refactor: reduce code duplication with merge-with-aliases helper

Add merge-with-aliases function to attrs module and use it across checks,
modules, packages, shells, and templates to eliminate repeated alias merging
logic. Also optimize get-libs by replacing filter+map with a fold operation.

snowfall-lib/attrs/default.nix

@@ -79,5 +79,19 @@ in
             value
         ) item)
       ) { } items;
+
+    ## Merge items with a merge function and apply aliases
+    ## Example Usage:
+    ## ```nix
+    ## merge-with-aliases merge-packages packages-metadata alias
+    ## ```
+    ## Result: Merged items with aliases applied
+    #@ (Attrs -> Attrs -> Attrs) -> [Attrs] -> Attrs -> Attrs
+    merge-with-aliases = merge-fn: items: alias:
+      let
+        items-without-aliases = foldl merge-fn { } items;
+        aliased-items = mapAttrs (name: value: items-without-aliases.${value}) alias;
+      in
+      items-without-aliases // aliased-items;
   };
 }

snowfall-lib/checks/default.nix

@@ -58,9 +58,7 @@ in
           // {
             ${metadata.name} = metadata.drv;
           };
-        checks-without-aliases = foldl merge-checks { } checks-metadata;
-        aliased-checks = mapAttrs (name: value: checks-without-aliases.${value}) alias;
-        checks = checks-without-aliases // aliased-checks // overrides;
+        checks = snowfall-lib.attrs.merge-with-aliases merge-checks checks-metadata alias // overrides;
       in
       filterPackages pkgs.stdenv.hostPlatform.system checks;
   };

snowfall-lib/default.nix

@@ -50,12 +50,15 @@ let
   #   result: { x = nixpkgs.lib; }
   get-libs =
     attrs:
-    let
-      # @PERF(jakehamilton): Replace filter+map with a fold.
-      attrs-with-libs = filterAttrs (name: value: builtins.isAttrs (value.lib or null)) attrs;
-      libs = builtins.mapAttrs (name: input: input.lib) attrs-with-libs;
-    in
-    libs;
+    fold
+      (acc: name:
+        let value = attrs.${name}; in
+        if builtins.isAttrs (value.lib or null)
+        then acc // { ${name} = value.lib; }
+        else acc
+      )
+      { }
+      (builtins.attrNames attrs);
 
   # Remove the `self` attribute from an attribute set.
   # Type: Attrs -> Attrs

snowfall-lib/flake/default.nix

@@ -97,12 +97,15 @@ rec {
     #@ Attrs -> Attrs
     get-libs =
       attrs:
-      let
-        # @PERF(jakehamilton): Replace filter+map with a fold.
-        attrs-with-libs = filterAttrs (name: value: builtins.isAttrs (value.lib or null)) attrs;
-        libs = builtins.mapAttrs (name: input: input.lib) attrs-with-libs;
-      in
-      libs;
+      foldl
+        (acc: name:
+          let value = attrs.${name}; in
+          if builtins.isAttrs (value.lib or null)
+          then acc // { ${name} = value.lib; }
+          else acc
+        )
+        { }
+        (builtins.attrNames attrs);
   };
 
   mkFlake =

snowfall-lib/module/default.nix

@@ -95,9 +95,7 @@ in
               in
               user-module // { _file = metadata.path; };
           };
-        modules-without-aliases = foldl merge-modules { } modules-metadata;
-        aliased-modules = mapAttrs (name: value: modules-without-aliases.${value}) alias;
-        modules = modules-without-aliases // aliased-modules // overrides;
+        modules = snowfall-lib.attrs.merge-with-aliases merge-modules modules-metadata alias // overrides;
       in
       modules;
   };

snowfall-lib/package/default.nix

@@ -77,9 +77,7 @@ in
           // {
             ${metadata.name} = metadata.drv;
           };
-        packages-without-aliases = foldl merge-packages { } packages-metadata;
-        aliased-packages = mapAttrs (name: value: packages-without-aliases.${value}) alias;
-        packages = packages-without-aliases // aliased-packages // overrides;
+        packages = snowfall-lib.attrs.merge-with-aliases merge-packages packages-metadata alias // overrides;
       in
       filterPackages pkgs.stdenv.hostPlatform.system packages;
   };

snowfall-lib/shell/default.nix

@@ -58,9 +58,7 @@ in
           // {
             ${metadata.name} = metadata.drv;
           };
-        shells-without-aliases = foldl merge-shells { } shells-metadata;
-        aliased-shells = mapAttrs (name: value: shells-without-aliases.${value}) alias;
-        shells = shells-without-aliases // aliased-shells // overrides;
+        shells = snowfall-lib.attrs.merge-with-aliases merge-shells shells-metadata alias // overrides;
       in
       filterPackages pkgs.stdenv.hostPlatform.system shells;
   };

snowfall-lib/template/default.nix

@@ -53,12 +53,10 @@ in
             ${metadata.name} =
               (overrides.${metadata.name} or { }) // (builtins.removeAttrs metadata [ "name" ]);
           };
-        templates-without-aliases = foldl merge-templates { } templates-metadata;
-        aliased-templates = mapAttrs (name: value: templates-without-aliases.${value}) alias;
         unused-overrides = builtins.removeAttrs overrides (
           builtins.map (metadata: metadata.name) templates-metadata
         );
-        templates = templates-without-aliases // aliased-templates // unused-overrides;
+        templates = snowfall-lib.attrs.merge-with-aliases merge-templates templates-metadata alias // unused-overrides;
       in
       templates;
   };