Set filetype to 'markdown' instead of 'codecompanion' in chat buffer

[Bekaboo]

Using 'markdown' as the filetype for codecompanion chat buffers can provide better compatibility with existing Markdown tools and settings. While setting filetype to 'codecompanion' helps distinguish the chat buffer from other normal buffers, it breaks several markdown features:

• Code snippets for markdown files does not work in chat buffers, especially math snippets (similar to here) which I heavily relied on.
• Autopairing rules for markdown files (like $|$ and _|_) does not work in chat buffers
• Other plugins or custom settings for markdown files are not valid in chat buffers, e.g. markdown-preview.nvim, otter.nvim, etc.

Making all the above work in codecompanion buffers is possible but requires many extra tweaks and even hacks since they are originally designed for markdown files.

Instead, we can set the filetype to 'markdown' and use a buffer-local variable vim.b.codecompanion to identify codecompanion buffers. This maintains full markdown compatibility while still allowing codecompanion-specific customization.

This could be made opt-in to avoid breaking existing setups. I have a working draft of this implementation (refactor needed to make it tidier):

diff --git a/lua/codecompanion/init.lua b/lua/codecompanion/init.lua
index b918622..a37803b 100644
--- a/lua/codecompanion/init.lua
+++ b/lua/codecompanion/init.lua
@@ -265,26 +265,31 @@ M.setup = function(opts)
   local group = "codecompanion.syntax"
   api.nvim_create_augroup(group, { clear = true })
   api.nvim_create_autocmd("FileType", {
-    pattern = "codecompanion",
+    pattern = "markdown",
     group = group,
-    callback = vim.schedule_wrap(function()
-      vim.iter(config.strategies.chat.variables):each(function(name, var)
-        vim.cmd.syntax('match CodeCompanionChatVariable "#' .. name .. '"')
-        if var.opts and var.opts.has_params then
-          vim.cmd.syntax('match CodeCompanionChatVariable "#' .. name .. ':\\d\\+-\\?\\d\\+"')
-        end
-      end)
-      vim.iter(config.strategies.agent.tools):each(function(name, _)
-        vim.cmd.syntax('match CodeCompanionChatTool "@' .. name .. '"')
-      end)
-      vim
-        .iter(config.strategies.agent)
-        :filter(function(name)
-          return name ~= "tools"
+    callback = vim.schedule_wrap(function(info)
+      if not api.nvim_buf_is_valid(info.buf) or not vim.b[info.buf].codecompanion then
+        return
+      end
+      api.nvim_buf_call(info.buf, function()
+        vim.iter(config.strategies.chat.variables):each(function(name, var)
+          vim.cmd.syntax('match CodeCompanionChatVariable "#' .. name .. '"')
+          if var.opts and var.opts.has_params then
+            vim.cmd.syntax('match CodeCompanionChatVariable "#' .. name .. ':\\d\\+-\\?\\d\\+"')
+          end
         end)
-        :each(function(name, _)
-          vim.cmd.syntax('match CodeCompanionChatAgent "@' .. name .. '"')
+        vim.iter(config.strategies.agent.tools):each(function(name, _)
+          vim.cmd.syntax('match CodeCompanionChatTool "@' .. name .. '"')
         end)
+        vim
+          .iter(config.strategies.agent)
+          :filter(function(name)
+            return name ~= "tools"
+          end)
+          :each(function(name, _)
+            vim.cmd.syntax('match CodeCompanionChatAgent "@' .. name .. '"')
+          end)
+      end)
     end),
   })
 
@@ -334,14 +339,14 @@ M.setup = function(opts)
     cmp.register_source("codecompanion_slash_commands", require(completion .. ".slash_commands").new(config))
     cmp.register_source("codecompanion_tools", require(completion .. ".tools").new(config))
     cmp.register_source("codecompanion_variables", require(completion .. ".variables").new())
-    cmp.setup.filetype("codecompanion", {
+    cmp.setup.filetype("markdown", {
       enabled = true,
-      sources = {
+      sources = vim.list_extend({
         { name = "codecompanion_models" },
         { name = "codecompanion_slash_commands" },
         { name = "codecompanion_tools" },
         { name = "codecompanion_variables" },
-      },
+      }, cmp.get_config().sources),
     })
   end
 
diff --git a/lua/codecompanion/keymaps.lua b/lua/codecompanion/keymaps.lua
index 7ad7f46..d8ffeb6 100644
--- a/lua/codecompanion/keymaps.lua
+++ b/lua/codecompanion/keymaps.lua
@@ -33,7 +33,8 @@ local function open_float(lines, opts)
   local height = window.height > 1 and window.height or opts.height or 17
 
   local bufnr = api.nvim_create_buf(false, true)
-  util.set_option(bufnr, "filetype", opts.filetype or "codecompanion")
+  vim.b[bufnr].codecompanion = true
+  util.set_option(bufnr, "filetype", opts.filetype or "markdown")
   local winnr = api.nvim_open_win(bufnr, true, {
     relative = opts.relative or "cursor",
     border = "single",
diff --git a/lua/codecompanion/providers/completion/blink/init.lua b/lua/codecompanion/providers/completion/blink/init.lua
index dd0a67e..d3cc84a 100644
--- a/lua/codecompanion/providers/completion/blink/init.lua
+++ b/lua/codecompanion/providers/completion/blink/init.lua
@@ -15,7 +15,7 @@ function M:get_trigger_characters()
 end
 
