neovim: add 'autoconfigure' setting

certain plugins need a custom configuration (available in passthru.initLua)
to work with nix. For instance unicode-vim needs to configure where to
find the data:
```
vim.g.Unicode_data_directory="${self.unicode-vim}/autoload/unicode"
```
if true, the wrapper automatically appends those snippets when necessary

first appearance of initLua in #352741

This will make testing those plugins easier.

pkgs/applications/editors/neovim/tests/default.nix

@@ -80,7 +80,12 @@ let
     sha256 = "1ykcvyx82nhdq167kbnpgwkgjib8ii7c92y3427v986n2s5lsskc";
   };
 
-  # neovim-drv must be a wrapped neovim
+  /* neovim-drv must be a wrapped neovim
+    - exposes lua config in $luarcGeneric
+    - exposes vim config in $vimrcGeneric
+
+  */
+
   runTest = neovim-drv: buildCommand:
     runCommandLocal "test-${neovim-drv.name}" ({
       nativeBuildInputs = [ ];
@@ -164,6 +169,13 @@ in
     ${nvim_with_plug}/bin/nvim -V3log.txt -i NONE -c 'color base16-tomorrow-night'  +quit! -e
   '';
 
+  nvim_with_autoconfigure = pkgs.neovim.overrideAttrs(oa: {
+    plugins = [ vimPlugins.unicode-vim ];
+    autoconfigure = true;
+    # legacy wrapper sets it to false
+    wrapRc = true;
+  });
+
   nvim_with_ftplugin = let
     # this plugin checks that it's ftplugin/vim.tex is loaded before $VIMRUNTIME/ftplugin/vim.tex
     # $VIMRUNTIME/ftplugin/vim.tex sources $VIMRUNTIME/ftplugin/initex.vim which sets b:did_ftplugin
@@ -324,6 +336,12 @@ in
 
   inherit nvim-with-luasnip;
 
+  autoconfigure = runTest nvim_with_autoconfigure ''
+      assertFileContains \
+        "$luarc" \
+        '${vimPlugins.unicode-vim.passthru.initLua}'
+  '';
+
   # check that bringing in one plugin with lua deps makes those deps visible from wrapper
   # for instance luasnip has a dependency on jsregexp
   can_require_transitive_deps =

pkgs/applications/editors/neovim/wrapper.nix

@@ -20,6 +20,10 @@ let
 
   wrapper = {
       extraName ? ""
+    # certain plugins need a custom configuration (available in passthru.initLua)
+    # to work with nix.
+    # if true, the wrapper automatically appends those snippets when necessary
+    , autoconfigure ? false
     # should contain all args but the binary. Can be either a string or list
     , wrapperArgs ? []
     , withPython2 ? false
@@ -87,11 +91,19 @@ let
     packpathDirs.myNeovimPackages = myVimPackage;
     finalPackdir = neovimUtils.packDir packpathDirs;
 
+    luaPluginRC = let
+      op = acc: normalizedPlugin:
+           acc ++ lib.optional (finalAttrs.autoconfigure && normalizedPlugin.plugin.passthru ? initLua) normalizedPlugin.plugin.passthru.initLua;
+      in
+        lib.foldl' op [] pluginsNormalized;
+
     rcContent = ''
       ${luaRcContent}
     '' + lib.optionalString (neovimRcContent' != null) ''
       vim.cmd.source "${writeText "init.vim" neovimRcContent'}"
-    '';
+    '' +
+      lib.concatStringsSep "\n" luaPluginRC
+    ;
 
     getDeps = attrname: map (plugin: plugin.${attrname} or (_: [ ]));
 
@@ -155,7 +167,7 @@ let
       __structuredAttrs = true;
       dontUnpack = true;
       inherit viAlias vimAlias withNodeJs withPython3 withPerl withRuby;
-      inherit wrapRc providerLuaRc packpathDirs;
+      inherit autoconfigure wrapRc providerLuaRc packpathDirs;
       inherit python3Env rubyEnv;
       inherit wrapperArgs generatedWrapperArgs;
       luaRcContent = rcContent;