plugins/completion: move to by-name

- Move nvim-cmp to plugins/cmp
- Move other completion plugins to plugins/by-name

plugins/cmp/options/sources-option.nix

@@ -0,0 +1,102 @@
+{ lib, helpers }:
+with lib;
+let
+  sourceType = types.submodule {
+    freeformType = with types; attrsOf anything;
+    options = {
+      name = mkOption {
+        type = types.str;
+        description = "The name of the source.";
+        example = "buffer";
+      };
+
+      option = helpers.mkNullOrOption (with types; attrsOf anything) ''
+        Any specific options defined by the source itself.
+
+        If direct lua code is needed use `helpers.mkRaw`.
+      '';
+
+      keyword_length = helpers.mkNullOrOption types.ints.unsigned ''
+        The source-specific keyword length to trigger auto completion.
+      '';
+
+      keyword_pattern = helpers.mkNullOrLua ''
+        The source-specific keyword pattern.
+      '';
+
+      trigger_characters = helpers.mkNullOrOption (with types; listOf str) ''
+        Trigger characters.
+      '';
+
+      priority = helpers.mkNullOrOption types.ints.unsigned ''
+        The source-specific priority value.
+      '';
+
+      group_index = helpers.mkNullOrOption types.ints.unsigned ''
+        The source group index.
+
+        For instance, you can set the `buffer`'s source `group_index` to a larger number
+        if you don't want to see `buffer` source items while `nvim-lsp` source is available:
+
+        ```nix
+          sources = [
+            {
+              name = "nvim_lsp";
+              group_index = 1;
+            }
+            {
+              name = "buffer";
+              group_index = 2;
+            }
+          ];
+        ```
+      '';
+
+      entry_filter = helpers.mkNullOrLuaFn ''
+        A source-specific entry filter, with the following function signature:
+
+        `function(entry: cmp.Entry, ctx: cmp.Context): boolean`
+
+        Returning `true` will keep the entry, while returning `false` will remove it.
+
+        This can be used to hide certain entries from a given source. For instance, you
+        could hide all entries with kind `Text` from the `nvim_lsp` filter using the
+        following source definition:
+
+        ```nix
+        {
+          name = "nvim_lsp";
+          entry_filter = \'\'
+            function(entry, ctx)
+              return require('cmp.types').lsp.CompletionItemKind[entry:get_kind()] ~= 'Text'
+            end
+          \'\';
+        }
+        ```
+
+        Using the `ctx` parameter, you can further customize the behaviour of the source.
+      '';
+    };
+  };
+in
+mkOption {
+  default = [ ];
+  type = with helpers.nixvimTypes; maybeRaw (listOf sourceType);
+  description = ''
+    The sources to use.
+    Can either be a list of `sourceConfigs` which will be made directly to a Lua object.
+    Or it can be a raw lua string which might be necessary for more advanced use cases.
+
+    WARNING:
+    If `plugins.cmp.autoEnableSources` Nixivm will automatically enable the corresponding source
+    plugins. This will work only when this option is set to a list.
+    If you use a raw lua string, you will need to explicitly enable the relevant source plugins in
+    your nixvim configuration.
+  '';
+  example = [
+    { name = "nvim_lsp"; }
+    { name = "luasnip"; }
+    { name = "path"; }
+    { name = "buffer"; }
+  ];
+}