From 10c0a8d94285d9a0c99ef2a7bf151c91540b5c75 Mon Sep 17 00:00:00 2001
From: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Date: Mon, 21 Jul 2025 11:35:02 -0700
Subject: [PATCH] feat(sidebar): allow external users identify selected code
 buffer

External users such as, for example, lualine may want to identify and
add special handling for Avante buffers. This is easily done for Avante
result, input, selected files and todos buffers as they all set a unique
file type. However the selected code buffer inherits file type from the
buffer where the code came from (to have proper syntax highlighting),
and so filetype can not be used to identify it as Avante buffer.

One option would be to add a custom buffer variable, such as
vim.b.avante_buf_type and use it in plugins. Unfortunately lualine
triggers everything on file type, so that would not work.

Solve this by setting file type of the selected code buffer to
"AvanteSelectedCode" and manually activate treesitter parser with
language of the source buffer if treesitter is active there. If the
original code buffer uses legacy syntax highlighting then activate it.
This keeps syntax highlighting active for the code while allowing
external users identify Avante selected code buffer.
---
 lua/avante/sidebar.lua | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/lua/avante/sidebar.lua b/lua/avante/sidebar.lua
index ada5031..e0452bd 100644
--- a/lua/avante/sidebar.lua
+++ b/lua/avante/sidebar.lua
@@ -1359,8 +1359,18 @@ function Sidebar:on_mount(opts)
         Utils.lock_buf(selected_code_buf)
       end
       if self.code.bufnr and api.nvim_buf_is_valid(self.code.bufnr) then
-        local filetype = api.nvim_get_option_value("filetype", { buf = self.code.bufnr })
-        api.nvim_set_option_value("filetype", filetype, { buf = selected_code_buf })
+        local ts_ok, ts_highlighter = pcall(require, "vim.treesitter.highlighter")
+        if ts_ok and ts_highlighter.active[self.code.bufnr] then
+          -- Treesitter highlighting is active in the code buffer, activate it
+          -- it in code selection buffer as well.
+          local filetype = vim.bo[self.code.bufnr].filetype
+          if filetype and filetype ~= "" then
+            vim.treesitter.start(selected_code_buf, vim.bo[self.code.bufnr].filetype)
+          end
+        end
+        -- Try the old syntax highlighting
+        local syntax = api.nvim_get_option_value("syntax", { buf = self.code.bufnr })
+        if syntax and syntax ~= "" then api.nvim_set_option_value("syntax", syntax, { buf = selected_code_buf }) end
       end
     end
   end
@@ -2127,7 +2137,7 @@ function Sidebar:create_selected_code_container()
         type = "win",
         winid = self:get_split_candidate("selected_code"),
       },
-      buf_options = buf_options,
+      buf_options = vim.tbl_deep_extend("force", buf_options, { filetype = "AvanteSelectedCode" }),
       win_options = vim.tbl_deep_extend("force", base_win_options, {}),
       size = {
         height = height,