          default = [];
+          example = [".git"];
+        };
       };
     };
     git = lib.types.submodule {

pkgs/populate/default.nix

@@ -45,7 +45,7 @@ let
   '';
 
   pop.file = target: source: let
-    configAttrs = ["useChecksum"];
+    configAttrs = ["useChecksum" "exclude"];
     config = filterAttrs (name: _: elem name configAttrs) source;
   in
     rsync' target config (quote source.path);
@@ -156,8 +156,11 @@ let
       source_path=$source_path/
     fi
     ${rsync}/bin/rsync \
-        ${optionalString (config.useChecksum or false) /* sh */ "--checksum"} \
+        ${optionalString config.useChecksum /* sh */ "--checksum"} \
         ${optionalString target.sudo /* sh */ "--rsync-path=\"sudo rsync\""} \
+        ${concatMapStringsSep " "
+          (pattern: /* sh */ "--exclude ${quote pattern}")
+          config.exclude} \
         -e ${quote (ssh' target)} \
         -vFrlptD \
         --delete-excluded \