Feat/dynamic system prompt

lua/CopilotChat/config.lua

@@ -14,7 +14,7 @@
 ---@field blend number?
 
 ---@class CopilotChat.config.Shared
----@field system_prompt string?
+---@field system_prompt string|fun(source: CopilotChat.source):string|nil
 ---@field model string?
 ---@field tools string|table<string>|nil
 ---@field sticky string|table<string>|nil

lua/CopilotChat/init.lua

@@ -189,6 +189,26 @@ local function list_prompts()
   return prompts_to_use
 end
 
+--- Resolve system prompt - handle both string and function types
+---@param system_prompt string|function|nil
+---@return string?
+local function resolve_system_prompt(system_prompt)
+  if not system_prompt then
+    return nil
+  end
+
+  if type(system_prompt) == 'function' then
+    local ok, result = pcall(system_prompt)
+    if not ok then
+      log.warn('Failed to resolve system prompt function: ' .. result)
+      return nil
+    end
+    return result
+  end
+
+  return system_prompt
+end
+
 --- Finish writing to chat buffer.
 ---@param start_of_chat boolean?
 local function finish(start_of_chat)
@@ -503,6 +523,9 @@ function M.resolve_prompt(prompt, config)
   config = vim.tbl_deep_extend('force', M.config, config or {})
   config, prompt = resolve(config, prompt or '')
 
+  -- Resolve system prompt (handle functions)
+  config.system_prompt = resolve_system_prompt(config.system_prompt, state.source)
+
   if config.system_prompt then
     for name, prompt in pairs(prompts_to_use) do
       if prompt.system_prompt then