coq-nvim: init plugin

still need to add most options, but this is enough to be usable
right now! This also sets up the work needed for other completion
frameworks, notably things like nvim-cmp and compe.

plugins/completion/coq.nix

@@ -0,0 +1,47 @@
+{ pkgs, lib, config, ... }:
+with lib;
+let
+  cfg = config.programs.nixvim.plugins.coq-nvim;
+  helpers = import ../helpers.nix { lib = lib; };
+  plugins = import ../plugin-defs.nix { inherit pkgs; };
+
+in {
+  options = {
+    programs.nixvim.plugins.coq-nvim = {
+      enable = mkEnableOption "Enable coq-nvim";
+
+      installArtifacts = mkEnableOption "Install coq-artifacts";
+
+      autoStart = mkOption {
+        type = with types; nullOr (oneOf [bool (enum ["shut-up"])]);
+        default = null;
+        description = "Auto-start or shut up";
+      };
+
+      recommendedKeymaps = mkOption {
+        type = with types; nullOr bool;
+        default = null;
+        description = "Use the recommended keymaps";
+      };
+    };
+  };
+  config = let
+    settings = {
+      auto_start = cfg.autoStart;
+      "keymap.recommended" = cfg.recommendedKeymaps;
+    };
+  in mkIf cfg.enable {
+    programs.nixvim = {
+      extraPlugins = [
+        plugins.coq-nvim
+      ] ++ optional cfg.installArtifacts plugins.coq-artifacts;
+      plugins.lsp = {
+        preConfig = ''
+          vim.g.coq_settings = ${helpers.toLuaObject settings}
+          local coq = require 'coq'
+        '';
+        setupWrappers = [(s: ''coq.lsp_ensure_capabilities(${s})'')];
+      };
+    };
+  };
+}