vimPlugins: reject aliases that shadow plugins

An alias that shadows a plugin only threw when that attribute was
evaluated with aliases enabled. CI evaluates with allowAliases = false,
so a shadowing alias passed review and left rust-tools-nvim unevaluable
for users. Check the alias names against the plugin set whenever
vimPlugins is evaluated, as mpvScripts does, and drop the per-alias check
this replaces.

pkgs/applications/editors/vim/plugins/aliases.nix

@@ -17,16 +17,8 @@ let
   # sets from building on Hydra.
   removeDistribute = alias: if lib.isDerivation alias then lib.dontDistribute alias else alias;
 
-  # Make sure that we are not shadowing something from
-  # all-packages.nix.
-  checkInPkgs =
-    n: alias: if builtins.hasAttr n prev then throw "Alias ${n} is still in vim-plugins" else alias;
-
   mapAliases =
-    aliases:
-    lib.mapAttrs (
-      n: alias: removeDistribute (removeRecurseForDerivations (checkInPkgs n alias))
-    ) aliases;
+    aliases: lib.mapAttrs (_: alias: removeDistribute (removeRecurseForDerivations alias)) aliases;
 
   deprecations = lib.mapAttrs (
     old: info:

pkgs/applications/editors/vim/plugins/default.nix

@@ -55,7 +55,14 @@ let
     inherit llvmPackages;
   };
 
-  aliases = if config.allowAliases then (import ./aliases.nix lib) else final: prev: { };
+  aliases =
+    final: prev:
+    let
+      defined = import ./aliases.nix lib final prev;
+      shadowed = builtins.attrNames (builtins.intersectAttrs prev defined);
+    in
+    assert lib.assertMsg (shadowed == [ ]) "vimPlugins aliases shadow plugins: ${toString shadowed}";
+    lib.optionalAttrs config.allowAliases defined;
 in
 lib.pipe initialPackages [
   (extends plugins)