 function M:enabled()
-  return vim.bo.filetype == "codecompanion"
+  return vim.bo.filetype == "markdown" and vim.b.codecompanion
 end
 
 function M:get_completions(ctx, callback)
diff --git a/lua/codecompanion/providers/completion/cmp/models.lua b/lua/codecompanion/providers/completion/cmp/models.lua
index b662d18..a82d104 100644
--- a/lua/codecompanion/providers/completion/cmp/models.lua
+++ b/lua/codecompanion/providers/completion/cmp/models.lua
@@ -8,7 +8,7 @@ function source.new(config)
 end
 
 function source:is_available()
-  return vim.bo.filetype == "codecompanion" and self.config.display.chat.show_settings
+  return vim.bo.filetype == "markdown" and vim.b.codecompanion and self.config.display.chat.show_settings
 end
 
 source.get_position_encoding_kind = function()
diff --git a/lua/codecompanion/providers/completion/cmp/slash_commands.lua b/lua/codecompanion/providers/completion/cmp/slash_commands.lua
index f3608a3..efc1e57 100644
--- a/lua/codecompanion/providers/completion/cmp/slash_commands.lua
+++ b/lua/codecompanion/providers/completion/cmp/slash_commands.lua
@@ -9,7 +9,7 @@ function source.new(config)
 end
 
 function source:is_available()
-  return vim.bo.filetype == "codecompanion"
+  return vim.bo.filetype == "markdown" and vim.b.codecompanion
 end
 
 function source:get_trigger_characters()
diff --git a/lua/codecompanion/providers/completion/cmp/tools.lua b/lua/codecompanion/providers/completion/cmp/tools.lua
index d793224..6c20bb6 100644
--- a/lua/codecompanion/providers/completion/cmp/tools.lua
+++ b/lua/codecompanion/providers/completion/cmp/tools.lua
@@ -5,7 +5,7 @@ function source.new(config)
 end
 
 function source:is_available()
-  return vim.bo.filetype == "codecompanion"
+  return vim.bo.filetype == "markdown" and vim.b.codecompanion
 end
 
 source.get_position_encoding_kind = function()
diff --git a/lua/codecompanion/providers/completion/cmp/variables.lua b/lua/codecompanion/providers/completion/cmp/variables.lua
index fdc2cb7..1634ceb 100644
--- a/lua/codecompanion/providers/completion/cmp/variables.lua
+++ b/lua/codecompanion/providers/completion/cmp/variables.lua
@@ -5,7 +5,7 @@ function source.new()
 end
 
 function source:is_available()
-  return vim.bo.filetype == "codecompanion"
+  return vim.bo.filetype == "markdown" and vim.b.codecompanion
 end
 
 source.get_position_encoding_kind = function()
diff --git a/lua/codecompanion/strategies/chat/init.lua b/lua/codecompanion/strategies/chat/init.lua
index 210146a..a0697cf 100644
--- a/lua/codecompanion/strategies/chat/init.lua
+++ b/lua/codecompanion/strategies/chat/init.lua
@@ -227,7 +227,8 @@ function Chat.new(args)
     create_buf = function()
       local bufnr = api.nvim_create_buf(false, true)
       api.nvim_buf_set_name(bufnr, string.format("[CodeCompanion] %d", id))
-      vim.bo[bufnr].filetype = "codecompanion"
+      vim.b[bufnr].codecompanion = true
+      vim.bo[bufnr].filetype = "markdown"
 
       return bufnr
     end,
diff --git a/lua/codecompanion/utils/buffers.lua b/lua/codecompanion/utils/buffers.lua
index 2925e13..0f070c0 100644
--- a/lua/codecompanion/utils/buffers.lua
+++ b/lua/codecompanion/utils/buffers.lua
@@ -11,7 +11,7 @@ function M.get_visible_lines()
   for _, win in ipairs(wins) do
     local bufnr = vim.api.nvim_win_get_buf(win)
 
-    if vim.api.nvim_get_option_value("filetype", { buf = bufnr }) ~= "codecompanion" then
+    if vim.api.nvim_get_option_value("filetype", { buf = bufnr }) ~= "markdown" or not vim.b[bufnr].codecompanion then
       local start_line = vim.api.nvim_win_call(win, function()
         return vim.fn.line("w0")
       end)
diff --git a/lua/legendary/extensions/codecompanion.lua b/lua/legendary/extensions/codecompanion.lua
index b96ff09..939739b 100644
--- a/lua/legendary/extensions/codecompanion.lua
+++ b/lua/legendary/extensions/codecompanion.lua
@@ -4,7 +4,11 @@ local function to_legendary_keymap(key, keymap)
     -- prefix makes it easier to search in legendary.nvim window
     desc = string.format("CodeCompanion: %s", require("legendary.util").get_desc(keymap)),
     -- keymaps are all for the chat buffer
-    filters = { filetype = "codecompanion" },
+    filters = {
+      function(_, context)
+        return context.buf and vim.api.nvim_buf_is_valid(context.buf) and vim.b[context.buf].codecompanion
+      end,
+    },
   }
 end

[olimorris]

Thanks for your hardwork and thoughtful comments. I completely see how currently this could be a big inconvenience. If you want to draft up a PR I'd be happy to take a look at it and start using it in my workflow to throughly test it out.