treesitter: add tree-sitter context plugin (#103)

plugins/default.nix

@@ -24,6 +24,7 @@
     ./languages/ledger.nix
     ./languages/nix.nix
     ./languages/treesitter.nix
+    ./languages/treesitter-context.nix
     ./languages/treesitter-refactor.nix
     ./languages/zig.nix
 

plugins/languages/treesitter-context.nix

@@ -0,0 +1,56 @@
+{
+  pkgs,
+  lib,
+  config,
+  ...
+}:
+with lib; {
+  options.plugins.treesitter-context = {
+    enable = mkEnableOption "Enable nvim-treesitter-context";
+
+    maxLines = mkOption {
+      type = types.nullOr types.ints.positive;
+      default = null;
+      description = "How many lines the window should span. Null means no limit";
+    };
+
+    trimScope = mkOption {
+      type = types.enum ["outer" "inner"];
+      default = "outer";
+      description = "Which context lines to discard if `max_lines` is exceeded";
+    };
+
+    maxWindowHeight = mkOption {
+      type = types.nullOr types.ints.positive;
+      default = null;
+      description = "Minimum editor window height to enable context";
+    };
+
+    patterns = mkOption {
+      type = types.attrsOf (types.listOf types.str);
+      default = {};
+      description = ''
+        Patterns to use for context delimitation. The 'default' key matches all filetypes
+      '';
+    };
+
+    exactPatterns = mkOption {
+      type = types.attrsOf types.bool;
+      default = {};
+      description = "Treat the coresponding entry in patterns as an exact match";
+    };
+  };
+
+  config = let
+    cfg = config.plugins.treesitter-context;
+  in
+    mkIf cfg.enable {
+      extraPlugins = with pkgs.vimPlugins; [nvim-treesitter-context];
+
+      plugins.treesitter.moduleConfig.context = {
+        max_lines = cfg.maxLines;
+        trim_scope = cfg.trimScope;
+        min_window_height = cfg.maxWindowHeight;
+      };
+    };
+}