fix: empty tool array reports an error for some LLM models (#2639)

Co-authored-by: pre-commit-ci-lite[bot] <117423508+pre-commit-ci-lite[bot]@users.noreply.github.com>

lua/avante/llm.lua

@@ -464,6 +464,10 @@ function M.generate_prompts(opts)
   if opts.tools then tools = vim.list_extend(tools, opts.tools) end
   if opts.prompt_opts and opts.prompt_opts.tools then tools = vim.list_extend(tools, opts.prompt_opts.tools) end
 
+  -- Set tools to nil if empty to avoid sending empty arrays to APIs that require
+  -- tools to be either non-existent or have at least one item
+  if #tools == 0 then tools = nil end
+
   local agents_rules = Prompts.get_agents_rules_prompt()
   if agents_rules then system_prompt = system_prompt .. "\n\n" .. agents_rules end
   local cursor_rules = Prompts.get_cursor_rules_prompt(selected_files)

tests/llm_spec.lua

@@ -112,4 +112,42 @@ describe("generate_prompts", function()
     llm.generate_prompts(opts)
     assert.are.same(opts.instructions, nil)
   end)
+
+  it("should set tools to nil when no tools are provided", function()
+    local opts = {}
+    local result = llm.generate_prompts(opts)
+    assert.are.same(result.tools, nil)
+  end)
+
+  it("should set tools to nil when empty tools array is provided", function()
+    local opts = {
+      tools = {},
+    }
+    local result = llm.generate_prompts(opts)
+    assert.are.same(result.tools, nil)
+  end)
+
+  it("should set tools to nil when empty prompt_opts.tools array is provided", function()
+    local opts = {
+      prompt_opts = {
+        tools = {},
+      },
+    }
+    local result = llm.generate_prompts(opts)
+    assert.are.same(result.tools, nil)
+  end)
+
+  it("should include tools when non-empty tools are provided", function()
+    local mock_tool = {
+      name = "test_tool",
+      description = "A test tool",
+      func = function() end,
+    }
+    local opts = {
+      tools = { mock_tool },
+    }
+    local result = llm.generate_prompts(opts)
+    assert.are.same(#result.tools, 1)
+    assert.are.same(result.tools[1].name, "test_tool")
+  end)
 end)