feat: add should_attach function

Used to determine if Copilot should attach to a buffer or not.
Fixes: zbirenbaum#74

Author: AntoineGS

README.md

@@ -101,6 +101,7 @@ require('copilot').setup({
   root_dir = function()
     return vim.fs.dirname(vim.fs.find(".git", { upward = true })[1])
   end,
+  should_attach = nil, -- type is fun(bufnr: integer, bufname: string): boolean
   server_opts_overrides = {},
 })
 ```
@@ -126,7 +127,6 @@ require("copilot.panel").refresh()
 ### suggestion
 
 When `auto_trigger` is `true`, copilot starts suggesting as soon as you enter insert mode.
-
 When `auto_trigger` is `false`, use the `next`, `prev` or `accept` keymap to trigger copilot suggestion.
 
 To toggle auto trigger for the current buffer, use `require("copilot.suggestion").toggle_auto_trigger()`.
@@ -305,6 +305,26 @@ They can also be added runtime, using the command `:Copilot workspace add [folde
 This allows changing the function that gets the root folder, the default looks for a parent folder that contains the folder `.git`.
 If none is found, it will use the current working directory.
 
+### should_attach
+
+This function is called to determine if copilot should attach to the buffer or not.
+It is useful if you would like to go beyond the filetypes and have more control over when copilot should attach.
+Since this happens before attaching to the buffer, it is good to prevent Copilot from reading sensitive files.
+
+An example of this would be:
+
+```lua
+require("copilot").setup {
+  should_attach = function(_, bufname)
+    if string.match(bufname, "env") then
+      return false
+    end
+
+    return true
+  end
+}
+```
+
 ## Commands
 
 `copilot.lua` defines the `:Copilot` command that can perform various actions. It has completion support, so try it out.

lua/copilot/client.lua

@@ -17,6 +17,8 @@ local M = {
   node_version_error = nil,
   startup_error = nil,
   initialized = false,
+  ---@type copilot_should_attach|nil
+  should_attach = nil,
 }
 
 ---@param id integer
@@ -93,6 +95,16 @@ end
 
 ---@param force? boolean
 function M.buf_attach(force)
+  if M.should_attach then
+    local bufnr = vim.api.nvim_get_current_buf()
+    local bufname = vim.api.nvim_buf_get_name(bufnr)
+
+    if not M.should_attach(bufnr, bufname) then
+      logger.debug("copilot is disabled by should_attach")
+      return
+    end
+  end
+
   if is_disabled then
     logger.warn("copilot is disabled")
     return
@@ -348,6 +360,7 @@ end
 
 function M.setup()
   M.config = prepare_client_config(config.get("server_opts_overrides"))
+  M.should_attach = config.get("should_attach") --[[@as copilot_should_attach|nil]]
 
   if not M.config then
     is_disabled = true

lua/copilot/config.lua

@@ -61,6 +61,9 @@ local default_config = {
   root_dir = function()
     return vim.fs.dirname(vim.fs.find(".git", { upward = true })[1])
   end,
+  ---@alias copilot_should_attach fun(bufnr: integer, bufname: string): boolean
+  ---@type copilot_should_attach|nil
+  should_attach = nil,
 }
 
 local mod = {