persist: convert the sane.persist.home.<store> => mappings back to a strongly-typed module & add a byPath shorthand

modules/persist/computed.nix

@@ -4,34 +4,15 @@ let
   path = sane-lib.path;
   cfg = config.sane.persist;
 
-  # take a directory attrset and fix its directory to be absolute
-  fixDir = relativeTo: dir: dir // {
-    directory = path.concat [ relativeTo dir.directory ];
-  };
-  fixDirs = relativeTo: dirs: map (fixDir relativeTo) dirs;
-
-  # set the `store` attribute on one dir attrset
-  fixStore = store: dir: dir // {
-    inherit store;
-  };
-  # String -> [a] -> [a]
-  # usually called on an attrset to map (AttrSet [a]) -> [a]
-  fixStoreForDirs = store: dirs: map (fixStore store) dirs;
-
-  # populate the `store` attr for all the substores in home
-  unfixed-home-dirs = builtins.concatLists (lib.mapAttrsToList fixStoreForDirs cfg.home);
-  # populate the `store` attr for all the substores in sys
-  unfixed-sys-dirs = builtins.concatLists (lib.mapAttrsToList fixStoreForDirs cfg.sys);
-
-  fixed-dirs = (fixDirs "/home/colin" unfixed-home-dirs) ++ (fixDirs "/" unfixed-sys-dirs);
-
-  dirToAttrs = dir: {
-    "${dir.directory}" = {
-      inherit (dir) user group mode store;
-    };
-  };
+  withPrefix = relativeTo: entries: lib.mapAttrs' (fspath: value: {
+    name = path.concat [ relativeTo fspath ];
+    inherit value;
+  }) entries;
 in
 {
-  # compute the `byPath` path => entry mapping from higher-level store => entry mappings.
-  sane.persist.byPath = lib.mkMerge (map dirToAttrs fixed-dirs);
+  # merge the `byPath` mappings from both `home` and `sys` into one namespace
+  sane.persist.byPath = lib.mkMerge [
+    (withPrefix "/home/colin" cfg.home.byPath)
+    (withPrefix "/" cfg.sys.byPath)
+  ];
 }

modules/persist/default.nix

@@ -80,12 +80,49 @@ let
     };
   };
 
-
-  # attrset from { "${storeName}" = [ dirEntry ] }
-  # the user can specify something like:
+  # this submodule creates one attr per store, so that the user can specify something like:
   #   <option>.private.".cache/vim" = { mode = "0700"; };
   # to place ".cache/vim" into the private store and create with the appropriate mode
-  dirsSubModule = types.attrsOf (types.listOf entryInStoreOrShorthand);
+  dirsSubModule = types.submodule ({ config, ... }: {
+    options = (mapAttrs (store: store-cfg: mkOption {
+      default = [];
+      type = types.listOf entryInStoreOrShorthand;
+      description = let
+        suffix = if store-cfg.storeDescription != null then
+          ": ${store-cfg.storeDescription}"
+        else "";
+      in "directories to persist in ${store}${suffix}";
+    }) cfg.stores) // {
+      byPath = mkOption {
+        type = types.attrsOf entryAtPath;
+        default = {};
+        description = ''
+          map of <path> => <path config> for all paths to be persisted.
+          this is computed from the other options, but users can also set it explicitly (useful for overriding)
+        '';
+      };
+    };
+    config = let
+      # set the `store` attribute on one dir attrset
+      annotateWithStore = store: dir: dir // {
+        inherit store;
+      };
+      # String -> [a] -> [a]
+      # usually called on an attrset to map (AttrSet [a]) -> [a]
+      annotatedDirsForStore = store: map (annotateWithStore store) config."${store}";
+      store-names = attrNames cfg.stores;
+      # flat list where each item is an entryInStore with an additional `store` attribute
+      annotated-dirs = lib.concatMap annotatedDirsForStore store-names;
+      # convert an `entryInStore` to an `entryAtPath`
+      dirToAttrs = dir: {
+        "${dir.directory}" = {
+          inherit (dir) user group mode store;
+        };
+      };
+    in {
+      byPath = lib.mkMerge (map dirToAttrs annotated-dirs);
+    };
+  });
 in
 {
   options = {