fix(lsp): do not convert vim.NIL to nil in lists

runtime/lua/vim/lsp/rpc.lua

@@ -50,8 +50,13 @@ recursive_convert_NIL = function(v, tbl_processed)
     return nil
   elseif not tbl_processed[v] and type(v) == 'table' then
     tbl_processed[v] = true
+    local inside_list = vim.tbl_islist(v)
     return vim.tbl_map(function(x)
+      if not inside_list or (inside_list and type(x) == "table") then
         return recursive_convert_NIL(x, tbl_processed)
+      else
+        return x
+      end
     end, v)
   end
 

test/functional/fixtures/fake-lsp-server.lua

@@ -464,6 +464,23 @@ function tests.invalid_header()
   io.stdout:write("Content-length: \r\n")
 end
 
+function tests.decode_nil()
+  skeleton {
+    on_init = function(_)
+      return { capabilities = {} }
+    end;
+    body = function()
+      notify('start')
+      notify("workspace/executeCommand", {
+        arguments = { "EXTRACT_METHOD", {metadata = {field = vim.NIL}}, 3, 0, 6123, vim.NIL },
+        command = "refactor.perform",
+        title = "EXTRACT_METHOD"
+      })
+      notify('finish')
+    end;
+  }
+end
+
 -- Tests will be indexed by TEST_NAME
 
 local kill_timer = vim.loop.new_timer()

test/functional/plugin/lsp_spec.lua

@@ -927,6 +927,48 @@ describe('LSP', function()
         end;
       }
     end)
+
+    it('should not trim vim.NIL from the end of a list', function()
+      local expected_handlers = {
+        {NIL, "shutdown", {}, 1};
+        {NIL, "finish", {}, 1};
+        {NIL, "workspace/executeCommand", {
+          arguments = { "EXTRACT_METHOD", {metadata = {}}, 3, 0, 6123, NIL },
+          command = "refactor.perform",
+          title = "EXTRACT_METHOD"
+        }, 1};
+        {NIL, "start", {}, 1};
+      }
+      local client
+      test_rpc_server {
+        test_name = "decode_nil";
+        on_setup = function()
+          exec_lua [[
+            BUFFER = vim.api.nvim_create_buf(false, true)
+            vim.api.nvim_buf_set_lines(BUFFER, 0, -1, false, {
+              "testing";
+              "123";
+            })
+          ]]
+        end;
+        on_init = function(_client)
+          client = _client
+          exec_lua [[
+            assert(lsp.buf_attach_client(BUFFER, TEST_RPC_CLIENT_ID))
+          ]]
+        end;
+        on_exit = function(code, signal)
+          eq(0, code, "exit code", fake_lsp_logfile)
+          eq(0, signal, "exit signal", fake_lsp_logfile)
+        end;
+        on_handler = function(err, method, params, client_id)
+          eq(table.remove(expected_handlers), {err, method, params, client_id}, "expected handler")
+          if method == 'finish' then
+            client.stop()
+          end
+        end;
+      }
+    end)
   end)
   describe('lsp._cmd_parts test', function()
     local function _cmd_parts(input)